QEMU(1)

📦

version 11.0.3 · 16 versions

👑 QEMU(1) — QEMU User Documentation 👑

okay bestie listen, this is the actual manual for QEMU — the QEMU(1) manpage, no cap. it's huge, so we're doing it in parts. this is part one. buckle up 💖

✨ NAME ✨

qemu — QEMU User Documentation. that's it, that's the name, slay.

🌸 SYNOPSIS 🌸

qemu-system-x86_64 [options] [disk_image]

🦋 DESCRIPTION 🦋

the QEMU PC System emulator simulates so many peripherals, and i need you to know about every single one of them because they're all icons:

i440FX host PCI bridge and PIIX3 PCI to ISA bridge
Cirrus CLGD 5446 PCI VGA card or a dummy VGA card with Bochs VESA extensions (hardware level, including all non standard modes).
PS/2 mouse and keyboard
2 PCI IDE interfaces with hard disk and CD-ROM support
Floppy disk
PCI and ISA network adapters
Serial ports
IPMI BMC, either and internal or external one
Creative SoundBlaster 16 sound card
ENSONIQ AudioPCI ES1370 sound card
Intel 82801AA AC97 Audio compatible sound card
Intel HD Audio Controller and HDA codec
Adlib (OPL2) - Yamaha YM3812 compatible chip
Gravis Ultrasound GF1 sound card
CS4231A compatible sound card
PC speaker
PCI UHCI, OHCI, EHCI or XHCI USB controller and a virtual USB-1.1 hub.

SMP is supported with a large number of virtual CPUs (upper limit is configuration dependent). literally as many as your config will let you have, periodt.

QEMU uses the PC BIOS from the Seabios project and the Plex86/Bochs LGPL VGA BIOS.

QEMU uses YM3812 emulation by Tatsuyuki Satoh.

QEMU uses GUS emulation (GUSEMU32 <http://www.deinmeister.de/gusemu/>) by Tibor "TS" Schütz. legends only tbh.

⚠️ heads up bestie: by default, GUS shares IRQ(7) with parallel ports, and so QEMU must be told to not have parallel ports in order to have a working GUS. it's giving "we can't both sit here".

qemu-system-x86_64 dos.img -device gus -parallel none

Alternatively:

qemu-system-x86_64 dos.img -device gus,irq=5

Or some other unclaimed IRQ. pick your fave free one 💅

CS4231A is the chip used in Windows Sound System and GUSMAX products.

The PC speaker audio device can be configured using the pcspk-audiodev machine property, i.e.

qemu-system-x86_64 some.img -audiodev <backend>,id=<name> -machine pcspk-audiodev=<name>

🎀 Machine-specific options 🎀

It supports the following machine-specific options:

x-south-bridge=PIIX3|piix4-isa (Experimental option to select a particular south bridge. Default: PIIX3)

💅 OPTIONS 💅

disk_image is a raw hard disk image for IDE hard disk 0. Some targets do not need a disk image. (some of them are just built different fr fr)

When dealing with options parameters as arbitrary strings containing commas, such as in "file=my,file" and "string=a,b", it's necessary to double the commas. For instance, "-fw_cfg name=z,string=a,,b" will be parsed as "-fw_cfg name=z,string=a,b". yes bestie, the comma comma is on purpose, don't @ me.

🌈 Standard options 🌈

-h — Display help and exit
-version — Display version information and exit
-machine [type=]name[,prop=value[,...]] — Select the emulated machine by name. Use -machine help to list available machines.

For architectures which aim to support live migration compatibility across releases, each release will introduce a new versioned machine type. For example, the 2.8.0 release introduced machine types "pc-i440fx-2.8" and "pc-q35-2.8" for the x86_64/i686 architectures.

To allow live migration of guests from QEMU version 2.8.0, to QEMU version 2.9.0, the 2.9.0 version must support the "pc-i440fx-2.8" and "pc-q35-2.8" machines too. To allow users live migrating VMs to skip multiple intermediate releases when upgrading, new releases of QEMU will support machine types from many previous versions.

Supported machine properties are:

accel=accels1[:accels2[:...]] — This is used to enable an accelerator. Depending on the target architecture, kvm, xen, hvf, nitro, nvmm, whpx, mshv or tcg can be available. By default, tcg is used. If there is more than one accelerator specified, the next one is used if the previous one fails to initialize.
vmport=on|off|auto — Enables emulation of VMWare IO port, for vmmouse etc. auto says to select the value based on accel and i8042. For accel=xen or i8042=off the default is off otherwise the default is on.
dump-guest-core=on|off — Include guest memory in a core dump. The default is on.
mem-merge=on|off — Enables or disables memory merge support. This feature, when supported by the host, de-duplicates identical memory pages among VMs instances (enabled by default).
aes-key-wrap=on|off — Enables or disables AES key wrapping support on s390-ccw hosts. This feature controls whether AES wrapping keys will be created to allow execution of AES cryptographic functions. The default is on.
dea-key-wrap=on|off — Enables or disables DEA key wrapping support on s390-ccw hosts. This feature controls whether DEA wrapping keys will be created to allow execution of DEA cryptographic functions. The default is on.
nvdimm=on|off — Enables or disables NVDIMM support. The default is off.
memory-encryption=<id> — Memory encryption object to use. The default is none.
hmat=on|off — Enables or disables ACPI Heterogeneous Memory Attribute Table (HMAT) support. The default is off.
spcr=on|off — Enables or disables ACPI Serial Port Console Redirection Table (SPCR) support. The default is on.
aux-ram-share=on|off — Allocate auxiliary guest RAM as an anonymous file that is shareable with an external process. This option applies to memory allocated as a side effect of creating various devices. It does not apply to memory-backend-objects, whether explicitly specified on the command line, or implicitly created by the -m command line option. The default is off.

To use the cpr-transfer migration mode, you must set aux-ram-share=on. (no exceptions bestie, it's the rule)

memory-backend='id' — An alternative to legacy -mem-path and mem-prealloc options. Allows to use a memory backend as main RAM.

For example:

-object memory-backend-file,id=pc.ram,size=512M,mem-path=/hugetlbfs,prealloc=on,share=on
-machine memory-backend=pc.ram
-m 512M

Migration compatibility note:

as backend id one shall use value of 'default-ram-id', advertised by machine type (available via query-machines QMP command), if migration to/from old QEMU (<5.0) is expected.
for machine types 4.0 and older, user shall use x-use-canonical-path-for-ramblock-id=off backend option if migration to/from old QEMU (<5.0) is expected.

For example:

-object memory-backend-ram,id=pc.ram,size=512M,x-use-canonical-path-for-ramblock-id=off
-machine memory-backend=pc.ram
-m 512M

cxl-fmw.0.targets.0=firsttarget,cxl-fmw.0.targets.1=secondtarget,cxl-fmw.0.size=size[,cxl-fmw.0.interleave-granularity=granularity] — Define a CXL Fixed Memory Window (CFMW).

Described in the CXL 2.0 ECN: CEDT CFMWS & QTG _DSM.

They are regions of Host Physical Addresses (HPA) on a system which may be interleaved across one or more CXL host bridges. The system software will assign particular devices into these windows and configure the downstream Host-managed Device Memory (HDM) decoders in root ports, switch ports and devices appropriately to meet the interleave requirements before enabling the memory devices.

targets.X=target provides the mapping to CXL host bridges which may be identified by the id provided in the -device entry. Multiple entries are needed to specify all the targets when the fixed memory window represents interleaved memory. X is the target index from 0.

size=size sets the size of the CFMW. This must be a multiple of 256MiB. The region will be aligned to 256MiB but the location is platform and configuration dependent.

interleave-granularity=granularity sets the granularity of interleave. Default 256 (bytes). Only 256, 512, 1k, 2k, 4k, 8k and 16k granularities supported.

Example:

-machine cxl-fmw.0.targets.0=cxl.0,cxl-fmw.0.targets.1=cxl.1,cxl-fmw.0.size=128G,cxl-fmw.0.interleave-granularity=512

sgx-epc.0.memdev=<memid>,sgx-epc.0.node=<numaid> — Define an SGX EPC section.
smp-cache.0.cache=cachename,smp-cache.0.topology=topologylevel — Define cache properties for SMP system.

cache=cachename specifies the cache that the properties will be applied on. This field is the combination of cache level and cache type. It supports l1d (L1 data cache), l1i (L1 instruction cache), l2 (L2 unified cache) and l3 (L3 unified cache).

topology=topologylevel sets the cache topology level. It accepts CPU topology levels including core, module, cluster, die, socket, book, drawer and a special value default. If default is set, then the cache topology will follow the architecture's default cache topology model. If another topology level is set, the cache will be shared at corresponding CPU topology level. For example, topology=core makes the cache shared by all threads within a core. The omitting cache will default to using the default level.

The default cache topology model for an i386 PC machine is as follows: l1d, l1i, and l2 caches are per core, while the l3 cache is per die.

Example:

-machine smp-cache.0.cache=l1d,smp-cache.0.topology=core,smp-cache.1.cache=l1i,smp-cache.1.topology=core

-M — as -machine.
-cpu model — Select CPU model (-cpu help for list and additional feature selection)

okay that's part one bestie, there's so much more coming, don't go anywhere 💜

-accel name[,prop=value[,...]] — okay so this is how you switch on an accelerator, aka the thing that makes your guest actually move at a normal human speed 💨 Depending on the target architecture, one of kvm, xen, hvf, nitro, nvmm, whpx, mshv or tcg can be available. By default, tcg is used. And if you list more than one accelerator? The next one gets used if the previous one fails to initialize. backup-plan energy, we love a safety net 💅
- igd-passthru=on|off — when Xen is in use, this controls whether Intel integrated graphics devices can be passed through to the guest (default=off).
- kernel-irqchip=on|off|split — controls KVM in-kernel irqchip support. The default is full acceleration of the interrupt controllers. On x86, split irqchip reduces the kernel attack surface, at a performance cost for non-MSI interrupts. Completely disabling the in-kernel irqchip is not recommended except for debugging purposes. fr fr, that one's a debugging-only situation 😭
- kvm-shadow-mem=size — defines the size of the KVM shadow MMU.
- one-insn-per-tb=on|off — makes the TCG accelerator put only one guest instruction into each translation block. This slows down emulation a lot, but it can be useful in some situations, such as when you're trying to analyse the logs produced by the -d option. it's giving "painful but necessary for the lore" 🙈
- split-wx=on|off — controls the use of split w^x mapping for the TCG code generation buffer. Some operating systems require this to be enabled, and in such a case this will default on. On other operating systems, this will default off, but you may enable this for testing or debugging.
- tb-size=n — controls the size (in MiB) of the TCG translation block cache.
- thread=single|multi — controls the number of TCG threads. When TCG is multi-threaded there will be one thread per vCPU, therefore taking advantage of additional host cores. The default is to enable multi-threading where both the back-end and front-ends support it and no incompatible TCG features have been enabled (e.g. icount/replay). more threads, more slay 🔥
- dirty-ring-size=n — when the KVM accelerator is used, this controls the size of the per-vCPU dirty page ring buffer (number of entries for each vCPU). It should be a value that is a power of two, and it should be 1024 or bigger (but still less than the maximum value that the kernel supports). 4096 could be a good initial value if you have no idea which is the best. Set this value to 0 to disable the feature. By default, this feature is disabled (dirty-ring-size=0). When enabled, KVM will instead record dirty pages in a bitmap.
- eager-split-size=n — KVM implements dirty page logging at the PAGE_SIZE granularity, and enabling dirty-logging on a huge-page requires breaking it into PAGE_SIZE pages in the first place. KVM on ARM does this splitting lazily by default. There are performance benefits in doing huge-page split eagerly, especially in situations where TLBI costs associated with break-before-make sequences are considerable and also if guest workloads are read intensive. The size here specifies how many pages to break at a time and needs to be a valid block size which is 1GiB/2MiB/4KiB, 32MiB/16KiB and 512MiB/64KiB for 4KiB/16KiB/64KiB PAGE_SIZE respectively. Be wary of specifying a higher size as it will have an impact on the memory. By default, this feature is disabled (eager-split-size=0).
- notify-vmexit=run|internal-error|disable,notify-window=n — enables or disables notify VM exit support on x86 host and specifies the corresponding notify window to trigger the VM exit if enabled. The run option enables the feature. It does nothing and continues if the exit happens. The internal-error option enables the feature. It raises an internal error. The disable option doesn't enable the feature. This feature can mitigate the CPU stuck issue due to event windows not opening up for a specified amount of time (i.e. notify-window). Default: notify-vmexit=run,notify-window=0.
- device=path — sets the path to the KVM device node. Defaults to /dev/kvm. This option can be used to pass the KVM device to use via a file descriptor by setting the value to /dev/fdset/NN.
- hyperv=on|off|auto — for the WHPX backend, determines whether to enable Hyper-V enlightenments. On x86_64, Hyper-V enlightenments are on by default. On AArch64, they're off by default.

-smp — the people's favourite 🎀

-smp [[cpus=]n][,maxcpus=maxcpus][,drawers=drawers][,books=books][,sockets=sockets][,dies=dies][,clusters=clusters][,modules=modules][,cores=cores][,threads=threads]

Simulate an SMP system with n CPUs initially present on the machine type board. On boards supporting CPU hotplug, the optional maxcpus parameter can be set to enable further CPUs to be added at runtime. When both parameters are omitted, the maximum number of CPUs will be calculated from the provided topology members and the initial CPU count will match the maximum number. When only one of them is given then the omitted one will be set to its counterpart's value. Both parameters may be specified, but the maximum number of CPUs must be equal to or greater than the initial CPU count. Product of the CPU topology hierarchy must be equal to the maximum number of CPUs. Both parameters are subject to an upper limit that is determined by the specific machine type chosen.

To control reporting of CPU topology information, values of the topology parameters can be specified. Machines may only support a subset of the parameters and different machines may have different subsets supported which vary depending on capacity of the corresponding CPU targets. So for a particular machine type board, an expected topology hierarchy can be defined through the supported sub-option. Unsupported parameters can also be provided in addition to the sub-option, but their values must be set as 1 in the purpose of correct parsing. tl;dr: don't set unsupported ones to anything but 1 or the parser gets confused 🙈

Either the initial CPU count, or at least one of the topology parameters must be specified. The specified parameters must be greater than zero, explicit configuration like cpus=0 is not allowed. Values for any omitted parameters will be computed from those which are given.

For example, the following sub-option defines a CPU topology hierarchy (2 sockets totally on the machine, 2 cores per socket, 2 threads per core) for a machine that only supports sockets/cores/threads. Some members of the option can be omitted but their values will be automatically computed:

-smp 8,sockets=2,cores=2,threads=2,maxcpus=8

The following sub-option defines a CPU topology hierarchy (2 sockets totally on the machine, 2 dies per socket, 2 modules per die, 2 cores per module, 2 threads per core) for PC machines which support sockets/dies/modules/cores/threads. Some members of the option can be omitted but their values will be automatically computed:

-smp 32,sockets=2,dies=2,modules=2,cores=2,threads=2,maxcpus=32

The following sub-option defines a CPU topology hierarchy (2 sockets totally on the machine, 2 clusters per socket, 2 cores per cluster, 2 threads per core) for ARM virt machines which support sockets/clusters/cores/threads. Some members of the option can be omitted but their values will be automatically computed:

-smp 16,sockets=2,clusters=2,cores=2,threads=2,maxcpus=16

Historically preference was given to the coarsest topology parameters when computing missing values (ie sockets preferred over cores, which were preferred over threads), however, this behaviour is considered liable to change. Prior to 6.2 the preference was sockets over cores over threads. Since 6.2 the preference is cores over sockets over threads. so if you're on old QEMU the vibes are simply different 🫶

For example, the following option defines a machine board with 2 sockets of 1 core before 6.2 and 1 socket of 2 cores after 6.2:

-smp 2

Note: The cluster topology will only be generated in ACPI and exposed to guest if it's explicitly specified in -smp. no sneaky auto-clusters, bestie ✨

-numa — NUMA time, stay with me, it's a lot but it's so worth it 💖

-numa node[,mem=size][,cpus=firstcpu[-lastcpu]][,nodeid=node][,initiator=initiator]

-numa node[,memdev=id][,cpus=firstcpu[-lastcpu]][,nodeid=node][,initiator=initiator]

-numa dist,src=source,dst=destination,val=distance

-numa cpu,node-id=node[,socket-id=x][,core-id=y][,thread-id=z]

-numa hmat-lb,initiator=node,target=node,hierarchy=hierarchy,data-type=type[,latency=lat][,bandwidth=bw]

-numa hmat-cache,node-id=node,size=size,level=level[,associativity=str][,policy=str][,line=size]

Define a NUMA node and assign RAM and VCPUs to it. Set the NUMA distance from a source node to a destination node. Set the ACPI Heterogeneous Memory Attributes for the given nodes. three whole jobs in one flag, main character energy fr 👑

Legacy VCPU assignment uses the cpus option where firstcpu and lastcpu are CPU indexes. Each cpus option represents a contiguous range of CPU indexes (or a single VCPU if lastcpu is omitted). A non-contiguous set of VCPUs can be represented by providing multiple cpus options. If cpus is omitted on all nodes, VCPUs are automatically split between them.

For example, the following option assigns VCPUs 0, 1, 2 and 5 to a NUMA node:

-numa node,cpus=0-2,cpus=5

Okay so the cpu option is the brand new alternative to the cpus option, and she's serving ✨topology✨ — she uses socket-id|core-id|thread-id properties to assign CPU objects to a node using the topology layout properties of the CPU. 💅

Heads up bestie: the exact set of properties is machine specific, and it depends on the machine type you're using and your smp options. Wanna know what's on the menu? Query it with the hotpluggable-cpus monitor command. 🔍

The node-id property says which node the CPU object gets assigned to, and it is required that the node be declared with the node option before it's used with the cpu option. No declaring-later shenanigans. 🙅‍♀️

For example:

-M pc \
-smp 1,sockets=2,maxcpus=2 \
-numa node,nodeid=0 -numa node,nodeid=1 \
-numa cpu,node-id=0,socket-id=0 -numa cpu,node-id=1,socket-id=1

The memdev option assigns RAM from a given memory backend device to a node. And ngl, you should use memdev over the legacy mem option — it's the recommended one. Why? Because memdev gives you better performance and more control over the backend's RAM, like the prealloc parameter of -memory-backend-ram, which lets memory be preallocated. 🔥

For compatibility reasons, the legacy mem option is supported in 5.0 and older machine types. But watch out: mem and memdev are mutually exclusive. If one node uses memdev, every other node has to use memdev too, and vice versa. No mixing, it's giving monogamy. 💀

Users must specify memory for all NUMA nodes via memdev (or the legacy mem, if it's available). And jsyk, in QEMU 5.2 the support for -numa node without memory specified was removed. 🫠

initiator is an extra option that points to an initiator NUMA node that has the best performance (the lowest latency or the largest bandwidth) to this NUMA node. Note that this option can only be set when the machine property hmat is set to on. 📌

The following example creates a machine with 2 NUMA nodes: node 0 has CPU, node 1 has only memory, and its initiator is node 0. Note that because node 0 has CPU, by default the initiator of node 0 is itself and must be itself:

-machine hmat=on \
-m 2G,slots=2,maxmem=4G \
-object memory-backend-ram,size=1G,id=m0 \
-object memory-backend-ram,size=1G,id=m1 \
-numa node,nodeid=0,memdev=m0 \
-numa node,nodeid=1,memdev=m1,initiator=0 \
-smp 2,sockets=2,maxcpus=2  \
-numa cpu,node-id=0,socket-id=0 \
-numa cpu,node-id=0,socket-id=1

Now, source and destination are NUMA node IDs, and distance is the NUMA distance from source to destination. The distance from a node to itself is always 10. ✨

If any pair of nodes is given a distance, then all pairs must be given distances. Although — when distances are only given in one direction for each pair of nodes, then the distances in the opposite directions are assumed to be the same. If, however, an asymmetrical pair of distances is given for even one node pair, then all node pairs must be provided distance values for both directions, even when they're symmetrical. 🙈

When a node is unreachable from another node, set the pair's distance to 255. 📵

Note that the -numa option doesn't allocate any of the specified resources — it just assigns existing resources to NUMA nodes. Which means you still have to use the -m and -smp options to allocate RAM and VCPUs respectively. Don't forget, bestie. 💖

hmat-lb sets System Locality Latency and Bandwidth Information between initiator and target NUMA nodes in the ACPI Heterogeneous Attribute Memory Table (HMAT). The initiator NUMA node can create memory requests (usually it has one or more processors), and the target NUMA node contains addressable memory. 🧠

In the hmat-lb option, node is the NUMA node IDs. hierarchy is the memory hierarchy of the target NUMA node:

if hierarchy is memory, the structure represents the memory performance;
if hierarchy is first-level|second-level|third-level, this structure represents aggregated performance of memory side caches for each domain.

type of data-type is the type of data represented by this structure instance:

if hierarchy is memory, data-type is access|read|write latency or access|read|write bandwidth of the target memory;
if hierarchy is first-level|second-level|third-level, data-type is access|read|write hit latency or access|read|write hit bandwidth of the target memory side cache.

lat is the latency value in nanoseconds. bw is the bandwidth value — the possible value and units are NUM[M|G|T], meaning the bandwidth value is NUM byte per second (or MiB/s, GiB/s or TiB/s depending on the used suffix). Note that if the latency or bandwidth value is 0, it means the corresponding latency or bandwidth information is not provided. 🚫

In the hmat-cache option, node-id is the NUMA-id of the memory belongs. size is the size of memory side cache in bytes. level is the cache level described in this structure — note that cache level 0 should not be used with the hmat-cache option. associativity is the cache associativity, and the possible value is none/direct(direct-mapped)/complex(complex cache indexing). policy is the write policy. line is the cache Line size in bytes.

For example, the following options describe 2 NUMA nodes. Node 0 has 2 cpus and a ram, node 1 has only a ram. The processors in node 0 access memory in node 0 with access-latency 5 nanoseconds, access-bandwidth is 200 MiB/s; The processors in NUMA node 0 access memory in NUMA node 1 with access-latency 10 nanoseconds, access-bandwidth is 100 MiB/s. And for memory side cache information, NUMA node 0 and 1 both have 1 level memory cache, size is 10KiB, policy is write-back, the cache Line size is 8 bytes:

-machine hmat=on \
-m 2G \
-object memory-backend-ram,size=1G,id=m0 \
-object memory-backend-ram,size=1G,id=m1 \
-smp 2,sockets=2,maxcpus=2 \
-numa node,nodeid=0,memdev=m0 \
-numa node,nodeid=1,memdev=m1,initiator=0 \
-numa cpu,node-id=0,socket-id=0 \
-numa cpu,node-id=0,socket-id=1 \
-numa hmat-lb,initiator=0,target=0,hierarchy=memory,data-type=access-latency,latency=5 \
-numa hmat-lb,initiator=0,target=0,hierarchy=memory,data-type=access-bandwidth,bandwidth=200M \
-numa hmat-lb,initiator=0,target=1,hierarchy=memory,data-type=access-latency,latency=10 \
-numa hmat-lb,initiator=0,target=1,hierarchy=memory,data-type=access-bandwidth,bandwidth=100M \
-numa hmat-cache,node-id=0,size=10K,level=1,associativity=direct,policy=write-back,line=8 \
-numa hmat-cache,node-id=1,size=10K,level=1,associativity=direct,policy=write-back,line=8

💖 `-add-fd` 💖

-add-fd fd=fd,set=set[,opaque=opaque]

Add a file descriptor to an fd set, bestie. Valid options are:

fd=fd — this option defines the file descriptor of which a duplicate is added to fd set. The file descriptor cannot be stdin, stdout, or stderr. 🙅‍♀️
set=set — this option defines the ID of the fd set to add the file descriptor to.
opaque=opaque — this option defines a free-form string that can be used to describe fd.

You can open an image using pre-opened file descriptors from an fd set, like so:

qemu-system-x86_64 \
 -add-fd fd=3,set=2,opaque="rdwr:/path/to/file" \
 -add-fd fd=4,set=2,opaque="rdonly:/path/to/file" \
 -drive file=/dev/fdset/2,index=0,media=disk

✨ `-set` ✨

-set group.id.arg=value

Set parameter arg for item id of type group. Short, sweet, slays. 🎀

🦋 `-global` 🦋

-global driver.prop=value
-global driver=driver,property=property,value=value

Set the default value of driver's property prop to value. For example:

qemu-system-x86_64 -global ide-hd.physical_block_size=4096 disk-image.img

In particular, you can use this to set driver properties for devices which are created automatically by the machine model. To create a device which isn't created automatically and set properties on it, use -device. 👑

And jsyk, -global driver.prop=value is shorthand for -global driver=driver,property=prop,value=value. The longhand syntax works even when driver contains a dot. Periodt. 💅

👑 `-boot` 👑

-boot [order=drives][,once=drives][,menu=on|off][,splash=sp_name][,splash-time=sp_time][,reboot-timeout=rb_timeout][,strict=on|off]

Specify the boot order drives as a string of drive letters. Which drive letters are valid depends on the target architecture — the x86 PC uses: a, b (floppy 1 and 2), c (first hard disk), d (first CD-ROM), n-p (Etherboot from network adapter 1-4). Hard disk boot is the default. 🖥️

To apply a particular boot order only on the first startup, specify it via once. Note that the order or once parameter should not be used together with the bootindex property of devices, since firmware implementations normally do not support both at the same time. Pick a lane, babe. 😭

Interactive boot menus/prompts can be enabled via menu=on, as far as firmware/BIOS supports them. The default is non-interactive boot.

A splash picture could be passed to bios, letting the user show it as a logo, when the option splash=sp_name is given and menu=on, if firmware/BIOS supports them. Currently Seabios for X86 system supports it. limitation: the splash file could be a jpeg file or a BMP file in 24 BPP format (true color). The resolution should be supported by the SVGA mode, so the recommended is 320x240, 640x480, 800x640. 🌸

A timeout could be passed to bios — guest will pause for rb_timeout ms when boot failed, then reboot. If rb_timeout is -1, guest will not reboot, and qemu passes -1 to bios by default. Currently Seabios for X86 system supports it. ⏳

Do strict boot via strict=on, as far as firmware/BIOS supports it. This only effects when boot priority is changed by bootindex options. The default is non-strict boot.

