QEMU(1)

📦

version 8.2.2 · 8 versions

🌸 NAME 🌸

okay so bestie, welcome to the QEMU manual — this page is literally called QEMU User Documentation, and it's the whole user-facing guide to the qemu family of emulators. buckle up 💖

✨ SYNOPSIS ✨

qemu-system-x86_64 [options] [disk_image]

🦋 DESCRIPTION 🦋

The QEMU PC System emulator simulates the following peripherals (yes, all of them, I'm not skipping a single one 🫶):

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

SMP is supported with up to 255 CPUs. yes bestie, 255. that's not a typo 💅

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.

🚨 okay so this next bit is a real gotcha, no cap: by default, GUS shares IRQ(7) with parallel ports, and so QEMU must be told to not have parallel ports to have working GUS.

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.

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. (<- important, some of y'all don't even need one 🌈)

⭐ Standard options ⭐

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

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

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

Supported machine properties are:

accel=accels1[:accels2[:...]] — This is used to enable an accelerator. Depending on the target architecture, kvm, xen, hvf, nvmm, whpx 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. For accel=xen 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.
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 (read this one fr fr 😭):

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 256KiB. Only 256KiB, 512KiB, 1024KiB, 2048KiB 4096KiB, 8192KiB and 16384KiB 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=512k

sgx-epc.0.memdev=memid,sgx-epc.0.node=numaid — Define an SGX EPC section.
-cpu model — Select CPU model (-cpu help for list and additional feature selection)
-accel name[,prop=value[,...]] — This is used to enable an accelerator. Depending on the target architecture, kvm, xen, hvf, nvmm, whpx 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.
- igd-passthru=on|off — When Xen is in use, this option controls whether Intel integrated graphics devices can be passed through to the guest (default=off)
- kernel-irqchip=on|off|split — Controls KVM in-kernel irqchip support. The default is full acceleration of the interrupt controllers. On x86, split irqchip reduces the kernel attack surface, at a performance cost for non-MSI interrupts. Disabling the in-kernel irqchip completely is not recommended except for debugging purposes.
- 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 can be useful in some situations, such as when 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 in such a case this will default on. On other operating systems, this will default off, but one may enable this for testing or debugging.
- tb-size=n — Controls the size (in MiB) of the TCG translation block cache.
- thread=single|multi — Controls number of TCG threads. When the TCG is multi-threaded there will be one thread per vCPU therefore taking advantage of additional host cores. The default is to enable multi-threading where both the back-end and front-ends support it and no incompatible TCG features have been enabled (e.g. icount/replay).

dirty-ring-size=n — ok so this one only matters when you're using the KVM accelerator 💅. It controls the size of the per-vCPU dirty page ring buffer — like, the number of entries for each vCPU, bestie. It should be a power of two, and it should be 1024 or bigger (but still less than the max value the kernel supports, obviously). 4096 could be a good initial value if you have no idea which is best — no shame, we've all been there 🫶. 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 — okay so KVM implements dirty page logging at PAGE_SIZE granularity, and enabling dirty-logging on a huge-page requires breaking it into PAGE_SIZE pages in the first place. KVM on ARM does this splitting lazily by default. There are performance benefits in doing huge-page split eagerly, especially in situations where TLBI costs associated with break-before-make sequences are considerable, and also if guest workloads are read intensive ✨. The size here specifies how many pages to break at a time and needs to be a valid block size which is 1GB/2MB/4KB, 32MB/16KB and 512MB/64KB for 4KB/16KB/64KB PAGE_SIZE respectively. Be wary of specifying a higher size as it will have an impact on the memory. 😭 By default this feature is disabled (eager-split-size=0).
notify-vmexit=run|internal-error|disable,notify-window=n — enables or disables notify VM exit support on x86 host and specifies the corresponding notify window to trigger the VM exit if enabled 👑. The run option enables the feature — it does nothing and continues if the exit happens. The internal-error option enables the feature — it raises an internal error 💀. The disable option doesn't enable the feature. This feature can mitigate the CPU stuck issue due to event windows not opening up for a specified amount of time (i.e. notify-window). Default: notify-vmexit=run,notify-window=0. 🌸

-smp — bestie, this is the topology option 🎀

[[cpus=]n][,maxcpus=maxcpus][,sockets=sockets][,dies=dies][,clusters=clusters][,cores=cores][,threads=threads]

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

To control reporting of CPU topology information, values of the topology parameters can be specified. Machines may only support a subset of the parameters, and different machines may have different subsets supported which vary depending on capacity of the corresponding CPU targets. So for a particular machine type board, an expected topology hierarchy can be defined through the supported sub-option. Unsupported parameters can also be provided in addition to the sub-option, but their values must be set as 1 in the purpose of correct parsing. 🦋

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 cores per die, 2 threads per core) for PC machines which support sockets/dies/cores/threads. Some members of the option can be omitted but their values will be automatically computed:

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

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 — the NUMA saga, hold onto your scrunchie 🎀

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

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

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

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

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

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

Define a NUMA node and assign RAM and VCPUs to it. Set the NUMA distance from a source node to a destination node. Set the ACPI Heterogeneous Memory Attributes for the given nodes. ✨

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 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

The memdev option assigns RAM from a given memory backend device to a node. It is recommended to use the memdev option over the legacy mem option. This is because the memdev option provides better performance and more control over the backend's RAM (e.g. the prealloc parameter of -memory-backend-ram allows memory preallocation). 🔥

For compatibility reasons, the legacy mem option is supported in 5.0 and older machine types. Note that mem and memdev are mutually exclusive. If one node uses memdev, the rest of the nodes have to use the memdev option, and vice versa. 🫶

Users must specify memory for all NUMA nodes by memdev (or legacy mem if available). In QEMU 5.2, the support for -numa node without memory specified was removed. 😭

initiator is an additional option that points to an initiator NUMA node that has 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. 🌸

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

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

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. 💀

Quick reminder bestie: the -numa option does NOT allocate anything. It just takes resources that already exist and assigns them to NUMA nodes. So you still gotta bring your own RAM with -m and your own VCPUs with -smp, okay? It's giving matchmaker, not magician. 💅

🧠 hmat-lb: the latency & bandwidth lore

Use hmat-lb to set System Locality Latency and Bandwidth Information between initiator and target NUMA nodes, in the ACPI Heterogeneous Attribute Memory Table (HMAT). The initiator NUMA node is the one making memory requests — usually it's got one or more processors. The target NUMA node is the one holding the addressable memory.

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

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

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

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

lat is the latency value in nanoseconds. bw is the bandwidth value, and the possible value and units are NUM[M|G|T] — meaning the bandwidth value is NUM byte per second (or MB/s, GB/s or TB/s depending on which suffix you used). Heads up: if the latency or bandwidth value is 0, that means the corresponding latency or bandwidth info is not provided.

🎀 hmat-cache: the cache lore

In hmat-cache, node-id is the NUMA-id of the memory it belongs to. size is the size of the memory side cache in bytes. level is the cache level described in this structure — and no cap, cache level 0 should not be used with the hmat-cache option. associativity is the cache associativity, and the possible values are none/direct(direct-mapped)/complex(complex cache indexing). policy is the write policy. line is the cache Line size in bytes.

🦋 the iconic example

For example, these 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

💖 the options, continued

-add-fd fd=fd,set=set[,opaque=opaque] — bestie, this one adds a file descriptor to an fd set. The valid options are:
- fd=fd — this defines the file descriptor of which a duplicate gets added to the fd set. Real talk: the file descriptor cannot be stdin, stdout, or stderr. 🙅‍♀️
- set=set — this defines the ID of the fd set you're adding the file descriptor to.
- opaque=opaque — this defines a free-form string you can use to describe the fd.

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

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 — sets the parameter arg for the item id of type group. slay, a little targeted config moment ✨
-global driver.prop=value
-global driver=driver,property=property,value=value — sets the default value of driver's property prop to value, like:

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

Specifically, you can use this to set driver properties for devices that get created automatically by the machine model. If you wanna create a device that is not created automatically and set properties on it, use -device instead. iykyk 💅

Also, -global driver.prop=value is just shorthand for -global driver=driver,property=prop,value=value. And the longhand syntax still works even when driver contains a dot. no cap.

-boot [order=drives][,once=drives][,menu=on|off][,splash=sp_name][,splash-time=sp_time][,reboot-timeout=rb_timeout][,strict=on|off] — specify the boot order drives as a string of drive letters. Which drive letters are valid depends on the target architecture. The x86 PC uses: a, b (floppy 1 and 2), c (first hard disk), d (first CD-ROM), n-p (Etherboot from network adapter 1-4), and 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, because firmware implementations normally don't 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, letting the user show it as a logo, when the option splash=sp_name is given and menu=on, if firmware/BIOS supports them. Currently Seabios for X86 system supports it. limitation: the splash file could be a jpeg file or a BMP file in 24 BPP format (true color). The resolution should be supported by the SVGA mode, so the recommended is 320x240, 640x480, 800x640.

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

Do strict boot via strict=on as far as firmware/BIOS supports it. This only has an effect 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, because it may be removed from future versions. so like... move on bestie, it's giving deprecated 🫶

-m [size=]megs[,slots=n,maxmem=size] — sets the 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. The optional pair slots, maxmem can be used to set the amount of hotpluggable memory slots and the maximum amount of memory. Note that maxmem must be aligned to the page size.

For example, this 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 are not specified, memory hotplug won't be enabled and the guest startup RAM will never increase. periodt. 💀

-mem-path path — allocate guest RAM from a temporarily created file in path.
-mem-prealloc — preallocate memory when using -mem-path.
-k language — use keyboard layout language (for example fr for French). This option is only needed where it's not easy to get raw PC keycodes (e.g. on Macs, with some X11 servers, or with a VNC or curses display). You don't normally need to use it on PC/Linux or PC/Windows hosts.

The available layouts are:

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

The default is en-us.

