QEMU User Documentation — QEMU documentation

# QEMU User Documentation

## Synopsis

    qemu-system-x86_64 [options] [disk_image]

## Description

The QEMU PC System emulator simulates the following peripherals:

- 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 a large number of virtual CPUs (upper limit is configuration dependent).

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

QEMU uses YM3812 emulation by Tatsuyuki Satoh.

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

Note that, 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.

When dealing with options parameters as arbitrary strings containing commas, such as in “file=my,file” and “string=a,b”, it’s necessary to double the commas. For instance,”-fw_cfg name=z,string=a,,b” will be parsed as “-fw_cfg name=z,string=a,b”.

### Standard options

`-h`

  Display help and exit

`-version`

  Display version information and exit

`-machine [type=]name[,prop=value[,...]]`

  Select the emulated machine by name. Use `-machine help` to list available machines.

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

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

  Supported machine properties are:

  `accel=accels1[:accels2[:...]]`

    This is used to enable an accelerator. Depending on the target architecture, kvm, xen, hvf, 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 and i8042. For accel=xen or i8042=off the default is off otherwise the default is on.

  `dump-guest-core=on|off`

    Include guest memory in a core dump. The default is on.

  `mem-merge=on|off`

    Enables or disables memory merge support. This feature, when supported by the host, de-duplicates identical memory pages among VMs instances (enabled by default).

  `aes-key-wrap=on|off`

    Enables or disables AES key wrapping support on s390-ccw hosts. This feature controls whether AES wrapping keys will be created to allow execution of AES cryptographic functions. The default is on.

  `dea-key-wrap=on|off`

    Enables or disables DEA key wrapping support on s390-ccw hosts. This feature controls whether DEA wrapping keys will be created to allow execution of DEA cryptographic functions. The default is on.

  `nvdimm=on|off`

    Enables or disables NVDIMM support. The default is off.

  `memory-encryption=`

    Memory encryption object to use. The default is none.

  `hmat=on|off`

    Enables or disables ACPI Heterogeneous Memory Attribute Table (HMAT) support. The default is off.

  `memory-backend='id'`

    An alternative to legacy `-mem-path` and `mem-prealloc` options. Allows to use a memory backend as main RAM.

    For example:

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

    Migration compatibility note:

    - as backend id one shall use value of ‘default-ram-id’, advertised by machine type (available via `query-machines` QMP command), if migration to/from old QEMU (<5.0) is expected.

    - for machine types 4.0 and older, user shall use `x-use-canonical-path-for-ramblock-id=off` backend option if migration to/from old QEMU (<5.0) is expected.

    For example:

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

  `cxl-fmw.0.targets.0=firsttarget,cxl-fmw.0.targets.1=secondtarget,cxl-fmw.0.size=size[,cxl-fmw.0.interleave-granularity=granularity]`

    Define a CXL Fixed Memory Window (CFMW).

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

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

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

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

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

    Example:

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

`sgx-epc.0.memdev=@var{memid},sgx-epc.0.node=@var{numaid}`

  Define an SGX EPC section.

`-cpu model`

  Select CPU model (`-cpu help` for list and additional feature selection)

`-accel name[,prop=value[,...]]`

  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`

    When the KVM accelerator is used, it controls the size of the per-vCPU dirty page ring buffer (number of entries for each vCPU). It should be a value that is power of two, and it should be 1024 or bigger (but still less than the maximum value that the kernel supports). 4096 could be a good initial value if you have no idea which is the best. Set this value to 0 to disable the feature. By default, this feature is disabled (dirty-ring-size=0). When enabled, KVM will instead record dirty pages in a bitmap.

  `eager-split-size=n`

    KVM implements dirty page logging at the PAGE_SIZE granularity and enabling dirty-logging on a huge-page requires breaking it into PAGE_SIZE pages in the first place. KVM on ARM does this splitting lazily by default. There are performance benefits in doing huge-page split eagerly, especially in situations where TLBI costs associated with break-before-make sequences are considerable and also if guest workloads are read intensive. The size here specifies how many pages to break at a time and needs to be a valid block size which is 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 specify the corresponding notify window to trigger the VM exit if enabled. `run` option enables the feature. It does nothing and continue if the exit happens. `internal-error` option enables the feature. It raises a internal error. `disable` option doesn’t enable the feature. This feature can mitigate the CPU stuck issue due to event windows don’t open up for a specified of time (i.e. notify-window). Default: notify-vmexit=run,notify-window=0.

  `device=path`

    Sets the path to the KVM device node. Defaults to `/dev/kvm`. This option can be used to pass the KVM device to use via a file descriptor by setting the value to `/dev/fdset/NN`.

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

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

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

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

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

  Historically preference was given to the coarsest topology parameters when computing missing values (ie sockets preferred over cores, which were preferred over threads), however, this behaviour is considered liable to change. Prior to 6.2 the preference was sockets over cores over threads. Since 6.2 the preference is cores over sockets over threads.

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

      -smp 2

  Note: The cluster topology will only be generated in ACPI and exposed to guest if it’s explicitly specified in -smp.

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

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

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

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

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

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

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

  Legacy VCPU assignment uses ‘`cpus`‘ option where firstcpu and lastcpu are CPU indexes. Each ‘`cpus`‘ option represent 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

  ‘`cpu`‘ option is a new alternative to ‘`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 ‘`hotpluggable-cpus`‘ monitor command. ‘`node-id`‘ property specifies node to which CPU object will be assigned, it’s required for node to be declared with ‘`node`‘ option before it’s used with ‘`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

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

  For compatibility reasons, 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 nodes have to use ‘`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’.

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

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

  source and destination are NUMA node IDs. distance is the NUMA distance from source to destination. The distance from a node to itself is always 10. If any pair of nodes is given a distance, then all pairs must be given distances. Although, when distances are only given in one direction for each pair of nodes, then the distances in the opposite directions are assumed to be the same. If, however, an asymmetrical pair of distances is given for even one node pair, then all node pairs must be provided distance values for both directions, even when they are symmetrical. When a node is unreachable from another node, set the pair’s distance to 255.

  Note that the -`numa` option doesn’t allocate any of the specified resources, it just assigns existing resources to NUMA nodes. This means that one still has to use the `-m`, `-smp` options to allocate RAM and VCPUs respectively.

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

  In ‘`hmat-lb`‘ option, node are NUMA node IDs. hierarchy is the memory hierarchy of the target NUMA node: if hierarchy is ‘memory’, the structure represents the memory performance; if hierarchy is ‘first-level|second-level|third-level’, this structure represents aggregated performance of memory side caches for each domain. type of ‘data-type’ is type of data represented by this structure instance: if ‘hierarchy’ is ‘memory’, ‘data-type’ is ‘access|read|write’ latency or ‘access|read|write’ bandwidth of the target memory; if ‘hierarchy’ is ‘first-level|second-level|third-level’, ‘data-type’ is ‘access|read|write’ hit latency or ‘access|read|write’ hit bandwidth of the target memory side cache.

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

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

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

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

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

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

  `fd=fd`

    This option defines the file descriptor of which a duplicate is added to fd set. The file descriptor cannot be stdin, stdout, or stderr.

  `set=set`

    This option defines the ID of the fd set to add the file descriptor to.

  `opaque=opaque`

    This option defines a free-form string that can be used to describe fd.

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

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

`-set group.id.arg=value`

  Set parameter arg for item id of type group

`-global driver.prop=value`

`-global driver=driver,property=property,value=value`

  Set default value of driver’s property prop to value, e.g.:

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

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

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

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

  Specify boot order drives as a string of drive letters. Valid drive letters depend on the target architecture. The x86 PC uses: a, b (floppy 1 and 2), c (first hard disk), d (first CD-ROM), n-p (Etherboot from network adapter 1-4), hard disk boot is the default. To apply a particular boot order only on the first startup, specify it via `once`. Note that the `order` or `once` parameter should not be used together with the `bootindex` property of devices, since the firmware implementations normally do not support both at the same time.

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

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

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

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

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

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

`-m [size=]megs[,slots=n,maxmem=size]`

  Sets guest startup RAM size to megs megabytes. Default is 128 MiB. Optionally, a suffix of “M” or “G” can be used to signify a value in megabytes or gigabytes respectively. Optional pair slots, maxmem could be used to set amount of hotpluggable memory slots and maximum amount of memory. Note that maxmem must be aligned to the page size.

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

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

  If slots and maxmem are not specified, memory hotplug won’t be enabled and the guest startup RAM will never increase.

`-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 is 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 example do exactly the same, 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.

  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, they’re marked with `in|out.`. You can set the input’s property with `in.prop` and the output’s property with `out.prop`. For example:

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

  NOTE: parameter validation is known to be incomplete, in many cases specifying an invalid option causes QEMU to print an error message and continue emulation without sound.