# try to boot from network first, then from hard disk
qemu-system-x86_64 -boot order=nc
# boot from CD-ROM first, switch back to default order after reboot
qemu-system-x86_64 -boot once=d
# boot with a splash picture for 5 seconds.
qemu-system-x86_64 -boot menu=on,splash=/root/boot.bmp,splash-time=5000

💀 okay bestie, real talk for a sec: the legacy format -boot drives is still supported but its use is discouraged, because it may be removed from future versions. It's giving deprecated. Proceed with caution, queen. 🫶

-m [size=]megs[,slots=n,maxmem=size] — sets the guest startup RAM size to megs megabytes. Default is 128 MiB. You can also slap a suffix of "M" or "G" on it to mean megabytes or gigabytes respectively. And if you want, the optional pair slots, maxmem lets you set the amount of hotpluggable memory slots and the maximum amount of memory. Heads up tho — maxmem must be aligned to the page size. ✨

Like, for example, this command-line sets the guest startup RAM size to 1GiB, creates 3 slots to hotplug additional memory, and sets the maximum memory the guest can reach to 4GiB:

qemu-system-x86_64 -m 1G,slots=3,maxmem=4G

And if slots and maxmem aren't specified, memory hotplug won't be enabled and the guest startup RAM will never increase. That's it, that's the deal. 🎀

-mem-path path — allocates guest RAM from a temporarily created file in path.
-mem-prealloc — preallocates memory when using -mem-path. Not me being extra, it's just what it does.
-k language — use keyboard layout language (for example fr for French). This option is only needed where it's not easy to get raw PC keycodes — like on Macs, with some X11 servers, or with a VNC or curses display. On PC/Linux or PC/Windows hosts you don't normally need it, bestie. 🦋

The available layouts are:

ar  de-ch  es  fo     fr-ca  hu  ja  mk     no  pt-br  sv
da  en-gb  et  fr     fr-ch  is  lt  nl     pl  ru     th
de  en-us  fi  fr-be  hr     it  lv  nl-be  pt  sl     tr

The default is en-us. 👑

-audio [driver=]driver[,model=value][,prop=value[,...]] — if the model option is specified, -audio is lowkey a shortcut for configuring both the guest audio hardware and the host audio backend in one go. The guest hardware model gets set with model=modelname. Use model=help to list the available device types.

These two examples do exactly the same thing, just to show how -audio can shorten the command line length:

qemu-system-x86_64 -audiodev pa,id=pa -device sb16,audiodev=pa
qemu-system-x86_64 -audio pa,model=sb16

If the model option is not specified, -audio is used to configure a default audio backend that will be used whenever the audiodev property isn't set on a device or machine. In particular, -audio none ensures that no audio is produced even for machines that have embedded sound hardware. Iconic, honestly.

In both cases, the driver option is the same as with the corresponding -audiodev option below. Use driver=help to list the available drivers. 🌈

-audiodev [driver=]driver,id=id[,prop=value[,...]] — adds a new audio backend driver identified by id. ✨

If no audio backend is specified, QEMU will attempt to select a default one. The -display option may influence which backend is selected.

There are global and driver specific properties. Some values can be set differently for input and output — they're marked with in|out.. You can set the input's property with in.prop and the output's property with out.prop. For example:

-audiodev alsa,id=example,in.frequency=44110,out.frequency=8000
-audiodev alsa,id=example,out.channels=1 # leaves in.channels unspecified

⚠️ NOTE: parameter validation is known to be incomplete. In many cases, specifying an invalid option causes QEMU to print an error message and continue emulation without sound. So like, your vibes may be silent and you won't even know why. 😭

Valid global options are:

id=identifier — identifies the audio backend. Gotta have a name, bestie.
timer-period=period — sets the timer period used by the audio subsystem in microseconds. Default is 10000 (10 ms).
in|out.mixing-engine=on|off — use QEMU's mixing engine to mix all streams inside QEMU and convert audio formats when not supported by the backend. When off, fixed-settings must be off too. Note that disabling this option means the selected backend must support multiple streams and the audio formats used by the virtual cards — otherwise you'll get no sound. It's not recommended to disable this option unless you want to use 5.1 or 7.1 audio, as the mixing engine only supports mono and stereo audio. Default is on.
in|out.fixed-settings=on|off — use fixed settings for host audio. When off, it will change based on how the guest opens the sound card. In this case you must not specify frequency, channels or format. Default is on.
in|out.frequency=frequency — specify the frequency to use when using fixed-settings. Default is 44100Hz.
in|out.channels=channels — specify the number of channels to use when using fixed-settings. Default is 2 (stereo).
in|out.format=format — specify the sample format to use when using fixed-settings. Valid values are: s8, s16, s32, u8, u16, u32, f32. Default is s16.
in|out.voices=voices — specify the number of voices to use. Default is 1.
in|out.buffer-length=usecs — sets the size of the buffer in microseconds.

-audiodev none,id=id[,prop=value[,...]] — creates a dummy backend that discards all outputs. This backend has no backend specific properties. Slay, minimal queen.
-audiodev alsa,id=id[,prop=value[,...]] — creates a backend using the ALSA. This backend is only available on Linux. 🐧

ALSA specific options are:

in|out.dev=device — specify the ALSA device to use for input and/or output. Default is default.
in|out.period-length=usecs — sets the period length in microseconds.
in|out.try-poll=on|off — attempt to use poll mode with the device. Default is off.
threshold=threshold — threshold (in microseconds) when playback starts. Default is 0.

-audiodev coreaudio,id=id[,prop=value[,...]] — creates a backend using Apple's Core Audio. This backend is only available on Mac OS and only supports playback. 🍎

Core Audio specific options are:

in|out.buffer-count=count — sets the count of the buffers.

-audiodev dbus,id=id[,prop=value[,...]] — creates a D-Bus backend. It must be associated with the display (as -display dbus,audiodev=id). (Since 7.0) ✨

D-Bus specific options are:

nsamples — number of samples per read/write (default to 480, 10ms at 48kHz) (Since 10.0).

-audiodev dsound,id=id[,prop=value[,...]] — creates a backend using Microsoft's DirectSound. This backend is only available on Windows and only supports playback. 🪟

DirectSound specific options are:

latency=usecs — add extra usecs microseconds latency to playback. Default is 10000 (10 ms).

-audiodev oss,id=id[,prop=value[,...]] — creates a backend using OSS. This backend is available on most Unix-like systems. 🐚

OSS specific options are:

in|out.dev=device — specify the file name of the OSS device to use. Default is /dev/dsp.
in|out.buffer-count=count — sets the count of the buffers.
in|out.try-poll=on|off — attempt to use poll mode with the device. Default is on.
try-mmap=on|off — try using memory mapped device access. Default is off.
exclusive=on|off — open the device in exclusive mode (vmix won't work in this case). Default is off.
dsp-policy=policy — sets the timing policy (between 0 and 10, where a smaller number means smaller latency but higher CPU usage). Use -1 to use buffer sizes specified by buffer and buffer-count. This option is ignored if you do not have OSS 4. Default is 5.

-audiodev pa,id=id[,prop=value[,...]] — creates a backend using PulseAudio. This backend is available on most systems. 💖

PulseAudio specific options are:

server=server — sets the PulseAudio server to connect to.
in|out.name=sink — use the specified source/sink for recording/playback.
in|out.latency=usecs — desired latency in microseconds. The PulseAudio server will try to honor this value but actual latencies may be lower or higher. It's giving "best effort." 🙈

-audiodev pipewire,id=id[,prop=value[,...]] — creates a backend using PipeWire. This backend is available on most systems. 🌸

PipeWire specific options are:

in|out.latency=usecs — desired latency in microseconds.
in|out.name=sink — use the specified source/sink for recording/playback.
in|out.stream-name — specify the name of pipewire stream.

-audiodev sdl,id=id[,prop=value[,...]] — creates a backend using SDL. This backend is available on most systems, but you should use your platform's native backend if possible. Like, SDL is fine but it's not the moment. 💅

SDL specific options are:

in|out.buffer-count=count — sets the count of the buffers.

-audiodev sndio,id=id[,prop=value[,...]] — creates a backend using SNDIO. This backend is available on OpenBSD and most other Unix-like systems. 🐡

Sndio specific options are:

in|out.dev=device — specify the sndio device to use for input and/or output. Default is default.
in|out.latency=usecs — sets the desired period length in microseconds.

-audiodev spice,id=id[,prop=value[,...]] — creates a backend that sends audio through SPICE. This backend requires -spice and is automatically selected in that case, so usually you can ignore this option. This backend has no backend specific properties. Main character energy: shows up on its own. 👑
-audiodev wav,id=id[,prop=value[,...]] — creates a backend that writes audio to a WAV file. 🎧

Backend specific options are:

path=path — write recorded audio into the specified file. Default is qemu.wav.

-device driver[,prop=value[,...]] — bestie, this is how you drop a device into the guest. prop=value sets that driver's properties, and which properties are even legal depends entirely on the driver you picked. Wanna know what your options are? Run -device help for the driver list and -device driver,help for that driver's properties. ✨

Some drivers, coming right up:

🎀 `-device ipmi-bmc-sim,id=id[,prop=value[,...]]`

Adds an IPMI BMC. This is a simulation of a hardware management interface processor that normally just... sits on a system. It provides a watchdog, plus the ability to reset and power-control the system. You gotta connect it to an IPMI interface or it's giving nothing, honestly — useless on its own. 💅

So about the slave address: that's the IPMI slave address to use for the BMC, and the default is 0x20. It's the BMC's address on the I2C network of management controllers. If you don't know what that means, ngl, it's safe to ignore it. 🫶

id=id — the BMC id that interfaces use to talk to this device.
slave_addr=val — sets the slave address for the BMC. Default is 0x20.
sdrfile=file — a file holding raw Sensor Data Records (SDR) data. Default is none.
fruareasize=val — the size of a Field Replaceable Unit (FRU) area. Default is 1024.
frudatafile=file — a file holding raw Field Replaceable Unit (FRU) inventory data. Default is none.
guid=uuid — the GUID value for the BMC, in standard UUID format. Set this and a "Get GUID" command to the BMC returns it; otherwise "Get GUID" returns an error. no cap. 😭
lan.channel=val — channel number of the fake LAN channel. It can be 0 or any integer from 0x1 to 0xb inclusive. Set it to 0 and the LAN channel is disabled; otherwise it's enabled at the channel number you picked. Default is 0.
lan.ipaddr=addr — the ipv4 address of the BMC LAN channel.
lan.ipsrc=val — the ipv4 address source of the BMC LAN channel. It can be 0 (unspecified source), 1 (static address), 2 (DHCP), 3 (BIOS or system software), or 4 (other source). Default is 0.
lan.macaddr=mac — the mac address of the BMC LAN channel.
lan.netmask=mask — the ipv4 subnet mask for the BMC LAN channel.
lan.defgw_ipaddr=addr — the default gateway ipv4 address for the BMC LAN channel.
lan.defgw_macaddr=mac — the default gateway mac address for the BMC LAN channel.

🌸 `-device ipmi-bmc-extern,id=id,chardev=id[,slave_addr=val]`

Adds a connection to an external IPMI BMC simulator. Instead of locally emulating the BMC like the one above, you connect out to an external entity that provides the IPMI services. iconic behavior.

A connection is made to an external BMC simulator. If you do this, it is strongly recommended that you use the reconnect-ms= chardev option so it reconnects to the simulator if the connection drops. 👑

⚠️ Real talk: if this is not used carefully, it can be a security issue, because the interface has the ability to send resets, NMIs, and power off the VM. The move is to have QEMU connect to an external simulator running on a secure port on localhost, so that neither the simulator nor QEMU is exposed to any outside network. fr fr, keep it local. 🔒

See the lanserv/README.vm file in the OpenIPMI library for more details on the external interface.

🦋 `-device isa-ipmi-kcs,bmc=id[,ioport=val][,irq=val]`

Adds a KCS IPMI interface on the ISA bus. This also adds a corresponding ACPI and SMBIOS entry, if appropriate.

bmc=id — the BMC to connect to, one of ipmi-bmc-sim or ipmi-bmc-extern from above.
ioport=val — the I/O address of the interface. Default is 0xca0 for KCS.
irq=val — the interrupt to use. Default is 5. To disable interrupts, set this to 0.

💖 `-device isa-ipmi-bt,bmc=id[,ioport=val][,irq=val]`

Like the KCS interface, but it defines a BT interface. Default port is 0xe4 and the default interrupt is 5.

✨ `-device pci-ipmi-kcs,bmc=id`

Adds a KCS IPMI interface on the PCI bus.

bmc=id — the BMC to connect to, one of ipmi-bmc-sim or ipmi-bmc-extern from above.

💜 `-device pci-ipmi-bt,bmc=id`

Like the KCS interface, but it defines a BT interface on the PCI bus.

👑 `-device intel-iommu[,option=...]`

This one is only supported by -machine q35, which enables Intel VT-d emulation inside the guest. It supports these options below:

intremap=on|off (default: auto) — enables the interrupt remapping feature. It's required to enable complete x2apic. Currently it only supports kvm kernel-irqchip modes off or split, while full kernel-irqchip is not yet supported. The default value is auto, which gets decided by the mode of kernel-irqchip.
caching-mode=on|off (default: off) — enables caching mode for the VT-d emulated device. When caching-mode is enabled, each guest DMA buffer mapping will generate an IOTLB invalidation from the guest IOMMU driver to the vIOMMU device in a synchronous way. It's required for -device vfio-pci to work with the VT-d device, because host assigned devices require setting up the DMA mapping on the host before guest DMA starts. slay.
device-iotlb=on|off (default: off) — enables device-iotlb capability for the emulated VT-d device. So far virtio/vhost should be the only real user for this parameter, paired with ats=on configured for the device.
aw-bits=39|48 (default: 39) — decides the address width of the IOVA address space. This address space has 39 bits width for 3-level IOMMU page tables, and 48 bits for 4-level IOMMU page tables.

Please also refer to the wiki page for general scenarios of VT-d emulation in QEMU: <https://wiki.qemu.org/Features/VT-d>.

🌈 `-device virtio-iommu-pci[,option=...]`

Only supported by -machine q35 (x86_64) and -machine virt (ARM). It supports these options below:

granule=val (possible values are 4k, 8k, 16k, 64k and host; default: host) — decides the default granule to be exposed by the virtio-iommu. If host, the granule matches the host page size.
aw-bits=val (val between 32 and 64, default depends on machine) — decides the address width of the IOVA address space.

🧚 `-device arm-smmuv3,primary-bus=id[,option=...]`

Only supported by -machine virt (ARM).

primary-bus=id — accepts either the default root complex (pcie.0) or a pxb-pcie based root complex.
accel=on|off (default: off) — enables the guest to leverage host SMMUv3 features for acceleration. Enabling accel configures the host SMMUv3 in nested mode to support vfio-pci passthrough.

The following options are available when accel=on. Note: 'auto' mode is not currently supported.

ril=on|off (default: on) — support for Range Invalidation, which allows the SMMUv3 driver to invalidate TLB entries for a range of IOVAs at once instead of issuing separate commands to invalidate each page. Must match with host SMMUv3 Range Invalidation support.
ats=on|off (default: off) — support for Address Translation Services, which enables PCIe devices to cache address translations in their local TLB and reduce latency. Host SMMUv3 must support ATS in order to enable this feature for the vIOMMU.
oas=val (supported values are 44 and 48. default: 44) — sets the Output Address Size in bits. The value set here must be less than or equal to the host SMMUv3's supported OAS, so that the intermediate physical addresses (IPA) consumed by host SMMU for stage-2 translation do not exceed the host's max supported IPA size.
ssidsize=val (val between 0 and 20. default: 0) — sets the Substream ID size in bits. When set to a non-zero value, PASID capability is advertised to the vIOMMU and accelerated use cases such as Shared Virtual Addressing (SVA) are supported. obsessed. 💅

🍓 `-device amd-iommu[,option=...]`

Enables emulation of an AMD-Vi I/O Memory Management Unit (IOMMU). Only available with -machine q35, and it supports the following options:

dma-remap=on|off (default: off) — support for DMA address translation and access permission checking for guests attaching passthrough devices to paging domains, using the AMD v1 I/O Page Table format. This enables -device vfio-pci,... to work correctly with a guest using the DMA remapping feature of the vIOMMU.
intremap=on|off (default: auto) — generic x86 IOMMU functionality implemented by the amd-iommu device. Enables interrupt remapping feature in guests, which is also required to enable x2apic support. Currently only available with kernel-irqchip=off|split, it is automatically enabled when either of those modes is in use, and disabled with kernel-irqchip=on.
xtsup=on|off (default: off) — interrupt remapping table supports x2apic mode, enabling the use of 128-bit IRTE format with 32-bit destination field by the guest. Required to support routing interrupts to vCPUs with APIC IDs larger than 0xff.

🎀 `-name name`

Sets the name of the guest. This name will be displayed in the SDL window caption. The name will also be used for the VNC server. Also optionally sets the top visible process name in Linux. Naming of individual threads can also be enabled on Linux to aid debugging. main character energy for your VM, honestly. ✨

💜 `-uuid uuid`

Set system UUID. literally that's it, bestie. 🫶

Block device options 💾✨

okay so bestie, the QEMU block device options have a long history — like, they've been through several glow-ups as the block layer got fancier and more complex. lowkey a whole saga. and because of that, a lot of the QEMU guides floating around online are still referencing the older, deprecated options, which is giving major confusion energy. so let's clear it up. 🧚

the most explicit way to describe disks is to use a combo of -device (which says what the hardware device is) and -blockdev (which describes the backend). basically: the device defines what the guest sees, and the backend describes how QEMU handles the data. this pairing is the only guaranteed stable interface for describing block devices, so it's the one you want for management tools and scripting. periodt. 💅

the -drive option smushes the device and backend into one single command line option, which is way more human friendly 🫶. but heads up: there's no interface stability guarantee with it, although some older board models still need updating to work with the modern blockdev forms.

and then there's the ancient ones like -hda, which are basically just macros that expand into -drive options for various drive interfaces. the original forms bake in a lot of assumptions from back when QEMU was emulating a legacy PC, so they're not recommended for modern configs. it's giving fossil vibes. 🦴

-fda file
-fdb file

Use file as floppy disk 0/1 image (see the Disk Images <#disk-images> chapter in the System Emulation Users Guide). 🎀

-hda file
-hdb file
-hdc file
-hdd file

Use file as hard disk 0, 1, 2 or 3 image on the default bus of the emulated machine — so like, that's the IDE bus on most x86 machines, but on other target architectures it could be SCSI, virtio, or something else entirely. See also the Disk Images <#disk-images> chapter in the System Emulation Users Guide. 🌸

-cdrom file

Use file as CD-ROM image on the default bus of the emulated machine (which is IDE1 master on x86, jsyk, so you literally cannot use -hdc and -cdrom at the same time there — pick one, bestie 😭). On systems that support it, you can use the host CD-ROM by passing /dev/cdrom as the filename. iconic.

-blockdev option[,option[,option[,...]]]

Define a new block driver node. ✨ some of the options apply to all block drivers, and other options are only accepted for a specific block driver. see below for the generic list plus the options for the most common block drivers.

Options that expect a reference to another node (like file) can be given in two ways. either you specify the node name of an already existing node — file=node-name — or you define a new node inline and add options for the referenced node after a dot, like file.filename=path,file.aio=native. 🦋

A block driver node created with -blockdev can be used for a guest device by specifying its node name for the drive property in a -device argument that defines a block device.

Valid options for any block driver node:

driver — Specifies the block driver to use for the given node. 👑
node-name — This defines the name of the block driver node by which it will be referenced later. the name must be unique, i.e. it must not match the name of a different block driver node, or (if you're also using -drive) the ID of a drive.

If no node name is specified, it gets auto-generated. but the generated node name is not intended to be predictable and changes between QEMU invocations, so don't go counting on it. For the top level, an explicit node name must be specified. no exceptions. 💀

read-only — Open the node read-only. Guest write attempts will fail. 🙈

Note that some block drivers support only read-only access, either generally or in certain configurations. In that case the default value read-only=off does not work and the option must be specified explicitly.

auto-read-only — If auto-read-only=on is set, QEMU may fall back to read-only usage even when read-only=off is requested, or even switch between modes as needed — like, depending on whether the image file is writable or whether a writing user is attached to the node. it's flexible like that. 💅
force-share — Override the image locking system of QEMU by forcing the node to utilize weaker shared access for permissions where it would normally request exclusive access. When there's the potential for multiple instances to have the same file open (whether this invocation of QEMU is the first or the second instance), both instances must permit shared access for the second instance to succeed at opening the file.

Enabling force-share=on requires read-only=on.

cache.direct — The host page cache can be avoided with cache.direct=on. this will attempt to do disk IO directly to the guest's memory. ngl QEMU may still perform an internal copy of the data.
cache.no-flush — In case you don't care about data integrity over host failures, you can use cache.no-flush=on. this option tells QEMU that it never needs to write any data to the disk but can instead keep things in cache. ⚠️ and if anything goes wrong — like your host losing power, the disk storage getting disconnected accidentally, etc. — your image will most probably be rendered unusable. not the vibe you want. 😭
discard=discard — discard is one of "ignore" (or "off") or "unmap" (or "on") and controls whether discard (also known as trim or unmap) requests are ignored or passed to the filesystem. Some machine types may not support discard requests. fr fr.
detect-zeroes=detect-zeroes — detect-zeroes is "off", "on" or "unmap" and enables the automatic conversion of plain zero writes by the OS to driver specific optimized zero write commands. You may even choose "unmap" if discard is set to "unmap" to allow a zero write to be converted to an unmap operation. slay. ✨

Driver-specific options for file 🗂️

This is the protocol-level block driver for accessing regular files.

filename — The path to the image file in the local filesystem
aio — Specifies the AIO backend (threads/native/io_uring, default: threads)
locking — Specifies whether the image file is protected with Linux OFD / POSIX locks. The default is to use the Linux Open File Descriptor API if available, otherwise no lock is applied. (auto/on/off, default: auto)

Example:

-blockdev driver=file,node-name=disk,filename=disk.img

Driver-specific options for raw 🌈

This is the image format block driver for raw images. It's usually stacked on top of a protocol level block driver such as file.

file — Reference to or definition of the data source block driver node (e.g. a file driver node)

Example 1:

-blockdev driver=file,node-name=disk_file,filename=disk.img
-blockdev driver=raw,node-name=disk,file=disk_file

Example 2:

-blockdev driver=raw,node-name=disk,file.driver=file,file.filename=disk.img

Driver-specific options for qcow2 💜

This is the image format block driver for qcow2 images. It's usually stacked on top of a protocol level block driver such as file.

file — Reference to or definition of the data source block driver node (e.g. a file driver node)
backing — Reference to or definition of the backing file block device (default is taken from the image file). It is allowed to pass null here in order to disable the default backing file. lowkey handy.
lazy-refcounts — Whether to enable the lazy refcounts feature (on/off; default is taken from the image file)
cache-size — The maximum total size of the L2 table and refcount block caches in bytes (default: the sum of l2-cache-size and refcount-cache-size)
l2-cache-size — The maximum size of the L2 table cache in bytes (default: if cache-size is not specified — 32M on Linux platforms, and 8M on non-Linux platforms; otherwise, as large as possible within the cache-size, while permitting the requested or the minimal refcount cache size)
refcount-cache-size — The maximum size of the refcount block cache in bytes (default: 4 times the cluster size; or if cache-size is specified, the part of it which is not used for the L2 cache)
cache-clean-interval — Clean unused entries in the L2 and refcount caches. The interval is in seconds. The default value is 600 on supporting platforms, and 0 on other platforms. Setting it to 0 disables this feature. 🧹
pass-discard-request — Whether discard requests to the qcow2 device should be forwarded to the data source (on/off; default: on if discard=unmap is specified, off otherwise)
pass-discard-snapshot — should we fire off discard requests at the data source when a snapshot thing happens (like deleting a snapshot) and it frees up clusters in the qcow2 file? It's on/off, and the default is on. Obsessed with being tidy ngl.
pass-discard-other — same energy but for every other moment a cluster gets freed. on/off, default is off. She's lowkey lazy about the side quests.
discard-no-unref — turn this on and data clusters stay preallocated even when nobody's using them anymore, e.g. because they got discarded or converted into zero clusters. Now, whether the old data actually gets thrown out or kept at the protocol level (aka in the image file itself) depends on your pass-discard-request setting, bestie — that's its whole job. Keeping clusters preallocated stops qcow2 fragmentation that would otherwise pop off from freeing them and re-allocating them later. And why do we care? Because besides the potential performance degradation, that fragmentation can lead to increased allocation of clusters past the end of the image file, which means image files whose file length grows way bigger than their guest disk size would have you believe. So if image file length is a concern for you (like when you're storing qcow2 images directly on block devices), you should consider enabling this option. 💅
overlap-check — which overlap checks do we run for writes to the image? Options are none/constant/cached/all, default is cached. For the deets or if you want finer granularity control, go refer to the QAPI documentation of blockdev-add. iykyk. 📖

Example 1:

-blockdev driver=file,node-name=my_file,filename=/tmp/disk.qcow2
-blockdev driver=qcow2,node-name=hda,file=my_file,overlap-check=none,cache-size=16777216

Example 2:

-blockdev driver=qcow2,node-name=disk,file.driver=http,file.filename=http://example.com/image.qcow2

🦋 Driver-specific options for other drivers 🦋

Please refer to the QAPI documentation of the blockdev-add QMP command. That's the assignment, bestie, go read it. 📚✨

💖 OPTIONS (the drive one) 💖

`-drive option[,option[,option[,...]]]`

Define a whole new drive. This includes creating a block driver node (that's the backend) and a guest device, so honestly it's mostly just a shortcut for defining the matching -blockdev and -device options. Two birds, one flag, iconic behavior tbh. 🎀

Heads up: -drive accepts all options that -blockdev accepts. And then, on top of that, it also knows these cuties:

file=file — this option says which disk image to use with this drive (peep the Disk Images chapter in the System Emulation Users Guide). If your filename contains a comma, you gotta double it — so for instance "file=my,,file" to use the file "my,file". Yes really, that's the escape hatch. 🫶

Special files such as iSCSI devices can be specified using protocol specific URLs. See the section for "Device URL Syntax" for more info.

if=interface — which type of interface the drive gets connected to. The available types are: ide, scsi, sd, mtd, floppy, pflash, virtio, none. Pick your fighter. ⭐
bus=bus,unit=unit — these define where the drive is connected by giving the bus number and the unit id.
index=index — defines where the drive is connected by using an index in the list of available connectors of a given interface type.
media=media — defines the type of the media: disk or cdrom.
snapshot=snapshot — snapshot is "on" or "off" and controls snapshot mode for the given drive (check -snapshot).
cache=cache — cache is "none", "writeback", "unsafe", "directsync" or "writethrough" and controls how the host cache is used to access block data. It's a shortcut that sets the cache.direct and cache.no-flush options (like in -blockdev), and additionally cache.writeback, which provides a default for the write-cache option of block guest devices (like in -device). The modes map out like this:
- writeback → cache.writeback=on, cache.direct=off, cache.no-flush=off
- none → cache.writeback=on, cache.direct=on, cache.no-flush=off
- writethrough → cache.writeback=off, cache.direct=off, cache.no-flush=off
- directsync → cache.writeback=off, cache.direct=on, cache.no-flush=off
- unsafe → cache.writeback=on, cache.direct=off, cache.no-flush=on

The default mode is cache=writeback.

aio=aio — aio is "threads", "native", or "io_uring" and picks between pthread based disk I/O, native Linux AIO, or the Linux io_uring API. Choose your vibe. 🌈
format=format — specify which disk format to use instead of detecting it. Pro tip: you can use format=raw to avoid interpreting an untrusted format header. She said safety first, no cap. 🔥
werror=action,rerror=action — say which action to take on write and read errors. The valid actions are: "ignore" (ignore the error and try to continue), "stop" (pause QEMU), "report" (report the error to the guest), "enospc" (pause QEMU only if the host disk is full; report the error to the guest otherwise). The default setting is werror=enospc and rerror=report.
copy-on-read=copy-on-read — copy-on-read is "on" or "off" and enables whether to copy read backing file sectors into the image file.
bps=b,bps_rd=r,bps_wr=w — set bandwidth throttling limits in bytes per second, either for all request types or just for reads or just for writes. Small values can lead to timeouts or hangs inside the guest, so be careful — a safe minimum for disks is 2 MiB/s. ⚠️
bps_max=bm,bps_rd_max=rm,bps_wr_max=wm — set bursts in bytes per second, either for all request types or just for reads or writes. Bursts let the guest I/O spike above the limit temporarily. She's allowed a lil treat. ✨
iops=i,iops_rd=r,iops_wr=w — set request rate limits in requests per second, either for all request types or just for reads or writes.
iops_max=bm,iops_rd_max=rm,iops_wr_max=wm — set bursts in requests per second, either for all request types or just for reads or writes. Again, bursts let the guest I/O temporarily spike above the limit.
iops_size=is — let every is bytes of a request count as a new request for iops throttling purposes. Use this to stop guests from circumventing iops limits by sending fewer but larger requests. Sneaky little guest, we see you. 👀
group=g — join a throttling quota group with the given name g. All drives that are members of the same group get accounted for together. Use this to stop guests from circumventing throttling limits by using many small disks instead of a single larger disk. Teamwork makes the scheme not work. 💀

By default, the cache.writeback=on mode is used. It reports data writes as completed as soon as the data is present in the host page cache. That's safe as long as your guest OS makes sure to correctly flush disk caches where needed. But if your guest OS does not handle volatile disk write caches correctly and your host crashes or loses power, then the guest may experience data corruption. 😭 Real stakes, bestie.

