QEMU(1)

📦

version 10.2.1 · 15 versions

💅 QEMU(1) — the manual, but make it make sense 💅

okay bestie, welcome to the QEMU user documentation. this is part 1, and we're about to get into it. no cap. 💖

✨ NAME ✨

qemu — QEMU User Documentation. that's it. that's the name. iconic. 💅

🌸 SYNOPSIS 🌸

qemu-system-x86_64 [options] [disk_image]

🦋 DESCRIPTION 🦋

The QEMU PC System emulator simulates the following peripherals, and honestly? the range is giving main character energy:

i440FX host PCI bridge and PIIX3 PCI to ISA bridge — the classic duo, no cap.
Cirrus CLGD 5446 PCI VGA card or dummy VGA card with Bochs VESA extensions (hardware level, including all non standard modes). — yes, all the non-standard modes are included, periodt.
PS/2 mouse and keyboard — the OGs.
2 PCI IDE interfaces with hard disk and CD-ROM support — two of them, because one is never enough.
Floppy disk — floppy disks are still a thing here, bestie.
PCI and ISA network adapters — networking? we got you.
Serial ports — serial ports, slay.
IPMI BMC, either an internal or external one — internal or external, your choice.
Creative SoundBlaster 16 sound card — legendary.
ENSONIQ AudioPCI ES1370 sound card — iconic.
Intel 82801AA AC97 Audio compatible sound card — AC97, we love.
Intel HD Audio Controller and HDA codec — HD audio, yes.
Adlib (OPL2) - Yamaha YM3812 compatible chip — Adlib, OPL2, YM3812 compatible.
Gravis Ultrasound GF1 sound card — GUS, the legend.
CS4231A compatible sound card — more sound.
PC speaker — beep beep.
PCI UHCI, OHCI, EHCI or XHCI USB controller and a virtual USB-1.1 hub. — USB galore.

SMP is supported with a large number of virtual CPUs (upper limit is configuration dependent). so like, you can have a lot of vCPUs, but the max depends on your config. don't @ me.

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.

⚠️ note: by default, GUS shares IRQ(7) with parallel ports and so QEMU must be told to not have parallel ports to have working GUS. like, it's a whole thing.

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. your call, bestie.

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. so check that before you come for me.

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. so double those commas, bestie. periodt.

🌟 Standard options 🌟

-h — Display help and exit. bestie, if you're lost, just do this.
-version — Display version information and exit. know your version, queen.
-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, 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= — 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.

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

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

sgx-epc.0.memdev=@var{memid},sgx-epc.0.node=@var{numaid} — Define an SGX EPC section.
-cpu model — Select CPU model (-cpu help for list and additional feature selection).
-accel name[,prop=value[,...]] — bestie, this turns on an accelerator. Depending on what target arch you're on, you might have kvm, xen, hvf, nvmm, whpx, mshv or tcg available. By default tcg is what you get. And if you list more than one accelerator? The next one gets used when the previous one fails to initialize. Teamwork fr fr.
- igd-passthru=on|off — when Xen is in play, 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. Default is full acceleration of the interrupt controllers. On x86, split irqchip reduces the kernel attack surface, but it costs you performance on non-MSI interrupts. Turning the in-kernel irqchip off entirely is not recommended unless you're literally just debugging. 💀
- 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's genuinely useful sometimes, like when you're trying to analyse the logs produced by the -d option.
- 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 on those it defaults on. On other operating systems it defaults off, but you can enable it for testing or debugging.
- tb-size=n — controls the size (in MiB) of the TCG translation block cache.
- thread=single|multi — controls number of TCG threads. When TCG is multi-threaded there's one thread per vCPU, so it takes advantage of extra host cores. 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).
- 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's a power of two, and it should be 1024 or bigger (but still less than the maximum value the kernel supports). 4096 could be a good initial value if you have no idea which is best. Set it 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 first. KVM on ARM does this splitting lazily by default. There are performance benefits in doing huge-page split eagerly, especially when 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 1GB/2MB/4KB, 32MB/16KB and 512MB/64KB for 4KB/16KB/64KB PAGE_SIZE respectively. Be wary of specifying a higher size because 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 and raises an internal error. The disable option doesn't enable the feature. This feature can mitigate the CPU stuck issue caused by 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.

-smp [[cpus=]n][,maxcpus=maxcpus][,drawers=drawers][,books=books][,sockets=sockets][,dies=dies][,clusters=clusters][,modules=modules][,cores=cores][,threads=threads] — simulates 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 is calculated from the provided topology members and the initial CPU count matches the maximum number. When only one of them is given, the omitted one gets 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 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 the 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 for the purpose of correct parsing.

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. ✨

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. 🌸

-numa — okay so this one has a whole lil family of forms, bestie:

-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]

What it does: defines a NUMA node and assigns RAM and VCPUs to it. Sets the NUMA distance from a source node to a destination node. Sets the ACPI Heterogeneous Memory Attributes for the given nodes. 🦋

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

The cpu option is a new alternative to the cpus option which uses socket-id|core-id|thread-id properties to assign CPU objects to a node using topology layout properties of CPU. The set of properties is machine specific, and depends on the used machine type/smp options. It could be queried with the hotpluggable-cpus monitor command. The node-id property specifies the node to which the CPU object will be assigned — it's required for the node to be declared with the node option before it's used with the cpu option.

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

okay so memdev — this one assigns RAM from a given memory backend device to a node. And bestie, please use memdev over the legacy mem option, fr fr. Why? Because memdev provides better performance and more control over the backend's RAM (like, the prealloc parameter of -memory-backend-ram allows memory preallocation, which is lowkey iconic ✨).

For compatibility reasons, the legacy mem option is still supported in 5.0 and older machine types. But ⚠️ note that mem and memdev are mutually exclusive. If one node uses memdev, the rest of the nodes have to use memdev too, and vice versa. No mixing, that's the law 💅.

Users must specify memory for all NUMA nodes by memdev (or the legacy mem if available in your machine type). And heads up: in QEMU 5.2, the support for -numa node without memory specified was removed. gone. bye. 💀

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

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

source and destination are NUMA node IDs. 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 are 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. This means that one still has to use the -m, -smp options to allocate RAM and VCPUs respectively. it's giving "organizer, not supplier" 🫶

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

In hmat-lb option, node are 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 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 latency value in nanoseconds. bw is bandwidth value, the possible value and units are NUM[M|G|T], mean that the bandwidth value are NUM byte per second (or MB/s, GB/s or TB/s depending on used suffix). Note that if latency or bandwidth value is 0, means the corresponding latency or bandwidth information is not provided. 🌸

In 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 the cache level 0 should not be used with hmat-cache option. associativity is the cache associativity, 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 MB/s; The processors in NUMA node 0 access memory in NUMA node 1 with access-latency 10 nanoseconds, access-bandwidth is 100 MB/s. And for memory side cache information, NUMA node 0 and 1 both have 1 level memory cache, size is 10KB, 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 fd=fd,set=set[,opaque=opaque] — add a file descriptor to an fd set 💖. 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:

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 group.id.arg=value — set parameter arg for item id of type group.
-global driver.prop=value
-global driver=driver,property=property,value=value — set the default value of driver's property prop to value, e.g.:

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 is not created automatically and set properties on it, use -device. 🎀

-global driver.prop=value is shorthand for -global driver=driver,property=prop,value=value. The longhand syntax works even when driver contains a dot. (iykyk)

-boot [order=drives][,once=drives][,menu=on|off][,splash=sp_name][,splash-time=sp_time][,reboot-timeout=rb_timeout][,strict=on|off] — specify boot order drives as a string of drive letters. Valid drive letters depend 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 the firmware implementations normally do not support both at the same time.

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, enabling user to show it as logo, when option splash=sp_name is given and menu=on, If firmware/BIOS supports them. Currently Seabios for X86 system support 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, qemu passes '-1' to bios by default. Currently Seabios for X86 system support 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

Note: The legacy format -boot drives is still supported but its use is discouraged as it may be removed from future versions. 🚨

-m [size=]megs[,slots=n,maxmem=size] — sets guest startup RAM size to megs megabytes. Default is 128 MiB. Optionally, a suffix of "M" or "G" can be used to signify a value in megabytes or gigabytes respectively. Optional pair slots, maxmem could be used to set amount of hotpluggable memory slots and maximum amount of memory. Note that maxmem must be aligned to the page size. 🧚

For example, the following command-line sets the guest startup RAM size to 1GB, creates 3 slots to hotplug additional memory and sets the maximum memory the guest can reach to 4GB:

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

If slots and maxmem aren't specified, memory hotplug just... doesn't get enabled, and the guest's startup RAM will never increase. That's it, that's the whole vibe. 💤

-mem-path path — allocate guest RAM from a temporarily created file living in path. ✨
-mem-prealloc — preallocate that memory when you're using -mem-path. No surprises later, bestie. 💅
-k language — set the keyboard layout to language (like fr for French, obviously). You only actually need this when raw PC keycodes are hard to come by — think Macs, some X11 servers, or a VNC/curses display. On a PC/Linux or PC/Windows host you genuinely do not need to bother. 🎀

Here's the full roster of layouts you can pick from:

   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][,...]] — okay so if you pass model, this one is a little shortcut that configures BOTH the guest audio hardware AND the host audio backend in a single go. Iconic efficiency. You set the guest hardware model with model=modelname, and model=help will list every available device type for you. 🦋

These two examples do literally the exact same thing — they're here to show off how -audio shortens your command line:

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

And if you don't specify model? Then -audio configures a default audio backend that gets used whenever the audiodev property isn't set on a device or machine. Notably, -audio none guarantees no audio is produced at all, even for machines with embedded sound hardware. Silence is golden, periodt. 🤫

Either way, the driver option works exactly the same as it does with the matching -audiodev option below. Use driver=help to list all the available drivers.

-audiodev [driver=]driver,id=id[,prop[=value][,...]] — adds a brand new audio backend driver, identified by id. There are global properties and driver-specific properties, and some values can be set differently for input vs output — those get marked with in|out.. So you 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, and in many cases specifying an invalid option just makes QEMU print an error message and then continue emulation without sound. 💀 Fair warning, bestie.

The valid global options are:

id=identifier — identifies the audio backend. That's its whole job. 👑
timer-period=period — sets the timer period the audio subsystem uses, in microseconds. Default is 10000 (10 ms).
in|out.mixing-engine=on|off — use QEMU's mixing engine to mix all the streams inside QEMU and convert audio formats when the backend doesn't support them. When this is off, fixed-settings must be off too. Heads up: disabling this means the selected backend must support multiple streams AND the audio formats your virtual cards use — otherwise you get no sound, full stop. It's not recommended to disable this unless you're going for 5.1 or 7.1 audio, because the mixing engine only supports mono and stereo. Default is on. 🎧
in|out.fixed-settings=on|off — use fixed settings for host audio. When it's off, settings will change based on how the guest opens the sound card — and in that case you must NOT specify frequency, channels or format. Default is on.
in|out.frequency=frequency — the frequency to use when fixed-settings is on. Default is 44100Hz.
in|out.channels=channels — the number of channels to use with fixed-settings. Default is 2 (stereo, as the universe intended 🎵).
in|out.format=format — the sample format to use with fixed-settings. Valid values are: s8, s16, s32, u8, u16, u32, f32. Default is s16.
in|out.voices=voices — how many 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 throws away all outputs. This backend has zero backend-specific properties. Very demure, very mindful. 🧘
-audiodev alsa,id=id[,prop[=value][,...]] — creates a backend using ALSA. This one's Linux-only, sorry to the rest of y'all. 🐧

ALSA-specific options are:

in|out.dev=device — 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) for when playback starts. Default is 0.

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

Core Audio-specific options are:

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

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

DirectSound-specific options are:

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

-audiodev oss,id=id[,prop[=value][,...]] — creates a backend using OSS. This one's available on most Unix-like systems, so it's the social butterfly of audio backends. 🦋

OSS-specific options are:

in|out.dev=device — 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 (heads up: vmix won't work in this case). Default is off.
dsp-policy=policy — sets the timing policy (a value between 0 and 10, where a smaller number means smaller latency but higher CPU usage). Use -1 to use the buffer sizes specified by buffer and buffer-count. This option gets ignored if you don't have OSS 4. Default is 5.

-audiodev pa,id=id[,prop[=value][,...]] — creates a backend using PulseAudio. Available on most systems, so like, everywhere basically. 💜

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 end up lower or higher. It's giving best effort. 🙈

-audiodev pipewire,id=id[,prop[=value][,...]] — creates a backend using PipeWire. Also 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 the pipewire stream.

-audiodev sdl,id=id[,prop[=value][,...]] — creates a backend using SDL. Available on most systems, but ngl, you should use your platform's native backend if you possibly can. ✨

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. Available on OpenBSD and most other Unix-like systems. 🐡

Sndio-specific options are:

in|out.dev=device — 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 one requires -spice and gets automatically selected in that case, so usually you can just ignore this option entirely. It has no backend-specific properties. 🌶️
-audiodev wav,id=id[,prop[=value][,...]] — creates a backend that writes audio out to a WAV file. Cute! 🎀

Backend-specific options are:

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

-device driver[,prop[=value][,...]] — add a device driver. prop=value sets driver properties, and which properties are valid depends entirely on the driver. To get help on possible drivers and properties, use -device help and -device driver,help. 📖

Some drivers are:

-device ipmi-bmc-sim,id=id[,prop[=value][,...]] — add an IPMI BMC. This simulates a hardware management interface processor that normally sits on a system — it provides a watchdog plus the ability to reset and power control the system. You need to connect this to an IPMI interface for it to actually be useful. 🛠️

The IPMI slave address to use for the BMC. The default is 0x20. This address is the BMC's address on the I2C network of management controllers. If you don't know what any of that means, it is safe to ignore it. Genuinely. 😌

id=id — the BMC id for interfaces to use this device.
slave_addr=val — define the slave address to use for the BMC. The default is 0x20.
sdrfile=file — file containing raw Sensor Data Records (SDR) data. The default is none.
fruareasize=val — size of a Field Replaceable Unit (FRU) area. The default is 1024.

frudatafile=file — a file stuffed with raw Field Replaceable Unit (FRU) inventory data. Default is none, so like, nothing. 💀
guid=uuid — the GUID value for the BMC, in standard UUID format. Set it and the Get GUID command to the BMC returns it. Don't set it and Get GUID throws an error. no in-between bestie.