  Valid global options are:

  `id=identifier`

    Identifies the audio backend.

  `timer-period=period`

    Sets the timer period used by the audio subsystem in microseconds. Default is 10000 (10 ms).

  `in|out.mixing-engine=on|off`

    Use QEMU’s mixing engine to mix all streams inside QEMU and convert audio formats when not supported by the backend. When off, fixed-settings must be off too. Note that disabling this option means that the selected backend must support multiple streams and the audio formats used by the virtual cards, otherwise you’ll get no sound. It’s not recommended to disable this option unless you want to use 5.1 or 7.1 audio, as mixing engine only supports mono and stereo audio. Default is on.

  `in|out.fixed-settings=on|off`

    Use fixed settings for host audio. When off, it will change based on how the guest opens the sound card. In this case you must not specify frequency, channels or format. Default is on.

  `in|out.frequency=frequency`

    Specify the frequency to use when using fixed-settings. Default is 44100Hz.

  `in|out.channels=channels`

    Specify the number of channels to use when using fixed-settings. Default is 2 (stereo).

  `in|out.format=format`

    Specify the sample format to use when using fixed-settings. Valid values are: `s8`, `s16`, `s32`, `u8`, `u16`, `u32`, `f32`. Default is `s16`.

  `in|out.voices=voices`

    Specify the number of voices to use. Default is 1.

  `in|out.buffer-length=usecs`

    Sets the size of the buffer in microseconds.

`-audiodev none,id=id[,prop[=value][,...]]`

  Creates a dummy backend that discards all outputs. This backend has no backend specific properties.

`-audiodev alsa,id=id[,prop[=value][,...]]`

  Creates 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) when playback starts. Default is 0.

`-audiodev coreaudio,id=id[,prop[=value][,...]]`

  Creates a backend using Apple’s Core Audio. This backend is only available on Mac OS and only supports playback.

  Core Audio specific options are:

  `in|out.buffer-count=count`

    Sets the count of the buffers.

`-audiodev dsound,id=id[,prop[=value][,...]]`

  Creates a backend using Microsoft’s DirectSound. This backend is only available on Windows and only supports playback.

  DirectSound specific options are:

  `latency=usecs`

    Add extra usecs microseconds latency to playback. Default is 10000 (10 ms).

`-audiodev oss,id=id[,prop[=value][,...]]`

  Creates a backend using OSS. This backend is available on most Unix-like systems.

  OSS specific options are:

  `in|out.dev=device`

    Specify the file name of the OSS device to use. Default is `/dev/dsp`.

  `in|out.buffer-count=count`

    Sets the count of the buffers.

  `in|out.try-poll=on|of`

    Attempt to use poll mode with the device. Default is on.

  `try-mmap=on|off`

    Try using memory mapped device access. Default is off.

  `exclusive=on|off`

    Open the device in exclusive mode (vmix won’t work in this case). Default is off.

  `dsp-policy=policy`

    Sets the timing policy (between 0 and 10, where 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.

`-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.

  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 automatically selected in that case, so usually you can ignore this option. 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.

  `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-ms=” chardev option to reconnect to the simulator if the connection is lost. 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=...]`

  This is only supported by `-machine q35`, which will enable Intel VT-d emulation within the guest. It supports below options:

  `intremap=on|off` (default: auto)

    This enables interrupt remapping feature. It’s required to enable complete x2apic. Currently it only supports kvm kernel-irqchip modes `off` or `split`, while full kernel-irqchip is not yet supported. The default value is “auto”, which will be decided by the mode of kernel-irqchip.

  `caching-mode=on|off` (default: off)

    This enables caching mode for the VT-d emulated device. When caching-mode is enabled, each guest DMA buffer mapping will generate an IOTLB invalidation from the guest IOMMU driver to the vIOMMU device in a synchronous way. It is required for `-device vfio-pci` to work with the VT-d device, because host assigned devices requires to setup the DMA mapping on the host before guest DMA starts.

  `device-iotlb=on|off` (default: off)

    This enables device-iotlb capability for the emulated VT-d device. So far virtio/vhost should be the only real user for this parameter, paired with ats=on configured for the device.

  `aw-bits=39|48` (default: 39)

    This decides the address width of IOVA address space. The address space has 39 bits width for 3-level IOMMU page tables, and 48 bits for 4-level IOMMU page tables.

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

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

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

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

    This decides the default granule to be be exposed by the virtio-iommu. If host, the granule matches the host page size.

  `aw-bits=val` (val between 32 and 64, default depends on machine)

    This decides the address width of the IOVA address space.

`-name name`

  Sets the name of the guest. This name will be displayed in the SDL window caption. The name will also be used for the VNC server. Also optionally set the top visible process name in Linux. Naming of individual threads can also be enabled on Linux to aid debugging.

`-uuid uuid`

  Set system UUID.

### 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. Many online guides to QEMU often reference older and deprecated options, which can lead to confusion.

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 is recommended for management tools and scripting.

The `-drive` option combines the device and backend into a single command line option which is a 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, they are 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`.

    `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.

    `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`

      Reference to or definition of the backing file block device (default is taken from the image file). It is allowed to pass `null` here in order to disable the default backing file.

    `lazy-refcounts`

      Whether to enable the lazy refcounts feature (on/off; default is taken from the image file)

    `cache-size`

      The maximum total size of the L2 table and refcount block caches in bytes (default: the sum of l2-cache-size and refcount-cache-size)

    `l2-cache-size`

      The maximum size of the L2 table cache in bytes (default: if cache-size is not specified - 32M on Linux platforms, and 8M on non-Linux platforms; otherwise, as large as possible within the cache-size, while permitting the requested or the minimal refcount cache size)

    `refcount-cache-size`

      The maximum size of the refcount block cache in bytes (default: 4 times the cluster size; or if cache-size is specified, the part of it which is not used for the L2 cache)

    `cache-clean-interval`

      Clean unused entries in the L2 and refcount caches. The interval is in seconds. The default value is 600 on supporting platforms, and 0 on other platforms. Setting it to 0 disables this feature.

    `pass-discard-request`

      Whether discard requests to the qcow2 device should be forwarded to the data source (on/off; default: on if discard=unmap is specified, off otherwise)

    `pass-discard-snapshot`

      Whether discard requests for the data source should be issued when a snapshot operation (e.g. deleting a snapshot) frees clusters in the qcow2 file (on/off; default: on)

    `pass-discard-other`

      Whether discard requests for the data source should be issued on other occasions where a cluster gets freed (on/off; default: off)

    `discard-no-unref`

      When enabled, data clusters will remain preallocated when they are no longer used, e.g. because they are discarded or converted to zero clusters. As usual, whether the old data is discarded or kept on the protocol level (i.e. in the image file) depends on the setting of the pass-discard-request option. Keeping the clusters preallocated prevents qcow2 fragmentation that would otherwise be caused by freeing and re-allocating them later. Besides potential performance degradation, such fragmentation can lead to increased allocation of clusters past the end of the image file, resulting in image files whose file length can grow much larger than their guest disk size would suggest. If image file length is of concern (e.g. when storing qcow2 images directly on block devices), you should consider enabling this option.

    `overlap-check`

      Which overlap checks to perform for writes to the image (none/constant/cached/all; default: cached). For details or finer granularity control refer to the QAPI documentation of `blockdev-add`.

    Example 1:

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

    Example 2:

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

  `Driver-specific options for other drivers`

    Please refer to the QAPI documentation of the `blockdev-add` QMP command.

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

  Define a new drive. This includes creating a block driver node (the backend) as well as a guest device, and is mostly a shortcut for defining the corresponding `-blockdev` and `-device` options.

  `-drive` accepts all options that are accepted by `-blockdev`. In addition, it knows the following options:

  `file=file`

    This option defines which disk image (see the Disk Images chapter in the System Emulation Users Guide) to use with this drive. If the filename contains comma, you must double it (for instance, “file=my,,file” to use file “my,file”).

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

  `if=interface`

    This option defines on which type on interface the drive is connected. Available types are: ide, scsi, sd, mtd, floppy, pflash, virtio, none.

  `bus=bus,unit=unit`

    These options define where is connected the drive by defining the bus number and the unit id.

  `index=index`

    This option defines where the drive is connected by using an index in the list of available connectors of a given interface type.

  `media=media`

    This option defines the type of the media: disk or cdrom.

  `snapshot=snapshot`

    snapshot is “on” or “off” and controls snapshot mode for the given drive (see `-snapshot`).