For those kinds of guests, you should consider using cache.writeback=off. That means the host page cache will still be used to read and write data, but the write notification gets sent to the guest only after QEMU has made sure to flush each write to the disk. Just know that this has a major impact on performance. Nothing in this life is free. 🫠

When using the -snapshot option, unsafe caching is always used.

Copy-on-read avoids accessing the same backing file sectors over and over and is useful when the backing file is over a slow network. By default copy-on-read is off.

Instead of -cdrom you can use:

qemu-system-x86_64 -drive file=file,index=2,media=cdrom

Instead of -hda, -hdb, -hdc, -hdd, you can use:

qemu-system-x86_64 -drive file=file,index=0,media=disk
qemu-system-x86_64 -drive file=file,index=1,media=disk
qemu-system-x86_64 -drive file=file,index=2,media=disk
qemu-system-x86_64 -drive file=file,index=3,media=disk

You can open an image using pre-opened file descriptors from an fd set, bestie, it's giving resourceful:

qemu-system-x86_64 \
 -add-fd fd=3,set=2,opaque="rdwr:/path/to/file" \
 -add-fd fd=4,set=2,opaque="rdonly:/path/to/file" \
 -drive file=/dev/fdset/2,index=0,media=disk

And you can hook a CDROM up to the slave of ide0 like so:

qemu-system-x86_64 -drive file=file,if=ide,index=1,media=cdrom

If you don't pass the file= argument at all? Boom, you've just defined an empty drive 🫶:

qemu-system-x86_64 -drive if=ide,index=1,media=cdrom

So instead of -fda, -fdb, you can also do:

qemu-system-x86_64 -drive file=file,index=0,if=floppy
qemu-system-x86_64 -drive file=file,index=1,if=floppy

By default the interface is ide and the index just auto-increments, no thoughts head empty, it handles it:

qemu-system-x86_64 -drive file=a -drive file=b

...gets interpreted exactly like:

qemu-system-x86_64 -hda a -hdb b

🌸 OPTIONS (still going, we're so back) 🌸

-mtdblock file — use file as your on-board Flash memory image. cute.
-sd file — use file as a SecureDigital card image. iconic SD card behaviour 💾✨
-snapshot — write to temporary files instead of disk image files. In this case, the raw disk image you're using does not get written back. You can however force the write back by pressing Ctrl+a s (peep the Disk Images <#disk-images> chapter in the System Emulation Users Guide).

Warning: snapshot is incompatible with -blockdev bestie. Instead, use qemu-img to manually create snapshot images to attach to your blockdev. And if you've got mixed -blockdev and -drive declarations, you can use the snapshot property on your drive declarations instead of this global option. periodt.

-fsdev local,id=id,path=path,security_model=security_model [,writeout=writeout][,readonly=on][,fmode=fmode][,dmode=dmode][,max_xattr=max][,throttling.option=value[,throttling.option=value[,...]]]
-fsdev synth,id=id[,readonly=on][,max_xattr=max] — define a new file system device. Valid options are:
- local — accesses to the filesystem are done by QEMU.
- synth — synthetic filesystem, only used by QTests.
- id=id — specifies the identifier for this device.
- path=path — specifies the export path for the file system device. Files under this path will be available to the 9p client on the guest.
- security_model=security_model — specifies the security model to use for this export path. The supported security models are "passthrough", "mapped-xattr", "mapped-file" and "none". In the "passthrough" security model, files are stored using the same credentials as they're created with on the guest — which requires QEMU to run as root. In "mapped-xattr", some of the file attributes like uid, gid, mode bits and link target are stored as file attributes. For "mapped-file" those attributes live in the hidden .virtfs_metadata directory, and heads up: directories exported by this security model cannot interact with other unix tools. "none" is the same as passthrough except the sever won't report failures if it fails to set file attributes like ownership. Security model is mandatory only for local fsdriver.
- writeout=writeout — this is an optional argument. The only supported value is "immediate". This means the host page cache will be used to read and write data, but write notification gets sent to the guest only when the data has been reported as written by the storage subsystem.
- readonly=on — enables exporting a 9p share as a readonly mount for guests. By default read-write access is given, obvs.
- fmode=fmode — specifies the default mode for newly created files on the host. Works only with the security models "mapped-xattr" and "mapped-file".
- dmode=dmode — specifies the default mode for newly created directories on the host. Works only with the security models "mapped-xattr" and "mapped-file".
- throttling.bps-total=b,throttling.bps-read=r,throttling.bps-write=w — specify bandwidth throttling limits in bytes per second, either for all request types or for reads or writes only.
- throttling.bps-total-max=bm,bps-read-max=rm,bps-write-max=wm — specify bursts in bytes per second, either for all request types or for reads or writes only. Bursts let the guest I/O spike above the limit temporarily, lil treat ✨
- throttling.iops-total=i,throttling.iops-read=r,throttling.iops-write=w — specify request rate limits in requests per second, either for all request types or for reads or writes only.
- throttling.iops-total-max=im,throttling.iops-read-max=irm,throttling.iops-write-max=iwm — specify bursts in requests per second, either for all request types or for reads or writes only. Bursts let the guest I/O spike above the limit temporarily.
- throttling.iops-size=is — let every is bytes of a request count as a new request for iops throttling purposes.
- max_xattr=max — specifies the maximum number of concurrent xattr FIDs allowed for this export. The default is 1024. Set to 0 for allowing an infinite number of xattr FIDs. This limit prevents host memory exhaustion attacks by capping the number of simultaneous xattr FIDs. lowkey a bouncer for your memory 🫶

The -fsdev option is used along with -device driver "virtio-9p-...".

-device virtio-9p-type,fsdev=id,mount_tag=mount_tag — options for the virtio-9p-... driver are:
- type — specifies the variant to be used. Supported values are "pci", "ccw" or "device", depending on the machine type.
- fsdev=id — specifies the id value specified along with the -fsdev option.
- mount_tag=mount_tag — specifies the tag name to be used by the guest to mount this export point.
-virtfs local,path=path,mount_tag=mount_tag ,security_model=security_model[,writeout=writeout][,readonly=on][,fmode=fmode][,dmode=dmode][,multidevs=multidevs][,max_xattr=max]
-virtfs synth,mount_tag=mount_tag[,max_xattr=max] — define a new virtual filesystem device and expose it to the guest using a virtio-9p-device (a.k.a. 9pfs), which essentially means a certain directory on host is made directly accessible by guest as a pass-through file system using the 9P network protocol for communication between host and guests — and if you want, even accessible and shared by several guests simultaneously. main character shared folder energy 💅

Note that -virtfs is actually just a convenience shortcut for its generalized form -fsdev -device virtio-9p-pci. iykyk.

The general form of pass-through file system options are:

local — accesses to the filesystem are done by QEMU.
synth — synthetic filesystem, only used by QTests.
id=id — specifies the identifier for the filesystem device.
path=path — specifies the export path for the file system device. Files under this path will be available to the 9p client on the guest.
security_model=security_model — specifies the security model to use for this export path. Supported security models are "passthrough", "mapped-xattr", "mapped-file" and "none". In "passthrough", files are stored using the same credentials as they're created with on the guest, which requires QEMU to run as root. In "mapped-xattr", some of the file attributes like uid, gid, mode bits and link target are stored as file attributes. For "mapped-file" those attributes are stored in the hidden .virtfs_metadata directory. Directories exported by this security model cannot interact with other unix tools. "none" is the same as passthrough except the sever won't report failures if it fails to set file attributes like ownership. Security model is mandatory only for local fsdriver.
writeout=writeout — this is an optional argument. The only supported value is "immediate". This means host page cache will be used to read and write data but write notification will be sent to the guest only when the data has been reported as written by the storage subsystem.
readonly=on — enables exporting a 9p share as a readonly mount for guests. By default read-write access is given.
fmode=fmode — specifies the default mode for newly created files on the host. Works only with the security models "mapped-xattr" and "mapped-file".
dmode=dmode — specifies the default mode for newly created directories on the host. Works only with the security models "mapped-xattr" and "mapped-file".
mount_tag=mount_tag — specifies the tag name to be used by the guest to mount this export point.
max_xattr=max — specifies the maximum number of concurrent xattr FIDs allowed for this export. The default is 1024. Set to 0 for allowing an infinite number of xattr FIDs. This limit prevents host memory exhaustion attacks by capping the number of simultaneous xattr FIDs.
multidevs=remap|forbid|warn — specifies how to deal with multiple devices being shared with the same 9p export, so you can avoid file ID collisions on the guest. Supported behaviours are either "remap" (the default, queen of the trio), "forbid" or "warn". 🦋

remap — okay so this one is like "what if more than one device is shared with the same 9p export?" It assumes the possibility that that's a thing, and therefore inode numbers from host are remapped for guest in a way that would prevent file ID collisions on guest. Remapping inodes in such cases is required because the original device IDs from host are never passed and exposed on guest. Instead all files of an export shared with virtfs always share the same device ID on guest. So two files with identical inode numbers but from actually different devices on host would otherwise cause a file ID collision and hence potential severe misbehaviours on guest. 💀
- warn — virtfs 9p expects only one device to be shared with the same export. If however more than one device is shared and accessed via the same 9p export then only a warning message is logged (once) by qemu on host side. And that's it bestie, no further action is performed in this case that would prevent file ID collisions on guest. This could thus lead to severe misbehaviours in this case like wrong files being accessed and data corruption on the exported tree. 😭
- forbid — assumes like "warn" that only one device is shared by the same 9p export, however it will not only log a warning message but also deny access to additional devices on guest. Note though that "forbid" does currently not block all possible file access operations (e.g. readdir() would still return entries from other devices). So it's strict, just not flawless. 🙈
-iscsi — Configure iSCSI session parameters.

🔌 USB convenience options 🔌

-usb — Enable USB emulation on machine types with an on-board USB host controller (if not enabled by default). Heads up though: on-board USB host controllers may not support USB 3.0. In this case -device qemu-xhci can be used instead on machines with PCI. 🫶
-usbdevice devname — Add the USB device devname, and enable an on-board USB controller if possible and necessary (just like it can be done via -machine usb=on). Note that this option is mainly intended for the user's convenience only. More fine-grained control can be achieved by selecting a USB host controller (if necessary) and the desired USB device via the -device option instead. For example, instead of using -usbdevice mouse it is possible to use -device qemu-xhci -device usb-mouse to connect the USB mouse to a USB 3.0 controller instead (at least on machines that support PCI and do not have an USB controller enabled by default yet). For more details, see the chapter about Connecting USB devices <#connecting-usb-devices> in the System Emulation Users Guide.

Possible devices for devname are:

braille — Braille device. This will use BrlAPI to display the braille output on a real or fake device (i.e. it also creates a corresponding braille chardev automatically beside the usb-braille USB device).
keyboard — Standard USB keyboard. Will override the PS/2 keyboard (if present).
mouse — Virtual Mouse. This will override the PS/2 mouse emulation when activated.
tablet — Pointer device that uses absolute coordinates (like a touchscreen). This means QEMU is able to report the mouse position without having to grab the mouse. Also overrides the PS/2 mouse emulation when activated.
wacom-tablet — Wacom PenPartner USB tablet.

🖥️ Display options 🖥️

-display type — Select type of display to use. This may also influence the default audio backend selection. (iconic behaviour honestly ✨)

Use -display help to list the available display types. Valid values for type are:

spice-app[,gl=on|off] — Start QEMU as a Spice server and launch the default Spice client application. The Spice server will redirect the serial consoles and QEMU monitors. (Since 4.0)
dbus — Export the display over D-Bus interfaces. (Since 7.0)

If no audio backend is specified and the dbus display backend is specified, the dbus audio backend is used by default.

The connection is registered with the "org.qemu" name (and queued when already owned).

addr=<dbusaddr> : D-Bus bus address to connect to.
p2p=yes|no : Use peer-to-peer connection, accepted via QMP add_client.
gl=on|off|core|es : Use OpenGL for rendering (the D-Bus interface will share framebuffers with DMABUF file descriptors).

sdl — Display video output via SDL (usually in a separate graphics window; see the SDL documentation for other possibilities). Valid parameters are:
- grab-mod=<mods> : Used to select the modifier keys for toggling the mouse grabbing in conjunction with the "g" key. <mods> can be either lshift-lctrl-lalt or rctrl.
- gl=on|off|core|es : Use OpenGL for displaying
- show-cursor=on|off : Force showing the mouse cursor
- window-close=on|off : Allow to quit qemu with window close button
gtk — Display video output in a GTK window. This interface provides drop-down menus and other UI elements to configure and control the VM during runtime. Valid parameters are:
- full-screen=on|off : Start in fullscreen mode
- gl=on|off : Use OpenGL for displaying
- grab-on-hover=on|off : Grab keyboard input on mouse hover
- show-tabs=on|off — Display the tab bar for switching between the various graphical interfaces (e.g. VGA and virtual console character devices) by default.
- show-cursor=on|off : Force showing the mouse cursor
- window-close=on|off : Allow to quit qemu with window close button
- show-menubar=on|off : Display the main window menubar, defaults to "on"
- zoom-to-fit=on|off — Expand video output to the window size, defaults to "off"
curses[,charset=<encoding>] — Display video output via curses. For graphics device models which support a text mode, QEMU can display this output using a curses/ncurses interface. Nothing is displayed when the graphics device is in graphical mode or if the graphics device does not support a text mode. Generally only the VGA device models support text mode. The font charset used by the guest can be specified with the charset option, for example charset=CP850 for IBM CP850 encoding. The default is CP437.
cocoa — Display video output in a Cocoa window. Mac only. This interface provides drop-down menus and other UI elements to configure and control the VM during runtime. Valid parameters are:
- full-grab=on|off — Capture all key presses, including system combos. This requires accessibility permissions, since it performs a global grab on key events. (default: off) See https://support.apple.com/en-in/guide/mac-help/mh32356/mac
- swap-opt-cmd=on|off — Swap the Option and Command keys so that their key codes match their position on non-Mac keyboards and you can use Meta/Super and Alt where you expect them. (default: off)
- show-cursor=on|off : Force showing the mouse cursor
- left-command-key=on|off : Disable forwarding left command key to host
- full-screen=on|off : Start in fullscreen mode
- zoom-to-fit=on|off — Expand video output to the window size, defaults to "off"
egl-headless[,rendernode=<file>] — Offload all OpenGL operations to a local DRI device. For any graphical display, this display needs to be paired with either VNC or SPICE displays.
vnc=<display> — Start a VNC server on display <display>
none — Do not display video output. The guest will still see an emulated graphics card, but its output will not be displayed to the QEMU user. This option differs from the -nographic option in that it only affects what is done with video output; -nographic also changes the destination of the serial and parallel port data. 🫥

-nographic — Normally, if QEMU is compiled with graphical window support, it displays output such as guest graphics, guest console, and the QEMU monitor in a window. With this option, you can totally disable graphical output so that QEMU is a simple command line application. The emulated serial port is redirected on the console and muxed with the monitor (unless redirected elsewhere explicitly). Therefore, you can still use QEMU to debug a Linux kernel with a serial console. Use C-a h for help on switching between the console and monitor. 🐧
-spice option[,option[,...]] — Enable the spice remote desktop protocol. Valid options are
- port=<nr> — Set the TCP port spice is listening on for plaintext channels.
- addr=<addr> — Set the IP address spice is listening on. Default is any address.
- ipv4=on|off; ipv6=on|off; unix=on|off — Force using the specified IP version.
- password-secret=<secret-id> — Set the ID of the secret object containing the password you need to authenticate.
sasl=on|off — makes the client prove who they are to spice with SASL, periodt. 💅 the actual auth method used is picked from the system/user's SASL config file for the 'qemu' service, which normally lives at /etc/sasl2/qemu.conf. running QEMU as an unprivileged user? no problem bestie, the env var SASL_CONF_PATH lets it hunt for the service config in alternate locations instead. so here's the tea: some SASL auth methods can also do data encryption (eg GSSAPI 🫶), but you should always pair SASL with the 'tls' and 'x509' settings so SSL and server certificates are actually on. that combo gives you data encryption, and that's what stops your auth credentials from getting compromised. no cap, do both.
disable-ticketing=on|off — lets clients connect with no authentication at all. wild, i know 🫣
disable-copy-paste=on|off — turns off copy paste between the client and the guest.
disable-agent-file-xfer=on|off — turns off the spice-vdagent based file-xfer between the client and the guest.
tls-port=<nr> — sets the TCP port spice is listening on for the encrypted channels.
x509-dir=<dir> — sets the x509 file directory. it expects the same filenames as -vnc $display,x509=$dir. ✨
x509-key-file=<file>; x509-key-password=<file>; x509-cert-file=<file>; x509-cacert-file=<file>; x509-dh-key-file=<file> — the x509 file names can also be configured individually, one by one, if that's your vibe.
tls-ciphers=<list> — specify which ciphers to use.
tls-channel=main|display|cursor|inputs|record|playback; plaintext-channel=main|display|cursor|inputs|record|playback — force a specific channel to be used with or without TLS encryption. you can specify these options multiple times to configure multiple channels, slay. there's also the special name "default" you can use to set the default mode. and for any channel you haven't explicitly forced into one mode, the spice client gets to pick tls/plaintext as he pleases 💀
image-compression=auto_glz|auto_lz|quic|glz|lz|off — configure image compression (lossless 🎀). default is auto_glz.
jpeg-wan-compression=auto|never|always; zlib-glz-wan-compression=auto|never|always — configure wan image compression (lossy, for when the link is slow 🐌). default is auto.
streaming-video=off|all|filter — configure video stream detection. default is off.
agent-mouse=on|off — enable/disable passing mouse events via vdagent. default is on.
playback-compression=on|off — enable/disable audio stream compression (using celt 0.5.1). default is on.
seamless-migration=on|off — enable/disable spice seamless migration. default is off.
video-codec=<codec> — hands the Spice server its preferred codec to use with the Gstreamer encoder. this one is only relevant when gl=on is specified, iykyk. if no codec is provided, then the codec gstreamer:h264 gets used as the default. and for the case where gl=off, the default codec is decided by the Spice server itself.
max-refresh-rate=rate — gives the maximum refresh rate (or FPS) at which the encoding requests should be sent to the Spice server. the default would be 30.
gl=on|off — enable/disable the OpenGL context. default is off.
rendernode=<file> — DRM render node for OpenGL rendering. if you don't specify one, it'll pick the first available. (Since 2.9) 🦋

🌈 `-vga type` 🌈

picks which VGA card gets emulated, bestie. the valid values for type are:

cirrus — Cirrus Logic GD5446 Video card. every Windows version starting from Windows 95 should recognize and use this graphic card 🙈 for optimal performances, use 16 bit color depth in the guest and the host OS. (this card was the default before QEMU 2.2)
std — Standard VGA card with Bochs VBE extensions. if your guest OS supports the VESA 2.0 VBE extensions (e.g. Windows XP) and you wanna run high resolution modes (>= 1280x1024x16), then this is the one, use it. (this card is the default since QEMU 2.2 👑)
vmware — VMWare SVGA-II compatible adapter. use it if you have a sufficiently recent XFree86/XOrg server, or a Windows guest with a driver for this card.
qxl — QXL paravirtual graphic card. it's VGA compatible (including VESA 2.0 VBE support ✨) and works best with qxl guest drivers installed. recommended choice when using the spice protocol.
tcx — (sun4m only) Sun TCX framebuffer. this is the default framebuffer for sun4m machines and offers both 8-bit and 24-bit colour depths at a fixed resolution of 1024x768.
cg3 — (sun4m only) Sun cgthree framebuffer. a simple 8-bit framebuffer for sun4m machines, available in both 1024x768 (OpenBIOS) and 1152x900 (OBP) resolutions, aimed at people wishing to run older Solaris versions 🧚
virtio — Virtio VGA card.
none — Disable VGA card. (a bold choice, honestly)

-full-screen — Start in full screen. main character energy, immediately 🎀
-g widthxheight[xdepth] — Set the initial graphical resolution and depth (PPC, SPARC only).

For PPC the default is 800x600x32.

For SPARC with the TCX graphics device, the default is 1024x768x8 with the option of 1024x768x24. For cgthree, the default is 1024x768x8 with the option of 1152x900x8 for people who wish to use OBP.

-vnc display[,option[,option[,...]]] — okay so normally, if QEMU is compiled with graphical window support, it shows you output like guest graphics, guest console, and the QEMU monitor in a window. with this option, you can have QEMU listen on VNC display display and redirect the VGA display over the VNC session 🖥️ it's very useful to enable the usb tablet device when you're using this option (that's option -device usb-tablet). and when you're using the VNC display, you must use the -k parameter to set the keyboard layout if you're not using en-us. the valid syntax for the display is:
- to=L — with this option, QEMU will try the next available VNC displays, until the number L, if the originally defined -vnc display isn't available. e.g. port 5900+display is already used by another application. by default, to=0.
- host:d — TCP connections will only be allowed from host on display d. by convention the TCP port is 5900+d. optionally, host can be omitted, in which case the server will accept connections from any host. 🙈
- unix:path — Connections will be allowed over UNIX domain sockets, where path is the location of a unix socket to listen for connections on.
- none — VNC is initialized but not started. the monitor change command can be used to later start the VNC server.

Following the display value there may be one or more option flags separated by commas. the valid options are:

reverse=on|off — Connect to a listening VNC client via a "reverse" connection. the client is specified by the display. for reverse network connections (host:d,reverse), the d argument is a TCP port number, not a display number. don't get it twisted 💅
websocket=on|off — Opens an additional TCP listening port dedicated to VNC Websocket connections. if a bare websocket option is given, the Websocket port is 5700+display. an alternative port can be specified with the syntax websocket=port.

If host is specified, connections will only be allowed from this host. it's possible to control the websocket listen address independently, using the syntax websocket=host:port.

Websocket can also be allowed over UNIX domain socket, using the syntax websocket=unix:path, where path is the location of a unix socket to listen for connections on. 🦋

If no TLS credentials are provided, the websocket connection runs in unencrypted mode. if TLS credentials are provided, the websocket connection requires encrypted client connections.

password=on|off — Require that password based authentication is used for client connections.

The password must be set separately using the set_password command in the QEMU Monitor <#qemu-monitor>. the syntax to change your password is: set_password <protocol> <password> where <protocol> could be either "vnc" or "spice".

If you'd like to change the <protocol> password expiration, you should use expire_password <protocol> <expiration-time> where expiration time could be one of the following options: now, never, +seconds or UNIX time of expiration. e.g. +60 to make the password expire in 60 seconds, or 1335196800 to make the password expire on "Mon Apr 23 12:00:00 EDT 2012" (that's the UNIX time for this date and time, bestie 🫶).

You can also use the keywords "now" or "never" for the expiration time, to allow the <protocol> password to expire immediately or never expire. iconic.

password-secret=<secret-id> — Require that password based authentication is used for client connections, using the password provided by the secret object identified by secret-id. 🔐

tls-creds=ID — hands over the ID of a set of TLS credentials so your VNC server can be secure secure 💖. They cover both the normal VNC server socket and the websocket socket (when one's enabled). The moment you set TLS creds, the VNC server socket turns on the VeNCrypt auth mechanism. Heads up: those credentials have to already exist — you make them first with the -object tls-creds argument. No improvising ✨
tls-authz=ID — gives the ID of the QAuthZ authorization object that the client's x509 distinguished name gets validated against. Lowkey cute detail: this object is only resolved at time of use, so you can delete it and recreate it on the fly while the VNC server is still running 👑. If it's missing? It defaults to denying access. Periodt.
sasl=on|off — requires the client to use SASL to authenticate with the VNC server. Which exact auth method gets used is controlled from the system / user's SASL config file for the 'qemu' service — usually hanging out at /etc/sasl2/qemu.conf. If you're running QEMU as an unprivileged user, there's an environment variable, SASL_CONF_PATH, that makes it search alternate locations for the service config 🌸.