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

Okay so instead of emulating the BMC locally like the thing above, this hooks you up to an external entity that serves the IPMI. Think of it as "I'm not doing this myself, I know a girl." ✨

A connection gets 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. And like — be careful, because if you don't handle this right it can be a security issue: this 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 neither the simulator nor QEMU is exposed to any outside network. periodt.

Peep the lanserv/README.vm file in the OpenIPMI library for more deets on the external interface. 💅

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

Adds a KCS IPMI interface on the ISA bus. It also adds a corresponding ACPI and SMBIOS entries, if appropriate. multitasking queen.

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

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

Same energy as 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. we love consistency. 🫶

👑 `-device intel-iommu[,option=...]`

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

intremap=on|off (default: auto) — enables the interrupt remapping feature. This is 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 auto 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 on, each guest DMA buffer mapping generates an IOTLB invalidation from the guest IOMMU driver to the vIOMMU device, synchronously. 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.
device-iotlb=on|off (default: off) — enables the 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. The address space is 39 bits wide for 3-level IOMMU page tables, and 48 bits for 4-level IOMMU page tables.

Also please 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=...]`

This is only supported by -machine q35 (x86_64) and -machine virt (ARM). It supports the options below:

granule=val (possible values are 4k, 8k, 16k, 64k and host; default: host) — decides the default granule 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`

This is only supported by -machine virt (ARM).

primary-bus=id — accepts either the default root complex (pcie.0) or a pxb-pcie based root complex.

💜 `-device amd-iommu[,option=...]`

Enables emulation of an AMD-Vi I/O Memory Management Unit (IOMMU). Only available with -machine q35, and it supports these 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 in guests, which is also required to enable x2apic support. Currently only available with kernel-irqchip=off|split, it's automatically enabled when either of those modes is in use, and disabled with kernel-irqchip=on.
xtsup=on|off (default: off) — the interrupt remapping table supports x2apic mode, enabling use of the 128-bit IRTE format with a 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 shows up in the SDL window caption. It's also used for the VNC server. Optionally it also sets the top visible process name in Linux. Naming of individual threads can also be enabled on Linux to aid debugging. main character energy fr fr. 👑

🌸 `-uuid uuid`

Set system UUID. that's it that's the whole thing. 💅

🍓 Block device options 🍓

Ok bestie, story time: the QEMU block device handling options have a long history and have gone through several iterations as the feature set and complexity of the block layer grew. A lot of online guides to QEMU reference older, deprecated options, which — and I cannot stress this enough — leads to so much confusion. 😭

The most explicit way to describe disks is a combo of -device to specify the hardware device and -blockdev to describe the backend. The device defines what the guest sees, and the backend describes how QEMU handles the data. It is the only guaranteed stable interface for describing block devices, and as such is recommended for management tools and scripting. no cap.

The -drive option combines the device and backend into a single command line option, which is more human friendly. There is however no interface stability guarantee, although some older board models still need updating to work with the modern blockdev forms.

Older options like -hda are essentially macros that expand into -drive options for various drive interfaces. The original forms bake in a lot of assumptions from the days when QEMU was emulating a legacy PC, and they are not recommended for modern configurations. it's giving 2005. 🙈

-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 (this is for example the IDE bus on most x86 machines, but it can also be SCSI, virtio or something else on other target architectures). 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, so you cannot use -hdc and -cdrom at the same time there 👀). On systems that support it, you can use the host CD-ROM by using /dev/cdrom as filename.

⭐ `-blockdev option[,option[,option[,...]]]`

Define a new block driver node. Some of the options apply to all block drivers, other options are only accepted for a specific block driver. See below for a list of generic options and options for the most common block drivers. 💖

Options that expect a reference to another node (e.g. 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, adding options for the referenced node after a dot (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 — 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 use -drive as well) the ID of a drive.

If no node name is specified, it is automatically generated. The generated node name is not intended to be predictable and changes between QEMU invocations. For the top level, an explicit node name must be specified. don't skip this one bestie. 🫶

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 this case, the default value read-only=off does not work and the option must be specified explicitly. ⚠️

auto-read-only — okay so if you set auto-read-only=on, QEMU is allowed to fall back to read-only usage even when you specifically asked for read-only=off. It can even switch between modes whenever it needs to — like, depending on whether the image file is writable or whether a writing user is attached to the node. 💅
force-share — this one overrides QEMU's image locking system and forces the node to use weaker shared access for permissions where it would normally be requesting exclusive access. Here's the tea ☕: when there's the potential for multiple instances to have the same file open (and it does not matter whether this QEMU invocation is the first instance or the second one), both instances must permit shared access for the second instance to succeed at opening the file. 😭

Enabling force-share=on requires read-only=on. No exceptions bestie, that's the rule. 🫶

cache.direct — you can dodge the host page cache entirely with cache.direct=on. It'll attempt to do disk IO directly to the guest's memory. Just so you know — QEMU may still perform an internal copy of the data anyway. 🙈
cache.no-flush — in case you literally do not care about data integrity over host failures, cache.no-flush=on is right there. This option tells QEMU that it never needs to write any data to the disk and can instead keep things in cache. If anything goes wrong — like your host losing power, the disk storage getting disconnected accidentally, etc. — your image will most probably be rendered unusable. 💀 So like, that's the vibe, proceed accordingly.
discard=discard — discard is one of "ignore" (or "off") or "unmap" (or "on") and it controls whether discard (also known as trim or unmap) requests are ignored or passed to the filesystem. Heads up though: some machine types may not support discard requests. 🦋
detect-zeroes=detect-zeroes — detect-zeroes is "off", "on" or "unmap" and it 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", which allows a zero write to be converted to an unmap operation. ✨

✨ 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). Fun fact: it is allowed to pass null here in order to disable the default backing file.
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 — whether discard requests for the data source should be issued when a snapshot operation (e.g. deleting a snapshot) frees clusters in the qcow2 file (on/off; default: on)
pass-discard-other — whether discard requests for the data source should be issued on other occasions where a cluster gets freed (on/off; default: off)
discard-no-unref — when enabled, data clusters will remain preallocated when they are no longer used, e.g. because they are discarded or converted to zero clusters. As usual, whether the old data is discarded or kept on the protocol level (i.e. in the image file) depends on the setting of the pass-discard-request option. Keeping the clusters preallocated prevents qcow2 fragmentation that would otherwise be caused by freeing and re-allocating them later. Besides potential performance degradation, such fragmentation can lead to increased allocation of clusters past the end of the image file, resulting in image files whose file length can grow much larger than their guest disk size would suggest. If image file length is of concern (e.g. when storing qcow2 images directly on block devices), you should consider enabling this option. 👑
overlap-check — which overlap checks to perform for writes to the image (none/constant/cached/all; default: cached). For details or finer granularity control refer to the QAPI documentation of blockdev-add.

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 it, that's the whole vibe check. 🧚

-drive option[,option[,option[,...]]] — define a new drive. This includes creating a block driver node (the backend) as well as a guest device, and it's mostly a shortcut for defining the corresponding -blockdev and -device options. 🚗

-drive accepts all options that are accepted by -blockdev. On top of that, it knows the following options:

file=file — this option defines which disk image (see the Disk Images <#disk-images> chapter in the System Emulation Users Guide) to use with this drive. If the filename contains a comma, you must double it (for instance, "file=my,,file" to use file "my,file"). Special files such as iSCSI devices can be specified using protocol specific URLs. See the section for "Device URL Syntax" for more information.
if=interface — this option defines on which type on interface the drive is connected. Available types are: ide, scsi, sd, mtd, floppy, pflash, virtio, none.
bus=bus,unit=unit — these options define where is connected the drive by defining the bus number and the unit id.
index=index — this option defines where the drive is connected by using an index in the list of available connectors of a given interface type.
media=media — this option defines the type of the media: disk or cdrom.
snapshot=snapshot — snapshot is "on" or "off" and controls snapshot mode for the given drive (see -snapshot).

cache=cache — bestie this one's the vibe controller for how the host cache touches your block data. cache can be "none", "writeback", "unsafe", "directsync" or "writethrough". It's a shortcut that sets the cache.direct and cache.no-flush options (just like in -blockdev), and on top of that it sets cache.writeback, which gives a default for the write-cache option of block guest devices (as in -device). The modes map 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 it picks between pthread based disk I/O, native Linux AIO, or the Linux io_uring API. Choose your fighter 💅
format=format — tells QEMU exactly which disk format to use instead of letting it detect the format itself. You can use this to say format=raw and dodge interpreting an untrusted format header. Safety first, queen 🎀
werror=action,rerror=action — what to do when write and read errors happen. 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 it decides whether to copy read backing file sectors into the image file.
bps=b,bps_rd=r,bps_wr=w — 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. A safe minimum for disks is 2 MB/s. Don't be stingy 🍓
bps_max=bm,bps_rd_max=rm,bps_wr_max=wm — burst limits in bytes per second, again either for all request types or for reads or writes only. Bursts let the guest I/O spike above the limit for a sec.
iops=i,iops_rd=r,iops_wr=w — request rate limits in requests per second, either for all request types or for reads or writes only.
iops_max=bm,iops_rd_max=rm,iops_wr_max=wm — burst limits 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.
iops_size=is — every is bytes of a request count as a new request for iops throttling purposes. Use this so guests can't sneak around the iops limits by sending fewer but bigger requests. Not on our watch 💀
group=g — join a throttling quota group with the given name g. Every drive that's a member of the same group gets accounted for together. Use this to stop guests from circumventing throttling limits by using a bunch of tiny disks instead of one big one.

By default, the cache.writeback=on mode is used. It reports data writes as completed as soon as the data is chilling in the host page cache. This is safe as long as your guest OS makes sure to correctly flush disk caches where needed. 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. 😭

For such 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 goes to the guest only after QEMU has made sure to flush each write to the disk. Be aware that this has a major impact on performance. The tradeoff is real, bestie.

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

Copy-on-read avoids accessing the same backing file sectors over and over, and it's 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:

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

You can connect a CDROM to the slave of ide0:

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

If you don't specify the "file=" argument, you define an empty drive:

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

Instead of -fda, -fdb, you can use:

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

By default, interface is "ide" and index is automatically incremented:

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

is interpreted like:

qemu-system-x86_64 -hda a -hdb b

-mtdblock file — use file as on-board Flash memory image. 🦋
-sd file — use file as SecureDigital card image.
-snapshot — write to temporary files instead of disk image files. In this case, the raw disk image you use is not written back. You can however force the write back by pressing C-a s (see the Disk Images <#disk-images> chapter in the System Emulation Users Guide).

Warning: snapshot is incompatible with -blockdev (instead use qemu-img to manually create snapshot images to attach to your blockdev). If you have mixed -blockdev and -drive declarations you can use the 'snapshot' property on your drive declarations instead of this global option. Fr fr, don't mix these up 🙈

-fsdev local,id=id,path=path,security_model=security_model [,writeout=writeout][,readonly=on][,fmode=fmode][,dmode=dmode] [,throttling.option=value[,throttling.option=value[,...]]]
-fsdev synth,id=id[,readonly=on]

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 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 be used for this export path. Supported security models are "passthrough", "mapped-xattr", "mapped-file" and "none". In "passthrough" security model, files are stored using the same credentials as they are created on the guest — this requires QEMU to run as root. In "mapped-xattr" security model, some of the file attributes like uid, gid, mode bits and link target are stored as file attributes. For "mapped-file" these attributes are stored in the hidden .virtfs_metadata directory. Directories exported by this security model cannot interact with other unix tools. "none" security model is the same as passthrough except the server 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 that 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 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 security models "mapped-xattr" and "mapped-file".

dmode=dmode — sets the default mode for directories that get freshly created on the host ✨ lowkey only works with the "mapped-xattr" and "mapped-file" security models, bestie, so don't come crying to me if you set it under passthrough 💅
throttling.bps-total=b,throttling.bps-read=r,throttling.bps-write=w — bandwidth throttling limits in bytes per second 🫶 either for literally every request type, or just for reads, or just for writes. your call, queen.
throttling.bps-total-max=bm,bps-read-max=rm,bps-write-max=wm — bursts in bytes per second 🔥 again either all-request-types or reads-only or writes-only. bursts let the guest I/O spike above the limit temporarily, it's giving "treat yourself" but for throughput 💖
throttling.iops-total=i,throttling.iops-read=r,throttling.iops-write=w — request rate limits, in requests per second 🌸 for all request types, or reads only, or writes only.
throttling.iops-total-max=im,throttling.iops-read-max=irm,throttling.iops-write-max=iwm — bursts in requests per second 💀 same deal, all types or reads or writes. bursts = guest I/O can spike above the limit for a sec.
throttling.iops-size=is — makes every is bytes of a request count as a whole new request for iops throttling purposes 🎀 math girlies rise.