  `cache=cache`

    cache is “none”, “writeback”, “unsafe”, “directsync” or “writethrough” and controls how the host cache is used to access block data. This is a shortcut that sets the `cache.direct` and `cache.no-flush` options (as in `-blockdev`), and additionally `cache.writeback`, which provides a default for the `write-cache` option of block guest devices (as in `-device`). The modes correspond to the following settings:

    | cache.writeback | cache.direct | cache.no-flush
    --- | --- | --- | ---
    writeback | on | off | off
    none | on | on | off
    writethrough | off | off | off
    directsync | off | on | off
    unsafe | on | off | on

    The default mode is `cache=writeback`.

  `aio=aio`

    aio is “threads”, “native”, or “io_uring” and selects between pthread based disk I/O, native Linux AIO, or Linux io_uring API.

  `format=format`

    Specify which disk format will be used rather than detecting the format. Can be used to specify format=raw to avoid interpreting an untrusted format header.

  `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 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. 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 allow the guest I/O to spike above the limit temporarily.

  `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 allow the guest I/O to spike above the limit temporarily.

  `iops_size=is`

    Let every is bytes of a request count as a new request for iops throttling purposes. Use this option to prevent guests from circumventing iops limits by sending fewer but larger requests.

  `group=g`

    Join a throttling quota group with given name g. All drives that are members of the same group are accounted for together. Use this option to prevent guests from circumventing throttling limits by using many small disks instead of a single larger disk.

  By default, the `cache.writeback=on` mode is used. It will report data writes as completed as soon as the data is present in the host page cache. This is safe as long as your guest OS makes sure to correctly flush disk caches where needed. If your guest OS does not handle volatile disk write caches correctly and your host crashes or loses power, then the guest may experience data corruption.

  For such guests, you should consider using `cache.writeback=off`. 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 after QEMU has made sure to flush each write to the disk. Be aware that this has a major impact on performance.

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

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

  Instead of `-cdrom` you can use:

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

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

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

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

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

  You can connect a CDROM to the slave of ide0:

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

  If you don’t specify the “file=” argument, you define an empty drive:

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

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

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

  By default, interface is “ide” and index is automatically incremented:

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

  is interpreted like:

      qemu-system-x86_64 -hda a -hdb b

`-mtdblock file`

  Use file as on-board Flash memory image.

`-sd file`

  Use file as SecureDigital card image.

`-snapshot`

  Write to temporary files instead of disk image files. In this case, the raw disk image you use is not written back. You can however force the write back by pressing C-a s (see the Disk Images chapter in the System Emulation Users Guide).

  Warning

  snapshot is incompatible with `-blockdev` (instead use qemu-img to manually create snapshot images to attach to your blockdev). If you have mixed `-blockdev` and `-drive` declarations you can use the ‘snapshot’ property on your drive declarations instead of this global option.

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

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

  Define a new file system device. Valid options are:

  `local`

    Accesses to the filesystem are done by QEMU.

  `synth`

    Synthetic filesystem, only used by QTests.

  `id=id`

    Specifies identifier for this device.

  `path=path`

    Specifies the export path for the file system device. Files under this path will be available to the 9p client on the guest.

  `security_model=security_model`

    Specifies the security model to be used for this export path. Supported security models are “passthrough”, “mapped-xattr”, “mapped-file” and “none”. In “passthrough” security model, files are stored using the same credentials as they are created on the guest. This requires QEMU to run as root. In “mapped-xattr” security model, some of the file attributes like uid, gid, mode bits and link target are stored as file attributes. For “mapped-file” these attributes are stored in the hidden .virtfs_metadata directory. Directories exported by this security model cannot interact with other unix tools. “none” security model is same as passthrough except the sever won’t report failures if it fails to set file attributes like ownership. Security model is mandatory only for local fsdriver.

  `writeout=writeout`

    This is an optional argument. The only supported value is “immediate”. This means that host page cache will be used to read and write data but write notification will be sent to the guest only when the data has been reported as written by the storage subsystem.

  `readonly=on`

    Enables exporting 9p share as a readonly mount for guests. By default read-write access is given.

  `fmode=fmode`

    Specifies the default mode for newly created files on the host. Works only with security models “mapped-xattr” and “mapped-file”.

  `dmode=dmode`

    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 allow the guest I/O to 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 allow the guest I/O to 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 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 -fsdev option.

  `mount_tag=mount_tag`

    Specifies the tag name to be used by the guest to mount this export point.

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

`-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 by using the 9P network protocol for communication between host and guests, if desired even accessible, 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.

  `synth`

    Synthetic filesystem, only used by QTests.

  `id=id`

    Specifies identifier for the filesystem device

  `path=path`

    Specifies the export path for the file system device. Files under this path will be available to the 9p client on the guest.

  `security_model=security_model`

    Specifies the security model to be used for this export path. Supported security models are “passthrough”, “mapped-xattr”, “mapped-file” and “none”. In “passthrough” security model, files are stored using the same credentials as they are created on the guest. This requires QEMU to run as root. In “mapped-xattr” security model, some of the file attributes like uid, gid, mode bits and link target are stored as file attributes. For “mapped-file” these attributes are stored in the hidden .virtfs_metadata directory. Directories exported by this security model cannot interact with other unix tools. “none” security model is same as passthrough except the sever won’t report failures if it fails to set file attributes like ownership. Security model is mandatory only for local fsdriver.

  `writeout=writeout`

    This is an optional argument. The only supported value is “immediate”. This means that host page cache will be used to read and write data but write notification will be sent to the guest only when the data has been reported as written by the storage subsystem.

  `readonly=on`

    Enables exporting 9p share as a readonly mount for guests. By default read-write access is given.

  `fmode=fmode`

    Specifies the default mode for newly created files on the host. Works only with security models “mapped-xattr” and “mapped-file”.

  `dmode=dmode`

    Specifies the default mode for newly created directories on the host. Works only with security models “mapped-xattr” and “mapped-file”.

  `mount_tag=mount_tag`

    Specifies the tag name to be used by the guest to mount this export point.

  `multidevs=multidevs`

    Specifies how to deal with multiple devices being shared with a 9p export. Supported behaviours are either “remap”, “forbid” or “warn”. The latter is the default behaviour on which virtfs 9p expects only one device to be shared with the same export, and if more than one device is shared and accessed via the same 9p export then only a warning message is logged (once) by qemu on host side. In order to avoid file ID collisions on guest you should either create a separate virtfs export for each device to be shared with guests (recommended way) or you might use “remap” instead which allows you to share multiple devices with only one export instead, which is achieved by remapping the original inode numbers from host to guest in a way that would prevent such collisions. Remapping inodes in such use cases is required because the original device IDs from host are never passed and exposed on guest. Instead all files of an export shared with virtfs always share the same device id on guest. So two files with identical inode numbers but from actually different devices on host would otherwise cause a file ID collision and hence potential misbehaviours on guest. “forbid” on the other hand assumes like “warn” that only one device is shared by the same export, however it will not only log a warning message but also deny access to additional devices on guest. Note though that “forbid” does currently not block all possible file access operations (e.g. readdir() would still return entries from other devices).

`-iscsi`

  Configure iSCSI session parameters.

### USB convenience options

`-usb`

  Enable USB emulation on machine types with an on-board USB host controller (if not enabled by default). Note that on-board USB host controllers may not support USB 3.0. In this case `-device qemu-xhci` can be used instead on machines with PCI.

`-usbdevice devname`

  Add the USB device devname, and enable an on-board USB controller if possible and necessary (just like it can be done via `-machine usb=on`). Note that this option is mainly intended for the user’s convenience only. More fine-grained control can be achieved by selecting a USB host controller (if necessary) and the desired USB device via the `-device` option instead. For example, instead of using `-usbdevice mouse` it is possible to use `-device qemu-xhci -device usb-mouse` to connect the USB mouse to a USB 3.0 controller instead (at least on machines that support PCI and do not have an USB controller enabled by default yet). For more details, see the chapter about Connecting USB devices 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:

    `full-grab=on|off`Capture all key presses, including system combos.

      This requires accessibility permissions, since it performs a global grab on key events. (default: off) See https://support.apple.com/en-in/guide/mac-help/mh32356/mac

    `swap-opt-cmd=on|off`Swap the Option and Command keys so that their

      key codes match their position on non-Mac keyboards and you can use Meta/Super and Alt where you expect them. (default: off)

    `show-cursor=on|off` : Force showing the mouse cursor

    `left-command-key=on|off` : Disable forwarding left command key to host

    `full-screen=on|off` : Start in fullscreen mode

    `zoom-to-fit=on|off`Expand video output to the window size,

      defaults to “off”

  `egl-headless[,rendernode=<file>]`

    Offload all OpenGL operations to a local DRI device. For any graphical display, this display needs to be paired with either VNC or SPICE displays.