So even though some SASL auth methods can also do data encryption (looking at you, GSSAPI), the recommendation is that SASL always gets combined with the 'tls' and 'x509' settings so SSL and server certificates are in play. That's what guarantees data encryption, which in turn prevents your authentication credentials from getting compromised 🔥. For the full rundown on using SASL auth, see the VNC security section in the System Emulation Users Guide.

sasl-authz=ID — the ID of the QAuthZ authorization object that the client's SASL username gets validated against 💅. Same deal as above: only resolved at time of use, so you can delete and recreate it live while the VNC server is active. Missing it defaults to denying access.
acl=on|off — the legacy way of enabling client authorization against the x509 distinguished name and SASL username. It spawns two authz-list objects with the IDs vnc.username and vnc.x509dname, and you have to configure the rules for those objects with the HMP ACL commands.

⚠️ This option is deprecated and should no longer be used. The new sasl-authz and tls-authz options are its replacement — it's giving "we don't do that anymore" 💀

lossy=on|off — turns on the lossy compression methods (gradient, JPEG, ...). With this set, your VNC client might receive lossy framebuffer updates depending on its encoding settings 🙈. It can save a lot of bandwidth… at the expense of quality. Trade-offs, bestie.
non-adaptive=on|off — disables adaptive encodings. Adaptive encodings are enabled by default — an adaptive encoding tries to detect frequently updated screen regions and send the updates in those regions using a lossy encoding (like JPEG), which is genuinely so helpful for saving bandwidth while playing videos 🎀. Disabling adaptive encodings restores the original static behavior of encodings like Tight.
share=allow-exclusive|force-shared|ignore — sets the display sharing policy:
- allow-exclusive lets clients ask for exclusive access. As suggested by the rfb spec, that's implemented by dropping other connections. Connecting multiple clients in parallel means every client has to ask for a shared session (vncviewer: -shared switch). This is the default.
- force-shared disables exclusive client access entirely. Iconic for shared desktop sessions, where you don't want somebody forgetting to specify -shared and disconnecting everybody else 😭
- ignore completely ignores the shared flag and lets everybody connect unconditionally. Doesn't conform to the rfb spec, but it is traditional QEMU behavior.
key-delay-ms — sets the keyboard delay, for key down and key up events, in milliseconds. Default is 10. Keyboards are low-bandwidth devices, so this little slowdown helps the device and the guest keep up and not lose events when events are arriving in bulk 🦋. What causes bulk arrivals, you ask? Flaky network connections, or scripts for automated testing.
audiodev=audiodev — uses the specified audiodev when the VNC client requests audio transmission ✨. If you're not passing an -audiodev argument, this option must be omitted. Otherwise it must be present and specify a valid audiodev. No half measures.
power-control=on|off — permits the remote client to issue shutdown, reboot or reset power control requests 👑

💻 i386 target only 💻

-win2k-hack — use this when you're installing Windows 2000, to dodge a disk full bug 🌈. Once Windows 2000 is installed you no longer need it (and ngl, this option slows down the IDE transfers). Synonym of -global ide-device.win2k-install-hack=on.
-no-fd-bootchk — disables boot signature checking for floppy disks in the BIOS. You may need this to boot from old floppy disks 💾. Synonym of -m fd-bootchk=off.
-acpitable — adds an ACPI table with the specified header fields and context from the specified files 📋:

-acpitable [sig=str][,rev=n][,oem_id=str][,oem_table_id=str][,oem_rev=n]
[,asl_compiler_id=str][,asl_compiler_rev=n][,data=file1[:file2]...]

For file=, it takes the whole ACPI table from the specified files, including all the ACPI headers (which is possibly overridden by other options). For data=, only the data portion of the table is used, and all the header information is specified on the command line. And here's a spicy one: if a SLIC table is supplied to QEMU, then the SLIC's oem_id and oem_table_id fields will override the same fields in the RSDT and the FADT (a.k.a. FACP), so that the field matches what's required by the Microsoft SLIC spec and the ACPI spec 🔥

-smbios file=binary — loads the SMBIOS entry from a binary file.
-smbios type=0[,vendor=str][,version=str][,date=str][,release=%d.%d][,uefi=on|off] — specifies SMBIOS type 0 fields ✨
-smbios type=1[,manufacturer=str][,product=str][,version=str][,serial=str][,uuid=uuid][,sku=str][,family=str] — specifies SMBIOS type 1 fields
-smbios type=2[,manufacturer=str][,product=str][,version=str][,serial=str][,asset=str][,location=str] — specifies SMBIOS type 2 fields
-smbios type=3[,manufacturer=str][,version=str][,serial=str][,asset=str][,sku=str] — specifies SMBIOS type 3 fields
-smbios type=4[,sock_pfx=str][,manufacturer=str][,version=str][,serial=str][,asset=str][,part=str][,processor-family=%d][,processor-id=%d] — specifies SMBIOS type 4 fields
-smbios type=9[,slot_designation=str][,slot_type=%d][,slot_data_bus_width=%d][,current_usage=%d][,slot_length=%d][,slot_id=%d][,slot_characteristics1=%d][,slot_characteristics12=%d][,pci_device=str] — specifies SMBIOS type 9 fields
-smbios type=11[,value=str][,path=filename] — specifies SMBIOS type 11 fields 🎀

This argument can be repeated multiple times, and the values get added in the order they're parsed. Applications planning to use OEM strings data are encouraged to use their application name as a prefix for the value string — that makes it way easier to pass information for multiple applications at the same time.

The value=str syntax provides the string data inline, while the path=filename syntax loads data from a file on disk. Note that the file is not permitted to contain any NUL bytes 🙈

Both the value and path options can be repeated multiple times and will be added to the SMBIOS table in the order in which they appear.

⚠️ Heads up: on the x86 architecture, the total size of all SMBIOS tables is limited to 65535 bytes. So the OEM strings data is not suitable for passing large amounts of data into the guest. Instead it should be used as an indicator, telling the guest where to locate the real data set — for example, by specifying the serial ID of a block device.

An example passing three strings is:

-smbios type=11,value=cloud-init:ds=nocloud-net;s=http://10.10.0.1:8000/,\
                value=anaconda:method=http://dl.fedoraproject.org/pub/fedora/linux/releases/25/x86_64/os,\
                path=/some/file/with/oemstringsdata.txt

In the guest OS this is visible with the dmidecode command:

$ dmidecode -t 11
Handle 0x0E00, DMI type 11, 5 bytes
OEM Strings
     String 1: cloud-init:ds=nocloud-net;s=http://10.10.0.1:8000/
     String 2: anaconda:method=http://dl.fedoraproject.org/pub/fedora/linux/releases/25/x86_64/os
     String 3: myapp:some extra data

-smbios type=17[,loc_pfx=str][,bank=str][,manufacturer=str][,serial=str][,asset=str][,part=str][,speed=%d] — specifies SMBIOS type 17 fields
-smbios type=41[,designation=str][,kind=str][,instance=%d][,pcidev=str] — specifies SMBIOS type 41 fields 💅

This argument can be repeated multiple times. Its main use is to let network interfaces be created as enoX on Linux — with X being the instance number — instead of the name depending on the interface's position on the PCI bus. So much tidier, fr fr.

Here is an example of use:

-netdev user,id=internet \
-device virtio-net-pci,mac=50:54:00:00:00:42,netdev=internet,id=internet-dev \
-smbios type=41,designation='Onboard LAN',instance=1,kind=ethernet,pcidev=internet-dev

In the guest OS, the device should then appear as eno1:

$ ip -brief l
lo               UNKNOWN        00:00:00:00:00:00 <LOOPBACK,UP,LOWER_UP>
eno1             UP             50:54:00:00:00:42 <BROADCAST,MULTICAST,UP,LOWER_UP>

⚠️ Currently, the PCI device has to be attached to the root bus. No exceptions bestie 🌸

🌸 Network options 🌸

okay bestie, networking era! This is where QEMU gets its whole internet-girlie moment. No cap, let's go. 💅

-nic [tap|passt|bridge|user|l2tpv3|vde|netmap|af-xdp|vhost-user|socket][,...][,mac=macaddr][,model=mn] — This option is a shortcut for configuring both the on-board (default) guest NIC hardware and the host network backend in one go. The host backend options are the same as with the corresponding -netdev options below. The guest NIC model can be set with model=modelname. Use model=help to list the available device types. The hardware MAC address can be set with mac=macaddr.

The following two example do exactly the same, to show how -nic can be used to shorten the command line length:

qemu-system-x86_64 -netdev user,id=n1,ipv6=off -device e1000,netdev=n1,mac=52:54:98:76:54:32
qemu-system-x86_64 -nic user,ipv6=off,model=e1000,mac=52:54:98:76:54:32

-nic none — Indicate that no network devices should be configured. It is used to override the default configuration (default NIC with "user" host network backend) which is activated if no other networking options are provided. literally the "no thanks, no networking today" button 💖
-netdev passt,id=str[,option][,...] — Configure a passt network backend which requires no administrator privilege to run. Valid options are:
- id=id — Assign symbolic name for use in monitor commands.
- path=file — Filename of the passt program to run. If it is not provided, passt command will be started with the help of the PATH environment variable.
- quiet=on|off — By default, quiet=on to disable informational message from passt. quiet=on is passed as --quiet to passt.
- vhost-user=on|off — By default, vhost-user=off and QEMU uses the stream network backend to communicate with passt. If vhost-user=on, passt is started with --vhost-user and QEMU uses the vhost-user network backend to communicate with passt.
- @mtu — Assign MTU via DHCP/NDP
- address — IPv4 or IPv6 address
- netmask — IPv4 mask
- mac — source MAC address
- gateway — IPv4 or IPv6 address as gateway
- interface — Interface for addresses and routes
- outbound — Bind to address as outbound source
- outbound-if4 — Bind to outbound interface for IPv4
- outbound-if6 — Bind to outbound interface for IPv6
- dns — IPv4 or IPv6 address as DNS
- search — Search domains
- fqdn — FQDN to configure client with
- dhcp-dns — Enable/disable DNS list in DHCP/DHCPv6/NDP
- dhcp-search — Enable/disable list in DHCP/DHCPv6/NDP
- map-host-loopback — Address to refer to host
- map-guest-addr — Addr to translate to guest's address
- dns-forward — Forward DNS queries sent to
- dns-host — Host nameserver to direct queries to
- tcp — Enable/disable TCP
- udp — Enable/disable UDP
- icmp — Enable/disable ICMP
- dhcp — Enable/disable DHCP
- ndp — Enable/disable NDP
- dhcpv6 — Enable/disable DHCPv6
- ra — Enable/disable route advertisements
- freebind — Bind to any address for forwarding
- ipv4 — Enable/disable IPv4
- ipv6 — Enable/disable IPv6
- tcp-ports — TCP ports to forward
- udp-ports — UDP ports to forward
- param=string — string will be passed to passt as a command line parameter, we can have multiple occurrences of the param parameter to pass multiple parameters to passt.

For instance, to pass --trace --log=trace.log:

qemu-system-x86_64 -nic passt,param=--trace,param=--log=trace.log

-netdev user,id=id[,option][,option][,...] — Configure user mode host network backend which requires no administrator privilege to run. Valid options are:
- id=id — Assign symbolic name for use in monitor commands.
- ipv4=on|off and ipv6=on|off — Specify that either IPv4 or IPv6 must be enabled. If neither is specified both protocols are enabled.
- net=addr[/mask] — Set IP network address the guest will see. Optionally specify the netmask, either in the form a.b.c.d or as number of valid top-most bits. Default is 10.0.2.0/24.
- host=addr — Specify the guest-visible address of the host. Default is the 2nd IP in the guest network, i.e. x.x.x.2.
- ipv6-net=addr[/int] — Set IPv6 network address the guest will see (default is fec0::/64). The network prefix is given in the usual hexadecimal IPv6 address notation. The prefix size is optional, and is given as the number of valid top-most bits (default is 64).
- ipv6-host=addr — Specify the guest-visible IPv6 address of the host. Default is the 2nd IPv6 in the guest network, i.e. xxxx::2.
- restrict=on|off — If this option is enabled, the guest will be isolated, i.e. it will not be able to contact the host and no guest IP packets will be routed over the host to the outside. This option does not affect any explicitly set forwarding rules. bestie, this is the "do not disturb" mode, but it still respects your manual forwarding rules ✨
- hostname=name — Specifies the client hostname reported by the built-in DHCP server.
- dhcpstart=addr — Specify the first of the 16 IPs the built-in DHCP server can assign. Default is the 15th to 31st IP in the guest network, i.e. x.x.x.15 to x.x.x.31.
- dns=addr — Specify the guest-visible address of the virtual nameserver. The address must be different from the host address. Default is the 3rd IP in the guest network, i.e. x.x.x.3.
- ipv6-dns=addr — Specify the guest-visible address of the IPv6 virtual nameserver. The address must be different from the host address. Default is the 3rd IP in the guest network, i.e. xxxx::3.
- dnssearch=domain — Provides an entry for the domain-search list sent by the built-in DHCP server. More than one domain suffix can be transmitted by specifying this option multiple times. If supported, this will cause the guest to automatically try to append the given domain suffix(es) in case a domain name can not be resolved.

Example:

qemu-system-x86_64 -nic user,dnssearch=mgmt.example.org,dnssearch=example.org

domainname=domain — Specifies the client domain name reported by the built-in DHCP server.
tftp=dir — When using the user mode network stack, activate a built-in TFTP server. The files in dir will be exposed as the root of a TFTP server. The TFTP client on the guest must be configured in binary mode (use the command bin of the Unix TFTP client). The built-in TFTP server is read-only; it does not implement any command for writing files. QEMU will not write to this directory.
tftp-server-name=name — In BOOTP reply, broadcast name as the "TFTP server name" (RFC2132 option 66). This can be used to advise the guest to load boot files or configurations from a different server than the host address.
bootfile=file — When using the user mode network stack, broadcast file as the BOOTP filename. In conjunction with tftp, this can be used to network boot a guest from a local directory.

Example (using pxelinux):

qemu-system-x86_64 -hda linux.img -boot n -device e1000,netdev=n1 \
    -netdev user,id=n1,tftp=/path/to/tftp/files,bootfile=/pxelinux.0

smb=dir[,smbserver=addr] — When using the user mode network stack, activate a built-in SMB server so that Windows OSes can access to the host files in dir transparently. The IP address of the SMB server can be set to addr. By default the 4th IP in the guest network is used, i.e. x.x.x.4.

In the guest Windows OS, the line:

10.0.2.4 smbserver

must be added in the file C:\WINDOWS\LMHOSTS (for windows 9x/Me) or C:\WINNT\SYSTEM32\DRIVERS\ETC\LMHOSTS (Windows NT/2000).

Then dir can be accessed in \\smbserver\qemu.

Note that a SAMBA server must be installed on the host OS.

hostfwd=[tcp|udp|unix]:[[hostaddr]:hostport|hostpath]-[guestaddr]:guestport — Redirect incoming TCP, UDP or UNIX connections to the host port hostport to the guest IP address guestaddr on guest port guestport. If guestaddr is not specified, its value is x.x.x.15 (default first address given by the built-in DHCP server). By specifying hostaddr, the rule can be bound to a specific host interface. If no connection type is set, TCP is used. This option can be given multiple times.

For example, to redirect host X11 connection from screen 1 to guest screen 0, use the following:

# on the host
qemu-system-x86_64 -nic user,hostfwd=tcp:127.0.0.1:6001-:6000
# this host xterm should open in the guest X11 server
xterm -display :1

To redirect telnet connections from host port 5555 to telnet port on the guest, use the following:

# on the host
qemu-system-x86_64 -nic user,hostfwd=tcp::5555-:23
telnet localhost 5555

Then when you use on the host telnet localhost 5555, you connect to the guest telnet server.

To redirect host unix socket /tmp/vm to guest tcp socket 23 use following:

# on the host
qemu-system-x86_64 -nic user,hostfwd=unix:/tmp/vm-:23

guestfwd=[tcp]:server:port-dev, guestfwd=[tcp]:server:port-cmd:command — bestie this one forwards guest TCP connections to the IP address server on port port, and sends them either to the character device dev OR to a program that gets run by cmd:command, which gets spawned fresh for every single connection. You can pass this option multiple times, no cap. 💅

Okay so you've got two whole vibes here. Option one: use a chardev directly and that one chardev gets used for QEMU's entire lifetime, like:

# open 10.10.1.1:4321 on bootup, connect 10.0.2.100:1234 to it whenever
# the guest accesses it
qemu-system-x86_64 -nic user,guestfwd=tcp:10.0.2.100:1234-<tcp:10.10.1.1:4321>

Or option two: execute a command on EVERY TCP connection the guest makes, so QEMU is basically doing its best inetd impression for that virtual server, periodt:

# call "netcat 10.10.1.1 4321" on every TCP connection to 10.0.2.100:1234
# and connect the TCP stream to its stdin/stdout
qemu-system-x86_64 -nic  'user,id=n1,guestfwd=tcp:10.0.2.100:1234-cmd:netcat 10.10.1.1 4321'

💖 `-netdev` 💖

🦋 tap,id=id[,fd=h][,ifname=name][,script=file][,downscript=dfile][,br=bridge][,helper=helper]

Set up a host TAP network backend with ID id. Slay.

Use the network script file file to configure it, and the network script dfile to deconfigure it. If name isn't given, the OS just picks one for you automatically, iconic of it. The default network configure script is /etc/qemu-ifup and the default network deconfigure script is /etc/qemu-ifdown. Want to disable script execution entirely? Use script=no or downscript=no.

If you're running QEMU as an unprivileged user, use the network helper to configure the TAP interface and attach it to the bridge. The default network helper executable is /usr/lib/qemu/qemu-bridge-helper and the default bridge device is br0.

fd=h can be used to specify the handle of an already opened host TAP interface.

Examples, because we love a visual learner 💖:

#launch a QEMU instance with the default network script
qemu-system-x86_64 linux.img -nic tap

#launch a QEMU instance with two NICs, each one connected
#to a TAP device
qemu-system-x86_64 linux.img \
        -netdev tap,id=nd0,ifname=tap0 -device e1000,netdev=nd0 \
        -netdev tap,id=nd1,ifname=tap1 -device rtl8139,netdev=nd1

#launch a QEMU instance with the default network helper to
#connect a TAP device to bridge br0
qemu-system-x86_64 linux.img -device virtio-net-pci,netdev=n1 \
        -netdev tap,id=n1,"helper=/usr/lib/qemu/qemu-bridge-helper"

🌸 bridge,id=id[,br=bridge][,helper=helper]

Connect a host TAP network interface to a host bridge device. That's the whole thing, bestie.

Use the network helper helper to configure the TAP interface and attach it to the bridge. Default network helper executable? /usr/lib/qemu/qemu-bridge-helper. Default bridge device? br0. We stay consistent. 💅

Examples:

#launch a QEMU instance with the default network helper to
#connect a TAP device to bridge br0
qemu-system-x86_64 linux.img -netdev bridge,id=n1 -device virtio-net,netdev=n1

#launch a QEMU instance with the default network helper to
#connect a TAP device to bridge qemubr0
qemu-system-x86_64 linux.img -netdev bridge,br=qemubr0,id=n1 -device virtio-net,netdev=n1

⭐ socket,id=id[,fd=h][,listen=[host]:port][,connect=host:port]

This host network backend connects the guest's network to another QEMU virtual machine using a TCP socket connection. If listen is specified, QEMU waits for incoming connections on port (host is optional, she's flexible like that). connect is used to connect to another QEMU instance that's using the listen option. fd=h specifies an already opened TCP socket.

Example:

# launch a first QEMU instance
qemu-system-x86_64 linux.img \
                 -device e1000,netdev=n1,mac=52:54:00:12:34:56 \
                 -netdev socket,id=n1,listen=:1234
# connect the network of this instance to the network of the first instance
qemu-system-x86_64 linux.img \
                 -device e1000,netdev=n2,mac=52:54:00:12:34:57 \
                 -netdev socket,id=n2,connect=127.0.0.1:1234

🧚 socket,id=id[,fd=h][,mcast=maddr:port[,localaddr=addr]]

Configure a socket host network backend to share the guest's network traffic with other QEMU virtual machines using a UDP multicast socket, which basically builds a whole bus for every QEMU sharing the same multicast address maddr and port. NOTES bestie, read them:

Several QEMU can be running on different hosts and share same bus (assuming correct multicast setup for these hosts).
mcast support is compatible with User Mode Linux (argument ethN=mcast), see <http://user-mode-linux.sf.net>.
Use fd=h to specify an already opened UDP multicast socket.

Example:

# launch one QEMU instance
qemu-system-x86_64 linux.img \
                 -device e1000,netdev=n1,mac=52:54:00:12:34:56 \
                 -netdev socket,id=n1,mcast=230.0.0.1:1234
# launch another QEMU instance on same "bus"
qemu-system-x86_64 linux.img \
                 -device e1000,netdev=n2,mac=52:54:00:12:34:57 \
                 -netdev socket,id=n2,mcast=230.0.0.1:1234
# launch yet another QEMU instance on same "bus"
qemu-system-x86_64 linux.img \
                 -device e1000,netdev=n3,mac=52:54:00:12:34:58 \
                 -netdev socket,id=n3,mcast=230.0.0.1:1234

Example (User Mode Linux compat.):

# launch QEMU instance (note mcast address selected is UML's default)
qemu-system-x86_64 linux.img \
                 -device e1000,netdev=n1,mac=52:54:00:12:34:56 \
                 -netdev socket,id=n1,mcast=239.192.168.1:1102
# launch UML
/path/to/linux ubd0=/path/to/root_fs eth0=mcast

Example (send packets from host's 1.2.3.4):

qemu-system-x86_64 linux.img \
                 -device e1000,netdev=n1,mac=52:54:00:12:34:56 \
                 -netdev socket,id=n1,mcast=239.192.168.1:1102,localaddr=1.2.3.4

🌈 stream,id=str[,server=on|off],addr.type=inet,addr.host=host,addr.port=port[,to=maxport][,numeric=on|off][,keep-alive=on|off][,mptcp=on|off][,addr.ipv4=on|off][,addr.ipv6=on|off][,reconnect-ms=milliseconds]

Configure a network backend to connect to another QEMU virtual machine or a proxy using a TCP/IP socket. 💖

server=on|off — if on, create a server socket.
addr.host=host,addr.port=port — socket address to listen on (server=on) or connect to (server=off).
to=maxport — if present, this is range of possible addresses, with port between port and maxport.
numeric=on|off — if on host and port are guaranteed to be numeric, otherwise a name resolution should be attempted (default: off).
keep-alive=on|off — enable keep-alive when connecting to this socket. Not supported for passive sockets, so don't even try it bestie.
mptcp=on|off — enable multipath TCP.
ipv4=on|off — whether to accept IPv4 addresses, default to try both IPv4 and IPv6.
ipv6=on|off — whether to accept IPv6 addresses, default to try both IPv4 and IPv6.
reconnect-ms=milliseconds — for a client socket, if a socket is disconnected, then attempt a reconnect after the given number of milliseconds. Setting this to zero disables this function. (default: 0)

Example (two guests connected using a TCP/IP socket):

# first VM
qemu-system-x86_64 linux.img \
              -device virtio-net,netdev=net0,mac=52:54:00:12:34:56 \
              -netdev stream,id=net0,server=on,addr.type=inet,addr.host=localhost,addr.port=1234
# second VM
qemu-system-x86_64 linux.img \
              -device virtio-net,netdev=net0,mac=52:54:00:12:34:57 \
              -netdev stream,id=net0,server=off,addr.type=inet,addr.host=localhost,addr.port=1234,reconnect-ms=5000

💜 stream,id=str[,server=on|off],addr.type=unix,addr.path=path[,abstract=on|off][,tight=on|off][,reconnect-ms=milliseconds]

Configure a network backend to connect to another QEMU virtual machine or a proxy using a stream oriented unix domain socket. Ok so:

server=on|off — if on create a server socket.
addr.path=path — filesystem path to use.
abstract=on|off — if on, this is a Linux abstract socket address.
tight=on|off — if false, pad an abstract socket address with enough null bytes to make it fill struct sockaddr_un member sun_path.
reconnect-ms=milliseconds — for a client socket, if a socket is disconnected, then attempt a reconnect after the given number of milliseconds. Setting this to zero disables this function. (default: 0)

Example (using passt as a replacement of -netdev user):

# start passt server as a non privileged user
passt
UNIX domain socket bound at /tmp/passt_1.socket
# start QEMU to connect to passt
qemu-system-x86_64 linux.img \
              -device virtio-net,netdev=net0 \
              -netdev stream,id=net0,server=off,addr.type=unix,addr.path=/tmp/passt_1.socket

Example (two guests connected using a stream oriented unix domain socket):

# first VM
qemu-system-x86_64 linux.img \
              -device virtio-net,netdev=net0,mac=52:54:00:12:34:56 \
              netdev stream,id=net0,server=on,addr.type=unix,addr.path=/tmp/qemu0
# second VM
qemu-system-x86_64 linux.img \
              -device virtio-net,netdev=net0,mac=52:54:00:12:34:57 \
              -netdev stream,id=net0,server=off,addr.type=unix,addr.path=/tmp/qemu0,reconnect-ms=5000

-netdev stream,id=str[,server=on|off],addr.type=fd,addr.str=file-descriptor[,reconnect-ms=milliseconds] — okay bestie, this one hooks your network backend up to another QEMU VM (or a proxy) over a stream-oriented socket file descriptor 💖
- server=on|off — flip this to on and boom, you're making a server socket 👑
- addr.str=file-descriptor — the file descriptor number you wanna use as the socket, that's the whole vibe
- reconnect-ms=milliseconds — for a client socket only: if the socket gets disconnected, wait this many milliseconds and then try to reconnect. Set it to zero and the reconnect feature is off, periodt. (default: 0)
-netdev dgram,id=str,remote.type=inet,remote.host=maddr,remote.port=port[,local.type=inet,local.host=addr] — configure a network backend that connects to a multicast address 🦋
- remote.host=maddr,remote.port=port — the multicast address, that's it, that's the destination
- local.host=addr — tells QEMU which host address to send the packets from

Example:

# launch one QEMU instance
qemu-system-x86_64 linux.img \
              -device virtio-net,netdev=net0,mac=52:54:00:12:34:56 \
              -netdev dgram,id=net0,remote.type=inet,remote.host=224.0.0.1,remote.port=1234
# launch another QEMU instance on same "bus"
qemu-system-x86_64 linux.img \
              -device virtio-net,netdev=net0,mac=52:54:00:12:34:57 \
              -netdev dgram,id=net0,remote.type=inet,remote.host=224.0.0.1,remote.port=1234
# launch yet another QEMU instance on same "bus"
qemu-system-x86_64 linux.img \
              -device virtio-net,netdev=net0,mac=52:54:00:12:34:58 \
              -netdev dgram,id=net0,remote.type=inet,remote.host=224.0.0.1,remote.port=1234

-netdev dgram,id=str,remote.type=inet,remote.host=maddr,remote.port=port[,local.type=fd,local.str=file-descriptor] — same multicast energy as above, but this time you're riding in on a UDP socket file descriptor ✨
- remote.host=maddr,remote.port=port — the multicast address, still the destination, no notes
- local.str=file-descriptor — the file descriptor QEMU uses to send packets out
-netdev dgram,id=str,local.type=inet,local.host=addr,local.port=port[,remote.type=inet,remote.host=addr,remote.port=port] — configure a backend that talks to another QEMU VM or a proxy over a datagram-oriented unix domain socket 💅
- local.host=addr,local.port=port — the IP address to send packets from
- remote.host=addr,remote.port=port — the destination IP address

Example (two guests connected using an UDP/IP socket):

# first VM
qemu-system-x86_64 linux.img \
              -device virtio-net,netdev=net0,mac=52:54:00:12:34:56 \
              -netdev dgram,id=net0,local.type=inet,local.host=localhost,local.port=1234,remote.type=inet,remote.host=localhost,remote.port=1235
# second VM
qemu-system-x86_64 linux.img \
              -device virtio-net,netdev=net0,mac=52:54:00:12:34:56 \
              -netdev dgram,id=net0,local.type=inet,local.host=localhost,local.port=1235,remote.type=inet,remote.host=localhost,remote.port=1234

-netdev dgram,id=str,local.type=unix,local.path=path[,remote.type=unix,remote.path=path] — again with the datagram-oriented unix socket thing, connecting to another QEMU VM or a proxy, iconic behavior honestly 🎀
- local.path=path — the filesystem path used to bind the socket
- remote.path=path — the filesystem path used as a destination (peep sendto(2) for the deets)

Example (two guests connected using an UDP/UNIX socket):

# first VM
qemu-system-x86_64 linux.img \
              -device virtio-net,netdev=net0,mac=52:54:00:12:34:56 \
              -netdev dgram,id=net0,local.type=unix,local.path=/tmp/qemu0,remote.type=unix,remote.path=/tmp/qemu1
# second VM
qemu-system-x86_64 linux.img \
              -device virtio-net,netdev=net0,mac=52:54:00:12:34:57 \
              -netdev dgram,id=net0,local.type=unix,local.path=/tmp/qemu1,remote.type=unix,remote.path=/tmp/qemu0

-netdev dgram,id=str,local.type=fd,local.str=file-descriptor — the last dgram flavor bestie, connecting to another QEMU VM or a proxy through a datagram-oriented socket file descriptor 🌸
- local.str=file-descriptor — the file descriptor used to send packets
-netdev l2tpv3,id=id,src=srcaddr,dst=dstaddr[,srcport=srcport][,dstport=dstport],txsession=txsession[,rxsession=rxsession][,ipv6=on|off][,udp=on|off][,cookie64=on|off][,counter=on|off][,pincounter=on|off][,txcookie=txcookie][,rxcookie=rxcookie][,offset=offset] — okay this is the L2TPv3 pseudowire host network backend and it's giving serious networking main character energy 🔥 L2TPv3 (RFC3931) is that popular protocol for hauling Ethernet (and other Layer 2) data frames between two systems. It lives in routers, firewalls, and the Linux kernel (from version 3.3 onwards).