The -fsdev option is used alongside -device driver "virtio-9p-..." 👑 they're a package deal, don't separate them.

`-device virtio-9p-type,fsdev=id,mount_tag=mount_tag`

Options for the virtio-9p-... driver are, bestie:

type — which variant you're using. Supported values are "pci", "ccw" or "device", depending on the machine type 🦋
fsdev=id — the id value you specified along with the -fsdev option.
mount_tag=mount_tag — the tag name the guest uses to mount this export point 🌈

`-virtfs`

-virtfs local,path=path,mount_tag=mount_tag
,security_model=security_model[,writeout=writeout][,readonly=on]
[,fmode=fmode][,dmode=dmode][,multidevs=multidevs]

-virtfs synth,mount_tag=mount_tag

Define a new virtual filesystem device and expose it to the guest using a virtio-9p-device (a.k.a. 9pfs) 🧚 which basically means a certain directory on the host is made directly accessible by the guest as a pass-through file system, using the 9P network protocol for host↔guest communication. and if you want? it can even be accessible and shared by several guests at the same time 💅 iconic behaviour honestly.

Note that -virtfs is actually just a convenience shortcut for its generalized form -fsdev -device virtio-9p-pci ✨ the glow-up is real but it's the same girl underneath.

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 — 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 — the security model for this export path. Supported models are "passthrough", "mapped-xattr", "mapped-file" and "none".
- In "passthrough", files are stored using the same credentials as they're created on the guest. this requires QEMU to run as root 😭 yeah. root. we don't make the rules.
- In "mapped-xattr", some 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 server won't report failures if it fails to set file attributes like ownership 🙈
- Security model is mandatory only for the local fsdriver, so heads up.
writeout=writeout — optional argument 💖 the only supported value is "immediate". It means the host page cache will be used to read and write data, but write notification gets sent to the guest only once the data has been reported as written by the storage subsystem. patient queen energy.
readonly=on — enables exporting the 9p share as a readonly mount for guests. By default, read-write access is given 🌸
fmode=fmode — the default mode for newly created files on the host. Works only with security models "mapped-xattr" and "mapped-file" ✨
dmode=dmode — the default mode for newly created directories on the host. Same deal: only works with "mapped-xattr" and "mapped-file" 💅
mount_tag=mount_tag — the tag name the guest uses to mount this export point.
multidevs=remap|forbid|warn — how to deal with multiple devices being shared with the same 9p export, so you avoid file ID collisions on the guest 🦋 supported behaviours are "remap" (default), "forbid" or "warn".
- remap : assumes the possibility that more than one device is shared with the same 9p export. So inode numbers from the host get remapped for the guest in a way that prevents file ID collisions on the guest. Remapping is required in these cases because the original device IDs from the host are never passed and exposed on the guest — instead, all files of an export shared with virtfs always share the same device ID on the guest. So two files with identical inode numbers but from actually different devices on the host would otherwise cause a file ID collision and hence potential severe misbehaviours on the guest 💀
- warn : virtfs 9p expects only one device to be shared with the same export. If more than one device is shared and accessed via the same 9p export, then only a warning message gets logged (once) by qemu on the host side. No further action is performed in this case that would prevent file ID collisions on the guest. This could lead to severe misbehaviours, like wrong files being accessed and data corruption on the exported tree 😭 not the vibe.
- forbid : assumes like "warn" that only one device is shared by the same 9p export, but it will not only log a warning message, it will also deny access to additional devices on the guest. Note though that "forbid" does currently not block all possible file access operations (e.g. readdir() would still return entries from other devices) 🙈

`-iscsi`

Configure iSCSI session parameters ⭐

🎀 USB convenience options 🎀

-usb — enable USB emulation on machine types with an on-board USB host controller (if it's not enabled by default). Note that on-board USB host controllers may not support USB 3.0 💀 in that 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's 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 don't have a 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 the type of display to use. 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)

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 — let the VM actually be closed when you hit the window close button 🪟

`gtk` 🎀

Show your video output in a GTK window, bestie. This one is so extra in the best way — it gives you drop-down menus and other UI goodies so you can configure and control the VM while it's running. Valid parameters are:

full-screen=on|off — start in fullscreen mode, main character energy, no distractions ✨
gl=on|off — use OpenGL for displaying, because we love a smooth render 💅
grab-on-hover=on|off — grab the keyboard input the moment your mouse hovers over it
show-tabs=on|off — display the tab bar for switching between the various graphical interfaces (e.g. VGA and virtual console character devices). Defaults to on 🗂️
show-cursor=on|off — force showing the mouse cursor, no hiding, we see you 👀
window-close=on|off — allow quitting qemu with the window close button
show-menubar=on|off — display the main window menubar, defaults to "on"
zoom-to-fit=on|off — expand the video output to the window size, defaults to "off"

`curses[,charset=<encoding>]` 🧚

Display video output via curses. For graphics device models that support a text mode, QEMU can show that output through a curses/ncurses interface. Heads up though: literally nothing gets displayed when the graphics device is in graphical mode, or if the graphics device doesn't support text mode at all. Generally only the VGA device models support text mode, iykyk.

You can tell it which font charset the guest is using 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, periodt. This interface brings drop-down menus and other UI elements so you can configure and control the VM while it's running. Valid parameters are:

full-grab=on|off — capture all key presses, including system combos. This one 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 their key codes match their position on non-Mac keyboards, and you can use Meta/Super and Alt exactly where you expect them. (default: off)
show-cursor=on|off — force showing the mouse cursor
left-command-key=on|off — disable forwarding the left command key to the host
full-screen=on|off — start in fullscreen mode
zoom-to-fit=on|off — expand the video output to the window size, defaults to "off"

`egl-headless[,rendernode=<file>]` 🌈

Offload all the OpenGL operations to a local DRI device. For any graphical display, this display needs to be paired with either VNC or SPICE displays — it can't go solo, it's a duo kind of situation 🫶

`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 won't be displayed to the QEMU user. This is different from the -nographic option in that it only affects what happens 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 becomes a simple command line application. The emulated serial port gets redirected on the console and muxed with the monitor (unless it's redirected elsewhere explicitly). So yeah — you can still use QEMU to debug a Linux kernel with a serial console, no big deal 🔥

Use C-a h for help on switching between the console and the 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 — require that the client use SASL to authenticate with spice. The exact choice of authentication method used is controlled from the system / user's SASL configuration file for the 'qemu' service. This is typically found in /etc/sasl2/qemu.conf. If running QEMU as an unprivileged user, an environment variable SASL_CONF_PATH can be used to make it search alternate locations for the service config. While some SASL auth methods can also provide data encryption (eg GSSAPI), it is recommended that SASL always be combined with the 'tls' and 'x509' settings to enable use of SSL and server certificates. This ensures a data encryption preventing compromise of authentication credentials. 🔐
disable-ticketing=on|off — allow client connects without authentication.
disable-copy-paste=on|off — disable copy paste between the client and the guest.
disable-agent-file-xfer=on|off — disable spice-vdagent based file-xfer between the client and the guest.
tls-port=<nr> — set the TCP port spice is listening on for encrypted channels.
x509-dir=<dir> — set the x509 file directory. Expects 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.
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. The options can be specified multiple times to configure multiple channels. The special name "default" can be used to set the default mode. For channels which are not explicitly forced into one mode, the spice client is allowed 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 slow links). 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> — provide the preferred codec the Spice server should use with the Gstreamer encoder. This option is only relevant when gl=on is specified. If no codec is provided, then the codec gstreamer:h264 would be used as default. And, for the case where gl=off, the default codec to be used is determined by the Spice server.
max-refresh-rate=rate — provide the maximum refresh rate (or FPS) at which the encoding requests should be sent to the Spice server. Default would be 30.
gl=[on|off] — enable/disable OpenGL context. Default is off.
rendernode=<file> — DRM render node for OpenGL rendering. If not specified, it will pick the first available. (Since 2.9)

`-vga type` 👑

Select the type of VGA card to emulate. Valid values for type are:

cirrus — Cirrus Logic GD5446 Video card. All Windows versions 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 if you want to use high resolution modes (>= 1280x1024x16) then you should use this option. (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 is VGA compatible (including VESA 2.0 VBE support). Works best with qxl guest drivers installed though. 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. This is 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.

`-full-screen` 🌸

Start in full screen. That's it, that's the whole vibe. Immersive mode activated ✨

-g widthxheight[xdepth] — sets the starting graphical resolution and depth, bestie. PPC and SPARC only, so don't come crying to me if x86 ignores it 💅

For PPC the default is 800x600x32.

For SPARC with the TCX graphics device, the default is 1024x768x8, with 1024x768x24 as an option. For cgthree, the default is 1024x768x8, with 1152x900x8 as an option for the people who wanna use OBP.

-vnc display[,option[,option[,...]]] — okay so normally, if QEMU got compiled with graphical window support, it shows you stuff like guest graphics, guest console, and the QEMU monitor in a window. With this option you can make QEMU listen on VNC display display and redirect the VGA display over that VNC session instead. It's super useful to enable the usb tablet device when you're using this (that's -device usb-tablet btw). And when you're using the VNC display, you must use the -k parameter to set the keyboard layout unless you're on en-us. The valid syntax for the display is:
- to=L — with this, QEMU will try the next available VNC displays until it hits number L, in case the originally defined -vnc display isn't available, e.g. port 5900+display is already taken by another app. Default is to=0.
- host:d — TCP connections will only be allowed from host on display d. By convention the TCP port is 5900+d. Optionally you can leave host out, and then the server will accept connections from any host.
- unix:path — connections are allowed over UNIX domain sockets, where path is the location of a unix socket to listen for connections on.
- none — VNC gets initialized but not started. You can use the monitor change command later to start the VNC server. 🌸

After the display value there can be one or more option flags, separated by commas. The valid options are:

reverse=on|off — connects 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. Heads up 👀
websocket=on|off — opens an extra TCP listening port dedicated to VNC Websocket connections. If you give a bare websocket option, the Websocket port is 5700+display. You can specify a different port with the syntax websocket=port.

If host is specified, connections will only be allowed from this host. You can control the websocket listen address independently using the syntax websocket=host:port.

Websocket can also be allowed over a 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 — requires that password based authentication is used for client connections.

The password has to 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 wanna change the <protocol> password expiration, use expire_password <protocol> <expiration-time> where expiration time can be one of: now, never, +seconds, or the UNIX time of expiration — e.g. +60 to make the password expire in 60 seconds, or 1335196800 to make it expire on "Mon Apr 23 12:00:00 EDT 2012" (that's the UNIX time for that date and time, iykyk).

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

password-secret=<secret-id> — requires password based authentication for client connections, using the password provided by the secret object identified by secret-id.
tls-creds=ID — gives the ID of a set of TLS credentials to use to secure the VNC server. They apply to both the normal VNC server socket and the websocket socket (if it's enabled). Setting TLS credentials makes the VNC server socket enable the VeNCrypt auth mechanism. The credentials should've been created earlier using the -object tls-creds argument.
tls-authz=ID — gives 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 it can be deleted and recreated on the fly while the VNC server is active. If it's missing, it defaults to denying access. 💀
sasl=on|off — requires that the client use SASL to authenticate with the VNC server. The exact choice of authentication method is controlled from the system / user's SASL configuration file for the 'qemu' service. This is typically found in /etc/sasl2/qemu.conf. If you're running QEMU as an unprivileged user, the environment variable SASL_CONF_PATH can be used to make it search alternate locations for the service config. While some SASL auth methods can also provide data encryption (eg GSSAPI), it's recommended that SASL always be combined with the 'tls' and 'x509' settings to enable use of SSL and server certificates. This ensures a data encryption preventing compromise of authentication credentials. See the VNC security <#vnc-security> section in the System Emulation Users Guide for details on using SASL authentication. ✨
sasl-authz=ID — gives the ID of the QAuthZ authorization object against which the client's SASL username will be validated. Only resolved at time of use, so it can be deleted and recreated on the fly while the VNC server is active. If it's missing, it defaults to denying access.
acl=on|off — the legacy method for enabling authorization of clients against the x509 distinguished name and SASL username. It creates two authz-list objects with IDs vnc.username and vnc.x509dname. The rules for these objects must be configured with the HMP ACL commands.