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

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

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

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

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

-audiodev [driver=]driver,id=id[,prop[=value][,...]] — adds a new audio backend driver identified by id. There are global and driver specific properties. Some values can be set differently for input and output, and they're marked with in|out.. You can set the input's property with in.prop and the output's property with out.prop. For example:

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

NOTE: parameter validation is known to be incomplete, bestie. In <em>many</em> cases, specifying an invalid option just makes QEMU print an error message and then keep emulating without sound. So you'll be sitting there like "why is it silent" and QEMU is like "idk I warned you." 💀

Valid global options are: (these ones work across backends, so learn them once and you're set 🫶)

id=identifier — identifies the audio backend. Basically its little name tag. 🏷️
timer-period=period — sets the timer period used by the audio subsystem, measured 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 it's off, fixed-settings must be off too. Careful though: disabling this means the backend you picked has to support multiple streams and whatever audio formats your virtual cards use — otherwise you get... no sound. 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 audio. Default is on. 🔥
in|out.fixed-settings=on|off — use fixed settings for host audio. When it's off, it changes based on how the guest opens the sound card. In that case you must not specify frequency, channels or format. Default is on. 🎚️
in|out.frequency=frequency — the frequency to use when you're using fixed-settings. Default is 44100Hz. 🎵
in|out.channels=channels — the number of channels to use when you're using fixed-settings. Default is 2 (stereo, iconic). 🎧
in|out.format=format — the sample format to use when you're using fixed-settings. Valid values are: s8, s16, s32, u8, u16, u32, f32. Default is s16. ✨
in|out.voices=voices — the number of voices to use. Default is 1. 🗣️
in|out.buffer-length=usecs — sets the size of the buffer, in microseconds. 📏

-audiodev none,id=id[,prop[=value][,...]] — creates a dummy backend that discards all outputs. This backend has no backend specific properties. It's giving "the void, but make it audio." 🕳️
-audiodev alsa,id=id[,prop[=value][,...]] — creates a backend using the ALSA. This backend is only available on Linux. 🐧

ALSA specific options are:

in|out.dev=device — specify the ALSA device to use for input and/or output. Default is default.
in|out.period-length=usecs — sets the period length, in microseconds.
in|out.try-poll=on|off — attempt to use poll mode with the device. Default is on.
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. This backend is only available on Mac OS and only supports playback (no recording, sorry 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. This backend is only available on Windows and only supports playback. 🪟

DirectSound specific options are:

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

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

OSS specific options are:

in|out.dev=device — specify the file name of the OSS device to use. Default is /dev/dsp.
in|out.buffer-count=count — sets the count of the buffers.
in|out.try-poll=on|of — attempt to use poll mode with the device. Default is on. (yep, that's how it's written in the source, no I will not be editing it 💅)
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 (between 0 and 10, where a smaller number means smaller latency but higher CPU usage). Use -1 to use buffer sizes specified by buffer and buffer-count. This option is ignored if you do not have OSS 4. Default is 5.

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

PulseAudio specific options are:

server=server — sets the PulseAudio server to connect to.
in|out.name=sink — use the specified source/sink for recording/playback.
in|out.latency=usecs — desired latency in microseconds. The PulseAudio server will try to honor this value, but actual latencies may be lower or higher. (It's doing its best okay 😭)

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

PipeWire specific options are:

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

-audiodev sdl,id=id[,prop[=value][,...]] — creates a backend using SDL. This backend is available on most systems, but you should use your platform's native backend if possible. (Like, SDL is the reliable friend, but native is the one who <em>gets</em> you. 💅)

SDL specific options are:

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

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

Sndio specific options are:

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

-audiodev spice,id=id[,prop[=value][,...]] — creates a backend that sends audio through SPICE. This backend requires -spice and is automatically selected in that case, so usually you can just ignore this option entirely. This backend has no backend specific properties. ✨
-audiodev wav,id=id[,prop[=value][,...]] — creates a backend that writes audio to a WAV file. 📼

Backend specific options are:

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

-device driver[,prop[=value][,...]] — add device driver. prop=value sets driver properties. Valid properties depend 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 is a simulation of a hardware management interface processor that normally sits on a system. It provides a watchdog and the ability to reset and power control the system. You need to connect this to an IPMI interface to make it 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 this means, it is safe to ignore it. (Truly. Nobody's testing you. 🫶)

id=id — the BMC id for interfaces to use this device.
slave_addr=val — define 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 — file containing raw Field Replaceable Unit (FRU) inventory data. The default is none.
guid=uuid — value for the GUID for the BMC, in standard UUID format. If this is set, get "Get GUID" command to the BMC will return it. Otherwise "Get GUID" will return an error.

-device ipmi-bmc-extern,id=id,chardev=id[,slave_addr=val] — add a connection to an external IPMI BMC simulator. Instead of locally emulating the BMC like the above item, instead connect to an external entity that provides the IPMI services. 🔌

A connection is made to an external BMC simulator. If you do this, it is strongly recommended that you use the reconnect= chardev option to reconnect to the simulator if the connection is lost.

Careful, bestie: note that if this is not used carefully, it can be a security issue, as the interface has the ability to send resets, NMIs, and power off the VM. It's best if QEMU makes a connection to an external simulator running on a secure port on localhost, so neither the simulator nor QEMU is exposed to any outside network. 🔒

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

-device isa-ipmi-kcs,bmc=id[,ioport=val][,irq=val] — add a KCS IPMI interface on the ISA bus. This also adds a corresponding ACPI and SMBIOS entries, if appropriate.
- bmc=id — the BMC to connect to, one of ipmi-bmc-sim or ipmi-bmc-extern above.
- ioport=val — define the I/O address of the interface. The default is 0xca0 for KCS.
- irq=val — define the interrupt to use. The default is 5. To disable interrupts, set this to 0.
-device isa-ipmi-bt,bmc=id[,ioport=val][,irq=val] — like the KCS interface, but defines a BT interface. The default port is 0xe4 and the default interrupt is 5. 🎀
-device pci-ipmi-kcs,bmc=id — add a KCS IPMI interface on the PCI bus.
- bmc=id — the BMC to connect to, one of ipmi-bmc-sim or ipmi-bmc-extern above.
-device pci-ipmi-bt,bmc=id — like the KCS interface, but defines a BT interface on the PCI bus. 🦋
-device intel-iommu[,option=...] — okay bestie, this one is only supported by -machine q35, and it switches on Intel VT-d emulation inside the guest ✨. It supports the options below:
- intremap=on|off (default: auto) — turns on the interrupt remapping feature 💅. You need it to enable complete x2apic. Right now it only supports kvm kernel-irqchip modes off or split, while full kernel-irqchip is not yet supported. The default is "auto", which gets decided by the mode of kernel-irqchip.
- caching-mode=on|off (default: off) — enables caching mode for the VT-d emulated device. When caching-mode is on, every guest DMA buffer mapping makes the guest IOMMU driver fire an IOTLB invalidation at the vIOMMU device, synchronously. It's required for -device vfio-pci to work with the VT-d device, because host assigned devices need the DMA mapping set up 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) — this 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.

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

-name name — sets the name of the guest 💖. This name gets displayed in the SDL window caption. The name will also be used for the VNC server. Also optionally sets the top visible process name in Linux. Naming of individual threads can also be enabled on Linux to aid debugging, iykyk.
-uuid uuid — sets the system UUID. simple as that 💅

🎀 Block device options 🎀

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 have grown. Not me seeing so many online guides to QEMU referencing older and deprecated options — that's literally how confusion happens 😭.

The most explicit way to describe disks is to use a combination 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 it's recommended for management tools and scripting 👑.

The -drive option combines the device and backend into a single command line option, which is a bit 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 which 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, so they're not recommended for modern configurations 💀.

-fda file, -fdb file — use file as floppy disk 0/1 image (see the 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 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 — this defines the name of the block driver node by which it will be referenced later. The name must be unique, i.e. it must not match the name of a different block driver node, or (if you 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.

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

Enabling force-share=on requires read-only=on. no cap.

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

🦋 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 is 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 is 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 — this is your reference to (or the actual definition of) the backing file block device. Default? It gets yanked from the image file itself. And yes, you're allowed to pass null here — that's the move when you wanna disable the default backing file entirely. 💅
lazy-refcounts — turns the lazy refcounts feature on or off (on/off). Default is taken from the image file, no cap.
cache-size — the maximum total size of the L2 table and refcount block caches, in bytes. Default: literally just the sum of l2-cache-size and refcount-cache-size. Math is mathing. ✨
l2-cache-size — max size of the L2 table cache, in bytes. Default is a whole vibe: if cache-size isn't specified, it's 32M on Linux platforms and 8M on non-Linux platforms. But if cache-size is specified, it's as large as possible within that cache-size, while still permitting the requested (or minimal) refcount cache size. Balanced, as all things should be. 🦋
refcount-cache-size — max size of the refcount block cache, in bytes. Default: 4 times the cluster size. Or, if cache-size is specified, it's whatever part of it isn't already being used for the L2 cache.
cache-clean-interval — cleans unused entries in the L2 and refcount caches. The interval is in seconds. Default value is 600 on supporting platforms, and 0 on other platforms. Setting it to 0 disables this feature completely. 🧹
pass-discard-request — should discard requests to the qcow2 device get forwarded to the data source? (on/off). Default: on if discard=unmap is specified, off otherwise.
pass-discard-snapshot — should discard requests for the data source be issued when a snapshot operation (like deleting a snapshot) frees clusters in the qcow2 file? (on/off). Default: on.
pass-discard-other — should discard requests for the data source be issued on other occasions where a cluster gets freed? (on/off). Default: off.
discard-no-unref — when this is enabled, data clusters stay preallocated even when they're no longer used — like when they get discarded or converted to zero clusters. As per usual, whether that old data is actually discarded or kept at the protocol level (i.e. in the image file) depends on the pass-discard-request setting. Keeping clusters preallocated stops qcow2 fragmentation that would otherwise happen from freeing and re-allocating them later. And ngl, besides potential performance degradation, that kind of 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. So if image file length is a concern for you (say, when you're storing qcow2 images directly on block devices), you should really 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, go 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 where the tea lives for everybody else. 🫖

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

Okay bestie, this one defines a new drive. It's doing a lot: it creates a block driver node (that's the backend) and a guest device. Mostly it's just a shortcut for defining the corresponding -blockdev and -device options. Two birds, one flag. 🐦

-drive accepts all options that are accepted by -blockdev. But wait, there's more — it also knows these:

file=file — this defines which disk image to use with this drive (peep the Disk Images chapter in the System Emulation Users Guide). Heads up though: if the filename contains a comma, you must double it — so for instance "file=my,,file" to use the file "my,file". Commas are dramatic like that. 😭

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

if=interface — defines which type of interface the drive is connected to. The available types are: ide, scsi, sd, mtd, floppy, pflash, virtio, none. Pick your fighter. 💅
bus=bus,unit=unit — these define where the drive is connected by defining the bus number and the unit id.
index=index — defines where the drive is connected by using an index in the list of available connectors of a given interface type.
media=media — defines the type of the media: disk or cdrom.
snapshot=snapshot — snapshot is "on" or "off" and controls snapshot mode for the given drive (see -snapshot).
cache=cache — cache is "none", "writeback", "unsafe", "directsync" or "writethrough", and it controls how the host cache is used to access block data. It's a shortcut that sets the cache.direct and cache.no-flush options (same as in -blockdev), plus cache.writeback, which provides a default for the write-cache option of block guest devices (same as in -device). The modes map to the following settings:
- 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 selects between pthread based disk I/O, native Linux AIO, or the Linux io_uring API. ✨
format=format — specify which disk format will be used rather than detecting the format. You can use this to specify format=raw to avoid interpreting an untrusted format header. Safety first, babes. 🛡️
werror=action,rerror=action — specify which action to take on write and read errors. 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 enables whether to copy read backing file sectors into the image file.
bps=b,bps_rd=r,bps_wr=w — specify bandwidth throttling limits in bytes per second, either for all request types or for reads or writes only. Lowkey warning: small values can lead to timeouts or hangs inside the guest. A safe minimum for disks is 2 MB/s.
bps_max=bm,bps_rd_max=rm,bps_wr_max=wm — specify bursts in bytes per second, either for all request types or for reads or writes only. Bursts let the guest I/O spike above the limit temporarily. Little treat. 🍓
iops=i,iops_rd=r,iops_wr=w — specify 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 — specify bursts in requests per second, either for all request types or for reads or writes only. Bursts let the guest I/O spike above the limit temporarily.
iops_size=is — okay so every is bytes of a request counts as a brand new request for iops throttling purposes. Why do we care? Because otherwise your guest is out here playing games, sending fewer-but-thicccer requests to slide right under your iops limits. Not on our watch bestie 💅
group=g — join a throttling quota group named g. Every drive that's a member of the same group gets accounted for together. Again: it stops guests from circumventing throttling limits by going "hehe what if I use a million tiny disks instead of one big one" 🍓 iconic behaviour, blocked.