  `vnc=<display>`

    Start a VNC server on display <display>

  `none`

    Do not display video output. The guest will still see an emulated graphics card, but its output will not be displayed to the QEMU user. This option differs from the -nographic option in that it only affects what is done with video output; -nographic also changes the destination of the serial and parallel port data.

`-nographic`

  Normally, if QEMU is compiled with graphical window support, it displays output such as guest graphics, guest console, and the QEMU monitor in a window. With this option, you can totally disable graphical output so that QEMU is a simple command line application. The emulated serial port is redirected on the console and muxed with the monitor (unless redirected elsewhere explicitly). Therefore, you can still use QEMU to debug a Linux kernel with a serial console. Use C-a h for help on switching between the console and monitor.

`-spice option[,option[,...]]`

  Enable the spice remote desktop protocol. Valid options are

  `port=<nr>`

    Set the TCP port spice is listening on for plaintext channels.

  `addr=<addr>`

    Set the IP address spice is listening on. Default is any address.

  `ipv4=on|off`; `ipv6=on|off`; `unix=on|off`

    Force using the specified IP version.

  `password-secret=<secret-id>`

    Set the ID of the `secret` object containing the password you need to authenticate.

  `sasl=on|off`

    Require that the client use SASL to authenticate with the spice. The exact choice of authentication method used is controlled from the system / user’s SASL configuration file for the ‘qemu’ service. This is typically found in /etc/sasl2/qemu.conf. If running QEMU as an unprivileged user, an environment variable SASL_CONF_PATH can be used to make it search alternate locations for the service config. While some SASL auth methods can also provide data encryption (eg GSSAPI), it is recommended that SASL always be combined with the ‘tls’ and ‘x509’ settings to enable use of SSL and server certificates. This ensures a data encryption preventing compromise of authentication credentials.

  `disable-ticketing=on|off`

    Allow client connects without authentication.

  `disable-copy-paste=on|off`

    Disable copy paste between the client and the guest.

  `disable-agent-file-xfer=on|off`

    Disable spice-vdagent based file-xfer between the client and the guest.

  `tls-port=<nr>`

    Set the TCP port spice is listening on for encrypted channels.

  `x509-dir=<dir>`

    Set the x509 file directory. Expects same filenames as -vnc $display,x509=$dir

  `x509-key-file=<file>`; `x509-key-password=<file>`; `x509-cert-file=<file>`; `x509-cacert-file=<file>`; `x509-dh-key-file=<file>`

    The x509 file names can also be configured individually.

  `tls-ciphers=<list>`

    Specify which ciphers to use.

  `tls-channel=[main|display|cursor|inputs|record|playback]`; `plaintext-channel=[main|display|cursor|inputs|record|playback]`

    Force 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)

`-vga type`

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

  `cirrus`

    Cirrus Logic GD5446 Video card. All Windows versions starting from Windows 95 should recognize and use this graphic card. For optimal performances, use 16 bit color depth in the guest and the host OS. (This card was the default before QEMU 2.2)

  `std`

    Standard VGA card with Bochs VBE extensions. If your guest OS supports the VESA 2.0 VBE extensions (e.g. Windows XP) and if you want to use high resolution modes (>= 1280x1024x16) then you should use this option. (This card is the default since QEMU 2.2)

  `vmware`

    VMWare SVGA-II compatible adapter. Use it if you have sufficiently recent XFree86/XOrg server or 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` width`x`height`[x`depth`]`

  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[,...]]]`

  Normally, if QEMU is compiled with graphical window support, it displays output such as guest graphics, guest console, and the QEMU monitor in a window. With this option, you can 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 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.

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

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

  `password=on|off`

    Require that password based authentication is used for client connections.

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

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

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

  `password-secret=<secret-id>`

    Require that password based authentication is used for client connections, using the password provided by the `secret` object identified by `secret-id`.

  `tls-creds=ID`

    Provides the ID of a set of TLS credentials to use to secure the VNC server. They will 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. The credentials should have been previously created using the `-object tls-creds` argument.

  `tls-authz=ID`

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

  `sasl=on|off`

    Require that the client use SASL to authenticate with the VNC server. The exact choice of authentication method used is controlled from the system / user’s SASL configuration file for the ‘qemu’ service. This is typically found in /etc/sasl2/qemu.conf. If running QEMU as an unprivileged user, an environment variable SASL_CONF_PATH can be used to make it search alternate locations for the service config. While some SASL auth methods can also provide data encryption (eg GSSAPI), it is recommended that SASL always be combined with the ‘tls’ and ‘x509’ settings to enable use of SSL and server certificates. This ensures a data encryption preventing compromise of authentication credentials. See the VNC security section in the System Emulation Users Guide for details on using SASL authentication.

  `sasl-authz=ID`

    Provides the ID of the QAuthZ authorization object against which the client’s SASL username will validated. This object is only resolved at time of use, so can be deleted and recreated on the fly while the VNC server is active. If missing, it will default 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 of `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. 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, VNC client may receive lossy framebuffer updates depending on its encoding settings. Enabling this option can save a lot of bandwidth at the expense of quality.

  `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 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 specify -shared disconnect everybody else. ‘ignore’ completely ignores the shared flag and allows everybody connect unconditionally. Doesn’t conform to the rfb spec but is traditional QEMU behavior.

  `key-delay-ms`

    Set 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 to 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 is 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). Synonym of `-global ide-device.win2k-install-hack=on`.

`-no-fd-bootchk`

  Disable boot signature checking for floppy disks in BIOS. May be needed to boot from old floppy disks. Synonym of `-m fd-bootchk=off`.

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

  Add ACPI table with specified header fields and context from specified files. For file=, take whole ACPI table from the specified files, including all ACPI headers (possible overridden by other options). For data=, only 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 SMBIOS entry from 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-family=%d][,processor-id=%d]`

  Specify SMBIOS type 4 fields

`-smbios type=9[,slot_designation=str][,slot_type=%d][,slot_data_bus_width=%d][,current_usage=%d][,slot_length=%d][,slot_id=%d][,slot_characteristics1=%d][,slot_characteristics12=%d][,pci_device=str]`

  Specify SMBIOS type 9 fields

`-smbios type=11[,value=str][,path=filename]`

  Specify SMBIOS type 11 fields

  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 a 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

  This argument can be repeated multiple times. Its main use is to allow network interfaces be created as `enoX` on Linux, with X being the instance number, instead of the name depending on the interface position on the PCI bus.

  Here is an example of use:

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

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

  ..parsed-literal:

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

  Currently, the PCI device has to be attached to the root bus.

### Network options

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

  This option is a shortcut for configuring both the on-board (default) guest NIC hardware and the host network backend in one go. The host backend options are the same as with the corresponding `-netdev` options below. The guest NIC model can be set with `model=modelname`. Use `model=help` to list the available device types. The hardware MAC address can be set with `mac=macaddr`.

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

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

`-nic none`

  Indicate that no network devices should be configured. It is used to override the default configuration (default NIC with “user” host network backend) which is activated if no other networking options are provided.

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

  Configure user mode host network backend which requires no administrator privilege to run. Valid options are:

  `id=id`

    Assign symbolic name for use in monitor commands.

  `ipv4=on|off and ipv6=on|off`

    Specify that either IPv4 or IPv6 must be enabled. If neither is specified both protocols are enabled.

  `net=addr[/mask]`

    Set IP network address the guest will see. Optionally specify the netmask, either in the form a.b.c.d or as number of valid top-most bits. Default is 10.0.2.0/24.

  `host=addr`

    Specify the guest-visible address of the host. Default is the 2nd IP in the guest network, i.e. x.x.x.2.

  `ipv6-net=addr[/int]`

    Set IPv6 network address the guest will see (default is fec0::/64). The network prefix is given in the usual hexadecimal IPv6 address notation. The prefix size is optional, and is given as the number of valid top-most bits (default is 64).

  `ipv6-host=addr`

    Specify the guest-visible IPv6 address of the host. Default is the 2nd IPv6 in the guest network, i.e. xxxx::2.

  `restrict=on|off`

    If this option is enabled, the guest will be isolated, i.e. it will not be able to contact the host and no guest IP packets will be routed over the host to the outside. This option does not affect any explicitly set forwarding rules.

  `hostname=name`

    Specifies the client hostname reported by the built-in DHCP server.

  `dhcpstart=addr`

    Specify the first of the 16 IPs the built-in DHCP server can assign. Default is the 15th to 31st IP in the guest network, i.e. x.x.x.15 to x.x.x.31.

  `dns=addr`

    Specify the guest-visible address of the virtual nameserver. The address must be different from the host address. Default is the 3rd IP in the guest network, i.e. x.x.x.3.

  `ipv6-dns=addr`

    Specify the guest-visible address of the IPv6 virtual nameserver. The address must be different from the host address. Default is the 3rd IP in the guest network, i.e. xxxx::3.