Lowkey the whole point: this transport lets a VM talk directly to another VM, router, or firewall. No middleman drama 🫶

src=srcaddr — source address, and yes it's mandatory ✋
dst=dstaddr — destination address, also mandatory
udp=on — select udp encapsulation (default is ip)
srcport=srcport — source udp port
dstport=dstport — destination udp port
ipv6=on — force v6, otherwise it defaults to v4
rxcookie=rxcookie; txcookie=txcookie — cookies are a weak form of security in the l2tpv3 spec ngl. Their function is mostly to prevent misconfiguration. By default they are 32 bit 🍓
cookie64=on — set cookie size to 64 bit instead of the default 32
counter=off — force a 'cut-down' L2TPv3 with no counter, exactly like draft-mkonstan-l2tpext-keyed-ipv6-tunnel-00
pincounter=on — works around broken counter handling in the peer. This may also help on networks which have packet reorder, so if your network is messy, here's your girl 💜
offset=offset — add an extra offset between header and data

For example, to attach a VM running on host 4.3.2.1 via L2TPv3 to the bridge br-lan on the remote Linux host 1.2.3.4:

# Setup tunnel on linux host using raw ip as encapsulation
# on 1.2.3.4
ip l2tp add tunnel remote 4.3.2.1 local 1.2.3.4 tunnel_id 1 peer_tunnel_id 1 \
    encap udp udp_sport 16384 udp_dport 16384
ip l2tp add session tunnel_id 1 name vmtunnel0 session_id \
    0xFFFFFFFF peer_session_id 0xFFFFFFFF
ifconfig vmtunnel0 mtu 1500
ifconfig vmtunnel0 up
brctl addif br-lan vmtunnel0

# on 4.3.2.1
# launch QEMU instance - if your network has reorder or is very lossy add ,pincounter

qemu-system-x86_64 linux.img -device e1000,netdev=n1 \
    -netdev l2tpv3,id=n1,src=4.2.3.1,dst=1.2.3.4,udp=on,srcport=16384,dstport=16384,rxsession=0xffffffff,txsession=0xffffffff,counter=on

-netdev vde,id=id[,sock=socketpath][,port=n][,group=groupname][,mode=octalmode] — set up a VDE backend to connect to PORT n of a vde switch running on the host and listening for incoming connections on socketpath. Use GROUP groupname and MODE octalmode to change the default ownership and permissions for the communication port. Heads up bestie: this option is only available if QEMU has been compiled with vde support enabled ⭐

Example:

# launch vde switch
vde_switch -F -sock /tmp/myswitch
# launch QEMU instance
qemu-system-x86_64 linux.img -nic vde,sock=/tmp/myswitch

-netdev af-xdp,id=str,ifname=name[,mode=native|skb][,force-copy=on|off][,queues=n][,start-queue=m][,inhibit=on|off][,sock-fds=x:y:...:z][,map-path=/path/to/socket/map][,map-start-index=i] — configure an AF_XDP backend to connect to a network interface 'name' using an AF_XDP socket 🌈 A specific program attach mode for a default XDP program can be forced with 'mode', which defaults to best-effort, where the likely most performant mode will be in use. The number of queues 'n' should generally match the number of queues in the interface, and defaults to 1. Traffic arriving on non-configured device queues will not be delivered to the network backend, so don't be surprised 🙈

# set number of queues to 4
ethtool -L eth0 combined 4
# launch QEMU instance
qemu-system-x86_64 linux.img -device virtio-net-pci,netdev=n1 \
    -netdev af-xdp,id=n1,ifname=eth0,queues=4

The start-queue option can be specified if a particular range of queues [m, m + n] should be in use. For example, this may be necessary in order to use certain NICs in native mode. Kernel allows the driver to create a separate set of XDP queues on top of regular ones, and only these queues can be used for AF_XDP sockets. NICs that work this way may also require an additional traffic redirection with ethtool to these special queues 👑

# set number of queues to 1
ethtool -L eth0 combined 1
# redirect all the traffic to the second queue (id: 1)
# note: drivers may require non-empty key/mask pair.
ethtool -N eth0 flow-type ether \
    dst 00:00:00:00:00:00 m FF:FF:FF:FF:FF:FE action 1
et

For the `inhibit` option set to `on` used along with `map-path`, the expectation is that the XDP program with the socket map is <pink>already loaded</pink> on the networking device and the map is pinned into the BPF file system — so yeah, it's already out there, living its best life 💅. The path to that pinned map then gets passed to QEMU, which goes ahead and creates the file descriptors and slots them into the existing socket map. No cap.

qemu-system-x86_64 linux.img -device virtio-net-pci,netdev=n1 \ -netdev af-xdp,id=n1,ifname=eth0,queues=2,inhibit=on,map-path=/sys/fs/bpf/xsks_map


Oh also — `map-start-index` can be used to specify the start offset for insertion into the socket map. Quick heads up though: the combination of `map-path` and `sock-fds` together? <red>Not supported.</red> Periodt. 🙅‍♀️

- **`-netdev vhost-user,chardev=id[,vhostforce=on|off][,queues=n]`** — sets up a vhost-user netdev, backed by a chardev `id`. That chardev should be a unix domain socket backed one. The vhost-user uses a specifically defined protocol to pass vhost ioctl replacement messages to an application on the other end of the socket. On non-MSIX guests, you can force the feature with `vhostforce`. And `queues=n` tells it how many queues to create for multiqueue vhost-user. 💖

  Here's the vibe:

qemu -m 512 -object memory-backend-file,id=mem,size=512M,mem-path=/hugetlbfs,share=on \ -numa node,memdev=mem \ -chardev socket,id=chr0,path=/path/to/socket \ -netdev type=vhost-user,id=net0,chardev=chr0 \ -device virtio-net-pci,netdev=net0


- **`-netdev vhost-vdpa[,vhostdev=/path/to/dev][,vhostfd=h]`** — sets up a vhost-vdpa netdev. 🦋

So a vDPA device is a device that uses a datapath which complies with the virtio specifications, but with a vendor specific control path. vDPA devices can be either physically located on the hardware, or emulated by software. Both are valid, both are iconic.

- **`-netdev hubport,id=id,hubid=hubid[,netdev=nd]`** — creates a hub port on the emulated hub with ID `hubid`. ✨

The hubport netdev lets you connect a NIC to a QEMU emulated hub instead of a single netdev. Or, alternatively, you can also connect the hubport to another netdev with ID `nd` by using the `netdev=nd` option. Your call, bestie.

- **`-net nic[,netdev=nd][,macaddr=mac][,model=type][,name=name][,addr=addr][,vectors=v]`** — the <yellow>legacy</yellow> option for configuring or creating an on-board (or machine default) Network Interface Card (NIC), and connecting it either to the emulated hub with ID 0 (that's the default hub), or to the netdev `nd`. If `model` is omitted, then the default NIC model associated with the machine type gets used.

> ⚠️ Heads up: the default NIC model may change in future QEMU releases, so it is **highly recommended** to always specify a model. Like, always.

Optionally, the MAC address can be changed to `mac`, the device address set to `addr` (PCI cards only), and a `name` can be assigned for use in monitor commands. Optionally, for PCI cards, you can specify the number `v` of MSI-X vectors that the card should have — this option currently only affects virtio cards; set `v = 0` to disable MSI-X. If no `-net` option is specified, a single NIC is created. QEMU can emulate several different models of network card. Use `-net nic,model=help` for a list of available devices for your target. 💜

- **`-net user|passt|tap|bridge|socket|l2tpv3|vde[,...][,name=name]`** — configure a host network backend (with the options corresponding to the same `-netdev` option) and connect it to the emulated hub 0 (the default hub). Use `name` to specify the name of the hub port. 🌈

# 🎀 Character device options 🎀

The general form of a character device option is:

-chardev backend,id=id[,mux=on|off][,options]


`Backend` is one of: `null`, `socket`, `udp`, `msmouse`, `hub`, `vc`, `ringbuf`, `file`, `pipe`, `console`, `serial`, `pty`, `stdio`, `braille`, `parallel`, `spicevmc`, `spiceport`. The specific backend will determine the applicable options. ✨

Use `-chardev help` to print all available chardev backend types. 👑

All devices must have an `id`, which can be any string up to 127 characters long. It is used to uniquely identify this device in other command line directives.

A character device may be used in multiplexing mode by multiple front-ends. Specify `mux=on` to enable this mode. A multiplexer is a "1:N" device, and here the "1" end is your specified chardev backend, and the "N" end is the various parts of QEMU that can talk to a chardev. If you create a chardev with `id=myid` and `mux=on`, QEMU will create a multiplexer with your specified ID, and you can then configure multiple front ends to use that chardev ID for their input/output. Up to four different front ends can be connected to a single multiplexed chardev. (Without multiplexing enabled, a chardev can only be used by a single front end.) 💅

For instance, you could use this to allow a single `stdio` chardev to be used by two serial ports *and* the QEMU monitor:

-chardev stdio,mux=on,id=char0 \ -mon chardev=char0,mode=readline \ -serial chardev:char0 \ -serial chardev:char0


You can have <pink>more than one</pink> multiplexer in a system configuration — for instance you could have a TCP port multiplexed between UART 0 and UART 1, and `stdio` multiplexed between the QEMU monitor and a parallel port:

-chardev stdio,mux=on,id=char0 \ -mon chardev=char0,mode=readline \ -parallel chardev:char0 \ -chardev tcp,...,mux=on,id=char1 \ -serial chardev:char1 \ -serial chardev:char1


When you're using a multiplexed character device, some escape sequences are interpreted in the input. See the chapter about Keys in the character backend multiplexer (anchor `#keys-in-the-character-backend-multiplexer`) in the System Emulation Users Guide for more details. 🧚

Note that some other command line options may implicitly create multiplexed character backends — for instance `-serial mon:stdio` creates a multiplexed `stdio` backend connected to the serial port and the QEMU monitor, and `-nographic` also multiplexes the console and the monitor to stdio.

If you need to aggregate data in the opposite direction (where one QEMU frontend interface receives input and output from multiple backend chardev devices), please refer to the paragraph below regarding chardev hub aggregator device configuration.

Every backend supports the `logfile` option, which supplies the path to a file to record all data transmitted via the backend. The `logappend` option controls whether the log file will be truncated or appended to when opened. 🍓

The available backends are:

## `-chardev null,id=id`

A void device. This device will not emit any data, and will drop any data it receives. The `null` backend does not take any options. It's giving <italic>nothing</italic>, and that's the point. 💀

## `-chardev socket,id=id[,TCP options or unix options][,server=on|off][,wait=on|off][,telnet=on|off][,websocket=on|off][,reconnect-ms=milliseconds][,tls-creds=id][,tls-authz=id]`

Create a two-way stream socket, which can be either a TCP or a unix socket. A unix socket will be created if `path` is specified.

> 🚨 Behaviour is **undefined** if TCP options are specified for a unix socket.

- `server=on|off` — specifies that the socket shall be a listening socket.
- `wait=on|off` — specifies that QEMU should not block waiting for a client to connect to a listening socket.
- `telnet=on|off` — specifies that traffic on the socket should interpret telnet escape sequences.
- `websocket=on|off` — specifies that the socket uses WebSocket protocol for communication.
- `reconnect-ms` — sets the timeout for reconnecting on non-server sockets when the remote end goes away. QEMU will delay this many milliseconds and then attempt to reconnect. Zero disables reconnecting, and is the default.
- `tls-creds` — requests enablement of the TLS protocol for encryption, and specifies the id of the TLS credentials to use for the handshake. The credentials must be previously created with the `-object tls-creds` argument.
- `tls-auth` — provides the ID of the QAuthZ authorization object against which the client's x509 distinguished name will be validated. This object is only resolved at time of use, so can be deleted and recreated on the fly while the chardev server is active. If missing, it will default to denying access.

TCP and unix socket options are given below:

### TCP options

`port=port[,host=host][,to=to][,ipv4=on|off][,ipv6=on|off][,nodelay=on|off]`

- `host` — for a listening socket, specifies the local address to be bound. For a connecting socket, specifies the remote host to connect to. `host` is optional for listening sockets. If not specified it defaults to `0.0.0.0`.
- `port` — for a listening socket, specifies the local port to be bound. For a connecting socket, specifies the port on the remote host to connect to. `port` can be given as either a port number or a service name. `port` is required.
- `to` — only relevant to listening sockets. If it is specified, and `port` cannot be bound, QEMU will attempt to bind to subsequent ports up to and including `to` until it succeeds. `to` must be specified as a port number.
- `ipv4=on|off` and `ipv6=on|off` — specify that either IPv4 or IPv6 must be used. If neither is specified the socket may use either protocol.
- `nodelay=on|off` — disables the Nagle algorithm.

### unix options

`path=path[,abstract=on|off][,tight=on|off]`

- `path` — specifies the local path of the unix socket. `path` is required.
- `abstract=on|off` — specifies the use of the abstract socket namespace, rather than the filesystem. Optional, defaults to `false`.
- `tight=on|off` — sets the socket length of abstract sockets to their minimum, rather than the full `sun_path` length. Optional, defaults to `true`.

## `-chardev udp,id=id[,host=host],port=port[,localaddr=localaddr][,localport=localport][,ipv4=on|off][,ipv6=on|off]`

Sends all traffic from the guest to a remote host over UDP. 🌸

`host` specifies the remote host to connect to. If not specified it defaults to `localhost`.

- **`port`** — the port on the remote host you're connecting to. lowkey mandatory, bestie, `port` is required ✨
- **`localaddr`** — the local address to bind to. skip it and it just defaults to `0.0.0.0` 💅
- **`localport`** — the local port to bind to. skip it and QEMU grabs whatever local port is available 🌸
- **`ipv4=on|off`** and **`ipv6=on|off`** — these force either IPv4 or IPv6 to be used. choose neither and the device can use either protocol, main character energy 🦋

- **`-chardev msmouse,id=id`** — forwards QEMU's emulated msmouse events straight to the guest. msmouse takes literally no options, it's giving minimalist 💖

- **`-chardev hub,id=id,chardevs.0=id[,chardevs.N=id]`** — explicitly creates a chardev backend hub device ✨ and the whole point is that it can aggregate input from multiple backend devices and forward it to a single frontend device. and bestie, it goes both ways: the hub takes the output from the frontend device and sends it back to all the connected backend devices. this is what makes seamless interaction between different backend devices and a single frontend interface possible 🫶. aggregation is supported for up to **4** chardev devices. **(Since 10.0)**

  for example, here's a use case with 2 backend devices: a virtual console `vc0` and a pseudo TTY `pty0`, connected to a single virtio hvc console frontend device with hub `hub0`. the virtual console renders text to an image, which can be shared over the VNC protocol. in turn, the pty backend provides bidirectional communication to the virtio hvc console over the pseudo TTY file. the example config can be:

-chardev pty,path=/tmp/pty,id=pty0 \ -chardev vc,id=vc0 \ -chardev hub,id=hub0,chardevs.0=pty0,chardevs.1=vc0 \ -device virtconsole,chardev=hub0 \ -vnc 0.0.0.0:0


once QEMU starts, a VNC client and any TTY emulator can be used to control a single hvc console:

Start TTY emulator

tio /tmp/pty

Start VNC client and switch to virtual console Ctrl-Alt-2

vncviewer :0


> heads up bestie: several frontend devices is **not** supported. and stacking of multiplexers and hub devices is **not** supported either. periodt 💀

- **`-chardev vc,id=id[[,width=width][,height=height]][[,cols=cols][,rows=rows]]`** — connects to a QEMU text console 🎀. `vc` can optionally be handed a specific size.
- `width` and `height` set the width and height of the console respectively, in pixels.
- `cols` and `rows` make the console get sized to fit a text console with the given dimensions. slay.

- **`-chardev ringbuf,id=id[,size=size]`** — creates a ring buffer with a fixed size `size` 💫. `size` has to be a power of two, and it defaults to `64K`.

- **`-chardev file,id=id,path=path[,input-path=input-path]`** — logs all traffic received from the guest to a file 🍓.
- `path` is the path of the file to be opened. this file gets created if it doesn't already exist, and overwritten if it does. `path` is required, no cap.
- if `input-path` is specified, that's the path of a second file that'll be used for input. if `input-path` isn't specified, no input will be available from the chardev. 🙈

> note that `input-path` is **not** supported on Windows hosts. 💀

- **`-chardev pipe,id=id,path=path`** — creates a two-way connection to the guest. the behaviour differs a lil bit between Windows hosts and other hosts:
- on Windows, a single duplex pipe gets created at `\\.pipe\path`.
- on other hosts, 2 pipes get created called `path.in` and `path.out`. data written to `path.in` will be received by the guest. data written by the guest can be read from `path.out`. QEMU will **not** create these fifos, and requires them to be present 🙏.

`path` forms part of the pipe path as described above. `path` is required. ✨

- **`-chardev console,id=id`** — sends traffic from the guest to QEMU's standard output 💖. console takes no options at all. it's only available on Windows hosts, iykyk.

- **`-chardev serial,id=id,path=path`** — sends traffic from the guest to a serial device on the host 🔥.
- on Unix hosts, `serial` will actually accept *any* tty device, not only serial lines. iconic.
- `path` is the name of the serial device to open.

- **`-chardev pty,id=id[,path=path]`** — creates a new pseudo-terminal on the host and connects to it 🦋.
- `pty` is **not** available on Windows hosts.
- if `path` is specified, QEMU creates a symbolic link at that location which points to the new PTY device 👑. this avoids having to make QMP or HMP monitor queries just to find out what the new PTY device path is. genius tbh.
- > bestie listen: QEMU removes the symlink when it exits *gracefully*, but it will **not** do so in case of crashes or on certain startup errors. it's recommended that you check and remove the symlink after QEMU terminates to account for this 🙈.

- **`-chardev stdio,id=id[,signal=on|off]`** — connects to the standard input and standard output of the QEMU process 🌈.
- `signal` controls whether signals are enabled on the terminal, which includes exiting QEMU with the key sequence <kbd>Control</kbd>+<kbd>c</kbd>. this option is enabled by default, so use `signal=off` to disable it. 💅

- **`-chardev braille,id=id`** — connects to a local BrlAPI server 🎀. braille takes no options.

- **`-chardev parallel,id=id,path=path`**
- `parallel` is only available on Linux, FreeBSD and DragonFlyBSD hosts.
- connect to a local parallel port.
- `path` is the path to the parallel port device. `path` is required. ⭐

- **`-chardev spicevmc,id=id,debug=debug,name=name`**
- `spicevmc` is only available when spice support is built in.
- `debug` — debug level for spicevmc.
- `name` — name of spice channel to connect to.
- connects to a spice virtual machine channel, such as `vdiport` 🔥.

- **`-chardev spiceport,id=id,debug=debug,name=name`**
- `spiceport` is only available when spice support is built in.
- `debug` — debug level for spicevmc.
- `name` — name of spice port to connect to.
- connects to a spice port, allowing a Spice client to handle the traffic identified by a name (preferably a fqdn). 💜

---

## 🔐 TPM device options 🔐

the general form of a TPM device option is:

-tpmdev backend,id=id[,options]


the specific backend type decides which options apply 👑. the `-tpmdev` option creates the TPM backend and it **requires** a `-device` option that specifies the TPM frontend interface model. no frontend, no vibes.

use `-tpmdev help` to print all the available TPM backend types. slay.

the available backends are:

- **`-tpmdev passthrough,id=id,path=path,cancel-path=cancel-path`** — (Linux-host only) enables access to the host's TPM using the passthrough driver 🔥.
  - `path` is the path to the host's TPM device — on a Linux host this would be `/dev/tpm0`. `path` is optional and by default `/dev/tpm0` is used.
  - `cancel-path` is the path to the host TPM device's sysfs entry, allowing cancellation of an ongoing TPM command. `cancel-path` is optional and by default QEMU will search for the sysfs entry to use. 🦋

  some notes about using the host's TPM with the passthrough driver:

  - the TPM device accessed by the passthrough driver must **not** be used by any other application on the host. 💀
  - since the host's firmware (BIOS/UEFI) has already initialized the TPM, the VM's firmware (BIOS/UEFI) will not be able to initialize the TPM again and may therefore not show a TPM-specific menu that would otherwise let the user configure the TPM, e.g., enable/disable or activate/deactivate the TPM 😭. further, if TPM ownership is released from within a VM, then the host's TPM will get disabled and deactivated. to enable and activate the TPM again afterwards, the host has to be rebooted and the user is required to enter the firmware's menu to enable and activate the TPM. if the TPM is left disabled and/or deactivated, most TPM commands will fail. 🙈

  to create a passthrough TPM use these two options:

-tpmdev passthrough,id=tpm0 -device tpm-tis,tpmdev=tpm0


note that the `-tpmdev` id is `tpm0` and is referenced by `tpmdev=tpm0` in the device option. ✨

- **`-tpmdev emulator,id=id,chardev=dev`** — (Linux-host only) enables access to a TPM emulator using a Unix domain socket based chardev backend 💖.
- `chardev` specifies the unique ID of a character device backend that provides the connection to the software TPM server.
- to create a TPM emulator backend device with chardev socket backend:

-chardev socket,id=chrtpm,path=/tmp/swtpm-sock -tpmdev emulator,id=tpm0,chardev=chrtpm -device tpm-tis,tpmdev=tpm0


---

## 👑 Boot Image or Kernel specific 👑

there are broadly **4** ways you can boot a system with QEMU:

- specify a firmware and let it control finding a kernel
- specify a firmware and pass a hint to the kernel to boot
- direct kernel image boot
- manually load files into the guest's address space

the third method is useful for quickly testing kernels, but since there's no firmware to pass configuration information to the kernel, the hardware must either be probeable, the kernel built for the exact configuration, or passed some configuration data (e.g. a DTB blob) which tells the kernel what drivers it needs 🔥. these exact details are often hardware specific.

the final method is the most generic way of loading images into the guest address space, and it's used mostly for bare metal type development where the reset vectors of the processor are taken into account. main character energy fr fr.

for x86 machines and some other architectures, `-bios` will generally do the right thing with whatever it is given 🎀. for other machines, the more strict `-pflash` option needs an image that is sized for the flash device for the given machine type.

please see the QEMU System Emulator Targets <#system-targets-ref> section of the manual for more detailed documentation. 💜

- **`-bios file`** — set the filename for the BIOS. 🌸
- **`-pflash file`** — use `file` as a parallel flash image. ⭐

the kernel options were designed to work with Linux kernels, although other things (like hypervisors) can be packaged up as a kernel executable image 🦋. the exact format of an executable image is usually architecture specific.

The way your kernel actually gets started is <hotpink>architecture-specific bestie</hotpink> — like, what address it gets loaded at, whether anything gets handed to it through CPU registers, what the hardware looks like when it wakes up, all of it. 👑 Typically it just follows whatever spec the Linux kernel laid down for that arch, so no surprises.