This option is deprecated and should no longer be used, bestie. The new sasl-authz and tls-authz options are its replacement. 🙈

lossy=on|off — enables lossy compression methods (gradient, JPEG, ...). If this is set, the VNC client may receive lossy framebuffer updates depending on its encoding settings. Turning this on can save a lot of bandwidth at the expense of quality.
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 updates in those regions using a lossy encoding (like JPEG). This can be really helpful to save bandwidth when you're 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, this is implemented by dropping other connections. Connecting multiple clients in parallel requires all clients asking for a shared session (vncviewer: -shared switch). This is the default. 'force-shared' disables exclusive client access — useful for shared desktop sessions, where you don't want someone forgetting to specify -shared and disconnecting everybody else 😭. 'ignore' completely ignores the shared flag and allows everybody to connect unconditionally. It doesn't conform to the rfb spec but it's the 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 slowdown can help the device and guest keep up and not lose events in case events arrive in bulk. Possible causes for that are flaky network connections, or scripts for automated testing.
audiodev=audiodev — use the specified audiodev when the VNC client requests audio transmission. When you're not using an -audiodev argument, this option must be omitted, otherwise it must be present and specify a valid audiodev.
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 avoid a disk full bug. After Windows 2000 is installed you no longer need this option (and lowkey it slows down the IDE transfers, so let it go). Synonym of -global ide-device.win2k-install-hack=on.
-no-fd-bootchk — disables boot signature checking for floppy disks in BIOS. You might need this to boot from old floppy disks. Synonym of -m fd-bootchk=off. 🦋
-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]...] — bestie, this one drops in an ACPI table with the header fields you give it plus context pulled from the files you point at. With file=, it takes the entire ACPI table from the specified files, all the ACPI headers included (and other options can override them). With data=, only the data portion of the table gets used, and every scrap of header info comes from the command line instead. And okay so heads up: if a SLIC table is supplied to QEMU, then SLIC's oem_id and oem_table_id fields will override the same ones in the RSDT and the FADT (a.k.a. FACP), so that the field matches what the Microsoft SLIC spec and the ACPI spec require. 💅
-smbios file=binary — load the SMBIOS entry from a binary file. simple as that ✨
-smbios type=0[,vendor=str][,version=str][,date=str][,release=%d.%d][,uefi=on|off] — specify SMBIOS type 0 fields 🎀
-smbios type=1[,manufacturer=str][,product=str][,version=str][,serial=str][,uuid=uuid][,sku=str][,family=str] — specify SMBIOS type 1 fields 🎀
-smbios type=2[,manufacturer=str][,product=str][,version=str][,serial=str][,asset=str][,location=str] — specify SMBIOS type 2 fields 🎀
-smbios type=3[,manufacturer=str][,version=str][,serial=str][,asset=str][,sku=str] — specify 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] — specify 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] — specify SMBIOS type 9 fields 🎀
-smbios type=11[,value=str][,path=filename] — specify SMBIOS type 11 fields 🌸

You can repeat this argument as many times as you want, and the values get added in the order they're parsed, fr fr. Apps that plan to use OEM strings data are encouraged to prefix their value string with their application name — that way info for multiple apps can be passed along at the same time without anyone stepping on anyone. 👑

The value=str syntax gives you the string data inline, while path=filename 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.

Okay so real talk: on the x86 architecture, the total size of all SMBIOS tables is limited to 65535 bytes. Which means the OEM strings data is not suitable for passing large amounts of data into the guest. Instead it should be used as an indicator to inform the guest where to locate the real data set — for example, by specifying the serial ID of a block device. iykyk 🧚

Here's an example passing three strings:

-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] — specify SMBIOS type 17 fields 🎀
-smbios type=41[,designation=str][,kind=str][,instance=%d][,pcidev=str] — specify SMBIOS type 41 fields 🌈

This argument can be repeated multiple times too. Its main use? Letting network interfaces be created as enoX on Linux, with X being the instance number, instead of the name depending on where the interface sits on the PCI bus. iconic behaviour honestly. ✨

Here's 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 cap. 💅

🌐 Network options 🦋

-nic [tap|passt|bridge|user|l2tpv3|vde|netmap|af-xdp|vhost-user|socket][,...][,mac=macaddr][,model=mn] — bestie this is the shortcut option, it configures BOTH the on-board (default) guest NIC hardware and the host network backend in one single go. The host backend options are the same as with the corresponding -netdev options below. The guest NIC model gets set with model=modelname — and if you use model=help it'll list all the available device types for you. The hardware MAC address? Set it with mac=macaddr. 🎀

The following two examples do exactly the same thing, just 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 — says no network devices should be configured at all. It's used to override the default configuration (default NIC with "user" host network backend) which gets activated if you don't provide any other networking options. 🙈
-netdev passt,id=str[,option][,...] — configure a passt network backend which requires no administrator privilege to run. valid options are:
- id=id — assign a symbolic name for use in monitor commands.
- path=file — filename of the passt program to run. If it isn't provided, the 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, and 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 the user mode host network backend, which requires no administrator privilege to run. valid options are:
- id=id — assign a 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 the 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 the 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. 😭
- hostname=name — specifies the client hostname reported by the built-in DHCP server. 🫶
dhcpstart=addr — bestie, this picks the first of the 16 IPs your built-in DHCP server is allowed to hand out. Default is the 15th to 31st IP in the guest network, i.e. x.x.x.15 to x.x.x.31.
dns=addr — the guest-visible address of the virtual nameserver 🧚. It must be different from the host address, no exceptions. Default is the 3rd IP in the guest network, i.e. x.x.x.3.
ipv6-dns=addr — same energy but for the IPv6 virtual nameserver ✨. Also has to be different from the host address. Default is the 3rd IP in the guest network, i.e. xxxx::3.
dnssearch=domain — drops an entry into the domain-search list the built-in DHCP server sends out. Want more than one domain suffix? Just pass this option multiple times, it's giving "yes and". If the guest supports it, it'll auto-try to append the given domain suffix(es) whenever a domain name can't be resolved. So convenient 💅

Example:

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

domainname=domain — sets the client domain name that the built-in DHCP server reports. Simple. Iconic. 👑
tftp=dir — when you're on the user mode network stack, this activates a built-in TFTP server 🎀. Everything in dir gets exposed as the root of that TFTP server. Heads up: the TFTP client on the guest has to be set to binary mode (use the command bin of the Unix TFTP client). The built-in TFTP server is read-only — it implements no command for writing files, and QEMU will not write to this directory. Periodt.
tftp-server-name=name — in the BOOTP reply, this broadcasts name as the "TFTP server name" (RFC2132 option 66). Use it to tell the guest to load boot files or configurations from a different server than the host address. Sneaky but legal 😌
bootfile=file — on the user mode network stack, this broadcasts file as the BOOTP filename. Pair it with tftp and you can network boot a guest straight from a local directory. Obsessed.

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] — on the user mode network stack, this activates a built-in SMB server so Windows OSes can access the host files in dir transparently 🪟✨. You can set the SMB server's IP address to addr. By default the 4th IP in the guest network is used, i.e. x.x.x.4.

In the guest Windows OS, this 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. Not optional, bestie, it's the whole vibe.

hostfwd=[tcp|udp|unix]:[[hostaddr]:hostport|hostpath]-[guestaddr]:guestport — redirects incoming TCP, UDP or UNIX connections to the host port hostport over to the guest IP address guestaddr on guest port guestport 🌈. If guestaddr isn't specified, its value is x.x.x.15 (the default first address given by the built-in DHCP server). Specify hostaddr and you can bind the rule to a specific host interface. No connection type set? Then TCP is used. This option can be given multiple times, go off 💅

For example, to redirect a 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 — forwards guest TCP connections to the IP address server on port port, either to the character device dev, or to a program executed by cmd:command which gets spawned for each connection 🦋. This option can be given multiple times.

You can either use a chardev directly and have that one used throughout QEMU's lifetime, like in the following example:

# 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 you can execute a command on every TCP connection established by the guest, so that QEMU behaves similar to an inetd process for that virtual server:

# 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]`

Configure a host TAP network backend with ID id 💖.

Use the network script file to configure it and the network script dfile to deconfigure it. If name isn't provided, the OS automatically provides one. The default network configure script is /etc/qemu-ifup and the default network deconfigure script is /etc/qemu-ifdown. Use script=no or downscript=no to disable script execution 🚫

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:

#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"

🌉 `-netdev bridge,id=id[,br=bridge][,helper=helper]`

Connect a host TAP network interface to a host bridge device 🌸.

Use the network helper 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.

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

🧦 `-netdev socket,id=id[,fd=h][,listen=[host]:port][,connect=host:port]`

This host network backend can be used to connect 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). connect is used to connect to another QEMU instance 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

📡 `-netdev socket,id=id[,fd=h][,mcast=maddr:port[,localaddr=addr]]`

Configure a socket host network backend to share the guest's network traffic with another QEMU virtual machines using a UDP multicast socket, effectively making a bus for every QEMU with same multicast address maddr and port 💀✨. NOTES:

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

okay and here's the User Mode Linux compat version, because apparently we're doing crossover episodes now 🦋

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

and if you need the packets to leave from a specific host address on your box, bestie you literally just say so:

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

-netdev 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] — setting up a network backend that connects to another QEMU VM (or a proxy) over a TCP/IP socket 🌐 yes it's giving main character networking energy.
- server=on|off — if it's on, you're creating a server socket ✨
- addr.host=host, addr.port=port — the socket address you listen on when server=on, or connect to when server=off 🎯
- to=maxport — if this is here, you've got a range of possible addresses, with the port landing anywhere between port and maxport 🌈
- numeric=on|off — if it's on, host and port are guaranteed numeric, otherwise a name resolution should be attempted. (default: off) 🙈
- keep-alive=on|off — turns on keep-alive when you connect to this socket. Heads up bestie: not supported for passive sockets 💀
- mptcp=on|off — enables multipath TCP 🛣️
- ipv4=on|off — whether to accept IPv4 addresses; defaults to trying both IPv4 and IPv6 🫶
- ipv6=on|off — whether to accept IPv6 addresses; defaults to trying both IPv4 and IPv6 🫶
- reconnect-ms=milliseconds — for a client socket, if the socket gets disconnected, it'll attempt a reconnect after the given number of milliseconds. Setting it 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

-netdev stream,id=str[,server=on|off],addr.type=unix,addr.path=path[,abstract=on|off][,tight=on|off][,reconnect-ms=milliseconds] — same idea, but the connection to another QEMU VM or a proxy goes over a stream oriented unix domain socket 🧚
- server=on|off — if it's on, you're creating a server socket ✨
- addr.path=path — the filesystem path to use 📁
- abstract=on|off — if it's on, this is a Linux abstract socket address 🌀
- tight=on|off — if it's 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 the socket gets disconnected, it'll attempt a reconnect after the given number of milliseconds. Zero disables it. (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] — yep, another one: connect to another QEMU VM or a proxy, but this time using a stream oriented socket file descriptor 🎀
- server=on|off — if it's on, you're creating a server socket ✨
- addr.str=file-descriptor — the file descriptor number to use as a socket 🔢
- reconnect-ms=milliseconds — for a client socket, if it gets disconnected, reconnect is attempted after the given number of milliseconds. Zero disables it. (default: 0) 🔁

-netdev dgram,id=str,remote.type=inet,remote.host=maddr,remote.port=port[,local.type=inet,local.host=addr] — network backend that connects to a multicast address 📡
- remote.host=maddr, remote.port=port — the multicast address 💌
- local.host=addr — specify the host address to send 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] — connect to a multicast address, but over a UDP socket file descriptor 🧡
- remote.host=maddr, remote.port=port — the multicast address 💌
- local.str=file-descriptor — the file descriptor to use to send packets 📤

-netdev dgram,id=str,local.type=inet,local.host=addr,local.port=port[,remote.type=inet,remote.host=addr,remote.port=port] — backend that connects to another QEMU VM or a proxy using a datagram oriented unix domain socket (yes the synopsis says inet here, bestie, we just read it as written 💅)
- local.host=addr, local.port=port — the IP address to use to send the 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] — connect to another QEMU VM or a proxy over a datagram oriented unix socket 🦋
- local.path=path — the filesystem path to use to bind the socket 📁
- remote.path=path — the filesystem path to use as a destination (see sendto(2)) 🎯

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 — connect to another QEMU VM or a proxy using a datagram oriented socket file descriptor ✨
- local.str=file-descriptor — the file descriptor to use 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] — this one configures an L2TPv3 pseudowire host network backend 🔥 and ngl, L2TPv3 (RFC3931) is a popular protocol to transport Ethernet (and other Layer 2) data frames between two systems. It is present in routers, firewalls and the Linux kernel (from version 3.3 onwards) 👑

This transport lets a VM talk directly to another VM, a router, or a firewall. No middleman, no drama. 💫

src=srcaddr — the source address. Mandatory, bestie, you cannot skip this one.
dst=dstaddr — the destination address. Also mandatory. 👑
udp=on — select udp encapsulation. The default is ip.
srcport=srcport — the source udp port.
dstport=dstport — the 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 specification. Their whole job is mostly to stop you from misconfiguring things. By default they're 32 bit.
cookie64=on — set the cookie size to 64 bit instead of the default 32.
counter=off — force a 'cut-down' L2TPv3 with no counter, exactly as in draft-mkonstan-l2tpext-keyed-ipv6-tunnel-00.
pincounter=on — work around broken counter handling on the peer. This may also help on networks where packets get reordered. 🫶
offset=offset — add an extra offset between the header and the data.

Okay so, 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 that connects 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: this option only exists if QEMU was 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] — set up an AF_XDP backend that connects to a network interface name using an AF_XDP socket. You can force a specific program attach mode for a default XDP program with mode; it defaults to best-effort, where the likely most performant mode gets used. The number of queues n should generally match the number of queues on the interface, and defaults to 1. Traffic arriving on non-configured device queues will not be delivered to the network backend. 💀

# 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 you want a particular range of queues [m, m + n] to be in use. For example, this may be necessary in order to use certain NICs in native mode. The kernel lets the driver create a separate set of XDP queues on top of the regular ones, and only these queues can be used for AF_XDP sockets. NICs that work this way may also need an extra 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
ethtool -N eth0 flow-type ether \
    dst 00:00:00:00:00:01 m FF:FF:FF:FF:FF:FE action 1
# launch QEMU instance
qemu-system-x86_64 linux.img -device virtio-net-pci,netdev=n1 \
    -netdev af-xdp,id=n1,ifname=eth0,queues=1,start-queue=1

The XDP program can also be loaded externally. In that case the inhibit option should be set to on. Either sock-fds or map-path can be used while inhibit is enabled. sock-fds can be provided with file descriptors for already open but not bound XDP sockets that are already added to a socket map for the corresponding queues. One socket per queue.

qemu-system-x86_64 linux.img -device virtio-net-pci,netdev=n1 \
    -netdev af-xdp,id=n1,ifname=eth0,queues=3,inhibit=on,sock-fds=15:16:17

For the inhibit option set to on used together with map-path, it's expected that the XDP program with the socket map is already loaded on the networking device and the map is pinned into the BPF file system. The path to the pinned map then gets passed to QEMU, which creates the file descriptors and inserts them into the existing socket map. ✨

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

Also, map-start-index can be used to specify the start offset for insertion into the socket map. The combination of map-path and sock-fds together is not supported.