  `dnssearch=domain`

    Provides an entry for the domain-search list sent by the built-in DHCP server. More than one domain suffix can be transmitted by specifying this option multiple times. If supported, this will cause the guest to automatically try to append the given domain suffix(es) in case a domain name can not be resolved.

    Example:

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

  `domainname=domain`

    Specifies the client domain name reported by the built-in DHCP server.

  `tftp=dir`

    When using the user mode network stack, activate a built-in TFTP server. The files in dir will be exposed as the root of a TFTP server. The TFTP client on the guest must be configured in binary mode (use the command `bin` of the Unix TFTP client). The built-in TFTP server is read-only; it does not implement any command for writing files. QEMU will not write to this directory.

  `tftp-server-name=name`

    In BOOTP reply, broadcast name as the “TFTP server name” (RFC2132 option 66). This can be used to advise the guest to load boot files or configurations from a different server than the host address.

  `bootfile=file`

    When using the user mode network stack, broadcast file as the BOOTP filename. In conjunction with `tftp`, this can be used to network boot a guest from a local directory.

    Example (using pxelinux):

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

  `smb=dir[,smbserver=addr]`

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

    In the guest Windows OS, the line:

        10.0.2.4 smbserver

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

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

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

  `hostfwd=[tcp|udp]:[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 `/path/to/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=/path/to/qemu-bridge-helper"

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

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

  Use the network helper helper to configure the TAP interface and attach it to the bridge. The default network helper executable is `/path/to/qemu-bridge-helper` and the default bridge device is `br0`.

  Examples:

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

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

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

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

  Example:

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

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

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

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

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

  `server=on|off`

    if `on` create a server socket

  `addr.host=host,addr.port=port`

    socket address to listen on (server=on) or connect to (server=off)

  `to=maxport`

    if present, this is range of possible addresses, with port between `port` and `maxport`.

  `numeric=on|off`

    if `on` `host` and `port` are guaranteed to be numeric, otherwise a name resolution should be attempted (default: `off`)

  `keep-alive=on|off`

    enable keep-alive when connecting to this socket. Not supported for passive sockets.

  `mptcp=on|off`

    enable multipath TCP

  `ipv4=on|off`

    whether to accept IPv4 addresses, default to try both IPv4 and IPv6

  `ipv6=on|off`

    whether to accept IPv6 addresses, default to try both IPv4 and IPv6

  `reconnect-ms=milliseconds`

    for a client socket, if a socket is disconnected, then attempt a reconnect after the given number of milliseconds. Setting this to zero disables this function. (default: 0)

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

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

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

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

  `server=on|off`

    if `on` create a server socket

  `addr.path=path`

    filesystem path to use

  `abstract=on|off`

    if `on`, this is a Linux abstract socket address.

  `tight=on|off`

    if false, pad an abstract socket address with enough null bytes to make it fill struct sockaddr_un member sun_path.

  `reconnect-ms=milliseconds`

    for a client socket, if a socket is disconnected, then attempt a reconnect after the given number of milliseconds. Setting this to zero disables this function. (default: 0)

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

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

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

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

`-netdev stream,id=str[,server=on|off],addr.type=fd,addr.str=file-descriptor[,reconnect-ms=milliseconds]`

  Configure a network backend to connect to another QEMU virtual machine or a proxy using a stream oriented socket file descriptor.

  `server=on|off`

    if `on` create a server socket

  `addr.str=file-descriptor`

    file descriptor number to use as a socket

  `reconnect-ms=milliseconds`

    for a client socket, if a socket is disconnected, then attempt a reconnect after the given number of milliseconds. Setting this to zero disables this function. (default: 0)

`-netdev dgram,id=str,remote.type=inet,remote.host=maddr,remote.port=port[,local.type=inet,local.host=addr]`

  Configure a network backend to connect to a multicast address.

  `remote.host=maddr,remote.port=port`

    multicast address

  `local.host=addr`

    specify the host address to send packets from

  Example:

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

`-netdev dgram,id=str,remote.type=inet,remote.host=maddr,remote.port=port[,local.type=fd,local.str=file-descriptor]`

  Configure a network backend to connect to a multicast address using a UDP socket file descriptor.

  `remote.host=maddr,remote.port=port`

    multicast address

  `local.str=file-descriptor`

    File descriptor to use to send packets

`-netdev dgram,id=str,local.type=inet,local.host=addr,local.port=port[,remote.type=inet,remote.host=addr,remote.port=port]`

  Configure a network backend to connect to another QEMU virtual machine or a proxy using a datagram oriented unix domain socket.

  `local.host=addr,local.port=port`

    IP address to use to send the packets from

  `remote.host=addr,remote.port=port`

    Destination IP address

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

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

`-netdev dgram,id=str,local.type=unix,local.path=path[,remote.type=unix,remote.path=path]`

  Configure a network backend to connect to another QEMU virtual machine or a proxy using a datagram oriented unix socket.

  `local.path=path`

    filesystem path to use to bind the socket

  `remote.path=path`

    filesystem path to use as a destination (see sendto(2))

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

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

`-netdev dgram,id=str,local.type=fd,local.str=file-descriptor`

  Configure a network backend to connect to another QEMU virtual machine or a proxy using a datagram oriented socket file descriptor.

  `local.str=file-descriptor`

    File descriptor to use to send packets

`-netdev l2tpv3,id=id,src=srcaddr,dst=dstaddr[,srcport=srcport][,dstport=dstport],txsession=txsession[,rxsession=rxsession][,ipv6=on|off][,udp=on|off][,cookie64=on|off][,counter=on|off][,pincounter=on|off][,txcookie=txcookie][,rxcookie=rxcookie][,offset=offset]`

  Configure a L2TPv3 pseudowire host network backend. L2TPv3 (RFC3931) is a popular protocol to transport Ethernet (and other Layer 2) data frames between two systems. It is present in routers, firewalls and the Linux kernel (from version 3.3 onwards).

  This transport allows a VM to communicate to another VM, router or firewall directly.

  `src=srcaddr`

    source address (mandatory)

  `dst=dstaddr`

    destination address (mandatory)

  `udp=on`

    select udp encapsulation (default is ip).

  `srcport=srcport`

    source udp port.

  `dstport=dstport`

    destination udp port.

  `ipv6=on`

    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=on`

    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=on,srcport=16384,dstport=16384,rxsession=0xffffffff,txsession=0xffffffff,counter=on

`-netdev vde,id=id[,sock=socketpath][,port=n][,group=groupname][,mode=octalmode]`

  Configure VDE backend to connect to PORT n of a vde switch running on host and listening for incoming connections on socketpath. Use GROUP groupname and MODE octalmode to change default ownership and permissions for communication port. 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]`

  Configure AF_XDP backend to connect to a network interface ‘name’ using AF_XDP socket. A specific program attach mode for a default XDP program can be forced with ‘mode’, defaults to best-effort, where the likely most performant mode will be in use. Number of queues ‘n’ should generally match the number or queues in the interface, defaults to 1. Traffic arriving on non-configured device queues will not be delivered to the network backend.

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

  ‘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]`

  Establish a vhost-user netdev, backed by a chardev id. The chardev should be a unix domain socket backed one. The vhost-user uses a specifically defined protocol to pass vhost ioctl replacement messages to an application on the other end of the socket. On non-MSIX guests, the feature can be forced with vhostforce. Use ‘queues=n’ to specify the number of queues to be created for multiqueue vhost-user.

  Example:

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

`-netdev vhost-vdpa[,vhostdev=/path/to/dev][,vhostfd=h]`

  Establish a vhost-vdpa netdev.

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

`-netdev hubport,id=id,hubid=hubid[,netdev=nd]`

  Create a hub port on the emulated hub with ID hubid.

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

`-net nic[,netdev=nd][,macaddr=mac][,model=type] [,name=name][,addr=addr][,vectors=v]`

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

`-net user|tap|bridge|socket|l2tpv3|vde[,...][,name=name]`

  Configure a host network backend (with the options corresponding to the same `-netdev` option) and connect it to the emulated hub 0 (the default hub). Use name to specify the name of the hub port.

### Character device options

The general form of a character device option is:

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

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

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

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

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

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

  You can have 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.

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

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

  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.

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

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

  `server=on|off` specifies that the socket shall be a listening socket.

  `wait=on|off` specifies that QEMU should not block waiting for a client to connect to a listening socket.

  `telnet=on|off` specifies that traffic on the socket should interpret telnet escape sequences.

  `websocket=on|off` specifies that the socket uses WebSocket protocol for communication.

  `reconnect-ms` sets the timeout for reconnecting on non-server sockets when the remote end goes away. qemu will delay this many milliseconds and then attempt to reconnect. Zero disables reconnecting, and is the default.