- **`-kernel`** *bzImage* — use *bzImage* as your kernel image. It can be a Linux kernel or be in <purple>multiboot</purple> format. either way, slay.
- **`-shim`** *shim.efi* — use `shim.efi` to boot the kernel 🦋
- **`-append`** *cmdline* — use *cmdline* as the kernel command line 📝
- **`-initrd`** *file* — use *file* as the initial ram disk.
- **`-initrd`** `"file1 arg=foo,file2"` — ok so this syntax is **only** available with multiboot, noted. 💅 You use *file1* and *file2* as modules and pass `arg=foo` as a parameter to the first module. Wanna put commas inside module parameters? Double them up on the command line to escape them — that's the trick:
- **`-initrd`** `"bzImage earlyprintk=xen,,keep root=/dev/xvda1,initrd.img"` — multiboot only, again. Use `bzImage` as the first module with `"earlyprintk=xen,keep root=/dev/xvda1"` as its command line, and `initrd.img` as the second module. 🤝
- **`-dtb`** *file* — use *file* as a device tree binary (dtb) image and hand it to the kernel on boot. 🌳

Finally — and this is the <rainbow>dev-only main character energy</rainbow> part — you can also manually load images straight into the address space of the guest. Most useful for developers who already know the layout of their guest and who carefully make sure something sane will happen when the reset vector executes. 😌

The generic loader gets invoked via the loader device:

-device loader,addr=<addr>,data=<data>,data-len=<data-len>[,data-be=<data-be>][,cpu-num=<cpu-num>]


There's also the guest loader, which works pretty much the same way but tweaks the DTB so that a hypervisor loaded via `-kernel` can find where the guest image is:

-device guest-loader,addr=<addr>[,kernel=<path>,[bootargs=<arguments>]][,initrd=<path>]


---

## 🛠️ Debug/Expert options 🛠️

> These are the ones where you're like "I know what I'm doing" — pls actually know what you're doing bestie.

- **`-compat`** `[deprecated-input=<input-policy>][,deprecated-output=<output-policy>]` — set the policy for handling **deprecated** management interfaces (experimental, fyi). ✨
  - `deprecated-input=accept` **(default)** — accept deprecated commands and arguments 🫶
  - `deprecated-input=reject` — reject deprecated commands and arguments 🙅‍♀️
  - `deprecated-input=crash` — crash on deprecated commands and arguments 💀 (yes, fr, it crashes)
  - `deprecated-output=accept` **(default)** — emit deprecated command results and events
  - `deprecated-output=hide` — suppress deprecated command results and events 🤫
  - **Limitation:** covers only syntactic aspects of QMP. Don't expect more than that, ok?

- **`-compat`** `[unstable-input=<input-policy>][,unstable-output=<output-policy>]` — set the policy for handling **unstable** management interfaces (also experimental). 🌈
  - `unstable-input=accept` **(default)** — accept unstable commands and arguments
  - `unstable-input=reject` — reject unstable commands and arguments
  - `unstable-input=crash` — crash on unstable commands and arguments 😭
  - `unstable-output=accept` **(default)** — emit unstable command results and events
  - `unstable-output=hide` — suppress unstable command results and events
  - **Limitation:** again, covers only syntactic aspects of QMP. same energy, same caveat. 💅

- **`-fw_cfg`** `[name=]name,file=file` — add a named fw_cfg entry whose contents come from the file *file*. If the filename has a comma in it you **must** double it (so `"file=my,,file"` to use the file `my,file`). 🍓

- **`-fw_cfg`** `[name=]name,string=str` — add a named fw_cfg entry whose contents come from the string *str*. Same comma deal: if *str* contains a comma you have to double it (so `"string=my,,string"` to use the string `my,string`).

  The terminating NUL character of the contents of *str* is **not** included as part of the fw_cfg item data. If you need contents with embedded NUL characters, you have to use the `file` parameter instead. 🫡

  The fw_cfg entries are passed by QEMU through to the guest.

  Example, bestie:

-fw_cfg name=opt/com.mycompany/blob,file=./my_blob.bin


This creates an fw_cfg entry named `opt/com.mycompany/blob` with contents from `./my_blob.bin`. iconic.

- **`-serial`** *dev* — redirect the virtual serial port to host character device *dev*. Default device is `vc` in graphical mode and `stdio` in non graphical mode. 🐎

You can use this option several times to simulate multiple serial ports — go off.

And you can use `-serial none` to suppress the creation of default serial devices.

Available character devices are:

- `vc[:WxH]` — virtual console. Optionally you can give a width and height in pixels with:

vc:800x600


It's also possible to specify width or height in characters:

vc:80Cx24C


- `pty[:path]` — **[Linux only]** pseudo TTY (a new PTY is automatically allocated).
- If *path* is specified, QEMU will create a symbolic link at that location which points to the new PTY device.
- This avoids having to make QMP or HMP monitor queries to find out what the new PTY device path is. 🙌
- Note that while QEMU will remove the symlink when it exits gracefully, it will **not** do so in case of crashes or on certain startup errors. It is recommended that the user checks and removes the symlink after QEMU terminates to account for this. 🧹
- `none` — no device is allocated. Note that for machine types which emulate systems where a serial device is always present in real hardware, this may be equivalent to the `null` option, in that the serial device is still present but all output is discarded. For boards where the number of serial ports is truly variable, this suppresses the creation of the device.
- `null` — the guest will see the UART or serial device as present in the machine, but all output is discarded and there is no input. Conceptually equivalent to redirecting the output to `/dev/null`. 🕳️
- `chardev:id` — use a named character device defined with the `-chardev` option.
- `/dev/XXX` — **[Linux only]** use host tty, e.g. `/dev/ttyS0`. The host serial port parameters are set according to the emulated ones.
- `/dev/parportN` — **[Linux only, parallel port only]** use host parallel port *N*. Currently SPP and EPP parallel port features can be used.
- `file:filename` — write output to *filename*. No character can be read. ✍️
- `stdio` — **[Unix only]** standard input/output
- `pipe:filename` — name pipe *filename*
- `COMn` — **[Windows only]** use host serial port *n*
- `udp:[remote_host]:remote_port[@[src_ip]:src_port]` — this implements UDP Net Console. When *remote_host* or *src_ip* are not specified they default to `0.0.0.0`. When you're not using a specified *src_port*, a random port is automatically chosen. 🎲
- If you just want a simple readonly console you can use `netcat` or `nc`, by starting QEMU with `-serial udp::4555` and nc as `nc -u -l -p 4555`. Any time QEMU writes something to that port it will appear in the netconsole session.
- If you plan to send characters back via netconsole or you want to stop and start QEMU a lot of times, you should have QEMU use the same source port each time by using something like `-serial udp::4555@:4556` to QEMU. Another approach is to use a patched version of netcat which can listen to a TCP port and send and receive characters via udp. If you have a patched version of netcat which activates telnet remote echo and single char transfer, then you can use the following options to set up a netcat redirector to allow telnet on port `5555` to access the QEMU port. 🧚

  QEMU Options:

-serial udp::4555@:4556


netcat options:

-u -P 4555 -L 0.0.0.0:4556 -t -p 5555 -I -T


telnet options:

localhost 5555


- `tcp:[host]:port[,server=on|off][,wait=on|off][,nodelay=on|off][,reconnect-ms=milliseconds]` — the TCP Net Console has two modes of operation. It can send the serial I/O to a location, or wait for a connection from a location. By default the TCP Net Console is sent to *host* at the *port*. If you use the `server=on` option QEMU will wait for a client socket application to connect to the port before continuing, unless the `wait=on|off` option was specified. The `nodelay=on|off` option disables the Nagle buffering algorithm. The `reconnect-ms` option only applies if `server=no` is set — if the connection goes down it will attempt to reconnect at the given interval. If *host* is omitted, `0.0.0.0` is assumed. Only one TCP connection at a time is accepted. You can use `telnet=on` to connect to the corresponding character device.
- Example to send tcp console to `192.168.0.2` port `4444`:

-serial <tcp:192.168.0.2:4444>


- Example to listen and wait on port `4444` for connection:

-serial <tcp::4444,server=on>


- Example to not wait and listen on ip `192.168.0.100` port `4444`:

-serial <tcp:192.168.0.100:4444,server=on,wait=off>


- `telnet:host:port[,server=on|off][,wait=on|off][,nodelay=on|off]` — the telnet protocol is used instead of raw tcp sockets. The options work the same as if you had specified `-serial tcp`. The difference is that the port acts like a telnet server or client using telnet option negotiation. This will also allow you to send the `MAGIC_SYSRQ` sequence if you use a telnet that supports sending the break sequence. Typically in unix telnet you do it with <kbd>Control</kbd>+<kbd>]</kbd> and then type `"send break"` followed by pressing the enter key. ✨

- **`websocket:host:port,server=on[,wait=on|off][,nodelay=on|off]`**
— WebSocket protocol instead of a raw TCP socket, bestie. The port is acting as a WebSocket **server**. Client mode? Not supported. Periodt.

- **`unix:path[,server=on|off][,wait=on|off][,reconnect-ms=milliseconds]`**
— A unix domain socket instead of a TCP socket. Works exactly like `-serial tcp` except the connections go through the unix domain socket *path* instead. Slay.

- **`mon:dev_string`**
— Okay so this one's special 💅 it lets the monitor get multiplexed onto another serial port. You reach the monitor by hitting <kbd>Ctrl</kbd>+<kbd>a</kbd> and then <kbd>c</kbd>. And *dev_string* can be literally any of the serial devices listed above. Want an example? Multiplexing the monitor onto a telnet server chilling on port 4444 looks like this:

-serial mon:telnet::4444,server=on,wait=off


> Heads up though — when the monitor is multiplexed onto stdio like this, <kbd>Ctrl</kbd>+<kbd>C</kbd> will **not** terminate QEMU anymore. It gets passed straight to the guest instead. No cap.

- **`braille`**
— Braille device 🫶 it uses BrlAPI to push the braille output onto a real *or* fake device.

- **`msmouse`**
— A three button serial mouse. Configure your guest to use the Microsoft protocol and you're good.

---

## 🖨️ `-parallel dev`

Redirect the virtual parallel port to host device *dev* (same devices as the serial port, yeah). On Linux hosts you can use `/dev/parportN` to hook up actual hardware sitting on the corresponding host parallel port.

You can pass this option several times and simulate up to **3** parallel ports. Iconic.

And to shut them all down? Use `-parallel none`.

---

## 👀 `-monitor dev`

Redirect the monitor to host device *dev* (again, same devices as the serial port). The default device is `vc` in graphical mode and `stdio` in non graphical mode. Use `-monitor none` to disable that default monitor. Easy.

---

## 🎛️ `-qmp dev`

Like `-monitor` but it opens in <rainbow>'control'</rainbow> mode. Say you want QMP available on localhost port 4444:

-qmp tcp:localhost:4444,server=on,wait=off


Lowkey important: not every option is configurable through this syntax. If you want maximum flexibility, use the `-mon` option with an accompanying `-chardev`. iykyk.

---

## ✨ `-qmp-pretty dev`

Like `-qmp`, but it uses pretty JSON formatting. Aesthetic.

---

## 💖 `-mon [chardev=]name[,mode=readline|control][,pretty=on|off]`

Sets up a monitor connected to the chardev *name*. QEMU gives you two monitors, and yes they have main character energy in different ways:

- the **Human Monitor Protocol** (`HMP`) — for human interaction
- the **QEMU Monitor Protocol** (`QMP`) — a JSON RPC-style protocol

Default is `HMP`, and `mode=control` switches you over to `QMP` instead. `pretty` is **only** valid when `mode=control`, and it turns on JSON pretty printing to make reading and debugging easier for us humans.

Cute little example:

-chardev socket,id=mon1,host=localhost,port=4444,server=on,wait=off \ -mon chardev=mon1,mode=control,pretty=on


That enables the QMP monitor on localhost port 4444 with pretty-printing. Chef's kiss.

---

## 🐛 `-debugcon dev`

Redirect the debug console to host device *dev* (yep, same devices as the serial port). Fun fact: the debug console is an I/O port, typically port `0xe9`, and writing to that I/O port sends the output to this device. Default device is `vc` in graphical mode and `stdio` in non graphical mode.

---

## 📌 `-pidfile file`

Stores the QEMU process PID in *file*. Super useful when you're launching QEMU from a script, fr fr.

---

## 🔬 `--preconfig`

Pauses QEMU for interactive configuration **before** the machine is created — which means you can query and configure properties that will affect machine initialization. Use the QMP command `x-exit-preconfig` to bail out of the preconfig state and move on to the next one (aka run the guest if `-S` isn't used, or pause a second time if `-S` *is* used).

> This option is **experimental**. Just so you know.

---

## ⏸️ `-S`

Does not start the CPU at startup. You'll have to type `c` in the monitor to get things moving. Iconic manual override.

---

## 💾 `-overcommit mem-lock=on|off|on-fault`, `-overcommit cpu-pm=on|off`

Run qemu with hints about host resource overcommit. By default it assumes the host overcommits *everything*.

Locking qemu and guest memory can be turned on with `mem-lock=on` or `mem-lock=on-fault` (off by default). This works when host memory isn't overcommitted, and it shrinks the worst-case latency for the guest. The `on-fault` option is better for cutting the memory footprint since it makes allocations lazy — but the pages still get locked in place once the guest or QEMU faults them in. Note that these two options are **mutually exclusive**, bestie, pick one.

Guest ability to manage the power state of host cpus (which raises latency for other processes on that same host cpu, but lowers latency for the guest) can be enabled with `cpu-pm=on` (off by default). Works best when host CPU isn't overcommitted. Heads up: while this is on, host estimates of CPU cycle and power utilization will be **incorrect**, because they don't account for guest idle time.

---

## 🐞 `-gdb dev`

Accepts a gdb connection on device *dev* (see the GDB usage <#gdb-usage> chapter in the System Emulation Users Guide). Careful though — this option does **not** pause QEMU execution. If you want QEMU to hold off starting the guest until you connect with gdb and issue a continue command, you also need to pass the `-S` option.

The most usual setup is listening on a local TCP socket:

-gdb tcp::3117


But you can specify other backends — UDP, pseudo TTY, or even stdio are all reasonable use cases. For example, a stdio connection lets you start QEMU from *within* gdb and establish the connection via a pipe:

(gdb) target remote | exec qemu-system-x86_64 -gdb stdio ...


---

## 🩳 `-s`

Shorthand for `-gdb <tcp::1234>`, aka open a gdbserver on TCP port `1234` (see the GDB usage <#gdb-usage> chapter in the System Emulation Users Guide). Short and sweet.

---

## 📝 `-d item1[,...]`

Enable logging of specified items. Use `-d help` for a list of log items. Go check what's available, don't guess 💅

---

## 📄 `-D logfile`

Output log in *logfile* instead of to stderr.

---

## 🎯 `-dfilter range1[,...]`

Filter debug output down to only what's relevant to a range of target addresses. The filter spec can be either `start+size`, `start-size` or `start..end`, where `start` `end` and `size` are the addresses and sizes required. For example:

-dfilter 0x8000..0x8fff,0xffffffc000080000+0x200,0xffffffc000060000-0x1000


Will dump output for any code in the `0x1000` sized block starting at `0x8000`, and the `0x200` sized block starting at `0xffffffc000080000`, and another `0x1000` sized block starting at `0xffffffc00005f000`. Math is mathing.

---

## 🎲 `-seed number`

Force the guest to use a deterministic pseudo-random number generator, seeded with *number*. Note this does **not** affect crypto routines within the host.

---

## 📂 `-L path`

Set the directory for the BIOS, VGA BIOS and keymaps.

To list all the data directories, use `-L help`. Bestie, use the help.

---

## ⚡ `-enable-kvm`

Enable KVM full virtualization support. Only available if KVM support was enabled when compiling. Fingers crossed 🤞

---

## 🧚 `-xen-domid id`

Specify xen guest domain id (XEN only).

---

## 🧲 `-xen-attach`

Attach to an existing xen domain. libxl will use this when starting QEMU (XEN only). Also restricts the set of available xen operations to the specified domain id (XEN only). Double xen energy.

---

## 🔁 `-no-reboot`

Exit instead of rebooting.

---

## 🛑 `-no-shutdown`

Don't exit QEMU on guest shutdown — instead just stop the emulation. This lets you, for instance, switch to the monitor and commit changes to the disk image. Lowkey a lifesaver.

---

## 🎬 `-action event=action`

The *action* parameter modifies QEMU's default behavior when certain guest events occur. It's basically a generic way of specifying the same behaviors that `-no-reboot` and `-no-shutdown` change.

Examples:

-action panic=none -action reboot=shutdown,shutdown=pause -device i6300esb -action watchdog=pause


---

## 💫 `-loadvm file`

Start right away with a saved state (`loadvm` in the monitor).

---

## 👻 `-daemonize`

Daemonize the QEMU process after initialization. QEMU won't detach from standard IO until it's ready to receive connections on any of its devices. This is a super useful way for external programs to launch QEMU without having to deal with initialization race conditions. No more chaos. 🫶

---

## 🧩 `-option-rom file`

Load the contents of *file* as an option ROM. Great for loading things like EtherBoot.

---

## ⏰ `-rtc [base=utc|localtime|datetime][,clock=host|rt|vm][,driftfix=none|slew]`

Specify *base* as `utc` or `localtime` to let the RTC start at the current UTC or local time, respectively. `localtime` is required for correct dates in MS-DOS or Windows. Wanna start at a specific point in time? Provide *datetime* in the format `2006-06-17T16:01:21` or `2006-06-17`. The default *base* is `UTC`.

By default the RTC is driven by the host system time, which lets you use the RTC as an accurate reference clock inside the guest — especially if the host time is smoothly following an accurate external reference clock, like via NTP. Want to isolate the guest time from the host? Set *clock* to `rt` instead, which provides a host monotonic clock if the host supports it. To even stop the RTC from progressing during suspension, set *clock* to `vm` (virtual clock). `clock=vm` is recommended *especially* in icount mode to preserve determinism — but note that in icount mode the speed of the virtual clock is variable and can in general differ from the host clock.

Enable *driftfix* (i386 targets only) if you're experiencing time drift problems, specifically with Windows' ACPI HAL. This option will try to figure out how many timer interrupts the Windows guest didn't process and will re-inject them. Fixing it, periodt.

---

## 🕰️ `-icount [shift=N|auto][,align=on|off][,sleep=on|off][,rr=record|replay,rrfile=filename[,rrsnapshot=snapshot]]`

Enable virtual instruction counter. The virtual cpu will execute one instruction every `2^N` ns of virtual time. If `auto` is specified, then the virtual cpu speed will be automatically adjusted to keep virtual time within a few seconds of real time. Letting the machine handle the vibes itself. ✨

<pink>**Important caveat bestie**</pink>: sure, this option can give you deterministic behavior, but it is **not** cycle accurate emulation, okay? Don't come for me. Modern CPUs are out here with superscalar out-of-order cores and complex cache hierarchies, so the number of instructions executed often has <italic>little or no correlation</italic> with actual performance. It's giving vibes, not benchmarks. 💀

When the virtual cpu is sleeping, the virtual time will advance at default speed — <italic>unless</italic> <pink>`sleep=off`</pink> is specified. With <pink>`sleep=off`</pink>, the virtual time jumps straight to the next timer deadline *instantly* whenever the virtual cpu goes into sleep mode, and it will **not** advance if no timer is enabled. From the guest's point of view this gives deterministic execution times. The default when `icount` is enabled is <pink>`sleep=on`</pink>. And heads up: <pink>`sleep=off`</pink> cannot be used together with either `shift=auto` or `align=on`. Not allowed. Sorry babe. 🚫

<pink>`align=on`</pink> activates the delay algorithm, which tries to synchronise the host clock and the virtual clock. The goal is a guest running at the real frequency imposed by the `shift` option. Whenever the guest clock is behind the host clock and `align=on` is specified, we print a message to the user to inform about the delay. Currently this option does **not** work when `shift` is `auto`. 📌 **Note:** the sync algorithm will work for those `shift` values for which the guest clock runs ahead of the host clock — typically when the `shift` value is high (how high depends on the host machine, so it's giving *it depends* energy). The default when `icount` is enabled is <pink>`align=off`</pink>.

When the <pink>`rr`</pink> option is specified, deterministic record/replay is enabled. The <pink>`rrfile=`</pink> option must also be provided to specify the path to the replay log — record mode writes data to this file, replay mode reads it back. If the <pink>`rrsnapshot`</pink> option is given, it specifies a VM snapshot name. In record mode a new VM snapshot with the given name is created at the start of execution recording; in replay mode this option specifies the snapshot name used to load the initial VM state. ✨

---

- **`-watchdog-action action`** — the `action` controls what QEMU does when the watchdog timer expires. Default is <pink>`reset`</pink> (forcefully reset the guest). Other possible actions: <pink>`shutdown`</pink> (attempt to gracefully shutdown the guest), <pink>`poweroff`</pink> (forcefully poweroff the guest), <pink>`inject-nmi`</pink> (inject a NMI into the guest), <pink>`pause`</pink> (pause the guest), <pink>`debug`</pink> (print a debug message and continue), or <pink>`none`</pink> (do nothing).

  Note that the `shutdown` action requires that the guest responds to ACPI signals, which it may not be able to do in the sort of situations where the watchdog would have expired — so `-watchdog-action shutdown` is **not recommended for production use**. 🫣

  Examples:

-device i6300esb -watchdog-action pause


- **`-echr numeric_ascii_value`** — change the escape character used for switching to the monitor when using monitor and serial sharing. The default is <pink>`0x01`</pink> when using the `-nographic` option, and `0x01` is equal to pressing <kbd>Control</kbd>+<kbd>a</kbd>. You can pick a different character from the ascii control keys, where 1 through 26 map to <kbd>Control</kbd>+<kbd>a</kbd> through <kbd>Control</kbd>+<kbd>z</kbd>. For instance you could use either of the following to change the escape character to <kbd>Control</kbd>+<kbd>t</kbd>. 🎀

-echr 0x14; -echr 20


---

The <pink>`-incoming`</pink> option specifies the migration channel for an incoming migration. It may be used multiple times to specify multiple migration channel types. The channel type is specified in `<channel>`, or is `main` for all other forms of `-incoming`. If multiple `-incoming` options are specified for a channel type, the **last one takes precedence**. 👑

-incoming tcp:[host]:port[,to=maxport][,ipv4=on|off][,ipv6=on|off]

-incoming rdma:host:port[,ipv4=on|off][,ipv6=on|off]


- Prepare for incoming migration, listen on a given tcp port. 🛰️

-incoming unix:socketpath


- Prepare for incoming migration, listen on a given unix socket.

-incoming fd:fd


- Accept incoming migration from a given file descriptor.

-incoming file:filename[,offset=offset]


- Accept incoming migration from a given file starting at `offset`. `offset` allows the common size suffixes, or a `0x` prefix, but **not both**.

-incoming exec:cmdline


- Accept incoming migration as an output from specified external command.

-incoming <channel>


- Accept incoming migration on the migration channel. For the syntax of `<channel>`, see the QAPI documentation of `MigrationChannel`. Examples:

-incoming '{"channel-type": "main", "addr": { "transport": "socket", "type": "unix", "path": "my.sock" }}'

-incoming main,addr.transport=socket,addr.type=unix,addr.path=my.sock

-incoming defer


- Wait for the URI to be specified via `migrate_incoming`. The monitor can be used to change settings (such as migration parameters) prior to issuing the `migrate_incoming` to allow the migration to begin. ⏳

---

- **`-only-migratable`** — only allow migratable devices. Devices will **not** be allowed to enter an unmigratable state. 🔒

- **`-nodefaults`** — don't create default devices. Normally QEMU sets the default devices like serial port, parallel port, virtual console, monitor device, VGA adapter, floppy and CD-ROM drive and others. The `-nodefaults` option disables **all** those default devices. Bye bye defaults 💅

- **`-prom-env variable=value`** — set OpenBIOS nvram variable to given value (**PPC, SPARC only**).

qemu-system-sparc -prom-env 'auto-boot?=false' \ -prom-env 'boot-device=sd(0,2,0):d' -prom-env 'boot-args=linux single'

qemu-system-ppc -prom-env 'auto-boot?=false' \ -prom-env 'boot-device=hd:2,\yaboot' \ -prom-env 'boot-args=conf=hd:2,\yaboot.conf'


- **`-semihosting`** — enable Semihosting mode (**ARM, M68K, Xtensa, MIPS, RISC-V only**). 🌸

> **Warning:** Note that this allows guest direct access to the host filesystem, so should only be used with a trusted guest OS. 🚨

See the `-semihosting-config` option documentation for further information about the facilities this enables.

- **`-semihosting-config`** — enable and configure Semihosting (**ARM, M68K, Xtensa, MIPS, RISC-V only**).

-semihosting-config [enable=on|off][,target=native|gdb|auto][,chardev=id][,userspace=on|off][,arg=str[,...]]


> **Warning:** Note that this allows guest direct access to the host filesystem, so should only be used with a trusted guest OS. 🚨

- `target=native|gdb|auto` — defines where the semihosting calls will be addressed: to QEMU (`native`) or to GDB (`gdb`). The default is `auto`, which means `gdb` during debug sessions and `native` otherwise.
- `chardev=str1` — send the output to a chardev backend output for `native` or `auto` output when not in gdb.
- `userspace=on|off` — allows code running in guest userspace to access the semihosting interface. The default is that only privileged guest code can make semihosting calls. Note that setting `userspace=on` should only be used if all guest code is trusted (for example, in bare-metal test case code).
- `arg=str1,arg=str2,...` — allows the user to pass input arguments, and can be used multiple times to build up a list. The old-style `-kernel`/`-append` method of passing a command line is still supported for backward compatibility. If both the `--semihosting-config arg` and the `-kernel`/`-append` are specified, the former is passed to semihosting as it always takes precedence. 🏆

- **`-sandbox`** — enable Seccomp mode 2 system call filter. `on` will enable syscall filtering and `off` will disable it. The default is `off`.

-sandbox arg[,obsolete=string][,elevateprivileges=string][,spawn=string][,resourcecontrol=string]


- `obsolete=string` — enable Obsolete system calls.
- `elevateprivileges=string` — disable `set*uid|gid` system calls.
- `spawn=string` — disable `*fork` and `execve`.
- `resourcecontrol=string` — disable process affinity and scheduler priority.

- **`-readconfig file`** — read device configuration from `file`. This approach is useful when you want to spawn a QEMU process with many command line options but you don't want to exceed the command line character limit. 📜

- **`-no-user-config`** — the `-no-user-config` option makes QEMU **not** load any of the user-provided config files on `sysconfdir`.

- **`-trace [[enable=]pattern][,events=file][,file=file]`** — specify tracing options. 🔍

- `[enable=]PATTERN` — immediately enable events matching `PATTERN` (either event name or a globbing pattern). This option is only available if QEMU has been compiled with the `simple`, `log` or `ftrace` tracing backend. To specify multiple events or patterns, specify the `-trace` option multiple times. Use `-trace help` to print a list of names of trace points.
- `events=FILE` — immediately enable events listed in `FILE`. The file must contain one event name (as listed in the `trace-events-all` file) per line; globbing patterns are accepted too. This option is only available if QEMU has been compiled with the `simple`, `log` or `ftrace` tracing backend.
- `file=FILE` — log output traces to `FILE`. This option is only available if QEMU has been compiled with the `simple` tracing backend.