-netdev vhost-user,chardev=id[,vhostforce=on|off][,queues=n] — establish a vhost-user netdev, backed by a chardev id. That chardev should be a unix domain socket backed one. 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, the feature can be forced with vhostforce. Use queues=n to specify the number of queues to be created for multiqueue vhost-user. 🔥

Example:

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] — establish a vhost-vdpa netdev.

A vDPA device is a device that uses a datapath which complies with the virtio specifications, with a vendor specific control path. vDPA devices can be physically located on the hardware or emulated by software. 🦋

-netdev hubport,id=id,hubid=hubid[,netdev=nd] — create 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. Alternatively, you can also connect the hubport to another netdev with ID nd by using the netdev=nd option. 🌸

-net nic[,netdev=nd][,macaddr=mac][,model=type][,name=name][,addr=addr][,vectors=v] — the legacy 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 (aka the default hub), or to the netdev nd. If model is omitted, then the default NIC model associated with the machine type gets used. Note that the default NIC model may change in future QEMU releases, so it's highly recommended to always specify a model. 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's 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

Okay so bestie, plot twist: you can have more than one multiplexer in a single system configuration 💅 like, actually. 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 get 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.

Also bestie, heads up 🚨 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. Not me learning that the hard way 😭.

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 the chardev hub aggregator device configuration. It's giving ✨foreshadowing✨.

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. Tiny but mighty, fr fr.

✨ 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 the chillest guy here, does absolutely nothing and slays at it.
-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. (Yeah, don't do that 🙈.)

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. (So like, zero is the ✨default vibe✨.)

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 🚫 (iconic behaviour honestly, no vibes-based auth here).

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 species 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 is 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 specifies the port on the remote host to connect to. port is required.

localaddr specifies the local address to bind to. If not specified it defaults to 0.0.0.0.

localport specifies the local port to bind to. If not specified any available local port will be used.

ipv4=on|off and ipv6=on|off specify that either IPv4 or IPv6 must be used. If neither is specified the device may use either protocol.

-chardev msmouse,id=id — Forward QEMU's emulated msmouse events to the guest 🐭. msmouse does not take any options.
-chardev hub,id=id,chardevs.0=id[,chardevs.N=id] — Explicitly create a chardev backend hub device 👑 with the possibility to aggregate input from multiple backend devices and forward it to a single frontend device. Additionally, hub device takes the output from the frontend device and sends it back to all the connected backend devices. This allows for seamless interaction between different backend devices and a single frontend interface. Aggregation supported for up to 4 chardev devices. (Since 10.0)

For example, the following is a use case of 2 backend devices: virtual console vc0 and a pseudo TTY pty0 connected to a single virtio hvc console frontend device with a hub hub0 help. Virtual console renders text to an image, which can be shared over the VNC protocol. In turn, pty backend provides bidirectional communication to the virtio hvc console over the pseudo TTY file. The example configuration can be as follows:

-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 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

Several frontend devices is not supported. Stacking of multiplexers and hub devices is not supported as well. Sorry bestie, the limit is real 😔.

-chardev vc,id=id[[,width=width][,height=height]][[,cols=cols][,rows=rows]] — Connect to a QEMU text console. vc may optionally be given a specific size.

width and height specify the width and height respectively of the console, in pixels.

cols and rows specify that the console be sized to fit a text console with the given dimensions.

-chardev ringbuf,id=id[,size=size] — Create a ring buffer 💫 with fixed size size. size must be a power of two and defaults to 64K.
-chardev file,id=id,path=path[,input-path=input-path] — Log all traffic received from the guest to a file 📝.

path specifies the path of the file to be opened. This file will be created if it does not already exist, and overwritten if it does. path is required.

If input-path is specified, this is the path of a second file which will be used for input. If input-path is not 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 — Create a two-way connection to the guest 🚰. The behaviour differs slightly between Windows hosts and other hosts:

On Windows, a single duplex pipe will be created at \\.pipe\path.

On other hosts, 2 pipes will be 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. (You gotta do it yourself bestie, QEMU isn't your mom 💅.)

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

-chardev console,id=id — Send traffic from the guest to QEMU's standard output 🖥️. console does not take any options.

console is only available on Windows hosts.

-chardev serial,id=id,path=path — Send 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.

path specifies the name of the serial device to open.

-chardev pty,id=id[,path=path] — Create a new pseudo-terminal on the host and connect to it 🌸.

pty is not available on Windows hosts.

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. (Convenience? We love her 💖.)

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. So like, go clean up after it, bestie 🧹.

-chardev stdio,id=id[,signal=on|off] — Connect to standard input and standard output of the QEMU process 🫶.
signal — controls if signals are enabled on the terminal, and bestie that includes exiting QEMU with the key sequence Control-c. It's on by default, so if you want it gone, hit it with signal=off. 💅
braille,id=id — connect to a local BrlAPI server. braille takes literally zero options, she's low maintenance. 🎀
parallel,id=id,path=**path — connect to a local parallel port.

parallel is only available on Linux, FreeBSD and DragonFlyBSD hosts. Sorry to everyone else, it's giving platform-exclusive. 🙈

path is the path to the parallel port device, and yeah, path is required. No path, no port, no vibes.

spicevmc,id=id,debug=debug,name=name — only available when spice support is built in, ok?

debug is the debug level for spicevmc.

name is the name of the spice channel to connect to.

This one connects to a spice virtual machine channel, like vdiport. ✨

spiceport,id=id,debug=debug,name=name — only available when spice support is built in.

debug is the debug level for spicevmc.

name is the name of the spice port to connect to.

Connect to a spice port, which lets a Spice client 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]

Whichever backend type you pick is gonna determine the applicable options, no cap. The -tpmdev option creates the TPM backend, and it requires a -device option that specifies the TPM frontend interface model. They're a package deal, fr fr. 💖

Run -tpmdev help to print out all the available TPM backend types.

The available backends are:

passthrough,id=id,path=path,cancel-path=cancel-path — (Linux-host only) enable access to the host's TPM using the passthrough driver. 👑

path specifies the path to the host's TPM device — so on a Linux host this would be /dev/tpm0. path is optional and by default /dev/tpm0 is used.

cancel-path specifies the path to the host TPM device's sysfs entry that allows 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, and bestie, read these:

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 — like letting the user 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 the following 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. Don't skip that part, she's important. 🎀

emulator,id=id,chardev=**dev — (Linux-host only) enable 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 the 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, and honestly? Pick your fighter:

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 be 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.

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. No improvising. 💅

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 in which the kernel is started — what address it's loaded at, what if any information is passed to it via CPU registers, the state of the hardware when it's started, and so on — is also architecture specific. Typically it follows the specification laid down by the Linux kernel for how kernels for that architecture must be started. Iykyk. ✨

-kernel bzImage — use bzImage as kernel image. The kernel can be either a Linux kernel or in multiboot format.
-shim shim.efi — use 'shim.efi' to boot the kernel.
-append cmdline — use cmdline as kernel command line.
-initrd file — use file as initial ram disk.
-initrd "file1 arg=foo,file2" — this syntax is only available with multiboot.

Use file1 and file2 as modules and pass arg=foo as parameter to the first module. Commas can be provided in module parameters by doubling them on the command line to escape them. 🎀

-initrd "bzImage earlyprintk=xen,,keep root=/dev/xvda1,initrd.img" — Multiboot only. 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 pass it to the kernel on boot.

Finally you can also manually load images directly into the address space of the guest. This is most useful for developers who already know the layout of their guest and take care to ensure something sane will happen when the reset vector executes. Main character energy only. 👑

The generic loader can be invoked by using the loader device:

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

There is also the guest loader which operates in a similar way but tweaks the DTB so 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 💀

-compat [deprecated-input=@var{input-policy}][,deprecated-output=@var{output-policy}] — set the policy for handling deprecated management interfaces (experimental):
- 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
- 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. 🙈

-compat [unstable-input=@var{input-policy}][,unstable-output=@var{output-policy}] — set the policy for handling unstable management interfaces (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: covers only syntactic aspects of QMP.

-fw_cfg [name=]name,file=**file — add a named fw_cfg entry with contents from file file. If the filename contains a comma, you must double it (for instance, "file=my,,file" to use file "my,file"). ✨
-fw_cfg [name=]name,string=**str — add a named fw_cfg entry with contents from string str. If the string contains a comma, you must double it (for instance, "string=my,,string" to use file "my,string").

The terminating NUL character of the contents of str will not be included as part of the fw_cfg item data. To insert contents with embedded NUL characters, you have to use the file parameter. 💅

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

Example:

-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. Ate. 🎀

-serial dev — redirect the virtual serial port to host character device dev. The default device is vc in graphical mode and stdio in non graphical mode.

This option can be used several times to simulate multiple serial ports. 🌸

You can use -serial none to suppress the creation of default serial devices.

Available character devices are:

vc[:WxH] — virtual console. Optionally, a width and height can be given in pixel with

vc:800x600

It is 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. 🦋

that way you never have to go poke QMP or HMP monitor queries to find out what the new PTY device path is. genuinely such a slay.

🚨 okay but listen: QEMU will remove the symlink when it exits gracefully — but it will not do that in case of crashes or on certain startup errors. so the recommendation is that you check and remove the symlink yourself after QEMU terminates, to account for that. bestie please actually do this 💅

`none`

No device is allocated, periodt. BUT — heads up — for machine types that 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. And for boards where the number of serial ports is truly variable? This suppresses the creation of the device entirely. 🫶

`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. it's giving void, it's giving the abyss staring back, and honestly? iconic. 🕳️✨

`chardev:id`

Use a named character device that you defined with the -chardev option. mix and match, bestie. 🎀

`/dev/XXX`

[Linux only] Use a 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. so it's a one-way street, we're writing and not reading, and that's just the vibe. 📝

`stdio`

[Unix only] standard input/output. the classic. the blueprint. 👑

`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. cute, right? 🌸

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

lowkey a whole pipeline, highkey obsessed. 🔥

`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 Control-] and then type "send break" followed by pressing the enter key. 💫

`websocket:host:port,server=on[,wait=on|off][,nodelay=on|off]`

The WebSocket protocol is used instead of raw tcp socket. The port acts as a WebSocket server. Client mode is not supported. so server girlies only, sorry bestie 😭

`unix:path[,server=on|off][,wait=on|off][,reconnect-ms=milliseconds]`

A unix domain socket is used instead of a tcp socket. The option works the same as if you had specified -serial tcp, except the unix domain socket path is used for connections. 🐍

`mon:dev_string`

This is a special option to allow the monitor to be multiplexed onto another serial port. The monitor is accessed with key sequence of Control-a and then pressing c. dev_string should be any one of the serial devices specified above.

An example to multiplex the monitor onto a telnet server listening on port 4444 would be:

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

⚠️ When the monitor is multiplexed to stdio in this way, Ctrl+C will not terminate QEMU any more but will be passed to the guest instead. so like. don't panic when ctrl+c stops working. it's not broken, it's ✨feature✨

`braille`

Braille device. This will use BrlAPI to display the braille output on a real or fake device. accessibility queen 👑💜

`msmouse`

Three button serial mouse. Configure the guest to use Microsoft protocol. 🐭

`-parallel dev`

Redirect the virtual parallel port to host device dev (same devices as the serial port). On Linux hosts, /dev/parportN can be used to use hardware devices connected on the corresponding host parallel port. 🖨️

This option can be used several times to simulate up to 3 parallel ports.

Use -parallel none to disable all parallel ports.

`-monitor dev`

Redirect the monitor to host device dev (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 the default monitor. 🎛️

`-qmp dev`

Like -monitor but opens in 'control' mode. For example, to make QMP available on localhost port 4444:

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

🫣 Not all options are configurable via this syntax; for maximum flexibility use the -mon option and an accompanying -chardev.

`-qmp-pretty dev`

Like -qmp but uses pretty JSON formatting. it's giving readable, it's giving aesthetically pleasing JSON, we love to see it 💅✨

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

Set up a monitor connected to the chardev name. QEMU supports two monitors: the Human Monitor Protocol (HMP; for human interaction), and the QEMU Monitor Protocol (QMP; a JSON RPC-style protocol). The default is HMP; mode=control selects QMP instead.

pretty is only valid when mode=control, turning on JSON pretty printing to ease human reading and debugging. 🌈

For example:

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

enables the QMP monitor on localhost port 4444 with pretty-printing. obsessed with this for us. 🫶

`-debugcon dev`

Redirect the debug console to host device dev (same devices as the serial port). The debug console is an I/O port which is typically port 0xe9; writing to that I/O port sends output to this device. The default device is vc in graphical mode and stdio in non graphical mode. 🐞

`-pidfile file`

Store the QEMU process PID in file. It is useful if you launch QEMU from a script. scripts stay winning 📜

`--preconfig`

Pause QEMU for interactive configuration before the machine is created, which allows querying and configuring properties that will affect machine initialization. Use QMP command 'x-exit-preconfig' to exit the preconfig state and move to the next state (i.e. run guest if -S isn't used, or pause the second time if -S is used).

🧪 This option is experimental. tread carefully bestie

`-S`

Do not start CPU at startup (you must type 'c' in the monitor). ✋🛑

`-overcommit mem-lock=on|off|on-fault`

`-overcommit cpu-pm=on|off`

Run qemu with hints about host resource overcommit. The default is to assume that host overcommits all resources.