So by default, the cache.writeback=on mode is what's happening. It reports data writes as done the second that data lands in the host page cache. That's totally safe… as long as your guest OS actually makes sure to correctly flush disk caches where it's needed 🫶 If your guest OS does not handle volatile disk write caches correctly and your host crashes or loses power — boom, your guest may experience data corruption 😭💀

For those guests, you should lowkey consider cache.writeback=off. What that means: the host page cache is still used to read and write data, but the write notification only gets sent to the guest after QEMU has made sure to flush each write to the disk. Heads up though — this has a major impact on performance 🙈

When you're using the -snapshot option, unsafe caching is always used. No exceptions, no negotiating.

Copy-on-read avoids accessing the same backing file sectors over and over, and it's genuinely useful when the backing file is sitting 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

And if you don't specify the "file=" argument at all, you're defining 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, like so:

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

which gets interpreted exactly like:

qemu-system-x86_64 -hda a -hdb b

✨ -mtdblock file ✨

Use file as an on-board Flash memory image 🦋

✨ -sd file ✨

Use file as a 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 (go check the Disk Images chapter in the System Emulation Users Guide, bestie, it's all in there 👑).

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. Not me warning you twice 💀

✨ -fsdev ✨

-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 proxy,id=id,socket=socket[,writeout=writeout][,readonly=on]

-fsdev proxy,id=id,sock_fd=sock_fd[,writeout=writeout][,readonly=on]

-fsdev synth,id=id[,readonly=on]

Define a new file system device 🎀 Valid options are:

local — accesses to the filesystem are done by QEMU.
proxy — accesses to the filesystem are done by virtfs-proxy-helper(1). This option is deprecated (since QEMU 8.1) and will be removed in a future version of QEMU. Use local instead, fr fr.
synth — synthetic filesystem, only used by QTests.
id=id — specifies the identifier for this device.
path=path — specifies the export path for the file system device. Files under this path will be available to the 9p client on the guest.
security_model=security_model — specifies the security model to use for this export path. The supported security models are "passthrough", "mapped-xattr", "mapped-file" and "none".

In the "passthrough" security model, files are stored using the same credentials as they are created on the guest. This requires QEMU to run as root 👑

In the "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 same as passthrough except the sever won't report failures if it fails to set file attributes like ownership.

Security model is mandatory only for local fsdriver. Other fsdrivers (like proxy) don't take security model as a parameter.

writeout=writeout — this is an optional argument. The only supported value is "immediate". This means that the 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.
socket=socket — enables the proxy filesystem driver to use the passed socket file for communicating with virtfs-proxy-helper(1).
sock_fd=sock_fd — enables the proxy filesystem driver to use the passed socket descriptor for communicating with virtfs-proxy-helper(1). Usually a helper like libvirt will create a socketpair and pass one of the fds as sock_fd.
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 — specifies the default mode for newly created directories on the host. Works only with security models "mapped-xattr" and "mapped-file".
throttling.bps-total=b,throttling.bps-read=r,throttling.bps-write=w — specify bandwidth throttling limits in bytes per second, either for all request types or for reads or writes only.
throttling.bps-total-max=bm,bps-read-max=rm,bps-write-max=wm — specify bursts in bytes per second, either for all request types or for reads or writes only. Bursts let the guest I/O spike above the limit temporarily ⚡
throttling.iops-total=i,throttling.iops-read=r,throttling.iops-write=w — specify request rate limits in requests per second, either for all request types or for reads or writes only.
throttling.iops-total-max=im,throttling.iops-read-max=irm,throttling.iops-write-max=iwm — specify bursts in requests per second, either for all request types or for reads or writes only. Bursts let the guest I/O spike above the limit temporarily 🌈
throttling.iops-size=is — let every is bytes of a request count as a new request for iops throttling purposes.

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

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

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

type — specifies the variant to be used. Supported values are "pci", "ccw" or "device", depending on the machine type.
fsdev=id — specifies the id value specified along with the -fsdev option.
mount_tag=mount_tag — specifies the tag name to be used by the guest to mount this export point.

✨ -virtfs ✨

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

-virtfs proxy,socket=socket,mount_tag=mount_tag
[,writeout=writeout][,readonly=on]

-virtfs proxy,sock_fd=sock_fd,mount_tag=mount_tag
[,writeout=writeout][,readonly=on]

-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 essentially means that a certain directory on host is made directly accessible by guest as a pass-through file system using the 9P network protocol for communication between host and guests — and if you want, even accessible and shared by several guests simultaneously 😳💖

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

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

local — accesses to the filesystem are done by QEMU.
proxy — accesses to the filesystem are done by virtfs-proxy-helper(1). This option is deprecated (since QEMU 8.1) and will be removed in a future version of QEMU. Use local instead.
synth — synthetic filesystem, only used by QTests.
id=id — specifies the identifier for the filesystem device.
path=path — specifies the export path for the file system device. Files under this path will be available to the 9p client on the guest.
security_model=security_model — tells QEMU which security model this export path should use. The supported ones are passthrough, mapped-xattr, mapped-file and none. Okay so here's the tea on each:
- passthrough — files get stored using the exact same credentials they were created with on the guest. Heads up bestie, this one means QEMU has to run as root 💀.
- mapped-xattr — some file attributes like uid, gid, mode bits and the link target get stashed away as file attributes.
- mapped-file — those same attributes live in the hidden .virtfs_metadata directory instead. Lowkey important: directories exported this way cannot interact with other unix tools.
- none — literally passthrough but the server won't report failures when it fails to set file attributes like ownership. Chill of it tbh.

Also: the security model is mandatory only for local fsdriver. Other fsdrivers (like proxy) don't take a security model as a parameter at all, periodt.

writeout=writeout — optional argument, and the only supported value is immediate. What it means: the host page cache will be used to read and write data, but the write notification gets sent to the guest only once the data has been reported as written by the storage subsystem. ✨
readonly=on — exports the 9p share as a readonly mount for guests. By default you get read-write access, so this is you opting into the locked-down vibe 🔒.
socket=socket — lets the proxy filesystem driver use the socket file you passed in to talk to virtfs-proxy-helper(1). Usually a helper like libvirt will create a socketpair and hand one of the fds over as sock_fd.
sock_fd — lets the proxy filesystem driver use the sock_fd you passed as the socket descriptor for interfacing with virtfs-proxy-helper(1).
fmode=fmode — sets the default mode for newly created files on the host. Only works with the mapped-xattr and mapped-file security models, fyi 🫶.
dmode=dmode — sets 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. Your little name tag for the vibes 🎀.
multidevs=multidevs — how to deal with multiple devices being shared through one 9p export. Supported behaviours are remap, forbid or warn. Let's break it down, bestie:
- warn is the default. Under it, virtfs 9p expects only one device to be shared with the same export — if more than one device is shared and accessed via that same 9p export, qemu just logs a warning message (once) on the host side.
- To avoid file ID collisions on the guest you should either create a separate virtfs export for each device you're sharing with guests (the recommended way, no cap) or use remap instead, which lets you share multiple devices with only one export. It pulls that off by remapping the original inode numbers from host to guest in a way that prevents those collisions. Remapping is required in these use 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 misbehaviours on the guest 😭.
- forbid assumes, like warn, that only one device is shared by the same export — but it won't just log a warning message, it will deny access to additional devices on the guest. Note though: 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 isn't 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 you can do it via -machine usb=on). Note that this option is mainly intended for the user's convenience only. More fine-grained control can be achieved by selecting a USB host controller (if necessary) and the desired USB device via the -device option instead. For example, instead of using -usbdevice mouse it is possible to use -device qemu-xhci -device usb-mouse to connect the USB mouse to a USB 3.0 controller instead (at least on machines that support PCI and do not have an USB controller enabled by default yet). For more details, see the chapter about Connecting USB devices in the System Emulation Users Guide. Possible devices for devname are:
- braille — Braille device. This will use BrlAPI to display the braille output on a real or fake device (i.e. it also creates a corresponding braille chardev automatically beside the usb-braille USB device).
- keyboard — Standard USB keyboard. Will override the PS/2 keyboard (if present).
- mouse — Virtual Mouse. This will override the PS/2 mouse emulation when activated.
- tablet — Pointer device that uses absolute coordinates (like a touchscreen). This means QEMU is able to report the mouse position without having to grab the mouse. Also overrides the PS/2 mouse emulation when activated.
- wacom-tablet — Wacom PenPartner USB tablet.