- **`-plugin file=file[,argname=argvalue]`** — load a plugin. 🧩

- `file=file` — load the given plugin from a shared library file.
- `argname=argvalue` — argument passed to the plugin. (Can be given multiple times.)

- **`-run-with`** — set QEMU process lifecycle options.

-run-with [async-teardown=on|off][,chroot=dir][,exit-with-parent=on|off][,user=username|uid:gid]


- **`async-teardown=on`** — turns on asynchronous teardown, and honestly it's giving main character energy 👑 At startup a whole new process gets created, called `cleanup/<QEMU_PID>`, and it shares the address space with the main QEMU process — it's made with `clone`. It just... waits for the main QEMU process to terminate completely, and *then* it exits. Which means QEMU can bail out <hotpink>so</hotpink> fast even when the guest was huge, because the teardown of the address space gets handed off to the cleanup process. And since the cleanup process shares the same cgroups as the main QEMU process, accounting is performed correctly. No chaos, no lies. 🫶 This only works if the cleanup process is not forcefully killed with `SIGKILL` before the main QEMU process has terminated completely.

- **`chroot=dir`** — does a `chroot` into the directory you name, immediately before starting guest execution. Lowkey *the* move when you're pairing it with `user=...`. 🎀

- **`exit-with-parent=on`** — QEMU dips out if the parent process of QEMU exits. This is for when QEMU runs a captive appliance, where the lifetime of the appliance is scoped to the parent process. Parent crashes? QEMU still gets cleaned up, bestie. ✨ This only works on Linux, FreeBSD and macOS platforms.

- **`user=username`** or **`user=uid:gid`** — drops root privileges before starting guest execution. QEMU uses the `setuid` and `setgid` system calls to switch over to the identity you specified. FYI: the `user=username` syntax will also apply the full set of supplementary groups for the user, whereas `user=uid:gid` will use only the `gid` group. 🦋

---

- **`-msg [timestamp=on|off][,guest-name=on|off]`** — controls the error message format. 💬

- `timestamp=on|off` — prefixes messages with a timestamp. Default is `off`.
- `guest-name=on|off` — prefixes messages with the guest name, but <yellow>only</yellow> if the `-name guest` option is set — otherwise the option is ignored. Default is `off`.

- **`-dump-vmstate file`** — dumps json-encoded vmstate information for the current machine type to the file in `file`. 📝

- **`-enable-sync-profile`** — enables synchronization profiling. Yes ma'am. 🔥

- **`-perfmap`** — generates a map file for Linux perf tools that lets basic profiling information be broken down into basic blocks.

- **`-jitdump`** — generates a dump file for Linux perf tools that maps basic blocks to symbol names, line numbers and JITted code. 🌈

## ✨ Generic object creation ✨

- **`-object typename[,prop1=value1,...]`** — creates a new object of type `typename`, setting properties in the order they're specified. Note that the `'id'` property **must** be set. These objects are placed in the `/objects` path. 👑

- **`-object memory-backend-file,id=id,size=size,mem-path=dir,share=on|off,discard-data=on|off,merge=on|off,dump=on|off,prealloc=on|off,host-nodes=host-nodes,policy=default|preferred|bind|interleave,align=align,offset=offset,readonly=on|off,rom=on|off|auto`** — creates a memory file backend object, which can be used to back the guest RAM with huge pages. 💅

  - The `id` parameter is a unique ID that will be used to reference this memory region in other parameters, e.g. `-numa`, `-device nvdimm`, etc.
  - The `size` option provides the size of the memory region, and accepts common suffixes, e.g. `500M`.
  - The `mem-path` provides the path to either a shared memory or huge page filesystem mount.
  - The `share` boolean option determines whether the memory region is marked as private to QEMU, or shared. The latter allows a co-operating external process to access the QEMU memory region.
  - Setting `share=on` might affect the ability to configure NUMA bindings for the memory backend under some circumstances — see `Documentation/vm/numa_memory_policy.txt` on the Linux kernel source tree for additional details. 🙈
  - Setting the `discard-data` boolean option to `on` indicates that file contents can be destroyed when QEMU exits, to avoid unnecessarily flushing data to the backing file. Note that `discard-data` is only an optimization, and QEMU might not discard file contents if it aborts unexpectedly or is terminated using `SIGKILL`.
  - The `merge` boolean option enables memory merge, also known as `MADV_MERGEABLE`, so that Kernel Samepage Merging will consider the pages for memory deduplication.
  - Setting the `dump` boolean option to `off` excludes the memory from core dumps. This feature is also known as `MADV_DONTDUMP`.
  - The `prealloc` boolean option enables memory preallocation.
  - The `host-nodes` option binds the memory range to a list of NUMA host nodes.
  - The `policy` option sets the NUMA policy to one of the following values:
    - `default` — default host policy
    - `preferred` — prefer the given host node list for allocation
    - `bind` — restrict memory allocation to the given host node list
    - `interleave` — interleave memory allocations across the given host node list
  - The `align` option specifies the base address alignment when QEMU `mmap(2)`s `mem-path`, and accepts common suffixes, eg `2M`. Some backend store specified by `mem-path` requires an alignment different than the default one used by QEMU, eg the device DAX `/dev/dax0.0` requires `2M` alignment rather than `4K`. In such cases, users can specify the required alignment via this option.
  - The `offset` option specifies the offset into the target file that the region starts at. You can use this parameter to back multiple regions with a single file.
  - The `pmem` option specifies whether the backing file specified by `mem-path` is in host persistent memory that can be accessed using the SNIA NVM programming model (e.g. Intel NVDIMM). If `pmem` is set to `'on'`, QEMU will take necessary operations to guarantee the persistence of its own writes to `mem-path` (e.g. in vNVDIMM label emulation and live migration). Also, we will map the backend-file with `MAP_SYNC` flag, which ensures the file metadata is in sync for `mem-path` in case of host crash or a power failure. `MAP_SYNC` requires support from both the host kernel (since Linux kernel `4.15`) and the filesystem of `mem-path` mounted with DAX option.
  - The `readonly` option specifies whether the backing file is opened read-only or read-write (default).
  - The `rom` option specifies whether to create Read Only Memory (ROM) that cannot be modified by the VM. Any write attempts to such ROM will be denied. Most use cases want proper RAM instead of ROM. However, selected use cases, like R/O NVDIMMs, can benefit from ROM. If set to `on`, create ROM; if set to `off`, create writable RAM; if set to `auto` (default), the value of the `readonly` option is used. This option is primarily helpful when we want to have writable RAM in configurations that would traditionally create ROM before the `rom` option was introduced: VM templating, where we want to open a file readonly (`readonly=on`) and mark the memory to be private for QEMU (`share=off`). For this use case, we need writable RAM instead of ROM, and want to also set `rom=off`.

- **`-object memory-backend-ram,id=id,merge=on|off,dump=on|off,share=on|off,prealloc=on|off,size=size,host-nodes=host-nodes,policy=default|preferred|bind|interleave`** — creates a memory backend object, which can be used to back the guest RAM. Memory backend objects offer more control than the `-m` option that is traditionally used to define guest RAM. Please refer to `memory-backend-file` for a description of the options. 🌸

- **`-object memory-backend-memfd,id=id,merge=on|off,dump=on|off,share=on|off,prealloc=on|off,size=size,host-nodes=host-nodes,policy=default|preferred|bind|interleave,seal=on|off,hugetlb=on|off,hugetlbsize=size`** — creates an anonymous memory file backend object, which allows QEMU to share the memory with an external process (e.g. when using vhost-user). The memory is allocated with `memfd` and optional sealing. (Linux only) 🐧

  - The `seal` option creates a sealed-file, that will block further resizing the memory (`'on'` by default).
  - The `hugetlb` option specify the file to be created resides in the hugetlbfs filesystem (since Linux `4.14`). Used in conjunction with the `hugetlb` option, the `hugetlbsize` option specify the hugetlb page size on systems that support multiple hugetlb page sizes (it must be a power of 2 value supported by the system).
  - In some versions of Linux, the `hugetlb` option is incompatible with the `seal` option (requires at least Linux `4.16`). ⚠️
  - Please refer to `memory-backend-file` for a description of the other options.
  - The `share` boolean option is `on` by default with memfd.

- **`-object memory-backend-shm,id=id,merge=on|off,dump=on|off,share=on|off,prealloc=on|off,size=size,host-nodes=host-nodes,policy=default|preferred|bind|interleave`** — creates a POSIX shared memory backend object, which allows QEMU to share the memory with an external process (e.g. when using vhost-user). 💜

  - `memory-backend-shm` is a more portable and less featureful version of `memory-backend-memfd`. It can then be used in any POSIX system, especially when `memfd` is not supported. 🌈
  - Please refer to `memory-backend-file` for a description of the options.
  - The `share` boolean option is `on` by default with shm. Setting it to `off` will cause a failure during allocation because it is not supported by this backend. 💀

- **`-object iommufd,id=id[,fd=fd]`** — okay bestie, this one sets up an iommufd backend so you can vibe-control DMA mapping through the `/dev/iommu` device. 🦋

The `id` param is a unique ID that frontends (like vfio-pci of vdpa, iykyk) use to connect with the iommufd backend.

The `fd` param is an optional pre-opened file descriptor that comes from opening `/dev/iommu`. Usually the iommufd gets shared across all subsystems, which lowkey slays because you get the benefit of centralized reference counting. 👑

- **`-object rng-builtin,id=id`** — this creates a random number generator backend that pulls entropy from QEMU's own builtin functions. 🌸 The `id` is a unique ID you'll use to reference this entropy backend from the `virtio-rng` device. And get this — by default, the `virtio-rng` device uses THIS RNG backend anyway, so it's the default main character. ✨

- **`-object rng-random,id=id,filename=/dev/random`** — creates a random number generator backend that gets its entropy from a device on the host. 💜 The `id` is a unique ID used to reference this entropy backend from the `virtio-rng` device. The `filename` param says which file to grab entropy from, and if you skip it, it defaults to `/dev/urandom`. no cap.

- **`-object rng-egd,id=id,chardev=chardevid`** — creates a random number generator backend that gets entropy from an external daemon running on the host. 🌈 The `id` is a unique ID used to reference this entropy backend from the `virtio-rng` device. The `chardev` param is the unique ID of a character device backend that provides the connection to the RNG daemon. 🎀

---

- **`-object tls-creds-anon,id=id,endpoint=endpoint,dir=/path/to/cred/dir,verify-peer=on|off`** — creates a TLS anonymous credentials object, which gives you TLS support on network backends. 🔥 The `id` is a unique ID that network backends use to access the credentials. The `endpoint` is either `server` or `client`, depending on whether the QEMU network backend using these credentials is acting as a client or a server. If `verify-peer` is enabled (that's the default, btw), then once the handshake finishes, the peer credentials get verified — though for anonymous credentials this is literally a no-op. 💀

The `dir` param tells QEMU where to find the credential files. For server endpoints, this directory may contain a file `dh-params.pem` that provides diffie-hellman parameters to use for the TLS server. If that file's missing, QEMU will generate a set of DH parameters at startup. Heads up: that's a computationally expensive operation that eats random pool entropy 😭, so it's recommended you generate a persistent set of parameters upfront and save them. fr fr.

- **`-object tls-creds-psk,id=id,endpoint=endpoint,dir=/path/to/keys/dir[,username=username]`** — creates a TLS Pre-Shared Keys (PSK) credentials object, which gives you TLS support on network backends. 🫶 The `id` is a unique ID that network backends use to access the credentials. The `endpoint` is either `server` or `client`, depending on whether the QEMU network backend using these credentials is acting as a client or a server. For clients only, `username` is the username that gets sent to the server — if you omit it, it defaults to `"qemu"`. 👑

The `dir` param tells QEMU where to find the keys file. It's called `"dir/keys.psk"` and contains `"username:key"` pairs. Easiest way to make this file? The GnuTLS `psktool` program. ✨

For server endpoints, `dir` may also contain a file `dh-params.pem` providing diffie-hellman parameters for the TLS server. If it's missing, QEMU generates a set of DH parameters at startup. Again — computationally expensive, consumes random pool entropy, so generate a persistent set upfront and save it. 💅

- **`-object tls-creds-x509,id=id,endpoint=endpoint,dir=/path/to/cred/dir,priority=priority,verify-peer=on|off,passwordid=id`** — creates a TLS anonymous credentials object (yep, same wording as above 😭), which gives you TLS support on network backends. The `id` is a unique ID that network backends use to access the credentials. The `endpoint` is either `server` or `client`, depending on whether the QEMU network backend using these credentials is acting as a client or a server. If `verify-peer` is enabled (the default), then once the handshake completes the peer credentials get verified. With x509 certificates, that implies clients must be given valid client certificates too. no cap. 🔐

The `dir` param tells QEMU where to find the credential files. For server endpoints, this directory may contain a file `dh-params.pem` providing diffie-hellman parameters for the TLS server. Missing file? QEMU generates a set of DH parameters at startup. (Say it with me: computationally expensive, consumes random pool entropy, generate a persistent set upfront and save it. 🎀)

For x509 certificate credentials, the directory contains further files providing the x509 certificates. The certificates must be stored in PEM format, in filenames `ca-cert.pem`, `ca-crl.pem` (optional), `server-cert.pem` (only servers), `server-key.pem` (only servers), `client-cert.pem` (only clients), and `client-key.pem` (only clients). 🌸

For the `server-key.pem` and `client-key.pem` files — which contain sensitive private keys, protect them bestie 😭 — it's possible to use an encrypted version by providing the `passwordid` parameter. This gives the ID of a previously created secret object containing the password for decryption. 🔥

The `priority` parameter lets you override the global default priority used by gnutls. This is useful if a system administrator needs to use a weaker set of crypto priorities for QEMU without potentially forcing that weakness onto all applications. Or conversely, if someone wants a stronger default for QEMU than for all other applications, they can do it through this parameter. Its format is a gnutls priority string as described at <https://gnutls.org/manual/html_node/Priority-Strings.html>. 💜

- **`-object tls-cipher-suites,id=id,priority=priority`** — creates a TLS cipher suites object, which controls the TLS cipher/protocol algorithms that applications are permitted to use. ✨

The `id` is a unique ID that frontends use to access the ordered list of permitted TLS cipher suites from the host.

The `priority` parameter lets you override the global default priority used by gnutls. Useful if a sysadmin needs weaker crypto priorities for QEMU without forcing that weakness onto all applications — or conversely, a stronger default for QEMU than everything else. Its format is a gnutls priority string as described at <https://gnutls.org/manual/html_node/Priority-Strings.html>. 🦋

One iconic use of this object is controlling UEFI HTTPS Boot. The `tls-cipher-suites` object exposes the ordered list of permitted TLS cipher suites from the host side to the guest firmware, via `fw_cfg`. The list is represented as an array of `IANA_TLS_CIPHER` objects, and the firmware uses the `IANA_TLS_CIPHER` array for configuring guest-side TLS. 👑

In the following example, the priority at which the host-side policy is retrieved is given by the `priority` property. Given that QEMU uses GNUTLS, `priority=@SYSTEM` may be used to refer to `/etc/crypto-policies/back-ends/gnutls.config`. 🌈

qemu-system-x86_64 \

-object tls-cipher-suites,id=mysuite0,priority=@SYSTEM \ -fw_cfg name=etc/edk2/https/ciphers,gen_id=mysuite0


---

- **`-object filter-buffer,id=id,netdev=netdevid,interval=t[,queue=all|rx|tx][,status=on|off][,position=head|tail|id=<id>][,insert=behind|before]`** — okay so interval `t` can't be `0` (not even playing, bestie 💀), and this filter batches packet delivery: all packets arriving in a given interval on netdev `netdevid` get delayed until the end of the interval. The interval is in **microseconds**. 🕐 `status` is optional and says whether the netfilter is `on` (enabled) or `off` (disabled) — the default status for a netfilter is `'on'`. ✨

`queue all|rx|tx` is an option you can apply to any netfilter. 🎀

- `all`: the filter is attached both to the receive and the transmit queue of the netdev (this is the default).
- `rx`: the filter is attached to the receive queue of the netdev, where it receives packets sent to the netdev.
- `tx`: the filter is attached to the transmit queue of the netdev, where it receives packets sent by the netdev.

`position head|tail|id=<id>` is an option to specify where the filter should be inserted in the filter list. It can be applied to any netfilter. 🌸

- `head`: the filter is inserted at the head of the filter list, before any existing filters.

- <pink>**`tail`**</pink> — the filter gets dropped at the **tail** of the filter list, i.e. behind everything already there. This is the default btw, so if you don't say anything, you get tail energy. 💅

- <pink>**`id=<id>`**</pink> — the filter gets slotted in either before or behind the filter you name with `<id>`. Peep the `insert` option right below for the deets. 👀

- <pink>**`insert behind|before`**</pink> — this is the one that says *where* the new filter goes relative to whatever you pointed at with `position=id=<id>`. And yes bestie, it works on **any** netfilter. No gatekeeping. ✨

- <purple>**`before`**</purple> — insert it before the filter you specified.
- <purple>**`behind`**</purple> — insert it behind the filter you specified. This one's the default, so it's the chill option. 🦋

---

## 🎀 `-object` stuff, continued 💖

### `filter-mirror` 🪞


Okay so `filter-mirror` sits on netdev `netdevid` and mirrors net packets over to chardev `chardevid`. It's giving surveillance but make it cute. 📸 If it's got the `vnet_hdr_support` flag, `filter-mirror` will mirror the packet with `vnet_hdr_len`. Periodt.

### `filter-redirector` 🔀


`filter-redirector` on netdev `netdevid` — it redirects the filter's net packet to chardev `chardevid`, **and** redirects `indev`'s packet to the filter. Two-way traffic, main character behaviour honestly. 🌈 If it's got the `vnet_hdr_support` flag, `filter-redirector` will redirect the packet with `vnet_hdr_len`.

> Heads up: when you create a `filter-redirector` you need the `outdev` id and the `indev` id to be **different** — `id` can not be the same. You can use just `indev` or just `outdev`, but at least one of `indev` or `outdev` needs to be specified. No skipping this one. 🫶

### `filter-rewriter` 📝


`filter-rewriter` is part of the COLO project, and it's lowkey the translator of the group. It rewrites tcp packets going to the secondary from the primary to keep the secondary tcp connection alive, and rewrites tcp packets going to the primary from the secondary so the client can actually handle them. 💫 If it's got the `vnet_hdr_support` flag, we can parse packets with a vnet header.

Usage, for the colo secondary, goes a lil something like this:

-object filter-redirector,id=f1,netdev=hn0,queue=tx,indev=red0 -object filter-redirector,id=f2,netdev=hn0,queue=rx,outdev=red1 -object filter-rewriter,id=rew0,netdev=hn0,queue=all


### `filter-dump` 📦

-object filter-dump,id=id,netdev=dev[,file=filename][,maxlen=len][,position=head|tail|id=<id>][,insert=behind|before]


Dumps the network traffic on netdev `dev` into the file you name with `filename`. At most `len` bytes per packet get stored (and `64k` is the default, so that's your starting point). The file format is **libpcap**, which means you can go analyze it with tools like `tcpdump` or `Wireshark`. Forensic girlie era. 🔍

### `colo-compare` ⚖️

-object colo-compare,id=<id>,primary_in=<chardevid>,secondary_in=<chardevid>,outdev=<chardevid>,iothread=<id>[,vnet_hdr_support][,notify_dev=<id>][,compare_timeout=<time_ms>][,expired_scan_cycle=<time_ms>][,max_queue_size=<maxsize>]


`colo-compare` grabs packets from the chardev backends you name in `primary_in` and `secondary_in`, and then compares whether the payloads of the primary packet and the secondary packet are the same. It's literally the vibe check. 🔥 If they match, it outputs the primary packet to the chardev backend in `outdev`; otherwise it notifies COLO-framework to do a checkpoint and sends the primary packet on to `outdev`.

To be more efficient about it, we need to put the task of comparison in another iothread — the `iothread` option is where you specify that iothread object (and your commandline should create it, so don't be out here naming something that doesn't exist 💀).

The `vnet_hdr_support` flag tells colo compare to pass the vnet header length when it sends and receives packets.

The `compare_timeout` option sets the maximum time that colo-compare will hold the packet for, in ms. ⏳

The `expired_scan_cycle` option sets the period for scanning expired primary node network packets, in ms.

The `max_queue_size` option sets the max compare queue size.

If you want to use **Xen COLO**, you need to specify `notify_dev` to tell colo-compare how to notify Xen colo-frame to do a checkpoint.

> `COLO-compare` must be used with the help of `filter-mirror`, `filter-redirector` and `filter-rewriter`. No solo runs, it needs its friends. 🫂

#### KVM COLO 💜

**primary:**

-netdev tap,id=hn0,vhost=off -device e1000,id=e0,netdev=hn0,mac=52:a4:00:12:78:66 -chardev socket,id=mirror0,host=3.3.3.3,port=9003,server=on,wait=off -chardev socket,id=compare1,host=3.3.3.3,port=9004,server=on,wait=off -chardev socket,id=compare0,host=3.3.3.3,port=9001,server=on,wait=off -chardev socket,id=compare0-0,host=3.3.3.3,port=9001 -chardev socket,id=compare_out,host=3.3.3.3,port=9005,server=on,wait=off -chardev socket,id=compare_out0,host=3.3.3.3,port=9005 -object iothread,id=iothread1 -object filter-mirror,id=m0,netdev=hn0,queue=tx,outdev=mirror0 -object filter-redirector,netdev=hn0,id=redire0,queue=rx,indev=compare_out -object filter-redirector,netdev=hn0,id=redire1,queue=rx,outdev=compare0 -object colo-compare,id=comp0,primary_in=compare0-0,secondary_in=compare1,outdev=compare_out0,iothread=iothread1


**secondary:**

-netdev tap,id=hn0,vhost=off -device e1000,netdev=hn0,mac=52:a4:00:12:78:66 -chardev socket,id=red0,host=3.3.3.3,port=9003 -chardev socket,id=red1,host=3.3.3.3,port=9004 -object filter-redirector,id=f1,netdev=hn0,queue=tx,indev=red0 -object filter-redirector,id=f2,netdev=hn0,queue=rx,outdev=red1


#### Xen COLO 🌸

**primary:**

-netdev tap,id=hn0,vhost=off -device e1000,id=e0,netdev=hn0,mac=52:a4:00:12:78:66 -chardev socket,id=mirror0,host=3.3.3.3,port=9003,server=on,wait=off -chardev socket,id=compare1,host=3.3.3.3,port=9004,server=on,wait=off -chardev socket,id=compare0,host=3.3.3.3,port=9001,server=on,wait=off -chardev socket,id=compare0-0,host=3.3.3.3,port=9001 -chardev socket,id=compare_out,host=3.3.3.3,port=9005,server=on,wait=off -chardev socket,id=compare_out0,host=3.3.3.3,port=9005 -chardev socket,id=notify_way,host=3.3.3.3,port=9009,server=on,wait=off -object filter-mirror,id=m0,netdev=hn0,queue=tx,outdev=mirror0 -object filter-redirector,netdev=hn0,id=redire0,queue=rx,indev=compare_out -object filter-redirector,netdev=hn0,id=redire1,queue=rx,outdev=compare0 -object iothread,id=iothread1 -object colo-compare,id=comp0,primary_in=compare0-0,secondary_in=compare1,outdev=compare_out0,notify_dev=notify_way,iothread=iothread1


**secondary:**


If you want to know the detail of the above command line, you can read the colo-compare git log. (Yes bestie, the lore is in the git log. Enjoy. 🧚)

### `cryptodev-backend-builtin` 🔐

-object cryptodev-backend-builtin,id=id[,queues=queues]


Creates a cryptodev backend that executes crypto operations from the QEMU cipher APIs. The `id` parameter is a unique ID that'll be used to reference this cryptodev backend from the `virtio-crypto` device. The `queues` parameter is optional — it specifies the queue number of the cryptodev backend, and the default of `queues` is `1`.

qemu-system-x86_64 \

[...] \ -object cryptodev-backend-builtin,id=cryptodev0 \ -device virtio-crypto-pci,id=crypto0,cryptodev=cryptodev0 \ [...]


### `cryptodev-vhost-user` 🧚‍♀️

-object cryptodev-vhost-user,id=id,chardev=chardevid[,queues=queues]


Creates a **vhost-user** cryptodev backend, backed by a chardev `chardevid`. The `id` parameter is a unique ID that'll be used to reference this cryptodev backend from the `virtio-crypto` device. The chardev should be a **unix domain socket** backed one. The vhost-user uses a specifically defined protocol to pass vhost ioctl replacement messages to an application on the other end of the socket. The `queues` parameter is optional — it specifies the queue number of the cryptodev backend for multiqueue vhost-user, and the default of `queues` is `1`.

qemu-system-x86_64 \

[...] \ -chardev socket,id=chardev0,path=/path/to/socket \ -object cryptodev-vhost-user,id=cryptodev0,chardev=chardev0 \ -device virtio-crypto-pci,id=crypto0,cryptodev=cryptodev0 \ [...]


### `secret` 🤫

-object secret,id=id,data=string,format=raw|base64[,keyid=secretid,iv=string]

-object secret,id=id,file=filename,format=raw|base64[,keyid=secretid,iv=string]


Defines a secret to store a password, an encryption key, or some other sensitive data. The sensitive data can either be passed directly via the `data` parameter, or indirectly via the `file` parameter.

> Not me having to say this but: using the `data` parameter is **insecure** unless the sensitive data is encrypted. Keep that energy in mind. 🙈

The sensitive data can be provided in **raw** format (which is the default), or **base64**. When encoded as JSON, the raw format only supports valid UTF-8 characters, so base64 is recommended for sending binary data. QEMU will convert from whichever format is provided to the format it needs internally. Like, for example, an RBD password can be provided in raw format, even though it'll be base64 encoded when it's passed onto the RBD sever. That's it, that's the glow-up. ✨

For extra protection ✨ you can encrypt the data that goes with a secret using the <hotpink>AES-256-CBC</hotpink> cipher. You're telling QEMU you want encryption by handing over the `keyid` and `iv` parameters. The `keyid` parameter gives the ID of a secret you already defined earlier that holds the AES-256 decryption key — that key needs to be 32 bytes long and base64 encoded, bestie, no exceptions. The `iv` parameter gives the random initialization vector used to encrypt this particular secret, and it should be a base64 encoded string of the 16-byte IV.