Locking qemu and guest memory can be enabled via mem-lock=on or mem-lock=on-fault (disabled by default). This works when host memory is not overcommitted and reduces the worst-case latency for guest. The on-fault option is better for reducing the memory footprint since it makes allocations lazy, but the pages still get locked in place once faulted by the guest or QEMU.

💀 Note that the two options are mutually exclusive. pick ONE, bestie, not both

Guest ability to manage power state of host cpus (increasing latency for other processes on the same host cpu, but decreasing latency for guest) can be enabled via cpu-pm=on (disabled by default). This works best when host CPU is not overcommitted. When used, host estimates of CPU cycle and power utilization will be incorrect, not taking into account guest idle time. 😴⚡

-gdb dev — bestie, this lets QEMU accept a gdb connection on the device dev (peep the "GDB usage" chapter in the System Emulation Users Guide for the full lore 💖).

⚠️ not me forgetting this — this option does NOT pause QEMU's execution. If you want QEMU to not start the guest until you connect with gdb and issue a continue command, you also have to pass the -S option to QEMU. Two flags, one job, no cap 💅

The most usual configuration is to listen on a local TCP socket:

-gdb tcp::3117

but you can specify other backends too — 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, i.e. open a gdbserver on TCP port 1234 (again, see the "GDB usage" chapter in the System Emulation Users Guide 🔥).
-d item1[,...] — turn on logging for the items you name ✨. Run -d help for a list of log items.
-D logfile — output the log in logfile instead of to stderr 🫶.
-dfilter range1[,...] — filter debug output down to only the stuff 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 you need. Like:

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

This will dump output for any code in the 0x1000 sized block starting at 0x8000, the 0x200 sized block starting at 0xffffffc000080000, and another 0x1000 sized block starting at 0xffffffc00005f000. 🎀

-seed number — force the guest to use a deterministic pseudo-random number generator, seeded with number. Lowkey important: this does not affect crypto routines within the host 🙈.
-L path — set the directory for the BIOS, VGA BIOS and keymaps. Want to list all the data directories? Just use -L help 💜.
-enable-kvm — enable KVM full virtualization support. Heads up, this option is only available if KVM support is enabled when compiling 🌈.
-xen-domid id — specify the 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). ✨
-no-reboot — exit instead of rebooting. periodt.
-no-shutdown — don't exit QEMU on guest shutdown; instead only stop the emulation. This lets you, for instance, switch to the monitor to commit changes to the disk image 👑.
-action event=action — the action parameter serves to modify QEMU's default behavior when certain guest events occur. It's the generic method for specifying the same behaviors that get modified by the -no-reboot and -no-shutdown parameters 💫.

Examples:

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

-loadvm file — start right away with a saved state (that's loadvm in the monitor, iykyk).
-daemonize — daemonize the QEMU process after initialization. QEMU will not detach from standard IO until it's ready to receive connections on any of its devices. This option is a super useful way for external programs to launch QEMU without having to cope with initialization race conditions 🦋.
-option-rom file — load the contents of file as an option ROM. This option is useful 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 a correct date in MS-DOS or Windows. To 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. This allows using the RTC as an accurate reference clock inside the guest, specifically if the host time is smoothly following an accurate external reference clock, e.g. via NTP. If you want to isolate the guest time from the host, you can set clock to rt instead, which provides a host monotonic clock if the host supports it. To even prevent the RTC from progressing during suspension, you can set clock to vm (virtual clock). clock=vm is recommended especially in icount mode in order to preserve determinism — however, 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 experience time drift problems, specifically with Windows' ACPI HAL. This option will try to figure out how many timer interrupts were not processed by the Windows guest and will re-inject them 🔥.

-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 ⏱️.

Note that while this option can give deterministic behavior, it does not provide cycle accurate emulation. Modern CPUs contain superscalar out of order cores with complex cache hierarchies. The number of instructions executed often has little or no correlation with actual performance. no cap.

When the virtual cpu is sleeping, the virtual time will advance at default speed unless sleep=off is specified. With sleep=off, the virtual time will jump to the next timer deadline instantly whenever the virtual cpu goes to sleep mode and will not advance if no timer is enabled. This behavior gives deterministic execution times from the guest point of view. The default if icount is enabled is sleep=on. sleep=off cannot be used together with either shift=auto or align=on 🚫.

align=on will activate the delay algorithm which will try to synchronise the host clock and the virtual clock. The goal is to have a guest running at the real frequency imposed by the shift option. Whenever the guest clock is behind the host clock and if align=on is specified then 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 this happens when the shift value is high (how high depends on the host machine). The default if icount is enabled is align=off 💖.

When the rr option is specified deterministic record/replay is enabled. The rrfile= option must also be provided to specify the path to the replay log. In record mode data is written to this file, and in replay mode it is read back. If the rrsnapshot option is given then 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 will do when the watchdog timer expires. The default is reset (forcefully reset the guest). Other possible actions are: shutdown (attempt to gracefully shutdown the guest), poweroff (forcefully poweroff the guest), inject-nmi (inject a NMI into the guest), pause (pause the guest), debug (print a debug message and continue), or none (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 — and thus -watchdog-action shutdown is not recommended for production use. fr fr, don't do it.

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 0x01 when using the -nographic option. 0x01 is equal to pressing Control-a. You can select a different character from the ascii control keys, where 1 through 26 map to Control-a through Control-z 🎀. For instance you could use either of the following to change the escape character to Control-t:

-echr 0x14; -echr 20

The -incoming 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. The offset allows the common size suffixes, or a 0x prefix, but not both 🚫.
-incoming exec:cmdline — accept incoming migration as an output from the 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 — okay so this one is the strict bouncer of the club 💅 only migratable devices get to come in. If a device would try to enter an unmigratable state, it simply will not be allowed to. periodt.
-nodefaults — bestie, by default QEMU is out here doing the MOST and setting up a whole lil starter pack of devices for you: serial port, parallel port, virtual console, monitor device, VGA adapter, floppy and CD-ROM drive, and others. This option says "no thank you, I'll build my own" and disables all those default devices. iconic honestly 🎀
-prom-env variable=value — sets an OpenBIOS nvram variable to the value you give it. PPC and SPARC only iykyk.

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 — turns on Semihosting mode. ARM, M68K, Xtensa, MIPS, RISC-V only ✨

⚠️ warning bestie, listen to me: this lets the guest have direct access to the host filesystem. So only ever do this with a trusted guest OS, fr fr. Do not play with this one.

For the deets on what facilities this unlocks, go read the -semihosting-config option docs below 🫶

-semihosting-config [enable=on|off][,target=native|gdb|auto][,chardev=id][,userspace=on|off][,arg=str[,...]] — enables AND configures Semihosting. ARM, M68K, Xtensa, MIPS, RISC-V only 🌸

⚠️ same warning as above, no cap: this gives the guest direct access to the host filesystem, so only use it with a trusted guest OS.

target=native|gdb|auto — says where the semihosting calls get addressed: to QEMU itself (native) or to GDB (gdb). Default is auto, which means it's gdb during debug sessions and native the rest of the time. main character behavior honestly 👑
chardev=str1 — sends the output to a chardev backend output for native or auto output when you're not in gdb.
userspace=on|off — lets code running in guest userspace touch the semihosting interface. By default, only privileged guest code can make semihosting calls. And heads up: setting userspace=on should only be done if all guest code is trusted (like, bare-metal test case code kinda trusted). Don't be reckless 💀
arg=str1,arg=str2,... — lets you pass input arguments, and you can use it multiple times to build up a whole list. The old-style -kernel/-append way of passing a command line is still supported for backward compatibility. And if you specify both --semihosting-config arg and -kernel/-append? The former gets passed to semihosting, because it always takes precedence ✨

-sandbox arg[,obsolete=string][,elevateprivileges=string][,spawn=string][,resourcecontrol=string] — enables Seccomp mode 2 system call filter. 'on' turns syscall filtering on and 'off' turns it off. Default is 'off'.
- obsolete=string — enables Obsolete system calls.
- elevateprivileges=string — disables the set*uid|gid system calls.
- spawn=string — disables *fork and execve.
- resourcecontrol=string — disables process affinity and schedular priority.
-readconfig file — reads device configuration from file. This approach is genuinely so useful when you wanna spawn a QEMU process with a ton of command line options but you don't wanna exceed the command line character limit. bye to that problem 🦋
-no-user-config — makes QEMU not load any of the user-provided config files on sysconfdir. simple as that 💅
-trace [[enable=]pattern][,events=file][,file=file] — specify tracing options ✨
- [enable=]PATTERN — immediately enables events matching PATTERN (either an 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, just pass the -trace option multiple times. And pro tip: use -trace help to print a list of names of trace points 👑
- events=FILE — immediately enables 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. Only available if QEMU was compiled with the simple, log or ftrace tracing backend.
- file=FILE — logs output traces to FILE. Only available if QEMU was compiled with the simple tracing backend.
-plugin file=file[,argname=argvalue] — load a plugin 💖
- file=file — loads the given plugin from a shared library file.
- argname=argvalue — an argument passed to the plugin. (Can be given multiple times.)
-run-with [async-teardown=on|off][,chroot=dir][,exit-with-parent=on|off][,user=username|uid:gid] — sets QEMU process lifecycle options 🌈
- async-teardown=on enables asynchronous teardown. A new process called "cleanup/<QEMU_PID>" gets created at startup, sharing the address space with the main QEMU process, using clone. It waits for the main QEMU process to terminate completely, and then it exits. This lets QEMU terminate very quickly even if the guest was huge, leaving the teardown of the address space to the cleanup process. And since the cleanup process shares the same cgroups as the main QEMU process, accounting is performed correctly. The catch tho: this only works if the cleanup process isn't forcefully killed with SIGKILL before the main QEMU process has terminated completely. don't do that 🙈
- chroot=dir can be used for doing a chroot to the specified directory immediately before starting the guest execution. This is especially useful in combination with user=....
- exit-with-parent=on causes QEMU to exit if the parent process of QEMU exits. You'd use this when QEMU runs a captive appliance, where the lifetime of the appliance is scoped to the parent process. And if the parent process crashes, QEMU still gets cleaned up. Only works on Linux, FreeBSD and macOS platforms.
- user=username or user=uid:gid can be used to drop root privileges before starting guest execution. QEMU will use the setuid and setgid system calls to switch to the specified identity. Note that 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. the more u know 🌟
-msg [timestamp[=on|off]][,guest-name[=on|off]] — controls 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 only if the -name guest option is set, otherwise the option is just ignored. Default is off.
-dump-vmstate file — dumps json-encoded vmstate information for the current machine type to file. 🍓
-enable-sync-profile — enables synchronization profiling. that's it, that's the whole vibe ✨
-perfmap — generates a map file for Linux perf tools that lets basic profiling information be broken down into basic blocks. so cool 🔥
-jitdump — generates a dump file for Linux perf tools that maps basic blocks to symbol names, line numbers and JITted code. obsessed with the detail honestly 💜

💖 Generic object creation 💖

-object typename[,prop1=value1,...] — creates a new object of type typename, setting properties in the order they're specified. Heads up bestie: the 'id' property must be set. These objects get 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. iconic 🎀

The id parameter is a unique ID that'll be used to reference this memory region in other parameters, like -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. so don't count on it 💀

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 🌈

align — sets the base address alignment for when QEMU does its mmap(2) thing on mem-path, and bestie it takes the usual suffixes, so like 2M is totally valid ✨. Some backends you point at with mem-path need a different alignment than the default QEMU rolls with — example: the device DAX /dev/dax0.0 needs 2M alignment, not 4K. So in those cases you just tell it what alignment you need via this option. 🎀
offset — the offset into the target file where the region starts. Use this when you wanna back multiple regions off of a single file. one file, many regions, it's giving efficiency 💅
pmem — says whether the backing file from mem-path lives in host persistent memory that you can get at through the SNIA NVM programming model (think Intel NVDIMM). If pmem is on, QEMU does the necessary little operations to guarantee its own writes to mem-path actually persist (like in vNVDIMM label emulation and live migration). Also it maps the backend-file with the MAP_SYNC flag, which keeps the file metadata in sync for mem-path in case the host crashes or the power dies 😭. Heads up: MAP_SYNC needs support from both the host kernel (since Linux kernel 4.15) and the filesystem of mem-path mounted with the DAX option.
readonly — whether the backing file gets opened read-only or read-write. (default is read-write, fyi)
rom — whether to create Read Only Memory (ROM) that the VM cannot modify, periodt. Any write attempt to that ROM gets denied 🚫. Most use cases want proper RAM, not ROM. But some selected use cases, like R/O NVDIMMs, lowkey benefit from ROM. If set to on, create ROM; if off, create writable RAM; if auto (the default), the value of the readonly option is used. This one is mainly helpful when you want writable RAM in configs that would traditionally create ROM before the rom option even existed — VM templating, where you wanna open a file readonly (readonly=on) and mark the memory private for QEMU (share=off). For that use case you need writable RAM instead of ROM, and you also wanna set rom=off. 💖

✨ `-object` ✨ (the saga continues)

🫶 `-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 give you way more control than the -m option that's traditionally used to define guest RAM. For a description of the options, go peek at memory-backend-file. 👑

🦋 `-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 lets QEMU share the memory with an external process (like when you're using vhost-user). The memory is allocated with memfd and optional sealing. (Linux only, sorry bestie 💀)

seal — creates a sealed-file, which blocks any further resizing of the memory (on by default).
hugetlb — specifies that the file being created lives in the hugetlbfs filesystem (since Linux 4.14). Used together with the hugetlb option, the hugetlbsize option specifies the hugetlb page size on systems that support multiple hugetlb page sizes (it must be a power of 2 value supported by the system).

ngl, in some versions of Linux the hugetlb option is incompatible with the seal option (needs at least Linux 4.16). 🙈

For the other options, refer to memory-backend-file.