💖 Display options 💖

-display type — Select type of display to use. 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 : Allow to quit qemu with window close button
gtk — Display video output in a GTK window. This interface provides drop-down menus and other UI elements to configure and control the VM during runtime. Valid parameters are:
- full-screen=on|off : Start in fullscreen mode
- gl=on|off : Use OpenGL for displaying
- grab-on-hover=on|off : Grab keyboard input on mouse hover
- show-tabs=on|off — Display the tab bar for switching between the various graphical interfaces (e.g. VGA and virtual console character devices) by default.
- show-cursor=on|off : Force showing the mouse cursor
- window-close=on|off : Allow to quit qemu with window close button
- show-menubar=on|off : Display the main window menubar, defaults to "on"
- zoom-to-fit=on|off — Expand video output to the window size, defaults to "off"
curses[,charset=<encoding>] — Display video output via curses. For graphics device models which support a text mode, QEMU can display this output using a curses/ncurses interface. Nothing is displayed when the graphics device is in graphical mode or if the graphics device does not support a text mode. Generally only the VGA device models support text mode. The font charset used by the guest can be specified with the charset option, for example charset=CP850 for IBM CP850 encoding. The default is CP437.
cocoa — Display video output in a Cocoa window. Mac only. This interface provides drop-down menus and other UI elements to configure and control the VM during runtime. Valid parameters are:
- show-cursor=on|off : Force showing the mouse cursor
- left-command-key=on|off : Disable forwarding left command key to host
egl-headless[,rendernode=<file>] — Offload all OpenGL operations to a local DRI device. For any graphical display, this display needs to be paired with either VNC or SPICE displays. ✨
vnc=<display> — Start a VNC server on display <display> 🦋

none — no video output at all, bestie. The guest still sees an emulated graphics card, but nothing gets shown to you. And heads up, this is not the same as -nographic — none only touches video output, while -nographic also reroutes where serial and parallel port data goes. Different vibes, fr fr. 🙈

-nographic — okay so normally, if QEMU was compiled with graphical window support, it pops output like guest graphics, guest console, and the QEMU monitor into a lil window. This option says "nope, no graphics at all" and turns QEMU into a plain old command line application. The emulated serial port gets redirected onto the console and muxed with the monitor (unless you explicitly redirected it somewhere else, of course). Which means you can still use QEMU to debug a Linux kernel over a serial console 💅. Press C-a h for help on switching between the console and the monitor. iconic.
-spice option[,option[,...]] — turns on the spice remote desktop protocol. The valid options are:
- port=<nr> — sets the TCP port spice is listening on for plaintext channels.
- addr=<addr> — sets 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> — sets the ID of the secret object holding 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 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. And 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. (iykyk, be careful 👀)
- 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> — sets the TCP port spice is listening on for encrypted channels.
- x509-dir=<dir> — sets the x509 file directory. Expects the same filenames as -vnc $display,x509=$dir.
- x509-key-file=<file>; x509-key-password=<file>; x509-cert-file=<file>; x509-cacert-file=<file>; x509-dh-key-file=<file> — the x509 file names can also be configured individually, one by one, no stress.
- 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.
- 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) ✨
-portrait — rotate graphical output 90 deg left (only PXA LCD).
-rotate deg — rotate graphical output some deg left (only PXA LCD).
-vga type — pick which type of VGA card to emulate. The valid values for type are:
- cirrus — Cirrus Logic GD5446 Video card. Every Windows version starting from Windows 95 should recognize and use this graphic card. For optimal performances, use 16 bit color depth in the guest and the host OS. (This card was the default before QEMU 2.2)
- std — Standard VGA card with Bochs VBE extensions. If your guest OS supports the VESA 2.0 VBE extensions (e.g. Windows XP) and you 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.
-g widthxheight[xdepth] — set the initial graphical resolution and depth (PPC, SPARC only).

For PPC the default is 800x600x32.

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

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

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

reverse=on|off — connect to a listening VNC client via a "reverse" connection. The client is specified by the display. For reverse network connections (host:d,reverse), the d argument is a TCP port number, not a display number.
websocket=on|off — opens an additional TCP listening port dedicated to VNC Websocket connections. If a bare websocket option is given, the Websocket port is 5700+display. An alternative port can be specified with the syntax websocket=port.

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

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

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

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

Bestie, quick PSA on password expiry before we move on — if you wanna change a <protocol> password expiration, hit up expire_password <protocol> <expiration-time>, where the expiration time is one of these: now, never, +seconds, or a straight-up UNIX time of expiration. So like +60 makes the password expire in 60 seconds, or 1335196800 makes it expire on "Mon Apr 23 12:00:00 EDT 2012" (that's literally the UNIX time for that exact date and time, no cap).

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

password-secret=<secret-id> — require password-based authentication for client connections, using the password handed over by the secret object identified by secret-id.
tls-creds=ID — the ID of a set of TLS credentials used to secure the VNC server. They apply to both the normal VNC server socket and the websocket socket (if enabled). Setting TLS credentials will cause the VNC server socket to enable the VeNCrypt auth mechanism. These credentials should have been created beforehand with the -object tls-creds argument. 🔐
tls-authz=ID — the ID of the QAuthZ authorization object that the client's x509 distinguished name gets validated against. 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 — require the client to 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 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. See the VNC security section in the System Emulation Users Guide for details on using SASL authentication. 👑
sasl-authz=ID — the ID of the QAuthZ authorization object that the client's SASL username gets validated against. 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 — legacy method for enabling authorization of clients against the x509 distinguished name and SASL username. It results in the creation of 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 a replacement. 💀

lossy=on|off — enable lossy compression methods (gradient, JPEG, ...). If this option is set, the VNC client may receive lossy framebuffer updates depending on its encoding settings. Enabling this can save a lot of bandwidth at the expense of quality. Trade-offs, we love them. 🎀
non-adaptive=on|off — disable adaptive encodings. Adaptive encodings are enabled by default. An adaptive encoding will try to detect frequently updated screen regions, and send updates in these regions using a lossy encoding (like JPEG). This can be really helpful to save bandwidth when playing videos. Disabling adaptive encodings restores the original static behavior of encodings like Tight.
share=[allow-exclusive|force-shared|ignore] — set the display sharing policy. 'allow-exclusive' allows clients to 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. Doesn't conform to the rfb spec but is traditional QEMU behavior. 🫶
key-delay-ms — set 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 are arriving in bulk. Possible causes for the latter are flaky network connections, or scripts for automated testing. ⌨️
audiodev=audiodev — use the specified audiodev when the VNC client requests audio transmission. When not using an -audiodev argument, this option must be omitted, otherwise it must be present and specify a valid audiodev.
power-control=on|off — permit the remote client to issue shutdown, reboot or reset power control requests.

🌈 i386 target only 🌈

-win2k-hack — use it when installing Windows 2000 to avoid a disk full bug. After Windows 2000 is installed, you no longer need this option (this option slows down the IDE transfers).
-no-fd-bootchk — disable boot signature checking for floppy disks in BIOS. May be needed to boot from old floppy disks. 💾
-no-acpi — disable ACPI (Advanced Configuration and Power Interface) support. Use it if your guest OS complains about ACPI problems (PC target machine only).
-no-hpet — disable HPET support. Deprecated, use -machine hpet=off instead. 🙈
-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]...] — add an ACPI table with the specified header fields and context from the specified files. For file=, take the whole ACPI table from the specified files, including all ACPI headers (possible overridden by other options). For data=, only the data portion of the table is used, all header information is specified in the command line. If a SLIC table is supplied to QEMU, then the SLIC's oem_id and oem_table_id fields will override the same in the RSDT and the FADT (a.k.a. FACP), in order to ensure the field matches required by the Microsoft SLIC spec and the ACPI spec.
-smbios file=binary — load the SMBIOS entry from a binary file.
-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-id=%d] — specify SMBIOS type 4 fields.
-smbios type=11[,value=str][,path=filename] — specify SMBIOS type 11 fields. 📝

This argument can be repeated multiple times, and values are added in the order they are parsed. Applications intending to use OEM strings data are encouraged to use their application name as a prefix for the value string. This facilitates passing information for multiple applications concurrently.

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

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

Note that on the x86 architecture, the total size of all SMBIOS tables is limited to 65535 bytes. Thus 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.

An example passing three strings is

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

In the guest OS this is visible with the dmidecode command

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

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

okay so you can repeat this argument multiple times, bestie — as many as you need. Its main use is letting network interfaces get created as enoX on Linux, where X is the instance number, instead of the name being all 🙃 depends-on-where-the-interface-sits-on-the-PCI-bus 🙃.

Here's the vibe in action:

-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

Then in the guest OS, the device should show up as eno1, like:

$ 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>

💀 rn, the PCI device has to be attached to the root bus. that's just the rule, no cap.

🌐 Network options 🌐

🫶 `-nic`

[tap|bridge|user|l2tpv3|vde|netmap|af-xdp|vhost-user|socket][,...][,mac=macaddr][,model=mn]

This one is literally a shortcut — a two-for-one deal. 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 the matching -netdev options down below. Wanna set the guest NIC model? That's model=modelname. Wanna see the available device types? model=help. And the hardware MAC address gets set with mac=macaddr.

These two examples do exactly the same thing — they're just showing off how -nic shortens your command line length:

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

🚫 `-nic none`

Indicate that no network devices should be configured. Periodt. It's here to override the default configuration (that'd be a default NIC with a user host network backend) which gets activated if you don't provide any other networking options at all.

👤 `-netdev user,id=id[,option][,option][,...]`

Configure a user mode host network backend — and the best part? It 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 the 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 — specify the first of the 16 IPs the built-in DHCP server can assign. Default is the 15th to 31st IP in the guest network, i.e. x.x.x.15 to x.x.x.31.
dns=addr — specify the guest-visible address of the virtual nameserver. The address must be different from the host address. Default is the 3rd IP in the guest network, i.e. x.x.x.3.
ipv6-dns=addr — specify the guest-visible address of the IPv6 virtual nameserver. The address must be different from the host address. Default is the 3rd IP in the guest network, i.e. xxxx::3.
dnssearch=domain — provides an entry for the domain-search list sent by the built-in DHCP server. More than one domain suffix can be transmitted by specifying this option multiple times. If supported, this will cause the guest to automatically try to append the given domain suffix(es) in case a domain name can not be resolved.

Example:

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

domainname=domain — specifies the client domain name reported by the built-in DHCP server.
tftp=dir — when using the user mode network stack, activate a built-in TFTP server. The files in dir will be exposed as the root of a TFTP server. The TFTP client on the guest must be configured in binary mode (use the command bin of the Unix TFTP client).
tftp-server-name=name — in the BOOTP reply, broadcast name as the "TFTP server name" (RFC2132 option 66). This can be used to advise the guest to load boot files or configurations from a different server than the host address.
bootfile=file — when using the user mode network stack, broadcast file as the BOOTP filename. In conjunction with tftp, this can be used to network boot a guest from a local directory.

Example (using pxelinux):

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

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

In the guest Windows OS, the line:

10.0.2.4 smbserver

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

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

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

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

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

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

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

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

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

guestfwd=[tcp]:server:port-dev
guestfwd=[tcp]:server:port-cmd:command

Forward guest TCP connections to the IP address server on port port 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 is not 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 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] — bestie, this one takes a host TAP interface and yeets it onto a host bridge device 🫶. You use the network helper helper to set up the TAP interface and hook it onto the bridge. Default helper executable? That's /usr/lib/qemu/qemu-bridge-helper, and the default bridge device is br0. Slay.