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

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

  TCP and unix socket options are given below:

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

    `host` for a listening socket specifies the local address to be bound. For a connecting socket species the remote host to connect to. `host` is optional for listening sockets. If not specified it defaults to `0.0.0.0`.

    `port` for a listening socket specifies the local port to be bound. For a connecting socket specifies the port on the remote host to connect to. `port` can be given as either a port number or a service name. `port` is required.

    `to` is only relevant to listening sockets. If it is specified, and `port` cannot be bound, QEMU will attempt to bind to subsequent ports up to and including `to` until it succeeds. `to` must be specified as a port number.

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

    `nodelay=on|off` disables the Nagle algorithm.

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

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

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

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

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

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

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

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

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

`-chardev msmouse,id=id`

  Forward QEMU’s emulated msmouse events to the guest. `msmouse` does not take any options.

`-chardev vc,id=id[[,width=width][,height=height]][[,cols=cols][,rows=rows]]`

  Connect to a QEMU text console. `vc` may optionally be given a specific size.

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

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

`-chardev ringbuf,id=id[,size=size]`

  Create a ring buffer with fixed size `size`. size must be a power of two and defaults to `64K`.

`-chardev file,id=id,path=path[,input-path=input-path]`

  Log all traffic received from the guest to a file.

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

  If `input-path` is specified, this is the path of a second file which will be used for input. If `input-path` is not specified, no input will be available from the chardev.

  Note that `input-path` is not supported on Windows hosts.

`-chardev pipe,id=id,path=path`

  Create a two-way connection to the guest. The behaviour differs slightly between Windows hosts and other hosts:

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

  On other hosts, 2 pipes will be created called `path.in` and `path.out`. Data written to `path.in` will be received by the guest. Data written by the guest can be read from `path.out`. QEMU will not create these fifos, and requires them to be present.

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

`-chardev console,id=id`

  Send traffic from the guest to QEMU’s standard output. `console` does not take any options.

  `console` is only available on Windows hosts.

`-chardev serial,id=id,path=path`

  Send traffic from the guest to a serial device on the host.

  On Unix hosts serial will actually accept any tty device, not only serial lines.

  `path` specifies the name of the serial device to open.

`-chardev pty,id=id[,path=path]`

  Create a new pseudo-terminal on the host and connect to it.

  `pty` is not available on Windows hosts.

  If `path` is specified, QEMU will create a symbolic link at that location which points to the new PTY device.

  This avoids having to make QMP or HMP monitor queries to find out what the new PTY device path is.

  Note that while QEMU will remove the symlink when it exits gracefully, it will not do so in case of crashes or on certain startup errors. It is recommended that the user checks and removes the symlink after QEMU terminates to account for this.

`-chardev stdio,id=id[,signal=on|off]`

  Connect to standard input and standard output of the QEMU process.

  `signal` controls if signals are enabled on the terminal, that includes exiting QEMU with the key sequence Control-c. This option is enabled by default, use `signal=off` to disable it.

`-chardev braille,id=id`

  Connect to a local BrlAPI server. `braille` does not take any 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. `path` is required.

`-chardev spicevmc,id=id,debug=debug,name=name`

  `spicevmc` is only available when spice support is built in.

  `debug` debug level for spicevmc

  `name` name of spice channel to connect to

  Connect to a spice virtual machine channel, such as vdiport.

`-chardev spiceport,id=id,debug=debug,name=name`

  `spiceport` is only available when spice support is built in.

  `debug` debug level for spicevmc

  `name` name of spice port to connect to

  Connect to a spice port, allowing a Spice client to handle the traffic identified by a name (preferably a fqdn).

### TPM device options

The general form of a TPM device option is:

`-tpmdev backend,id=id[,options]`

  The specific backend type will determine the applicable options. The `-tpmdev` option creates the TPM backend and requires a `-device` option that specifies the TPM frontend interface model.

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

The available backends are:

`-tpmdev passthrough,id=id,path=path,cancel-path=cancel-path`

  (Linux-host only) Enable access to the host’s TPM using the passthrough driver.

  `path` specifies the path to the host’s TPM device, i.e., on a Linux host this would be `/dev/tpm0`. `path` is optional and by default `/dev/tpm0` is used.

  `cancel-path` specifies the path to the host TPM device’s sysfs entry allowing for cancellation of an ongoing TPM command. `cancel-path` is optional and by default QEMU will search for the sysfs entry to use.

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

  The TPM device accessed by the passthrough driver must not be used by any other application on the host.

  Since the host’s firmware (BIOS/UEFI) has already initialized the TPM, the VM’s firmware (BIOS/UEFI) will not be able to initialize the TPM again and may therefore not show a TPM-specific menu that would otherwise allow the user to configure the TPM, e.g., allow the user to enable/disable or activate/deactivate the TPM. Further, if TPM ownership is released from within a VM then the host’s TPM will get disabled and deactivated. To enable and activate the TPM again afterwards, the host has to be rebooted and the user is required to enter the firmware’s menu to enable and activate the TPM. If the TPM is left disabled and/or deactivated most TPM commands will fail.

  To create a passthrough TPM use the following two options:

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

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

`-tpmdev emulator,id=id,chardev=dev`

  (Linux-host only) Enable access to a TPM emulator using Unix domain socket based chardev backend.

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

  To create a TPM emulator backend device with chardev socket backend:

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

### Boot Image or Kernel specific

There are broadly 4 ways you can boot a system with QEMU.

> - specify a firmware and let it control finding a kernel

> - specify a firmware and pass a hint to the kernel to boot

> - direct kernel image boot

> - manually load files into the guest’s address space

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

The final method is the most generic way of loading images into the guest address space and used mostly for `bare metal` type development where the reset vectors of the processor are taken into account.

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

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 although other things (like hypervisors) can be packaged up as a kernel executable image. The exact format of a executable image is usually architecture specific.

The way in which the kernel is started (what address it is loaded at, what if any information is passed to it via CPU registers, the state of the hardware when it is 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 kernel image. The kernel can be either a Linux kernel or in multiboot format.

`-append cmdline`

  Use cmdline as kernel command line

`-initrd file`

  Use file as initial ram disk.

`-initrd "file1 arg=foo,file2"`

  This syntax is only available with multiboot.

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

`-initrd "bzImage earlyprintk=xen,,keep root=/dev/xvda1,initrd.img"`

  Multiboot only. Use bzImage as the first module with “`earlyprintk=xen,keep root=/dev/xvda1`” as its command line, and initrd.img as the second module.

`-dtb file`

  Use file as a device tree binary (dtb) image and pass it to the kernel on boot.

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

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

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

there is also the guest loader which operates in a similar way but tweaks the DTB so a hypervisor loaded via `-kernel` can find where the guest image is:

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

### Debug/Expert options

`-compat [deprecated-input=@var{input-policy}][,deprecated-output=@var{output-policy}]`

  Set 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 named fw_cfg entry with contents from file file. If the filename contains comma, you must double it (for instance, “file=my,,file” to use file “my,file”).

`-fw_cfg [name=]name,string=str`

  Add named fw_cfg entry with contents from string str. If the string contains comma, you must double it (for instance, “string=my,,string” to use file “my,string”).

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

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

  Example:

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

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

`-serial dev`

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

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

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

  Available character devices are:

  `vc[:WxH]`

    Virtual console. Optionally, a width and height can be given in pixel with

        vc:800x600

    It is also possible to specify width or height in characters:

        vc:80Cx24C

  `pty[:path]`

    [Linux only] Pseudo TTY (a new PTY is automatically allocated).

    If `path` is specified, QEMU will create a symbolic link at that location which points to the new PTY device.

    This avoids having to make QMP or HMP monitor queries to find out what the new PTY device path is.

    Note that while QEMU will remove the symlink when it exits gracefully, it will not do so in case of crashes or on certain startup errors. It is recommended that the user checks and removes the symlink after QEMU terminates to account for this.

  `none`

    No device is allocated. Note that for machine types which emulate systems where a serial device is always present in real hardware, this may be equivalent to the `null` option, in that the serial device is still present but all output is discarded. For boards where the number of serial ports is truly variable, this suppresses the creation of the device.

  `null`

    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-ms=milliseconds]`

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

    `Example to send tcp console to 192.168.0.2 port 4444`

      -serial tcp:192.168.0.2:4444

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

      -serial tcp::4444,server=on

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

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

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

    The telnet protocol is used instead of raw tcp sockets. The options work the same as if you had specified `-serial tcp`. The difference is that the port acts like a telnet server or client using telnet option negotiation. This will also allow you to send the MAGIC_SYSRQ sequence if you use a telnet that supports sending the break sequence. Typically in unix telnet you do it with Control-] and then type “send break” followed by pressing the enter key.