Oh and 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 lets QEMU 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. So it can be used on any POSIX system, especially when memfd isn't supported. 🌈

For a description of the options, refer to memory-backend-file.

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. no cap 🚫

💜 `-object iommufd,id=id[,fd=fd]`

Creates an iommufd backend which allows control of DMA mapping through the /dev/iommu device.

id — a unique ID which frontends (such as vfio-pci of vdpa) will use to connect with the iommufd backend.
fd — an optional pre-opened file descriptor resulting from /dev/iommu opening. Usually the iommufd is shared across all subsystems, which brings the benefit of centralized reference counting. iconic 🎀

🎲 `-object rng-builtin,id=id`

Creates a random number generator backend which obtains entropy from QEMU builtin functions. The id parameter is a unique ID that will be used to reference this entropy backend from the virtio-rng device. By default, the virtio-rng device uses this RNG backend. 💅

🎲 `-object rng-random,id=id,filename=/dev/random`

Creates a random number generator backend which obtains entropy from a device on the host. The id parameter is a unique ID that will be used to reference this entropy backend from the virtio-rng device. The filename parameter specifies which file to obtain entropy from, and if you omit it, it defaults to /dev/urandom. ✨

🎲 `-object rng-egd,id=id,chardev=chardevid`

Creates a random number generator backend which obtains entropy from an external daemon running on the host. The id parameter is a unique ID that will be used to reference this entropy backend from the virtio-rng device. The chardev parameter 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 can be used to provide TLS support on network backends. The id parameter is a unique ID which network backends will use to access the credentials. The endpoint is either server or client, depending on whether the QEMU network backend using the credentials will be acting as a client or as a server. If verify-peer is enabled (it's the default), then once the handshake is done, the peer credentials get verified — though for anonymous credentials this is a no-op. 😌

The dir parameter tells QEMU where to find the credential files. For server endpoints, this directory may contain a file dh-params.pem providing diffie-hellman parameters to use for the TLS server. If the file is missing, QEMU will generate a set of DH parameters at startup. That's a computationally expensive operation that consumes random pool entropy, so it's recommended that you generate a persistent set of parameters upfront and save them. 💾

🔐 `-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 can be used to provide TLS support on network backends. The id parameter is a unique ID which network backends will use to access the credentials. The endpoint is either server or client, depending on whether the QEMU network backend using the credentials will be acting as a client or as a server. For clients only, username is the username which will be sent to the server. If you omit it, it defaults to "qemu".

The dir parameter tells QEMU where to find the keys file. It's called "dir/keys.psk" and contains "username:key" pairs. This file can most easily be created using the GnuTLS psktool program. 🛠️

For server endpoints, dir may also contain a file dh-params.pem providing diffie-hellman parameters to use for the TLS server. If the file is missing, QEMU will generate a set of DH parameters at startup. This is a computationally expensive operation that consumes random pool entropy, so it's recommended that a persistent set of parameters be generated upfront and saved. 🔥

🔐 `-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, which can be used to provide TLS support on network backends. The id parameter is a unique ID which network backends will use to access the credentials. The endpoint is either server or client, depending on whether the QEMU network backend using the credentials will be acting as a client or as a server. If verify-peer is enabled (it's the default), then once the handshake is completed, the peer credentials will be verified. With x509 certificates, this implies that the clients must be provided with valid client certificates too. 👑

okay bestie, we were literally mid-sentence in the -object tls-creds-x509 glow-up, so let's keep that thread going 💅

The dir parameter is the lil map that tells QEMU where to find the credential files. For server endpoints, this directory may contain a file called dh-params.pem, which hands over the diffie-hellman parameters to use for the TLS server. If that file is missing? QEMU just generates a set of DH parameters at startup. But no cap — that is a computationally expensive operation and it eats up random pool entropy, so the recommendation is fr fr: generate a persistent set of parameters upfront and save them. Your future self will thank you 🫶

For x509 certificate credentials, the directory is gonna hold even more files with the x509 certificates. The certificates must be stored in PEM format, in these exact filenames:

ca-cert.pem
ca-crl.pem (optional)
server-cert.pem (only servers)
server-key.pem (only servers)
client-cert.pem (only clients)
client-key.pem (only clients)

For the server-key.pem and client-key.pem files which contain sensitive private keys 😭 it is possible to use an encrypted version by providing the passwordid parameter. That gives the ID of a previously created secret object containing the password for decryption. Locked down, iconic 🔐

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

-object tls-cipher-suites ✨

-object tls-cipher-suites,id=id,priority=priority

Creates a TLS cipher suites object, which can be used to control the TLS cipher/protocol algorithms that applications are permitted to use. Controlling the vibes, literally 💅

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

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

An example of use of this object is to control 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. 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 🌸

-object filter-buffer,id=id,netdev=netdevid,interval=t[,queue=all|rx|tx][,status=on|off][,position=head|tail|id=<id>][,insert=behind|before]

Interval t can't be 0, okay? This filter batches the packet delivery: all packets arriving in a given interval on netdev netdevid are delayed until the end of the interval. Interval is in microseconds. status is optional and indicates whether the netfilter is on (enabled) or off (disabled), and the default status for netfilter will be on.

queue all|rx|tx is an option that can be applied to any netfilter.

all: the filter is attached both to the receive and the transmit queue of the netdev (default).
rx: the filter is attached to the receive queue of the netdev, where it will receive packets sent to the netdev.
tx: the filter is attached to the transmit queue of the netdev, where it will receive 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.
tail: the filter is inserted at the tail of the filter list, behind any existing filters (default).
id=<id>: the filter is inserted before or behind the filter specified by <id>, see the insert option below.

insert behind|before is an option to specify where to insert the new filter relative to the one specified with position=id=<id>. It can be applied to any netfilter.

before: insert before the specified filter.
behind: insert behind the specified filter (default).

-object filter-mirror 🦋

-object filter-mirror,id=id,netdev=netdevid,outdev=chardevid,queue=all|rx|tx[,vnet_hdr_support][,position=head|tail|id=<id>][,insert=behind|before]

filter-mirror on netdev netdevid, mirrors net packet to chardev chardevid. If it has the vnet_hdr_support flag, filter-mirror will mirror packet with vnet_hdr_len. Reflections, but make it network 🌈

-object filter-redirector 🎀

-object filter-redirector,id=id,netdev=netdevid,indev=chardevid,outdev=chardevid,queue=all|rx|tx[,vnet_hdr_support][,position=head|tail|id=<id>][,insert=behind|before]

filter-redirector on netdev netdevid, redirect filter's net packet to chardev chardevid, and redirect indev's packet to filter. If it has the vnet_hdr_support flag, filter-redirector will redirect packet with vnet_hdr_len.

heads up bestie: to create a filter-redirector we need to differ outdev id from indev id, id can not be the same. We can just use indev or outdev, but at least one of indev or outdev needs to be specified.

-object filter-rewriter 💜

-object filter-rewriter,id=id,netdev=netdevid,queue=all|rx|tx,[vnet_hdr_support][,position=head|tail|id=<id>][,insert=behind|before]

Filter-rewriter is a part of COLO project. It will rewrite tcp packet to secondary from primary to keep secondary tcp connection, and rewrite tcp packet to primary from secondary make tcp packet can be handled by client. If it has the vnet_hdr_support flag, we can parse packet with vnet header.

usage: colo secondary:

-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

-object filter-dump 🍓

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

Dump the network traffic on netdev dev to the file specified by filename. At most len bytes (64k by default) per packet are stored. The file format is libpcap, so it can be analyzed with tools such as tcpdump or Wireshark. Evidence collection, but make it slay 🔥

-object 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=@var{ms}][,expired_scan_cycle=@var{ms}][,max_queue_size=@var{size}]

Colo-compare gets packet from primary_in chardevid and secondary_in, then compares whether the payload of primary packet and secondary packet are the same. If same, it will output primary packet to out_dev, else it will notify COLO-framework to do checkpoint and send primary packet to out_dev. In order to improve efficiency, we need to put the task of comparison in another iothread. If it has the vnet_hdr_support flag, colo compare will send/recv packet with vnet_hdr_len.

The <compare_timeout=@var{ms>} determines the maximum time of the colo-compare hold the packet. The <expired_scan_cycle=@var{ms>} is to set the period of scanning expired primary node network packets. The <max_queue_size=@var{size>} is to set the max compare queue size depend on user environment. If user wants to use Xen COLO, they need to add the notify_dev to notify Xen colo-frame to do checkpoint.

COLO-compare must be used with the help of filter-mirror, filter-redirector and filter-rewriter. No going solo, it's a group project 💀

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

and bestie, we are SO not done yet — there is more coming, don't you dare close the tab 🫶✨

and the secondary: half of the COLO setup gets its own lil stack, no gatekeeping 👇

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 🧚

bestie, the Xen version is a whole different beast, and honestly? it's giving main character energy. here's the primary side:

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

and the secondary side keeps it cute and simple:

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

If you want to know the detail of above command line, you can read the colo-compare git log. that's it, that's the tip. go read the git log bestie, i don't make the rules 💅

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

Makes a cryptodev backend that runs crypto operations straight off the QEMU cipher APIs. The id is a unique ID you'll use to point at this cryptodev backend from the virtio-crypto device. The queues param is optional and sets 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 \
  [...]

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

Makes a vhost-user cryptodev backend, backed by a chardev chardevid. The id is a unique ID you'll use 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 param is optional and sets the queue number of 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 \
  [...]

`-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 — a spot to stash a password, an encryption key, or some other sensitive data. You can hand the sensitive data over either directly through the data parameter, or indirectly through the file parameter.

Using the data parameter is insecure unless the sensitive data is encrypted. like, do not do this casually bestie, i'm serious 😭

The sensitive data can be provided in raw format (that's 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. eg, an RBD password can be provided in raw format, even though it will be base64 encoded when passed onto the RBD sever.

For added protection, it is possible to encrypt the data associated with a secret using the AES-256-CBC cipher. Use of encryption is indicated by providing the keyid and iv parameters. The keyid parameter provides the ID of a previously defined secret that contains the AES-256 decryption key. This key should be 32-bytes long and be base64 encoded. The iv parameter provides the random initialization vector used for encryption of this particular secret and should be a base64 encrypted string of the 16-byte IV.

The simplest (insecure) usage is to provide the secret inline:

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

The simplest secure usage is to provide the secret via a file:

# printf "letmein" > mypasswd.txt # QEMU_SYSTEM_MACRO
-object secret,id=sec0,file=mypasswd.txt,format=raw

For greater security, AES-256-CBC should be used. To illustrate usage, consider the openssl command line tool which can encrypt the data. Note that when encrypting, the plaintext must be padded to the cipher block size (32 bytes) using the standard PKCS#5/6 compatible padding algorithm.

First a master key needs to be created in base64 encoding:

# openssl rand -base64 32 > key.b64
# KEY=$(base64 -d key.b64 | hexdump  -v -e '/1 "%02X"')

Each secret to be encrypted needs to have a random initialization vector generated. These do not need to be kept secret:

# openssl rand -base64 16 > iv.b64
# IV=$(base64 -d iv.b64 | hexdump  -v -e '/1 "%02X"')

The secret to be defined can now be encrypted, in this case we're telling openssl to base64 encode the result, but it could be left as raw bytes if desired:

# SECRET=$(printf "letmein" |
           openssl enc -aes-256-cbc -a -K $KEY -iv $IV)

When launching QEMU, create a master secret pointing to key.b64 and specify that to be used to decrypt 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)

`-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]` 👑

Create a Secure Encrypted Virtualization (SEV) guest object, which can be used to provide the guest memory encryption support on AMD processors. slay, encrypted memory, we love to see it 🔥

When memory encryption is enabled, one of the physical address bit (aka the C-bit) is utilized to mark if a memory page is protected. The cbitpos is used to provide the C-bit position. The C-bit position is Host family dependent hence user must provide this value. On EPYC, the value should be 47.

When memory encryption is enabled, we loose certain bits in physical address space. The reduced-phys-bits is used to provide the number of bits we loose in physical address space. Similar to C-bit, the value is Host family dependent. On EPYC, a guest will lose a maximum of 1 bit, so the value should be 1.

The sev-device provides the device file to use for communicating with the SEV firmware running inside AMD Secure Processor. The default device is '/dev/sev'. If hardware supports memory encryption then /dev/sev devices are created by CCP driver.

The policy provides the guest policy to be enforced by the SEV firmware and restrict what configuration and operational commands can be performed on this guest by the hypervisor. The policy should be provided by the guest owner and is bound to the guest and cannot be changed throughout the lifetime of the guest. The default is 0.

If guest policy allows sharing the key with another SEV guest then handle can be use to provide handle of the guest from which to share the key.

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

The kernel-hashes adds the hashes of given kernel/initrd/cmdline to a designated guest firmware page for measured Linux boot with -kernel. The 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 \
    .....

-object igvm-cfg,file=file — bestie, this one builds an IGVM configuration object that sets up the guest's initial state from a file that follows the Independent Guest Virtual Machine (IGVM) file format. 💖

Right now it's only supported by -machine q35 and -machine pc. That's it, that's the whole list, no cap.