Examples, and yes they're giving iconic:

#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 links your guest's network to another QEMU VM through a TCP socket connection, no cap 🌈. If you say listen, QEMU just sits there waiting for incoming connections on port (host is optional, lowkey). And connect? That's for dialing into another QEMU instance that used the listen option. fd=h lets you hand it an already-opened TCP socket, iykyk.

Example time:

# 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]] — okay so this sets up a socket host network backend that shares the guest's network traffic with other QEMU VMs over a UDP multicast socket, which basically makes a bus for every QEMU sharing the same multicast address maddr and port 💅. NOTES, bestie, read them:
1. Several QEMU can be running on different hosts and share same bus (assuming correct multicast setup for these hosts).
2. mcast support is compatible with User Mode Linux (argument ethN=mcast), see http://user-mode-linux.sf.net.
3. Use fd=h to specify an already opened UDP multicast socket.

Example:

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

Example (User Mode Linux compat.):

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

Example (send packets from host's 1.2.3.4):

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

-netdev l2tpv3,id=id,src=srcaddr,dst=dstaddr[,srcport=srcport][,dstport=dstport],txsession=txsession[,rxsession=rxsession][,ipv6=on|off][,udp=on|off][,cookie64][,counter][,pincounter][,txcookie=txcookie][,rxcookie=rxcookie][,offset=offset] — this is the L2TPv3 pseudowire host network backend, and it's kind of a big deal 🔥. L2TPv3 (RFC3931) is a popular protocol for transporting Ethernet (and other Layer 2) data frames between two systems. It lives in routers, firewalls, and the Linux kernel (from version 3.3 onwards). This transport lets a VM talk to another VM, router, or firewall directly. Periodt.
- src=srcaddr — source address (mandatory).
- dst=dstaddr — destination address (mandatory).
- udp — select udp encapsulation (default is ip).
- srcport=srcport — source udp port.
- dstport=dstport — destination udp port.
- ipv6 — force v6, otherwise defaults to v4.
- rxcookie=rxcookie; txcookie=txcookie — Cookies are a weak form of security in the l2tpv3 specification. Their function is mostly to prevent misconfiguration. By default they are 32 bit.
- cookie64 — Set cookie size to 64 bit instead of the default 32.
- counter=off — Force a 'cut-down' L2TPv3 with no counter as in draft-mkonstan-l2tpext-keyed-ipv6-tunnel-00.
- pincounter=on — Work around broken counter handling in peer. This may also help on networks which have packet reorder.
- offset=offset — Add an extra offset between header and data.

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

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

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

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

-netdev vde,id=id[,sock=socketpath][,port=n][,group=groupname][,mode=octalmode] — VDE backend vibes ✨. This 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 though: this option is only available if QEMU has been compiled with vde support enabled 🙈.

Example:

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

-netdev af-xdp,id=str,ifname=name[,mode=native|skb][,force-copy=on|off][,queues=n][,start-queue=m][,inhibit=on|off][,sock-fds=x:y:...:z] — AF_XDP backend, bestie, and it's giving speed 🦋. This 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, which defaults to best-effort — meaning the likely most performant mode will be in use. Number of queues n should generally match the number or queues in the interface, and defaults to 1. Traffic arriving on non-configured device queues will not be delivered to the network backend. No cap.

# 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

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

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

XDP program can also be loaded externally. In this case inhibit option should be set to on and sock-fds provided with file descriptors for already open but not bound XDP sockets already added to a socket map for 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

-netdev vhost-user,chardev=id[,vhostforce=on|off][,queues=n] — okay so this establishes a vhost-user netdev, backed by a chardev id. The chardev should be a unix domain socket backed one, fr fr. The vhost-user uses a specifically defined protocol to pass vhost ioctl replacement messages to an application on the other end of the socket. On non-MSIX guests, the feature can be forced with vhostforce. Use queues=n to specify the number of queues to be created for multiqueue vhost-user. Main character energy 👑

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] — bestie, this one sets up a vhost-vdpa netdev 💅

So like, a vDPA device is a device that uses a datapath which complies with the virtio specifications, but has a vendor specific control path. And here's the tea: vDPA devices can be either physically sitting on the hardware, or emulated by software. Both! Iconic.

-netdev hubport,id=id,hubid=hubid[,netdev=nd] — makes a hub port on the emulated hub with ID hubid 🎀

The way that hubport netdev works is it lets you connect a NIC to a QEMU emulated hub instead of to a single netdev. OR — and this is the cute part — you can also connect the hubport to another netdev with ID nd using the netdev=nd option. Your choice, queen.

-net nic[,netdev=nd][,macaddr=mac][,model=type][,name=name][,addr=addr][,vectors=v] — the legacy option to configure or create an on-board (or machine default) Network Interface Card (NIC) and connect it either to the emulated hub with ID 0 (i.e. the default hub), or to the netdev nd. ⚠️

If model is omitted, then the default NIC model associated with the machine type is used. But heads up — the default NIC model may change in future QEMU releases, so it is highly recommended to always specify a model. Like, always. Fr fr.

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. Also 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 to get a list of available devices for your target. Slay 🫶

-net user|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 💖

Okay so 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, vc, ringbuf, file, pipe, console, serial, pty, stdio, braille, parallel, spicevmc, spiceport. The specific backend will determine the applicable options, bestie.

Use -chardev help to print all available chardev backend types. ✨

All devices must have an id, which can be any string up to 127 characters long. It is used to uniquely identify this device in other command line directives. So don't skip it.

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.) Main character energy honestly 👑

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

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

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

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

When you're using a multiplexed character device, some escape sequences are interpreted in the input. See the chapter about Keys in the character backend multiplexer in the System Emulation Users Guide for more details. iykyk 📖

Not me about to forget this one — 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. Sneaky.

There is currently no support for multiplexing in the other direction (where a single QEMU front end takes input and output from multiple chardevs). Sad, but true.

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

✨ The available backends are: ✨

-chardev null,id=id — a void device. This device will not emit any data, and will drop any data it receives. The null backend does not take any options. It's giving nothing and that's the point 💀
-chardev socket,id=id[,TCP options or unix options][,server=on|off][,wait=on|off][,telnet=on|off][,websocket=on|off][,reconnect=seconds][,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. ⚠️ 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 sets the timeout for reconnecting on non-server sockets when the remote end goes away. qemu will delay this many seconds and then attempt to reconnect. Zero disables reconnecting, and is the default.

tls-creds requests enablement of the TLS protocol for encryption, and specifies the id of the TLS credentials to use for the handshake. The credentials must be previously created with the -object tls-creds argument.

tls-auth provides the ID of the QAuthZ authorization object against which the client's x509 distinguished name will be validated. This object is only resolved at time of use, so can be deleted and recreated on the fly while the chardev server is active. If missing, it will default to denying access. 🚫

TCP and unix socket options are given below:

TCP options:

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

host for a listening socket specifies the local address to be bound. For a connecting socket 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. Simple, clean, iconic 🐭
-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. So like, be careful bestie 💜

If input-path is specified, that's the path of a second file, and it gets used for input. No input-path? Then no input is available from the chardev at all. Periodt.

Heads up bestie: input-path is not supported on Windows hosts. 💀

-chardev pipe,id=id,path=path — makes a two-way connection to the guest. The behaviour is a lil different depending on whether you're on Windows or not:

On Windows, one single duplex pipe gets created at \\.pipe\path.

On other hosts, you get 2 pipes called path.in and path.out. Anything you write to path.in the guest receives. Anything the guest writes, you can read from path.out. And no, QEMU will not create these fifos for you — they gotta already be there. 🙈

path is the part that makes up the pipe path like we said above, and path is required.

-chardev console,id=id — sends traffic from the guest straight to QEMU's standard output. console takes zero options, she's low maintenance. ✨

console is only available on Windows hosts.

-chardev serial,id=id,path=path — sends traffic from the guest to a serial device on the host.

On Unix hosts, serial will literally accept any tty device, not just serial lines. She's flexible like that. 💅

path specifies the name of the serial device to open.

-chardev pty,id=id — creates a brand new pseudo-terminal on the host and connects to it. pty takes no options whatsoever.

pty is not available on Windows hosts.

-chardev stdio,id=id[,signal=on|off] — connects to standard input and standard output of the QEMU process itself. main character energy fr.

signal controls whether signals are enabled on the terminal — and yes, that includes being able to exit QEMU with the key sequence Control-c. This option is enabled by default, so use signal=off if you want it gone.

-chardev braille,id=id — connects to a local BrlAPI server. braille takes no options.
-chardev parallel,id=id,path=path

parallel is only available on Linux, FreeBSD and DragonFlyBSD hosts.

Connect to a local parallel port.

path specifies the path to the parallel port device, and path is required.

-chardev spicevmc,id=id,debug=debug,name=name — spicevmc is only available when spice support is built in.

debug — debug level for spicevmc

name — name of the spice channel to connect to

Connects to a spice virtual machine channel, like vdiport.

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

debug — debug level for spicevmc

name — name of the spice port to connect to

Connects 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]

The specific backend type is what decides which options actually apply. And listen — 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, no solo acts. 🫶

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

The available backends are:

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

path specifies the path to the host's TPM device — so on a Linux host that'd 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 for cancellation of an ongoing TPM command. cancel-path is optional, and by default QEMU will go searching for the sysfs entry to use.

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

The TPM device accessed by the passthrough driver must not be used by any other application on the host.
Since the host's firmware (BIOS/UEFI) has already initialized the TPM, the VM's firmware (BIOS/UEFI) will not be able to initialize the TPM again, and so it may 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. And further: if TPM ownership gets released from inside a VM, then the host's TPM will get disabled and deactivated. To enable and activate the TPM again after that, the host has to be rebooted and the user is required to enter the firmware's menu to enable and activate the TPM. And if the TPM is left disabled and/or deactivated, most TPM commands will fail. 😭

To create a passthrough TPM, use these following two options:

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

Note that the -tpmdev id here is tpm0, and it's referenced by tpmdev=tpm0 in the device option. iykyk 💅

-tpmdev emulator,id=id,chardev=dev — (Linux-host only) enables access to a TPM emulator using a Unix domain socket based chardev backend.

chardev specifies the unique ID of a character device backend that provides the connection to the software TPM server.

To create a TPM emulator backend device with 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:

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 great for quickly testing kernels, but since there's no firmware to pass configuration information to the kernel, the hardware must either be probeable, or the kernel must be built for the exact configuration, or it must be passed some configuration data (like a DTB blob) telling it what drivers it needs. The exact details are often hardware specific, ngl.

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's given. For other machines, the stricter -pflash option needs an image that is sized for the flash device for that given machine type. no cap.