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

    The WebSocket protocol is used instead of raw tcp socket. The port acts as a WebSocket server. Client mode is not supported.

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

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

  `mon:dev_string`

    This is a special option to allow the monitor to be multiplexed onto another serial port. The monitor is accessed with key sequence of Control-a and then pressing c. dev_string should be any one of the serial devices specified above. An example to multiplex the monitor onto a telnet server listening on port 4444 would be:

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

    When the monitor is multiplexed to stdio in this way, Ctrl+C will not terminate QEMU any more but will be passed to the guest instead.

  `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.

`-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.

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

`-gdb dev`

  Accept a gdb connection on device dev (see the GDB usage chapter in the System Emulation Users Guide). Note that this option does not pause QEMU execution – if you want QEMU to not start the guest until you connect with gdb and issue a `continue` command, you will need to 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; UDP, pseudo TTY, or even stdio are all reasonable use cases. For example, a stdio connection allows you to 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).

`-d item1[,...]`

  Enable logging of specified items. Use ‘-d help’ for a list of log items.

`-D logfile`

  Output log in logfile instead of to stderr

`-dfilter range1[,...]`

  Filter debug output to 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.

`-seed number`

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

`-L path`

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

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

`-enable-kvm`

  Enable KVM full virtualization support. This option is only available if KVM support is enabled when compiling.

`-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.

`-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.

`-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)

`-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.

`-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 of the RTC as 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.

  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.

`-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.

  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 the 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.

`-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.

`-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.

`-runas user`

  Immediately before starting guest execution, drop root privileges, switching to the specified user. This option is deprecated, use `-run-with user=...` instead.

`-prom-env variable=value`

  Set OpenBIOS nvram variable to given value (PPC, SPARC only).

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

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

`-semihosting`

  Enable Semihosting mode (ARM, M68K, Xtensa, MIPS, RISC-V only).

  Warning

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

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

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

  Enable and configure Semihosting (ARM, M68K, Xtensa, MIPS, RISC-V only).

  Warning

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

  `target=native|gdb|auto`

    Defines where the semihosting calls will be addressed, to QEMU (`native`) or to GDB (`gdb`). The default is `auto`, which means `gdb` during debug sessions and `native` otherwise.

  `chardev=str1`

    Send the output to a chardev backend output for native or auto output when not in gdb

  `userspace=on|off`

    Allows code running in guest userspace to access the semihosting interface. The default is that only privileged guest code can make semihosting calls. Note that setting `userspace=on` should only be used if all guest code is trusted (for example, in bare-metal test case code).

  `arg=str1,arg=str2,...`

    Allows the user to pass input arguments, and can be used multiple times to build up a list. The old-style `-kernel`/`-append` method of passing a command line is still supported for backward compatibility. If both the `--semihosting-config arg` and the `-kernel`/`-append` are specified, the former is passed to semihosting as it always takes precedence.

`-old-param`

  Old param mode (ARM only).

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

  Enable Seccomp mode 2 system call filter. ‘on’ will enable syscall filtering and ‘off’ will disable it. The 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`

  Read device configuration from file. This approach is useful when you want to spawn QEMU process with many command line options but you don’t want to exceed the command line character limit.

`-no-user-config`

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

`-trace [[enable=]pattern][,events=file][,file=file]`

  Specify tracing options.

  `[enable=]PATTERN`

  > Immediately enable events matching PATTERN (either event name or a globbing pattern). This option is only available if QEMU has been compiled with the `simple`, `log` or `ftrace` tracing backend. To specify multiple events or patterns, specify the `-trace` option multiple times.

  > Use `-trace help` to print a list of names of trace points.

  `events=FILE`

  > Immediately enable events listed in FILE. The file must contain one event name (as listed in the `trace-events-all` file) per line; globbing patterns are accepted too. This option is only available if QEMU has been compiled with the `simple`, `log` or `ftrace` tracing backend.

  `file=FILE`

  > Log output traces to FILE. This option is only available if QEMU has been compiled with the `simple` tracing backend.

`-plugin file=file[,argname=argvalue]`

  Load a plugin.

  `file=file`

    Load the given plugin from a shared library file.

  `argname=argvalue`

    Argument passed to the plugin. (Can be given multiple times.)

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

  Set QEMU process lifecycle options.

  `async-teardown=on` enables asynchronous teardown. A new process called “cleanup/<QEMU_PID>” will be created at startup sharing the address space with the main QEMU process, using clone. It will wait for the main QEMU process to terminate completely, and then exit. This allows QEMU to terminate very quickly even if the guest was huge, leaving the teardown of the address space to the cleanup process. Since the cleanup process shares the same cgroups as the main QEMU process, accounting is performed correctly. This only works if the cleanup process is not forcefully killed with SIGKILL before the main QEMU process has terminated completely.

  `chroot=dir` can be used for doing a chroot to the specified directory immediately before starting the guest execution. This is especially useful in combination with -runas.

  `user=username` or `user=uid:gid` can be used to drop root privileges before starting guest execution. QEMU will use the `setuid` and `setgid` system calls to switch to the specified identity. Note that the `user=username` syntax will also apply the full set of supplementary groups for the user, whereas the `user=uid:gid` will use only the `gid` group.

`-msg [timestamp[=on|off]][,guest-name[=on|off]]`

  Control error message format.

  `timestamp=on|off`

    Prefix messages with a timestamp. Default is off.

  `guest-name=on|off`

    Prefix messages with guest name but only if -name guest option is set otherwise the option is ignored. Default is off.

`-dump-vmstate file`

  Dump json-encoded vmstate information for current machine type to file in file

`-enable-sync-profile`

  Enable synchronization profiling.

`-perfmap`

  Generate a map file for Linux perf tools that will allow basic profiling information to be broken down into basic blocks.

`-jitdump`

  Generate 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,...]`

  Create a new object of type typename setting properties in the order they are specified. Note that the ‘id’ property must be set. These objects are placed in the ‘/objects’ path.

  `-object memory-backend-file,id=id,size=size,mem-path=dir,share=on|off,discard-data=on|off,merge=on|off,dump=on|off,prealloc=on|off,host-nodes=host-nodes,policy=default|preferred|bind|interleave,align=align,offset=offset,readonly=on|off,rom=on|off|auto`

    Creates a memory file backend object, which can be used to back the guest RAM with huge pages.

    The `id` parameter is a unique ID that will be used to reference this memory region in other parameters, e.g. `-numa`, `-device nvdimm`, etc.

    The `size` option provides the size of the memory region, and accepts common suffixes, e.g. `500M`.

    The `mem-path` provides the path to either a shared memory or huge page filesystem mount.

    The `share` boolean option determines whether the memory region is marked as private to QEMU, or shared. The latter allows a co-operating external process to access the QEMU memory region.

    Setting share=on might affect the ability to configure NUMA bindings for the memory backend under some circumstances, see Documentation/vm/numa_memory_policy.txt on the Linux kernel source tree for additional details.

    Setting the `discard-data` boolean option to on indicates that file contents can be destroyed when QEMU exits, to avoid unnecessarily flushing data to the backing file. Note that `discard-data` is only an optimization, and QEMU might not discard file contents if it aborts unexpectedly or is terminated using SIGKILL.

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

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

    The `prealloc` boolean option enables memory preallocation.

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

    The `policy` option sets the NUMA policy to one of the following values:

    `default`

      default host policy

    `preferred`

      prefer the given host node list for allocation

    `bind`

      restrict memory allocation to the given host node list

    `interleave`

      interleave memory allocations across the given host node list

    The `align` option specifies the base address alignment when QEMU mmap(2) `mem-path`, and accepts common suffixes, eg `2M`. Some backend store specified by `mem-path` requires an alignment different than the default one used by QEMU, eg the device DAX /dev/dax0.0 requires 2M alignment rather than 4K. In such cases, users can specify the required alignment via this option.

    The `offset` option specifies the offset into the target file that the region starts at. You can use this parameter to back multiple regions with a single file.

    The `pmem` option specifies whether the backing file specified by `mem-path` is in host persistent memory that can be accessed using the SNIA NVM programming model (e.g. Intel NVDIMM). If `pmem` is set to ‘on’, QEMU will take necessary operations to guarantee the persistence of its own writes to `mem-path` (e.g. in vNVDIMM label emulation and live migration). Also, we will map the backend-file with MAP_SYNC flag, which ensures the file metadata is in sync for `mem-path` in case of host crash or a power failure. MAP_SYNC requires support from both the host kernel (since Linux kernel 4.15) and the filesystem of `mem-path` mounted with DAX option.

    The `readonly` option specifies whether the backing file is opened read-only or read-write (default).