The file parameter is where you point at the IGVM file you wanna load. When you hand it over, that IGVM file populates the VM's initial memory and — depending on the platform — it can also define the initial processor state, the memory map and parameters. It's giving ✨foundational✨.

Heads up bestie: the IGVM file is expected to contain the firmware for the VM, so you literally cannot pass an igvm-cfg object alongside other ways of specifying firmware — like the -bios parameter on x86 machines. Pick a lane, babe. 🚫

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 \
    .....

-object authz-simple,id=id,identity=string — creates an authorization object that controls access to network services. 🔐

The identity parameter identifies the user, and its format depends on the network service that the authorization object is associated with. For authorizing based on TLS x509 certificates, the identity must be the x509 distinguished name. And careful — you have to escape any commas in the distinguished name. Don't skip that step, it's giving comma chaos. 😭

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 due to the x509 distinguished name containing whitespace, and the escaping of ','. 💅

-object authz-listfile,id=id,filename=path,refresh=on|off — another authorization object that controls access to network services. 🎀

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 no rules match, then the default policy value gets returned instead. First match wins, periodt.

The rules can either be an exact string match, or they can use the simple UNIX glob pattern matching so wildcards are allowed. 🦋

If refresh is set to true, the file will be monitored and automatically reloaded whenever its content changes. Obsessed with a self-updating ACL ngl.

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 \
    ...

-object authz-pam,id=id,service=string — yet another authorization object that controls access to network services. 🌸

The service parameter provides the name of a PAM service to use for authorization. It requires that a file /etc/pam.d/service exists, to provide the configuration for the account subsystem. (Yes, literally the file named after your service value. Cute.)

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/qemu/vnc.allow — wait, at /etc/pam.d/qemu-vnc that contains:

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

Finally the /etc/qemu/vnc.allow file would contain the list of x509 distinguished names that are permitted access:

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 — okay this one is the main character of scalability. 👑

It creates a dedicated event loop thread that devices can be assigned to. This is known as an IOThread. By default, device emulation happens in vCPU threads or the main event loop thread, and that can become a scalability bottleneck. IOThreads let device emulation and I/O run on other host CPUs. Slay. 🔥

The id parameter is a unique ID that'll be used to reference this IOThread from -device ...,iothread=id. Multiple devices can be assigned to an IOThread. Note that not all devices support an iothread parameter — vibe check your device first.

The query-iothreads QMP command lists IOThreads and reports their thread IDs, so the user can configure host CPU pinning/affinity. 🧚

IOThreads use an adaptive polling algorithm 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. The algorithm's default parameters are suitable for many cases, but they can be adjusted based on knowledge of the workload and/or host device latency.

The poll-max-ns parameter is the maximum number of nanoseconds to busy wait for events. Polling can be disabled by setting this value to 0.
The poll-grow parameter is the multiplier used to increase the polling time when the algorithm detects it's missing events due to not polling long enough.
The poll-shrink parameter is the divisor used to decrease the polling time when the algorithm detects it's spending too long polling without encountering events.
The aio-max-batch parameter is the maximum number of requests in a batch for the AIO engine — 0 means that the engine will use its default.

The IOThread parameters can be modified at run-time using the qom-set command (where iothread1 is the IOThread's id):

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

During the graphical emulation, you can use special key combinations from the following table to change modes. 💅 By default the modifier is Ctrl+Alt (used in the table below), which can be changed with -display suboption mod= where appropriate. For example, -display sdl,grab-mod=lshift-lctrl-lalt changes the modifier key to Ctrl+Alt+Shift, while -display sdl,grab-mod=rctrl changes it to the right Ctrl key. ✨

✨ Multiplexer Keys ✨

okay bestie, these are the combos for when you're kicking it in the QEMU window itself 🫶 — <cyan>Ctrl+Alt+<i>key</i></cyan> vibes:

Ctrl+Alt+f — toggle full screen 💅 go big or go home
Ctrl+Alt++ — enlarge the screen (zoomies ✨)
Ctrl+Alt+- — shrink the screen
Ctrl+Alt+0 — restore the screen's un-scaled dimensions (back to factory vibe 🎀)
Ctrl+Alt+n — switch to virtual console 'n'. the standard console mappings are lowkey iconic:
- 1: Target system display 👑
- 2: Monitor
- 3: Serial port
Ctrl+Alt+g — toggle mouse and keyboard grab 🖱️⌨️

and in the virtual consoles, you can use Ctrl+Up, Ctrl+Down, Ctrl+PageUp and Ctrl+PageDown to move in the back log 🌈 (scrollback strolling, no cap).

🎀 Multiplexer Keys 🎀

so during emulation, if you're using a character backend multiplexer — which is literally the default if you're using -nographic — then several commands are available via an escape sequence 🌸. these key sequences all start with an escape character, which is Ctrl+a by default, but can be changed with -echr. the list below assumes you're using the default 💜.

Ctrl+a h — print this help 🙈 (ur welcome)
Ctrl+a x — exit emulator 💀 bye bestie
Ctrl+a s — save disk data back to file (if -snapshot)
Ctrl+a t — toggle console timestamps ⏰
Ctrl+a b — send break (magic sysrq in Linux) 🔥
Ctrl+a c — rotate between the frontends connected to the multiplexer (usually this switches between the monitor and the console) 🦋
Ctrl+a Ctrl+a — send the escape character to the frontend ✨ (yes, the double tap, main character energy fr fr)

ngl if you forget all of these, just hit Ctrl+a h and the machine will read them back to you. slay. 💖

✨ NOTES ✨

okay bestie so this is the part where we get a lil fancy 🎀 — because you don't have to use boring normal file images for your emulated storage devices. QEMU can also reach out over the network and grab stuff like iSCSI devices. These get specified with a ✨special URL syntax✨.

🌐 iSCSI

iSCSI support lets QEMU access iSCSI resources directly and use them as images for the guest storage. Both disk and cdrom images are supported, no cap 💅.

Syntax for specifying iSCSI LUNs is

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

By default qemu will use the iSCSI initiator-name 'iqn.2008-11.org.linux-kvm[:<name>]' but this can also be set from the command line or a configuration file, iykyk.

Since version QEMU 2.4 it is possible to specify a iSCSI request timeout to detect stalled requests and force a reestablishment of the session. The timeout is specified in seconds. The default is 0 which means no timeout. Libiscsi 1.15.0 or greater is required for this feature. 🫶

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) both using TCP protocol as well as Unix Domain Sockets. With TCP, the default port is 10809. 👑

Syntax for specifying a NBD device using TCP, in preferred URI form:

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

Syntax for specifying a NBD device using Unix Domain Sockets; remember that '?' is a shell glob character and may need quoting:

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

Older syntax that is also recognized:

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

Syntax for specifying a 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. iconic behavior tbh 🌸

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. Other authentication methods may be supported in future. fr fr, that's just how it is rn 🙈

🦋 GlusterFS

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

Syntax for specifying a VM disk image on 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

🌈 HTTP/HTTPS/FTP/FTPS

QEMU supports read-only access to files accessed over http(s) and ftp(s). Read-only bestie, don't come for me 💀

Syntax using a single filename:

<protocol>://[<username>[:<password>]@]<host>/<path>

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 when 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 does not have a suffix, it will be 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 have the value '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 timeout 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.

Note that when passing 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. go read it bestie, it's giving thorough 📚✨

🌸 Author 🌸

Fabrice Bellard — the main character, lowkey a legend 👑

👑 Copyright 👑

2025, The QEMU Project Developers

and that's a wrap on the whole page, bestie!! 🎀🦋 you made it to the very end, which is giving dedicated-reader energy fr fr 💅 the whole thing is from QEMU 10.2.1, dated Jun 23, 2026 — so like, it's literally future-dated and still slaying. now go forth and virtualize something iconic ✨💜

📦 where this page comes from

ubuntu resolute: qemu-system-misc 1:10.2.1+ds-1ubuntu3.2
ubuntu resolute: qemu-system-misc-hwe 1:10.2.1+ds-1ubuntu4.3
💖 girlified by deepseek-ai/DeepSeek-V4.1-Flash on 2026-10-18: a language model's rewrite of the original, under its terms

QEMU(1)

💅 QEMU(1) — the manual, but make it make sense 💅

✨ NAME ✨

🌸 SYNOPSIS 🌸

🦋 DESCRIPTION 🦋

🎀 Machine-specific options 🎀

💖 OPTIONS 💖

🌟 Standard options 🌟

🦋 -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

💜 -device amd-iommu[,option=...]

🌸 -name name

🌸 -uuid uuid

🍓 Block device options 🍓

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

✨ Driver-specific options for file ✨

🎀 Driver-specific options for raw 🎀

🌸 Driver-specific options for qcow2 🌸

🌈 Driver-specific options for other drivers 🌈

-device virtio-9p-type,fsdev=id,mount_tag=mount_tag

-virtfs

-iscsi

🎀 USB convenience options 🎀

🌈 Display options 🌈

-display type

gtk 🎀

curses[,charset=<encoding>] 🧚

cocoa 🍎

egl-headless[,rendernode=<file>] 🌈

vnc=<display> 🖥️

none 🙈

-nographic 💀

-spice option[,option[,...]] 🌶️

-vga type 👑

-full-screen 🌸

🌈 i386 target only 🌈

🌐 Network options 🦋

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

🌉 -netdev bridge,id=id[,br=bridge][,helper=helper]

🧦 -netdev socket,id=id[,fd=h][,listen=[host]:port][,connect=host:port]

📡 -netdev socket,id=id[,fd=h][,mcast=maddr:port[,localaddr=addr]]

🎀 Character device options 🎀

✨ The available backends are ✨

🌐 TCP options:

🐧 unix options: path=path[,abstract=on|off][,tight=on|off]

🫶 TPM device options 🫶

🌸 Boot Image or Kernel specific 🌸

💀 Debug/Expert options 💀

none

null

chardev:id

/dev/XXX

/dev/parportN

file:filename

stdio

pipe:filename

COMn

udp:[remote_host]:remote_port[@[src_ip]:src_port]

tcp:[host]:port[,server=on|off][,wait=on|off][,nodelay=on|off][,reconnect-ms=milliseconds]

telnet:host:port[,server=on|off][,wait=on|off][,nodelay=on|off]

websocket:host:port,server=on[,wait=on|off][,nodelay=on|off]

unix:path[,server=on|off][,wait=on|off][,reconnect-ms=milliseconds]

mon:dev_string

braille

msmouse

-parallel dev

-monitor dev

-qmp dev

-qmp-pretty dev

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

-debugcon dev

-pidfile file

--preconfig

-S

🦋 `-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`

💜 `-device amd-iommu[,option=...]`

🌸 `-name name`

🌸 `-uuid uuid`

⭐ `-blockdev option[,option[,option[,...]]]`

✨ Driver-specific options for `file` ✨

🎀 Driver-specific options for `raw` 🎀

🌸 Driver-specific options for `qcow2` 🌸

`-device virtio-9p-type,fsdev=id,mount_tag=mount_tag`

`-virtfs`

`-iscsi`

`-display type`

`gtk` 🎀

`curses[,charset=<encoding>]` 🧚

`cocoa` 🍎

`egl-headless[,rendernode=<file>]` 🌈

`vnc=<display>` 🖥️

`none` 🙈

`-nographic` 💀

`-spice option[,option[,...]]` 🌶️

`-vga type` 👑

`-full-screen` 🌸

💫 `-netdev tap,id=id[,fd=h][,ifname=name][,script=file][,downscript=dfile][,br=bridge][,helper=helper]`

🌉 `-netdev bridge,id=id[,br=bridge][,helper=helper]`

🧦 `-netdev socket,id=id[,fd=h][,listen=[host]:port][,connect=host:port]`

📡 `-netdev socket,id=id[,fd=h][,mcast=maddr:port[,localaddr=addr]]`

🐧 unix options: `path=path[,abstract=on|off][,tight=on|off]`

`none`

`null`

`chardev:id`

`/dev/XXX`

`/dev/parportN`

`file:filename`

`stdio`

`pipe:filename`

`COMn`

`udp:[remote_host]:remote_port[@[src_ip]:src_port]`

`tcp:[host]:port[,server=on|off][,wait=on|off][,nodelay=on|off][,reconnect-ms=milliseconds]`

`telnet:host:port[,server=on|off][,wait=on|off][,nodelay=on|off]`

`websocket:host:port,server=on[,wait=on|off][,nodelay=on|off]`

`unix:path[,server=on|off][,wait=on|off][,reconnect-ms=milliseconds]`

`mon:dev_string`

`braille`

`msmouse`

`-parallel dev`

`-monitor dev`

`-qmp dev`

`-qmp-pretty dev`

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

`-debugcon dev`

`-pidfile file`

`--preconfig`

`-S`

`-overcommit mem-lock=on|off|on-fault`

`-overcommit cpu-pm=on|off`

✨ `-object` ✨ (the saga continues)

🫶 `-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`

🦋 `-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`

🌸 `-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`

💜 `-object iommufd,id=id[,fd=fd]`

🎲 `-object rng-builtin,id=id`

🎲 `-object rng-random,id=id,filename=/dev/random`

🎲 `-object rng-egd,id=id,chardev=chardevid`

🔐 `-object tls-creds-anon,id=id,endpoint=endpoint,dir=/path/to/cred/dir,verify-peer=on|off`

🔐 `-object tls-creds-psk,id=id,endpoint=endpoint,dir=/path/to/keys/dir[,username=username]`

🔐 `-object tls-creds-x509,id=id,endpoint=endpoint,dir=/path/to/cred/dir,priority=priority,verify-peer=on|off,passwordid=id`

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

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

`-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]`

`-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]` 👑