Please see the QEMU System Emulator Targets 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, though 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 the kernel is started — what address it's loaded at, what if any information gets 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. ✨

-kernel bzImage — use bzImage as the kernel image. The kernel can be either a Linux kernel or in multiboot format.
-append cmdline — use cmdline as the 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 a 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. 👑

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's 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 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 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 the file file.
-fw_cfg [name=]name,string=str — add a named fw_cfg entry with contents from the string str.

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

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

Example:

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

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

🌈 serial girlies rise 🌈

-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 up to 4 serial ports. Obsessed, honestly.

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 — [Linux only] Pseudo TTY (a new PTY is automatically allocated)
none — No device is allocated. Note that for machine types which emulate systems where a serial device is always present in real hardware, this may be equivalent to the null option, in that the serial device is still present but all output is discarded. For boards where the number of serial ports is truly variable, this suppresses the creation of the device.
null — A guest will see the UART or serial device as present in the machine, but all output is discarded, and there is no input. Conceptually equivalent to redirecting the output to /dev/null.
chardev:id — Use a named character device defined with the -chardev option.
/dev/XXX — [Linux only] Use host tty, e.g. /dev/ttyS0. The host serial port parameters are set according to the emulated ones.
/dev/parportN — [Linux only, parallel port only] Use host parallel port N. Currently SPP and EPP parallel port features can be used.
file:filename — Write output to filename. No character can be read.
stdio — [Unix only] standard input/output
pipe:filename — name pipe filename
COMn — [Windows only] Use host serial port n
udp:[remote_host]:remote_port[@[src_ip]:src_port] — This implements UDP Net Console. When remote_host or src_ip are not specified they default to 0.0.0.0. When not using a specified src_port a random port is automatically chosen.

If you just want a simple readonly console you can use netcat or nc, by starting QEMU with: -serial udp::4555 and nc as: nc -u -l -p 4555. Any time QEMU writes something to that port it will appear in the netconsole session.

If you plan to send characters back via netconsole or you want to stop and start QEMU a lot of times, you should have QEMU use the same source port each time by using something like -serial udp::4555@:4556 to QEMU. Another approach is to use a patched version of netcat which can listen to a TCP port and send and receive characters via udp. If you have a patched version of netcat which activates telnet remote echo and single char transfer, then you can use the following options to set up a netcat redirector to allow telnet on port 5555 to access the QEMU port.

QEMU Options:

-serial udp::4555@:4556

netcat options:

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

telnet options:

localhost 5555

tcp:[host]:port[,server=on|off][,wait=on|off][,nodelay=on|off][,reconnect=seconds] — 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=on 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.
unix:path[,server=on|off][,wait=on|off][,reconnect=seconds] — 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.

braille — Braille device. This will use BrlAPI to display the braille output on a real or fake device.
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. aesthetic ✨
-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.

-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.
-singlestep — This is a deprecated synonym for the TCG accelerator property one-insn-per-tb. bestie it's deprecated, use the new thing okay?
--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.
-S — Do not start CPU at startup (you must type 'c' in the monitor).
-overcommit mem-lock=on|off
-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 (disabled by default). This works when host memory is not overcommitted and reduces the worst-case latency for guest.

...Guest ability to manage power state of host cpus (which lowkey means increasing latency for other processes on the same host cpu, but decreasing latency for the guest, the tradeoff is real bestie) can be turned on via cpu-pm=on — and it's disabled by default. The way this works best is when the host CPU is not overcommitted. Also heads up: when you use it, the host's estimates of CPU cycle and power utilization will be incorrect, because they don't take guest idle time into account. Not a bug, just math being math 💅

-gdb dev — Accept a gdb connection on device dev (peep the GDB usage chapter in the System Emulation Users Guide for the full tea). Important: this option does not pause QEMU execution — so if you want QEMU to hold off starting the guest until you connect with gdb and hit continue, you gotta also pass the -S option to QEMU. 🫶

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, no cap. 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 (see the GDB usage chapter in the System Emulation Users Guide). Short and slay ✨
-d item1[,...] — Enable logging of specified items. Use -d help for a list of log items. Iconic little lookup moment 💖
-D logfile — Output log in logfile instead of to stderr.
-dfilter range1[,...] — Filter debug output to only that relevant to a range of target addresses. The filter spec can be either start+size, start-size or start..end where start, end and size are the addresses and sizes required. For example:

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

Will dump output for any code in the 0x1000 sized block starting at 0x8000 and the 0x200 sized block starting at 0xffffffc000080000 and another 0x1000 sized block starting at 0xffffffc00005f000. Math girlies rise up 🌸

-seed number — Force the guest to use a deterministic pseudo-random number generator, seeded with number. Note: this does not affect crypto routines within the host. Just so we're clear 💀
-L path — Set the directory for the BIOS, VGA BIOS and keymaps.

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

-enable-kvm — Enable KVM full virtualization support. This option is only available if KVM support is enabled when compiling. So if it's not there, it's not you, it's the build 🙈
-xen-domid id — Specify xen guest domain id (XEN only).
-xen-attach — Attach to existing xen domain. libxl will use this when starting QEMU (XEN only). Restrict set of available xen operations to specified domain id (XEN only).
-no-reboot — Exit instead of rebooting. Periodt.
-no-shutdown — Don't exit QEMU on guest shutdown, but instead only stop the emulation. This allows for instance switching to monitor to commit changes to the disk image. Sneaky but useful 💅
-action event=action — The action parameter serves to modify QEMU's default behavior when certain guest events occur. It provides a generic method for specifying the same behaviors that are 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 (loadvm in monitor). Instantly in your feels, no loading screen 💖
-daemonize — Daemonize the QEMU process after initialization. QEMU will not detach from standard IO until it is ready to receive connections on any of its devices. This option is a useful way for external programs to launch QEMU without having to cope with initialization race conditions. Considerate king behavior honestly 👑
-option-rom file — Load the contents of file as an option ROM. This option is useful to load things like EtherBoot.
-rtc [base=utc|localtime|datetime][,clock=host|rt|vm][,driftfix=none|slew]

Specify base as utc or localtime to let the RTC start at the current UTC or local time, respectively. localtime is required for correct 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 host support 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. Sorry to the perfectionists 💀

When the virtual cpu is sleeping, the virtual time will advance at default speed unless sleep=on is specified. With sleep=on, 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=off. sleep=on 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. Time travel era 🦋

-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. Bestie, 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

-incoming tcp:[host]:port[,to=maxport][,ipv4=on|off][,ipv6=on|off]
-incoming rdma:host:port[,ipv4=on|off][,ipv6=on|off] — Prepare for incoming migration, listen on a given tcp port.
-incoming unix:socketpath — Prepare for incoming migration, listen on a given unix socket.
-incoming fd:fd — Accept incoming migration from a given file descriptor.
-incoming file:filename[,offset=offset] — Accept incoming migration from a given file starting at offset. offset allows the common size suffixes, or a 0x prefix, but not both. Pick a lane 💅
-incoming exec:cmdline — Accept incoming migration as an output from specified external command.
-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. Main character patience energy ✨
-only-migratable — Only allow migratable devices. Devices will not be allowed to enter an unmigratable state.
-nodefaults — Don't create default devices. Normally, QEMU sets the default devices like serial port, parallel port, virtual console, monitor device, VGA adapter, floppy and CD-ROM drive and others. The -nodefaults option will disable all those default devices. Full control, full slay 🎀

-chroot dir — deprecated bestie, we don't do this anymore 😭 use -run-with chroot=... instead, ok?? It does one thing: right before guest execution kicks off, it chroots into dir. Super handy when you're pairing it with -runas — the two of them are like a little duo 💅
-runas user — right before guest execution starts, QEMU drops root privileges and switches to user. Bye bye root, hello least-privilege era ✨
-prom-env variable=value — sets an OpenBIOS nvram variable to value. (PPC, SPARC only, so if you're on anything else this is just noise to you 🫶)

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'

Look at those backslashes doing their lil line-continuation thing, iconic behavior honestly 🦋

-semihosting — enables Semihosting mode. (ARM, M68K, Xtensa, MIPS, Nios II, RISC-V only — everybody else, this isn't for you 🙈)

⚠️ WARNING, and I mean it: this literally lets the guest reach straight into the host filesystem. So only ever, ever use this with a guest OS you fully trust. No cap. 💀

Want the full tea on what this actually unlocks? Go read the -semihosting-config docs below.

-semihosting-config [enable=on|off][,target=native|gdb|auto][,chardev=id][,userspace=on|off][,arg=str[,...]] — turns Semihosting on and lets you fine-tune it. (ARM, M68K, Xtensa, MIPS, Nios II, RISC-V only)

⚠️ Same warning, same energy: this gives the guest direct access to the host filesystem. Trusted guest OS only, bestie. Periodt. 🔥

target=native|gdb|auto — picks where the semihosting calls get sent: either to QEMU (native) or to GDB (gdb). Default is auto, which is giving "gdb while you're in a debug session, native every other time" 🌈
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 gets to make semihosting calls. And note: only set userspace=on if literally all the guest code is trusted (like, bare-metal test case code vibes) 👑
arg=str1,arg=str2,... — lets you pass input arguments, and you can use it multiple times to build up a whole list. The old-school -kernel/-append way of passing a command line is still supported for backward compatibility 🫶. And if you specify both the --semihosting-config arg and -kernel/-append? The former goes to semihosting, because it always takes precedence 💅

-old-param — old param mode. (ARM only)
-sandbox arg[,obsolete=string][,elevateprivileges=string][,spawn=string][,resourcecontrol=string] — enables the Seccomp mode 2 system call filter 🛡️. on turns syscall filtering on and off turns it off. Default is off.
- obsolete=string — enable obsolete system calls 🌸
- elevateprivileges=string — disable set*uid|gid system calls
- spawn=string — disable *fork and execve 🙈
- resourcecontrol=string — disable process affinity and schedular priority
-readconfig file — reads the device configuration from file. This is the move when you wanna spawn a QEMU process with a bajillion command line options but you do NOT wanna hit the command line character limit — your shell will thank you 🎀
-no-user-config — makes QEMU not load any of the user-provided config files on sysconfdir. i.e. "I brought my own config, thank you very much" energy
-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 only exists if QEMU was compiled with the simple, log or ftrace tracing backend. Wanna hit multiple events or patterns? Just pass -trace multiple times, no biggie ✨

Pro tip from me to you: run -trace help and it prints you a whole list of trace point names 📋

events=FILE — immediately enables the events listed in FILE. The file has to have one event name per line (the names as listed in the trace-events-all file); 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. simple backend girlies, this one's for you 💅