The most simple (and yeah, <red>insecure</red> 😭) way is to just drop the secret inline:

qemu-system-x86_64 -object secret,id=sec0,data=letmein,format=raw


The most simple *secure* way is to hand it over via a file:

printf "letmein" > mypasswd.txt # QEMU_SYSTEM_MACRO

-object secret,id=sec0,file=mypasswd.txt,format=raw


For greater security, bestie, use AES-256-CBC. To show you how, look at the `openssl` command line tool — it can do the encryption for you. Heads up though: when you're encrypting, the plaintext has to be padded to the cipher block size (32 bytes) using the standard PKCS#5/6 compatible padding algorithm. ✨

First you need to make a master key, in base64 encoding:

openssl rand -base64 32 > key.b64

KEY=$(base64 -d key.b64 | hexdump -v -e '/1 "%02X"')


Every secret you wanna encrypt needs its own random initialization vector generated. These don't have to stay secret 👀

openssl rand -base64 16 > iv.b64

IV=$(base64 -d iv.b64 | hexdump -v -e '/1 "%02X"')


Now the secret you want to define can be encrypted — in this case we're telling `openssl` to base64 encode the result, but you could leave it as raw bytes if that's your vibe:

SECRET=$(printf "letmein" |

openssl enc -aes-256-cbc -a -K $KEY -iv $IV)


When you launch QEMU, create a master secret pointing to `key.b64` and say that's the one to use for decrypting the user password. Pass the contents of `iv.b64` to the second secret:

qemu-system-x86_64 \

-object secret,id=secmaster0,format=base64,file=key.b64 \ -object secret,id=sec0,keyid=secmaster0,format=base64,\ data=$SECRET,iv=$(<iv.b64)


---

## <rainbow>-object sev-guest</rainbow> 🌈

-object sev-guest,id=id,cbitpos=cbitpos,reduced-phys-bits=val,[sev-device=string,policy=policy,handle=handle,dh-cert-file=file,session-file=file,kernel-hashes=on|off]


Okay so this one makes a <purple>Secure Encrypted Virtualization</purple> (SEV) guest object, and it's the thing that gives you guest memory encryption support on AMD processors. AMD girlies rise 🫶

When memory encryption is on, one of the physical address bits (aka the <pink>C-bit</pink>) gets used to mark whether a memory page is protected. The `cbitpos` gives you the C-bit position. Fun fact: the C-bit position depends on the Host family, so *you* have to provide this value — no autodetection. On EPYC, the value should be `47`.

When memory encryption is on, we lose some bits in physical address space. The `reduced-phys-bits` gives you the number of bits we lose in physical address space. Same deal as the C-bit, the value is Host family dependent. On EPYC, a guest loses a maximum of 1 bit, so the value should be `1`.

The `sev-device` gives the device file to use for talking to the SEV firmware that runs inside the AMD Secure Processor. Default device is `/dev/sev`. And if your hardware supports memory encryption, the `/dev/sev` devices get created by the CCP driver.

The `policy` gives the guest policy that the SEV firmware enforces, and it restricts what configuration and operational commands the hypervisor can perform on this guest. The guest owner should provide the policy, and it's bound to the guest — it literally cannot be changed throughout the lifetime of the guest. Default is `0`.

If the guest policy allows sharing the key with another SEV guest, then `handle` can be used to give the handle of the guest you're sharing the key from. Sharing is caring 💅

The `dh-cert-file` and `session-file` give the guest owner's Public Diffie-Hillman key as defined in the SEV spec. The PDH and session parameters are used for establishing a cryptographic session with the guest owner to negotiate the keys used for attestation. The file **must** be encoded in base64.

The `kernel-hashes` adds the hashes of the given kernel/initrd/cmdline to a designated guest firmware page for measured Linux boot with `-kernel`. Default is `off`. (Since 6.2)

e.g. to launch a SEV guest:

qemu-system-x86_64 \

...... \ -object sev-guest,id=sev0,cbitpos=47,reduced-phys-bits=1 \ -machine ...,memory-encryption=sev0 \ .....


## <cyan>-object igvm-cfg</cyan> 🦋

-object igvm-cfg,file=file


Makes an IGVM configuration object that defines the initial state of the guest using a file that conforms to the <mint>Independent Guest Virtual Machine</mint> (IGVM) file format.

Right now this is only supported by `-machine q35` and `-machine pc`. Like, don't try it elsewhere bestie 😅

The `file` parameter specifies the IGVM file to load. When you provide it, the IGVM file is used to populate the initial memory of the virtual machine and — depending on the platform — can define the initial processor state, memory map and parameters.

The IGVM file is expected to contain the firmware for the virtual machine, which means an `igvm-cfg` object **cannot** be provided alongside other ways of specifying firmware, like the `-bios` parameter on x86 machines. Pick a lane 🚫

e.g. to launch a machine providing the firmware in an IGVM file:

qemu-system-x86_64 \

...... \ -object igvm-cfg,id=igvm0,file=bios.igvm \ -machine ...,igvm-cfg=igvm0 \ .....


## <lavender>-object authz-simple</lavender> 🎀

-object authz-simple,id=id,identity=string


Makes an authorization object that controls access to network services. Gatekeeping, but make it ~secure~ ✨

The `identity` parameter identifies the user, and its format depends on the network service the authorization object is associated with. For authorizing based on TLS x509 certificates, the identity has to be the x509 distinguished name. And ngl, be careful — you gotta escape any commas in the distinguished name.

An example authorization object to validate a x509 distinguished name would look like:

qemu-system-x86_64 \

... \ -object 'authz-simple,id=auth0,identity=CN=laptop.example.com,,O=Example Org,,L=London,,ST=London,,C=GB' \ ...


Note the use of quotes because the x509 distinguished name contains whitespace, plus the escaping of `','`. iykyk 💅

## <peach>-object authz-listfile</peach> 🌸

-object authz-listfile,id=id,filename=path,refresh=on|off


Makes an authorization object that controls access to network services. (Yes, another one — QEMU really said "access control for days".)

The `filename` parameter is the fully qualified path to a file containing the access control list rules in JSON format.

An example set of rules that match against SASL usernames might look like:

{ "rules": [ { "match": "fred", "policy": "allow", "format": "exact" }, { "match": "bob", "policy": "allow", "format": "exact" }, { "match": "danb", "policy": "deny", "format": "glob" }, { "match": "dan*", "policy": "allow", "format": "exact" }, ], "policy": "deny" }


When checking access, the object iterates over all the rules, and the first rule to match has its policy value returned as the result. If, like, *nothing* matches, then the default policy value is returned.

The rules can either be an exact string match, or they can use the simple UNIX glob pattern matching so wildcards are allowed. Best of both worlds fr fr 🐚

If `refresh` is set to `true`, the file gets monitored and automatically reloaded whenever its content changes. Obsessed with that actually.

Same as with the `authz-simple` object, the format of the identity strings being matched depends on the network service — but it's usually a TLS x509 distinguished name, or a SASL username.

An example authorization object to validate a SASL username would look like:

qemu-system-x86_64 \

... \ -object authz-simple,id=auth0,filename=/etc/qemu/vnc-sasl.acl,refresh=on \ ...


## <yellow>-object authz-pam</yellow> 🌟

-object authz-pam,id=id,service=string


Makes an authorization object that controls access to network services. (Third one, we're collecting them like stickers.)

The `service` parameter provides the name of a PAM service to use for authorization. It requires that a file `/etc/pam.d/service` exist to provide the configuration for the account subsystem.

An example authorization object to validate a TLS x509 distinguished name would look like:

qemu-system-x86_64 \

... \ -object authz-pam,id=auth0,service=qemu-vnc \ ...


There would then be a corresponding config file for PAM at `/etc/pam.d/qemu-vnc` that contains:

account requisite pam_listfile.so item=user sense=allow \ file=/etc/qemu/vnc.allow


and then bestie, the <pink>`/etc/qemu/vnc.allow`</pink> file itself would hold the whole list of x509 distinguished names that are allowed in — like, the actual guest list for your VM's fancy party:

CN=laptop.example.com,O=Example Home,L=London,ST=London,C=GB


---

- **`-object iothread,id=id,poll-max-ns=poll-max-ns,poll-grow=poll-grow,poll-shrink=poll-shrink,aio-max-batch=aio-max-batch`** — ok so this makes a ✨dedicated event loop thread✨ that devices can be assigned to. It's called an IOThread, and it's kind of a big deal.

So the whole lore: by default, device emulation happens in vCPU threads or in the main event loop thread. Cute, except that can lowkey become a scalability bottleneck 😭. IOThreads let device emulation and I/O run on other host CPUs instead, which is the slay.

The `id` parameter is a unique ID, and you use it to reference this IOThread from `-device ...,iothread=id`. Multiple devices can be assigned to one IOThread, no gatekeeping. But heads up: **not all devices support an `iothread` parameter**, so don't come for me if one gets picky.

The `query-iothreads` QMP command lists IOThreads and reports their thread IDs, so you know what's what — that way the user can configure host CPU pinning/affinity. Very main character of you tbh.

Now the fun part: IOThreads use an <cyan>adaptive polling algorithm</cyan> to reduce event loop latency. Instead of entering a blocking system call to monitor file descriptors and then paying the cost of being woken up when an event occurs, the polling algorithm spins waiting for events for a short time (iconic behaviour fr fr). The algorithm's default parameters are suitable for many cases, but you can adjust them based on your knowledge of the workload and/or host device latency.

- **`poll-max-ns`** — the maximum number of nanoseconds to busy wait for events. You can *fully* disable polling by setting this value to `0`. periodt.
- **`poll-grow`** — the multiplier used to increase the polling time when the algorithm detects it's missing events because it wasn't polling long enough. it's giving "bestie wake up".
- **`poll-shrink`** — the divisor used to decrease the polling time when the algorithm detects it's spending too long polling without ever encountering events. she's learning to chill 💅
- **`aio-max-batch`** — the maximum number of requests in a batch for the AIO engine. `0` means the engine will just use its default, no cap.
- The IOThread parameters can be modified at run-time using the `qom-set` command (where `iothread1` here is the IOThread's `id`):

(qemu) qom-set /objects/iothread1 poll-max-ns 100000


---

# ✨ Multiplexer Keys ✨

So during the graphical emulation, you can use special key combinations from the following table to change modes 🔥. By default the modifier is <kbd>Ctrl</kbd>+<kbd>Alt</kbd> (that's what's used in the table below), and you can change it with `-display` suboption `mod=` where appropriate. For example, `-display sdl,grab-mod=lshift-lctrl-lalt` changes the modifier key to <kbd>Ctrl</kbd>+<kbd>Alt</kbd>+<kbd>Shift</kbd>, while `-display sdl,grab-mod=rctrl` changes it to the right <kbd>Ctrl</kbd> key. Customisation queen 👑

- <kbd>Ctrl</kbd>+<kbd>Alt</kbd>+<kbd>f</kbd> — Toggle full screen
- <kbd>Ctrl</kbd>+<kbd>Alt</kbd>+<kbd>+</kbd> — Enlarge the screen
- <kbd>Ctrl</kbd>+<kbd>Alt</kbd>+<kbd>-</kbd> — Shrink the screen
- <kbd>Ctrl</kbd>+<kbd>Alt</kbd>+<kbd>0</kbd> — Restore the screen's un-scaled dimensions
- <kbd>Ctrl</kbd>+<kbd>Alt</kbd>+<kbd>n</kbd> — Switch to virtual console *'n'*. The standard console mappings are:
  - `1`: Target system display
  - `2`: Monitor
  - `3`: Serial port
- <kbd>Ctrl</kbd>+<kbd>Alt</kbd>+<kbd>g</kbd> — Toggle mouse and keyboard grab.

And inside the virtual consoles, you can use <kbd>Ctrl</kbd>+<kbd>Up</kbd>, <kbd>Ctrl</kbd>+<kbd>Down</kbd>, <kbd>Ctrl</kbd>+<kbd>PageUp</kbd> and <kbd>Ctrl</kbd>+<kbd>PageDown</kbd> to move around in the back log 🦋.

---

# ✨ Multiplexer Keys ✨

okay so during emulation, if you're using a character backend multiplexer (which is literally the default if you're using `-nographic`), then there's a whole bunch of commands available to you via an escape sequence 👑. These key sequences all start with an escape character, which is <kbd>Ctrl</kbd>+<kbd>a</kbd> by default — but you can change that with `-echr`. The list below assumes you're rocking the default.

- <kbd>Ctrl</kbd>+<kbd>a</kbd> <kbd>h</kbd> — Print this help
- <kbd>Ctrl</kbd>+<kbd>a</kbd> <kbd>x</kbd> — Exit emulator
- <kbd>Ctrl</kbd>+<kbd>a</kbd> <kbd>s</kbd> — Save disk data back to file (if `-snapshot`)
- <kbd>Ctrl</kbd>+<kbd>a</kbd> <kbd>t</kbd> — Toggle console timestamps
- <kbd>Ctrl</kbd>+<kbd>a</kbd> <kbd>b</kbd> — Send break (magic sysrq in Linux)
- <kbd>Ctrl</kbd>+<kbd>a</kbd> <kbd>c</kbd> — Rotate between the frontends connected to the multiplexer (usually this switches between the monitor and the console)
- <kbd>Ctrl</kbd>+<kbd>a</kbd> <kbd>Ctrl</kbd>+<kbd>a</kbd> — Send the escape character to the frontend

---

> ngl bestie, that double <kbd>Ctrl</kbd>+<kbd>a</kbd> at the end is the escape hatch for your escape hatch. when you need to actually send a literal <kbd>Ctrl</kbd>+<kbd>a</kbd> through to whatever's on the other side, that's the move 🫶

# 📝 NOTES

bestie, plot twist: QEMU doesn't only do boring local files for your emulated storage devices 💅 it can also go full main-character and pull storage off the **network**, like iSCSI devices and friends. The way you tell it that? A special URL syntax, obvs. Let's go through each one, no cap. 🦋

---

## iSCSI 🍓

Your girl QEMU can talk to iSCSI resources **directly** and use them as images for the guest's storage. Both **disk** and **cdrom** images are supported — yes, both, we contain multitudes.

The syntax for specifying iSCSI LUNs is:

iscsi://<target-ip>[:<port>]/<target-iqn>/<lun>


By default QEMU uses the iSCSI initiator-name `iqn.2008-11.org.linux-kvm[:<name>]` — but bestie you can absolutely set this yourself, either from the command line or from a config file. 😌

Since version **QEMU 2.4** you can also specify an **iSCSI request timeout**, which detects stalled requests and forces a reestablishment of the session 🔥 It's specified in seconds, and the default is `0`, which means *no timeout* — like, it just waits forever, iconic but also stressful. Heads up: this feature needs **Libiscsi 1.15.0 or greater**.

Example (without authentication):

qemu-system-x86_64 -iscsi initiator-name=iqn.2001-04.com.example:my-initiator \ -cdrom iscsi://192.0.2.1/iqn.2001-04.com.example/2 \ -drive file=iscsi://192.0.2.1/iqn.2001-04.com.example/1


Example (CHAP username/password via URL):

qemu-system-x86_64 -drive file=iscsi://user%password@192.0.2.1/iqn.2001-04.com.example/1


Example (CHAP username/password via environment variables):

LIBISCSI_CHAP_USERNAME="user" \ LIBISCSI_CHAP_PASSWORD="password" \ qemu-system-x86_64 -drive file=iscsi://192.0.2.1/iqn.2001-04.com.example/1


---

## NBD 🌈

QEMU supports **NBD** (Network Block Devices) using both the **TCP protocol** and **Unix Domain Sockets**. With TCP, the default port is `10809` — memorise that, it's giving very specific.

Syntax for specifying an NBD device using TCP, in the *preferred URI form*:

nbd://<server-ip>[:<port>]/[<export>]


Syntax for specifying an NBD device using Unix Domain Sockets — and bestie, remember that `?` is a **shell glob character**, so it may need quoting 🙈:

nbd+unix:///[<export>]?socket=<domain-socket>


Older syntax that is also recognized (yes, grandma syntax still ate):

nbd:<server-ip>:<port>[:exportname=<export>]


Syntax for specifying an NBD device using Unix Domain Sockets:

nbd:unix:<domain-socket>[:exportname=<export>]


Example for TCP:

qemu-system-x86_64 --drive file=nbd:192.0.2.1:30000


Example for Unix Domain Sockets:

qemu-system-x86_64 --drive file=nbd:unix:/tmp/nbd-socket


---

## SSH 🔐

QEMU supports **SSH** (Secure Shell) access to remote disks. Very demure, very encrypted.

Examples:

qemu-system-x86_64 -drive file=ssh://user@host/path/to/disk.img qemu-system-x86_64 -drive file.driver=ssh,file.user=user,file.host=host,file.port=22,file.path=/path/to/disk.img


Currently authentication **must** be done using `ssh-agent` — that's literally the only way rn. Other authentication methods may be supported in the future 👀 timeline pending.

---

## GlusterFS 💜

GlusterFS is a **user space distributed file system**. QEMU supports using GlusterFS volumes for hosting VM disk images via **TCP** and **Unix Domain Sockets** transport protocols.

Syntax for specifying a VM disk image on a GlusterFS volume is:

URI: gluster[+type]://[host[:port]]/volume/path[?socket=...][,debug=N][,logfile=...]

JSON: 'json:{"driver":"qcow2","file":{"driver":"gluster","volume":"testvol","path":"a.img","debug":N,"logfile":"...", "server":[{"type":"tcp","host":"...","port":"..."}, {"type":"unix","socket":"..."}]}}'


Example:

URI: qemu-system-x86_64 --drive file=gluster://192.0.2.1/testvol/a.img, file.debug=9,file.logfile=/var/log/qemu-gluster.log

JSON: qemu-system-x86_64 'json:{"driver":"qcow2", "file":{"driver":"gluster", "volume":"testvol","path":"a.img", "debug":9,"logfile":"/var/log/qemu-gluster.log", "server":[{"type":"tcp","host":"1.2.3.4","port":24007}, {"type":"unix","socket":"/var/run/glusterd.socket"}]}}' qemu-system-x86_64 -drive driver=qcow2,file.driver=gluster,file.volume=testvol,file.path=/path/a.img, file.debug=9,file.logfile=/var/log/qemu-gluster.log, file.server.0.type=tcp,file.server.0.host=1.2.3.4,file.server.0.port=24007, file.server.1.type=unix,file.server.1.socket=/var/run/glusterd.socket


See also `http://www.gluster.org` 🎀

---

## HTTP/HTTPS/FTP/FTPS 🌸

QEMU supports **read-only** access to files accessed over http(s) and ftp(s). Read-only, bestie — don't try to write back, it's not that kind of relationship.

Syntax using a single filename:


where:

- **`protocol`** — `'http'`, `'https'`, `'ftp'`, or `'ftps'`.
- **`username`** — optional username for authentication to the remote server.
- **`password`** — optional password for authentication to the remote server.
- **`host`** — address of the remote server.
- **`path`** — path on the remote server, **including any query string**.

The following options are also supported:

- **`url`** — the full URL, for when you're passing options to the driver explicitly.
- **`readahead`** — the amount of data to read ahead with each range request to the remote server. This value may optionally have the suffix `'T'`, `'G'`, `'M'`, `'K'`, `'k'` or `'b'`. If it doesn't have a suffix, it's assumed to be in **bytes**. The value **must be a multiple of 512 bytes**. It defaults to `256k`.
- **`sslverify`** — whether to verify the remote server's certificate when connecting over SSL. It can be `'on'` or `'off'`. It defaults to `'on'`.
- **`cookie`** — send this cookie (it can also be a list of cookies separated by `';'`) with each outgoing request. Only supported when using protocols such as HTTP which support cookies — otherwise, ignored. 💀
- **`timeout`** — set the timeout in seconds of the CURL connection. This is the time that CURL waits for a response from the remote server to get the size of the image to be downloaded. If not set, the default timeout of `5` seconds is used.
- **`force-range`** — don't issue a HEAD HTTP request to discover if the http server supports range requests, and rely only on GET requests. This is especially useful for **S3 presigned URLs** where HEAD requests are unauthorized. It defaults to `'false'`.

> Ngl, this one matters: when you pass options to qemu **explicitly**, `driver` is the value of `<protocol>`.

Example: boot from a remote Fedora 20 live ISO image ✨

qemu-system-x86_64 --drive media=cdrom,file=https://archives.fedoraproject.org/pub/archive/fedora/linux/releases/20/Live/x86_64/Fedora-Live-Desktop-x86_64-20-1.iso,readonly

qemu-system-x86_64 --drive media=cdrom,file.driver=http,file.url=http://archives.fedoraproject.org/pub/fedora/linux/releases/20/Live/x86_64/Fedora-Live-Desktop-x86_64-20-1.iso,readonly


Example: boot from a remote Fedora 20 cloud image using a local overlay for writes, copy-on-read, and a readahead of 64k 🧚

qemu-img create -f qcow2 -o backing_file='json:{"file.driver":"http",, "file.url":"<http://archives.fedoraproject.org/pub/archive/fedora/linux/releases/20/Images/x86_64/Fedora-x86_64-20-20131211.1-sda.qcow2>",, "file.readahead":"64k"}' /tmp/Fedora-x86_64-20-20131211.1-sda.qcow2

qemu-system-x86_64 -drive file=/tmp/Fedora-x86_64-20-20131211.1-sda.qcow2,copy-on-read=on


Example: boot from an image stored on a VMware vSphere server with a self-signed certificate, using a local overlay for writes, a readahead of 64k and a timeout of 10 seconds 👑

qemu-img create -f qcow2 -o backing_file='json:{"file.driver":"https",, "file.url":"<https://user:password@vsphere.example.com/folder/test/test-flat.vmdk?dcPath=Datacenter&dsName=datastore1>",, "file.sslverify":"off",, "file.readahead":"64k",, "file.timeout":10}' /tmp/test.qcow2

qemu-system-x86_64 -drive file=/tmp/test.qcow2


---

# 👀 SEE ALSO

The HTML documentation of QEMU for more precise information and Linux user mode emulator invocation.

# 🫶 Author

Fabrice Bellard

# 📜 Copyright

2026, The QEMU Project Developers

---

and that's the whole page bestie, we ate and left absolutely no crumbs 💅 this was `11.0.3`, dated `Aug 25, 2026`, from `QEMU(1)` — slay, periodt, go read the HTML docs if you want the precise-precise version 🌟

📦 where this page comes from

ubuntu stonking: qemu-system-misc 1:11.0.3+ds-2ubuntu2
ubuntu stonking: qemu-system-misc-hwe 1:11.0.3+ds-2ubuntu4
💖 girlified by deepseek-ai/DeepSeek-V4.1-Flash on 2026-11-03: a language model's rewrite of the original, under its terms

QEMU(1)

👑 QEMU(1) — QEMU User Documentation 👑

✨ NAME ✨

🌸 SYNOPSIS 🌸

🦋 DESCRIPTION 🦋

🎀 Machine-specific options 🎀

💅 OPTIONS 💅

🌈 Standard options 🌈

💖 -add-fd 💖

✨ -set ✨

🦋 -global 🦋

👑 -boot 👑

🎀 -device ipmi-bmc-sim,id=id[,prop=value[,...]]

🌸 -device ipmi-bmc-extern,id=id,chardev=id[,slave_addr=val]

🦋 -device isa-ipmi-kcs,bmc=id[,ioport=val][,irq=val]

💖 -device isa-ipmi-bt,bmc=id[,ioport=val][,irq=val]

✨ -device pci-ipmi-kcs,bmc=id

💜 -device pci-ipmi-bt,bmc=id

👑 -device intel-iommu[,option=...]

🌈 -device virtio-iommu-pci[,option=...]

🧚 -device arm-smmuv3,primary-bus=id[,option=...]

🍓 -device amd-iommu[,option=...]

🎀 -name name

💜 -uuid uuid

Block device options 💾✨

🦋 Driver-specific options for other drivers 🦋

💖 OPTIONS (the drive one) 💖

-drive option[,option[,option[,...]]]

🌸 OPTIONS (still going, we're so back) 🌸

🔌 USB convenience options 🔌

🖥️ Display options 🖥️

🌈 -vga type 🌈

💻 i386 target only 💻

🌸 Network options 🌸

💖 -netdev 💖

🦋 tap,id=id[,fd=h][,ifname=name][,script=file][,downscript=dfile][,br=bridge][,helper=helper]

🌸 bridge,id=id[,br=bridge][,helper=helper]

⭐ socket,id=id[,fd=h][,listen=[host]:port][,connect=host:port]

🧚 socket,id=id[,fd=h][,mcast=maddr:port[,localaddr=addr]]

🌈 stream,id=str[,server=on|off],addr.type=inet,addr.host=host,addr.port=port[,to=maxport][,numeric=on|off][,keep-alive=on|off][,mptcp=on|off][,addr.ipv4=on|off][,addr.ipv6=on|off][,reconnect-ms=milliseconds]

💜 stream,id=str[,server=on|off],addr.type=unix,addr.path=path[,abstract=on|off][,tight=on|off][,reconnect-ms=milliseconds]

Start TTY emulator

Start VNC client and switch to virtual console Ctrl-Alt-2

qemu-system-x86_64 \

qemu-system-x86_64 \

qemu-system-x86_64 \

qemu-system-x86_64 -object secret,id=sec0,data=letmein,format=raw

printf "letmein" > mypasswd.txt # QEMU_SYSTEM_MACRO

openssl rand -base64 32 > key.b64

KEY=$(base64 -d key.b64 | hexdump -v -e '/1 "%02X"')

openssl rand -base64 16 > iv.b64

IV=$(base64 -d iv.b64 | hexdump -v -e '/1 "%02X"')

SECRET=$(printf "letmein" |

qemu-system-x86_64 \

qemu-system-x86_64 \

qemu-system-x86_64 \

qemu-system-x86_64 \

qemu-system-x86_64 \

qemu-system-x86_64 \

💖 `-add-fd` 💖

✨ `-set` ✨

🦋 `-global` 🦋

👑 `-boot` 👑

🎀 `-device ipmi-bmc-sim,id=id[,prop=value[,...]]`

🌸 `-device ipmi-bmc-extern,id=id,chardev=id[,slave_addr=val]`

🦋 `-device isa-ipmi-kcs,bmc=id[,ioport=val][,irq=val]`

💖 `-device isa-ipmi-bt,bmc=id[,ioport=val][,irq=val]`

✨ `-device pci-ipmi-kcs,bmc=id`

💜 `-device pci-ipmi-bt,bmc=id`

👑 `-device intel-iommu[,option=...]`

🌈 `-device virtio-iommu-pci[,option=...]`

🧚 `-device arm-smmuv3,primary-bus=id[,option=...]`

🍓 `-device amd-iommu[,option=...]`

🎀 `-name name`

💜 `-uuid uuid`

`-drive option[,option[,option[,...]]]`

🌈 `-vga type` 🌈

💖 `-netdev` 💖