-plugin file=file[,argname=argvalue] — loads 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. 🫶)
-async-teardown — this option is deprecated and should no longer be used. The new option -run-with async-teardown=on is its replacement 💖
-run-with [async-teardown=on|off][,chroot=dir] — 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 exits. Why do we care? Because it 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 ✨. One catch: this only works if the cleanup process isn't forcefully killed with SIGKILL before the main QEMU process has terminated completely. 💀

chroot=dir does a chroot into the specified directory immediately before starting the guest execution. Especially useful in combination with -runas 🫶

-msg [timestamp[=on|off]][,guest-name[=on|off]] — controls the error message format 💬
- timestamp=on|off — prefixes messages with a timestamp. Default is off.
- guest-name=on|off — prefixes messages with the guest name, but only if the -name guest option is set — otherwise the option is just ignored. Default is off. ngl, conditional prefixes are so drama 🙈
-dump-vmstate file — dumps json-encoded vmstate information for the current machine type to file in file 📦
-enable-sync-profile — enables synchronization profiling ✨
-perfmap — generates a map file for Linux perf tools that lets basic profiling information be broken down into basic blocks 🔬
-jitdump — generates a dump file for Linux perf tools that maps basic blocks to symbol names, line numbers and JITted code 🗺️

🎀 Generic object creation 🎀

-object typename[,prop1=value1,...] — creates a new object of type typename, setting properties in the order they're specified. Note that the id property MUST be set, ok?? 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 you can use to back the guest RAM with huge pages 👑

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 gives you the size of the memory region, and it accepts the 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 decides whether the memory region is marked as private to QEMU, or shared. The shared vibe allows a co-operating external process to access the QEMU memory region 🤝

share is also required for pvrdma devices, because of limitations in the RDMA API that Linux provides. Not our fault, it's the API's fault 😭

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 in the Linux kernel source tree for the extra 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. Careful though: discard-data is only an optimization, and QEMU might not discard file contents if it aborts unexpectedly or gets terminated using SIGKILL. 💀

The merge boolean option enables memory merge, also known as MADV_MERGEABLE, so that Kernel Samepage Merging will consider the pages for memory deduplication 🧠✨

Setting the dump boolean option to off excludes the memory from core dumps. This feature is also known as MADV_DONTDUMP.

The prealloc boolean option enables memory preallocation.

The host-nodes option binds the memory range to a list of NUMA host nodes.

The policy option sets the NUMA policy to one of these values:

default — default host policy 🌈
preferred — prefer the given host node list for allocation 💖
bind — restrict memory allocation to the given host node list 🔒
interleave — interleave memory allocations across the given host node list 🎀

The align option specifies the base address alignment when QEMU mmap(2)s mem-path, and it accepts common suffixes, e.g. 2M. Some backend store specified by mem-path needs an alignment different from the default one QEMU uses — e.g. the device DAX /dev/dax0.0 requires 2M alignment rather than 4K. In those cases, you can just specify the alignment you need via this option 💅

offset — where in the target file this region actually kicks off, bestie. Use it to back a whole bunch of regions with just one file. ✨
pmem — is the backing file from mem-path sitting in host persistent memory that's reachable through the SNIA NVM programming model (think Intel NVDIMM)? If you set pmem to on, QEMU does the whole little routine to guarantee its own writes to mem-path actually persist (like in vNVDIMM label emulation and live migration). It also maps the backend file with the MAP_SYNC flag, which keeps the file metadata in sync for mem-path even if the host crashes or the power dies 😭. Heads up though: MAP_SYNC needs love from both the host kernel (Linux kernel 4.15 and up) and the filesystem of mem-path mounted with the DAX option.
readonly — does the backing file get opened read-only, or read-write? Read-write is the default, periodt.
rom — should we make Read Only Memory (ROM) that the VM literally cannot modify? Any write attempt to that ROM gets denied, no cap. Most use cases want proper RAM, not ROM. But some selected use cases — R/O NVDIMMs, we're looking at you 👀 — really do benefit from ROM. Set it to on and you get ROM; off and you get writable RAM; auto (the default) and it just uses whatever the readonly option says. This one's mainly here for 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, so you also set rom=off. 💅

-object memory-backend-ram,id=id,merge=on|off,dump=on|off,share=on|off,prealloc=on|off,size=size,host-nodes=host-nodes,policy=default|preferred|bind|interleave — makes a memory backend object, which can back the guest RAM. These objects give you way more control than the -m option that's traditionally used to define guest RAM. For a rundown of the options, go peek at memory-backend-file (it's giving very much the same energy). 🫶
-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 — makes an anonymous memory file backend object, which lets QEMU share the memory with an external process (like when you're using vhost-user, iykyk). The memory is allocated with memfd plus optional sealing. Linux only, bestie. 🐧
- The seal option creates a sealed-file, which blocks any further resizing of the memory (it's on by default).
- The hugetlb option says 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 (and it has to be a power of 2 value that the system actually supports).
- On some versions of Linux, the hugetlb option is incompatible with the seal option (needs at least Linux 4.16).
- For the other options, go refer to memory-backend-file.
- The share boolean option is on by default with memfd. ✨
-object rng-builtin,id=id — makes a random number generator backend that gets its entropy from QEMU builtin functions. The id parameter is a unique ID that'll be used to reference this entropy backend from the virtio-rng device. And fun fact: by default, the virtio-rng device uses this RNG backend. 🎀
-object rng-random,id=id,filename=/dev/random — makes a random number generator backend that pulls entropy from a device on the host. The id parameter is a unique ID used to reference this entropy backend from the virtio-rng device. The filename parameter says which file to get entropy from, and if you leave it out it defaults to /dev/urandom.
-object rng-egd,id=id,chardev=chardevid — makes a random number generator backend that gets entropy from an external daemon running on the host. The id parameter is a unique ID 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 — makes a TLS anonymous credentials object, which can be used to give TLS support on network backends. The id parameter is a unique ID that network backends use to access the credentials. The endpoint is either server or client, depending on whether the QEMU network backend using these credentials is acting as a client or a server. If verify-peer is enabled (and yes, that's the default) then once the handshake is done, the peer credentials get verified — though for anonymous credentials that's a total 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 that file's missing, QEMU just generates a set of DH parameters at startup — which is a computationally expensive operation that eats up random pool entropy, so like, highly recommend generating a persistent set of parameters upfront and saving them. 💖

-object tls-creds-psk,id=id,endpoint=endpoint,dir=/path/to/keys/dir[,username=username] — makes a TLS Pre-Shared Keys (PSK) credentials object, which can be used to give TLS support on network backends. The id parameter is a unique ID that network backends use to access the credentials. The endpoint is either server or client, depending on whether the QEMU network backend using these credentials is acting as a client or a server. For clients only, username is the username that gets sent to the server — and 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 it contains username:key pairs. Easiest way to make this file? The GnuTLS psktool program.

For server endpoints, dir may also contain a file dh-params.pem providing diffie-hellman parameters to use for the TLS server. If the file's missing, QEMU generates a set of DH parameters at startup. Again: computationally expensive, munches random pool entropy, so generate a persistent set of parameters up front and save them. ⭐

-object tls-creds-x509,id=id,endpoint=endpoint,dir=/path/to/cred/dir,priority=priority,verify-peer=on|off,passwordid=id — makes a TLS anonymous credentials object, which can be used to give TLS support on network backends. The id parameter is a unique ID that network backends use to access the credentials. The endpoint is either server or client, depending on whether the QEMU network backend using these credentials is acting as a client or a server. If verify-peer is enabled (the default, bestie) then once the handshake completes, the peer credentials get verified. With x509 certificates, that implies the clients have to be given valid client certificates too. No shortcuts. 🎀

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's missing, QEMU generates a set of DH parameters at startup. (You know the drill: computationally expensive, consumes random pool entropy, generate a persistent set upfront and save it.) 💜

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

For the server-key.pem and client-key.pem files — which contain sensitive private keys, so be careful — it's 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. 🔐

The priority parameter lets you override the global default priority used by gnutls. Super handy if a system administrator needs a weaker set of crypto priorities for QEMU without forcing that weakness onto literally every other application. Or, flip side, if someone wants a stronger default for QEMU than for all the other apps, they can do it 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,id=id,priority=priority — okay bestie, this one makes a TLS cipher suites object, and what it does is let you control which TLS cipher/protocol algorithms your apps are even allowed to use. 💅

The id parameter is a unique ID, and frontends use it to go grab the ordered list of permitted TLS cipher suites from the host. ✨

The priority parameter lets you override the global default priority that gnutls uses. This is lowkey so useful if a sysadmin needs QEMU to run a weaker set of crypto priorities without forcing that weakness onto literally every other app on the system. Or, flip side, if you want a stronger default just for QEMU than for everything else — you do that with this parameter too. Its format is a gnutls priority string, described over at https://gnutls.org/manual/html_node/Priority-Strings.html. 🦋

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

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

# qemu-system-x86_64 \
    -object tls-cipher-suites,id=mysuite0,priority=@SYSTEM \
    -fw_cfg name=etc/edk2/https/ciphers,gen_id=mysuite0

-object filter-buffer,id=id,netdev=netdevid,interval=t[,queue=all|rx|tx][,status=on|off][,position=head|tail|id=<id>][,insert=behind|before] — so the interval t can't be 0 (fr fr, don't try it), and this filter batches packet delivery: every packet arriving in a given interval on netdev netdevid gets delayed until the end of the interval. The interval is in microseconds. ⏱️

status is optional and says whether the netfilter is on (enabled) or off (disabled) — the default status for netfilter is on. ✨

queue all|rx|tx is an option you can slap onto 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 receives packets sent to the netdev.
tx: the filter is attached to the transmit queue of the netdev, where it receives packets sent by the netdev.

position head|tail|id=<id> is how you say where the filter should be inserted in the filter list. Also applies 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> — peep the insert option below. 👀

insert behind|before says where to insert the new filter relative to the one you specified with position=id=<id>. Yep, applies to any netfilter:

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

-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 packets to chardev chardevid. And if it has the vnet_hdr_support flag, filter-mirror will mirror the packet with vnet_hdr_len. 🪞✨
-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 redirects the filter's net packet to chardev chardevid, and redirects indev's packet to the filter. If it has the vnet_hdr_support flag, filter-redirector will redirect packets with vnet_hdr_len. 🎀

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

-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 part of the COLO project. It rewrites TCP packets going to the secondary from the primary to keep the secondary's TCP connection alive, and rewrites TCP packets going to the primary from the secondary so the client can actually handle them. If it has the vnet_hdr_support flag, we can parse packets with a 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,id=id,netdev=dev[,file=filename][,maxlen=len][,position=head|tail|id=<id>][,insert=behind|before] — dumps the network traffic on netdev dev into the file specified by filename. At most len bytes (64k by default) per packet get stored. The file format is libpcap, so you can analyze it with tools like tcpdump or Wireshark. 🕵️♀️📦
-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 grabs packets from primary_in chardevid and secondary_in, then compares whether the payload of the primary packet and the secondary packet are the same. If they're the same, it outputs the primary packet to out_dev. If not, it notifies the COLO-framework to do a checkpoint and sends the primary packet to out_dev. To be efficient about it, we need to put the comparison task in another iothread. And if it has the vnet_hdr_support flag, colo compare will send/recv packets with vnet_hdr_len. 🫶

compare_timeout=@var{ms} determines the maximum time that colo-compare holds the packet. expired_scan_cycle=@var{ms} sets the period for scanning expired primary node network packets. max_queue_size=@var{size} sets the max compare queue size, depending on your environment. And if you want to use Xen COLO, you need to add notify_dev so it can notify the Xen colo-frame to do a checkpoint. 👑

COLO-compare must be used with the help of filter-mirror, filter-redirector and filter-rewriter. No cap, it doesn't fly solo.

KVM COLO

primary:

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

secondary:

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

Xen COLO

primary:

-netdev tap,id=hn0,vhost=off,script=/etc/qemu-ifup,downscript=/etc/qemu-ifdown
-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=nofity_way,iothread=iothread1

                        secondary:
                        -netdev tap,id=hn0,vhost=off,script=/etc/qemu-ifup,down script=/etc/qemu-ifdown
                        -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

okay and if you're like "bestie what is even happening in that command line", the manpage literally says: go read the colo-compare git log. that's it. that's the documentation. slay, i guess 💅

-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 later to point at this backend from the virtio-crypto device. queues is optional and sets the queue number of the cryptodev backend — the default for 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] — creates a vhost-user cryptodev backend, backed by a chardev called chardevid. id is a unique ID used to reference this cryptodev backend from the virtio-crypto device. the 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. queues is optional and sets the queue number of the cryptodev backend for multiqueue vhost-user — 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 to stash a password, encryption key, or honestly any other sensitive data. the sensitive data can go in directly via the data parameter, or sneak in indirectly via the file parameter. heads up: using the data parameter is insecure unless that sensitive data is encrypted. 🔐

the sensitive data can be handed over in raw format (that's the default), or as base64. when it's encoded as JSON, raw format only supports valid UTF-8 characters, so base64 is the recommended move for sending binary data. QEMU will convert from whichever format you give it into whatever format it needs internally. like, an RBD password can be provided in raw format even though it'll be base64 encoded when it gets passed on to the RBD sever.

for extra protection you can encrypt the data attached to a secret using the AES-256-CBC cipher. you know encryption is on when you provide the keyid and iv parameters. keyid gives the ID of a previously defined secret that holds the AES-256 decryption key — that key should be 32-bytes long and base64 encoded. iv provides the random initialization vector used for encrypting this particular secret, and it should be a base64 encrypted string of the 16-byte IV.

the simplest (and, again, insecure) usage is just to yeet the secret inline:

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

the simplest secure usage is to hand the secret over 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 show how, the manpage pulls in the openssl command line tool, which can encrypt the data. note that when you're 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"')

every secret that's going to be encrypted needs its own 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"')

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

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

when launching QEMU, create a master secret pointing at key.b64 and say that's the one to use 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] — creates a Secure Encrypted Virtualization (SEV) guest object, which you'd use to get guest memory encryption support on AMD processors. 👑

when memory encryption is enabled, one of the physical address bits (aka the C-bit) is utilized to mark whether a memory page is protected. cbitpos is where you provide the C-bit position. the C-bit position is Host family dependent, so yes, the user must provide this value. on EPYC, the value should be 47.

when memory encryption is enabled, we lose certain bits in physical address space. reduced-phys-bits is where you provide the number of bits we lose in physical address space. similar to the 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.

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

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

if the guest policy allows sharing the key with another SEV guest, then handle can be used to provide the handle of the guest to share the key from.

dh-cert-file and session-file provide the guest owner's Public Diffie-Hillman key defined in the 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.

kernel-hashes adds the hashes of the 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 authz-simple,id=id,identity=string — creates an authorization object that will control access to network services. ✨

identity identifies the user, and its format depends on the network service the authorization object is associated with. for authorizing based on TLS x509 certificates, identity must be the x509 distinguished name. note that care must be taken to escape any commas in the distinguished name.

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

# qemu-system-x86_64 \
    ... \
    -object 'authz-simple,id=auth0,identity=CN=laptop.example.com,,O=Example Org,,L=London,,ST=London,,C=GB' \
    ...

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

-object authz-listfile,id=id,filename=path,refresh=on|off — creates an authorization object that will control access to network services. (yes, same energy as the one above, different flavor 🌸)

filename 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:

ok so bestie, picture the rules list like this 💅

                        {
                          "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 it's checking access, the object iterates over every single rule, and the first one that matches is the one whose policy value gets returned as the result. And if literally nothing matches? Then the default policy value gets returned. no cap, first match wins 🫶

The rules can either be an exact string match, or they can use the simple UNIX glob pattern matching so wildcards can do their thing ✨

If refresh is set to true, the file gets monitored and automatically reloaded the second its content changes. main character file behavior fr 💖

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

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

   # qemu-system-x86_64 \
       ... \
       -object authz-simple,id=auth0,filename=/etc/qemu/vnc-sasl.acl,refresh=on \
       ...

-object authz-pam,id=id,service=string — makes an authorization object that controls access to network services 🎀

The service parameter hands over the name of a PAM service to use for authorization. It requires that a file /etc/pam.d/service exist, because that's what provides the configuration for the account subsystem. no file, no service, periodt.

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

   # qemu-system-x86_64 \
       ... \
       -object authz-pam,id=auth0,service=qemu-vnc \
       ...

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

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

And 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 — 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 lowkey? That can become a scalability bottleneck. IOThreads let device emulation and I/O run on other host CPUs instead. glow up ✨

The id parameter is a unique ID that gets used to reference this IOThread from -device ...,iothread=id. Multiple devices can be assigned to one IOThread. But heads up — not all devices support an iothread parameter 🙈

The query-iothreads QMP command lists IOThreads and reports their thread IDs, so you can configure host CPU pinning/affinity. very demure, very mindful 💅

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 just spins waiting for events for a short time. The algorithm's default parameters are suitable for a lot of cases, but you can adjust them based on your 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 because it didn't poll 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 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

ok now the fun part, the key combos 💖

During the graphical emulation, you can use special key combinations from the following table to change modes. By default the modifier is Ctrl-Alt (that's what the table below uses), and you can change it with the -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. cute, right? 🎀

Ctrl-Alt-f — toggle full screen
Ctrl-Alt-+ — enlarge the screen
Ctrl-Alt-- — shrink the screen
Ctrl-Alt-u — restore the screen's un-scaled dimensions
Ctrl-Alt-n — switch to virtual console 'n'. Standard console mappings are:
1. 1 — target system display
2. 2 — monitor
3. 3 — serial port
Ctrl-Alt-g — toggle mouse and keyboard grab.

In the virtual consoles, you can use Ctrl-Up, Ctrl-Down, Ctrl-PageUp and Ctrl-PageDown to move in the back log. scrolling through history like it's your camera roll 📱

During emulation, if you're using a character backend multiplexer (which is 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
Ctrl-a x — exit emulator
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

🦋

🎀 iSCSI 🎀

iSCSI support lets QEMU hit iSCSI resources directly and use them as guest storage, bestie. Both disk and cdrom images are supported. No middleman, just vibes.

The syntax for specifying iSCSI LUNs is:

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

By default qemu uses the iSCSI initiator-name 'iqn.2008-11.org.linux-kvm[:<name>]', but bestie you can also set this from the command line or a configuration file. Your call 💅

Since version QEMU 2.4 it's possible to specify an 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. (yes it's giving "update ur libs" energy 🙈)

Example (without authentication):

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

Example (CHAP username/password via URL):

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

Example (CHAP username/password via environment variables):

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

🌈 NBD 🌈

QEMU supports NBD (Network Block Devices) using both the TCP protocol and Unix Domain Sockets. With TCP, the default port is 10809. Slay.

Syntax for specifying a NBD device using TCP, in the 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 honestly.

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. (manifesting 🕯️)

💜 GlusterFS 💜

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

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

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

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

Example:

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

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

🌸 HTTP/HTTPS/FTP/FTPS 🌸

QEMU supports read-only access to files accessed over http(s) and ftp(s). (read-only bestie, don't try to write, it's not gonna happen 🙈)

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.

💖 AUTHOR 💖

Fabrice Bellard

🌟 COPYRIGHT 🌟

2026, The QEMU Project Developers

and that's a wrap bestie!! 💅✨ This was version 8.2.2 of the QEMU(1) page, dated Apr 08, 2026 — go forth and virtualize responsibly, ily 🫶🎀🦋

📦 where this page comes from

ubuntu noble: qemu-system-misc 1:8.2.2+ds-0ubuntu1.16
💖 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)

🌸 NAME 🌸

✨ SYNOPSIS ✨

🦋 DESCRIPTION 🦋

🎀 Machine-specific options 🎀

💜 OPTIONS 💜

⭐ Standard options ⭐

🧠 hmat-lb: the latency & bandwidth lore

🎀 hmat-cache: the cache lore

🦋 the iconic example

💖 the options, continued

🎀 Block device options 🎀

🦋 Driver-specific options for file 🦋

🌸 Driver-specific options for raw 🌸

💜 Driver-specific options for qcow2 💜

🌈 Driver-specific options for other drivers 🌈

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

✨ -mtdblock file ✨

✨ -sd file ✨

✨ -snapshot ✨

✨ -fsdev ✨

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

✨ -virtfs ✨

🌈 USB convenience options 🌈

💖 Display options 💖

🌈 i386 target only 🌈

🌐 Network options 🌐

🫶 -nic

🚫 -nic none

👤 -netdev user,id=id[,option][,option][,...]

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

💖 Character device options 💖

✨ The available backends are: ✨

🎀 TPM device options 🎀

🌈 Boot Image or Kernel specific 🌈

💅 Debug/Expert options 💅

🌈 serial girlies rise 🌈

🎀 Generic object creation 🎀

🎀 iSCSI 🎀

🌈 NBD 🌈

🦋 SSH 🦋

💜 GlusterFS 💜

🌸 HTTP/HTTPS/FTP/FTPS 🌸

👑 SEE ALSO 👑

💖 AUTHOR 💖

🌟 COPYRIGHT 🌟

🦋 Driver-specific options for `file` 🦋

🌸 Driver-specific options for `raw` 🌸

💜 Driver-specific options for `qcow2` 💜

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

🫶 `-nic`

🚫 `-nic none`

👤 `-netdev user,id=id[,option][,option][,...]`

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