    The `rom` option specifies whether to create Read Only Memory (ROM) that cannot be modified by the VM. Any write attempts to such ROM will be denied. Most use cases want proper RAM instead of ROM. However, selected use cases, like R/O NVDIMMs, can benefit from ROM. If set to `on`, create ROM; if set to `off`, create writable RAM; if set to `auto` (default), the value of the `readonly` option is used. This option is primarily helpful when we want to have writable RAM in configurations that would traditionally create ROM before the `rom` option was introduced: VM templating, where we want to open a file readonly (`readonly=on`) and mark the memory to be private for QEMU (`share=off`). For this use case, we need writable RAM instead of ROM, and want to also set `rom=off`.

  `-object memory-backend-ram,id=id,merge=on|off,dump=on|off,share=on|off,prealloc=on|off,size=size,host-nodes=host-nodes,policy=default|preferred|bind|interleave`

    Creates a memory backend object, which can be used to back the guest RAM. Memory backend objects offer more control than the `-m` option that is traditionally used to define guest RAM. Please refer to `memory-backend-file` for a description of the options.

  `-object memory-backend-memfd,id=id,merge=on|off,dump=on|off,share=on|off,prealloc=on|off,size=size,host-nodes=host-nodes,policy=default|preferred|bind|interleave,seal=on|off,hugetlb=on|off,hugetlbsize=size`

    Creates an anonymous memory file backend object, which allows QEMU to share the memory with an external process (e.g. when using vhost-user). The memory is allocated with memfd and optional sealing. (Linux only)

    The `seal` option creates a sealed-file, that will block further resizing the memory (‘on’ by default).

    The `hugetlb` option specify the file to be created resides in the hugetlbfs filesystem (since Linux 4.14). Used in conjunction with the `hugetlb` option, the `hugetlbsize` option specify the hugetlb page size on systems that support multiple hugetlb page sizes (it must be a power of 2 value supported by the system).

    In some versions of Linux, the `hugetlb` option is incompatible with the `seal` option (requires at least Linux 4.16).

    Please refer to `memory-backend-file` for a description of the other options.

    The `share` boolean option is on by default with memfd.

  `-object memory-backend-shm,id=id,merge=on|off,dump=on|off,share=on|off,prealloc=on|off,size=size,host-nodes=host-nodes,policy=default|preferred|bind|interleave`

    Creates a POSIX shared memory backend object, which allows QEMU to share the memory with an external process (e.g. when using vhost-user).

    `memory-backend-shm` is a more portable and less featureful version of `memory-backend-memfd`. It can then be used in any POSIX system, especially when memfd is not supported.

    Please refer to `memory-backend-file` for a description of the options.

    The `share` boolean option is on by default with shm. Setting it to off will cause a failure during allocation because it is not supported by this backend.

  `-object iommufd,id=id[,fd=fd]`

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

    The `id` parameter is a unique ID which frontends (such as vfio-pci of vdpa) will use to connect with the iommufd backend.

    The `fd` parameter is an optional pre-opened file descriptor resulting from `/dev/iommu` opening. Usually the iommufd is shared across all subsystems, bringing the benefit of centralized reference counting.

  `-object rng-builtin,id=id`

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

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

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

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

    Creates a random number generator backend which obtains entropy from an external daemon running on the host. The `id` parameter is a unique ID that will be used to reference this entropy backend from the `virtio-rng` device. The `chardev` parameter is the unique ID of a character device backend that provides the connection to the RNG daemon.

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

    Creates a TLS anonymous credentials object, which can be used to provide TLS support on network backends. The `id` parameter is a unique ID which network backends will use to access the credentials. The `endpoint` is either `server` or `client` depending on whether the QEMU network backend that uses the credentials will be acting as a client or as a server. If `verify-peer` is enabled (the default) then once the handshake is completed, the peer credentials will be verified, though this is a no-op for anonymous credentials.

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

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

    Creates a TLS Pre-Shared Keys (PSK) credentials object, which can be used to provide TLS support on network backends. The `id` parameter is a unique ID which network backends will use to access the credentials. The `endpoint` is either `server` or `client` depending on whether the QEMU network backend that uses the credentials will be acting as a client or as a server. For clients only, `username` is the username which will be sent to the server. If omitted it defaults to “qemu”.

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

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

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

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

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

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

    For the server-key.pem and client-key.pem files which contain sensitive private keys, it is possible to use an encrypted version by providing the passwordid parameter. This provides the ID of a previously created `secret` object containing the password for decryption.

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

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

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

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

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

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

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

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

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

    Interval t can’t be 0, this filter batches the packet delivery: all packets arriving in a given interval on netdev netdevid are delayed until the end of the interval. Interval is in microseconds. `status` is optional that indicate whether the netfilter is on (enabled) or off (disabled), the default status for netfilter will be ‘on’.

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

    `all`: the filter is attached both to the receive and the transmit queue of the netdev (default).

    `rx`: the filter is attached to the receive queue of the netdev, where it will receive packets sent to the netdev.

    `tx`: the filter is attached to the transmit queue of the netdev, where it will receive packets sent by the netdev.

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

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

    `tail`: the filter is inserted at the tail of the filter list, behind any existing filters (default).

    `id=<id>`: the filter is inserted before or behind the filter specified by <id>, see the insert option below.

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

    `before`: insert before the specified filter.

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

  `-object filter-mirror,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,mirror net packet to chardevchardevid, if it has the vnet_hdr_support flag, filter-mirror will mirror 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,redirect filter’s net packet to chardev chardevid,and redirect indev’s packet to filter.if it has the vnet_hdr_support flag, filter-redirector will redirect packet with vnet_hdr_len. Create a filter-redirector we need to differ outdev id from indev id, id can not be the same. we can just use indev or outdev, but at least one of indev or outdev need 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 a part of COLO project.It will rewrite tcp packet to secondary from primary to keep secondary tcp connection,and rewrite tcp packet to primary from secondary make tcp packet can be handled by client.if it has the vnet_hdr_support flag, we can parse packet with vnet header.

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

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

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

  `-object colo-compare,id=id,primary_in=chardevid,secondary_in=chardevid,outdev=chardevid,iothread=id[,vnet_hdr_support][,notify_dev=id][,compare_timeout=@var{ms}][,expired_scan_cycle=@var{ms}][,max_queue_size=@var{size}]`

    Colo-compare gets packet from primary_in chardevid and secondary_in, then compare whether the payload of primary packet and secondary packet are the same. If same, it will output primary packet to out_dev, else it will notify COLO-framework to do checkpoint and send primary packet to out_dev. In order to improve efficiency, we need to put the task of comparison in another iothread. If it has the vnet_hdr_support flag, colo compare will send/recv packet with vnet_hdr_len. The compare_timeout=@var{ms} determines the maximum time of the colo-compare hold the packet. The expired_scan_cycle=@var{ms} is to set the period of scanning expired primary node network packets. The max_queue_size=@var{size} is to set the max compare queue size depend on user environment. If user want to use Xen COLO, need to add the notify_dev to notify Xen colo-frame to do checkpoint.

    COLO-compare must be used with the help of filter-mirror, filter-redirector and filter-rewriter.

        KVM COLO

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

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

        Xen COLO

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

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

    If you want to know the detail of above command line, you can read the colo-compare git log.

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

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

        # qemu-system-x86_64 \
          [...] \
              -object cryptodev-backend-builtin,id=cryptodev0 \
              -device virtio-crypto-pci,id=crypto0,cryptodev=cryptodev0 \
          [...]

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

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

        # qemu-system-x86_64 \
          [...] \
              -chardev socket,id=chardev0,path=/path/to/socket \
              -object cryptodev-vhost-user,id=cryptodev0,chardev=chardev0 \
              -device virtio-crypto-pci,id=crypto0,cryptodev=cryptodev0 \
          [...]

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

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

    Defines a secret to store a password, encryption key, or some other sensitive data. The sensitive data can either be passed directly via the data parameter, or indirectly via the file parameter. Using the data parameter is insecure unless the sensitive data is encrypted.

    The sensitive data can be provided in raw format (the default), or base64. When encoded as JSON, the raw format only supports valid UTF-8 characters, so base64 is recommended for sending binary data. QEMU will convert from which ever format is provided to the format it needs internally. eg, an RBD password can be provided in raw format, even though it will be base64 encoded when passed onto the RBD sever.

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

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

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

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

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

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

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

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

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

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

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

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

    When launching QEMU, create a master secret pointing to `key.b64` and specify that to be used to decrypt the user password. Pass the contents of `iv.b64` to the second secret

        # qemu-system-x86_64 \
            -object secret,id=secmaster0,format=base64,file=key.b64 \
            -object secret,id=sec0,keyid=secmaster0,format=base64,\
                data=$SECRET,iv=$(<iv.b64)

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

    Create a Secure Encrypted Virtualization (SEV) guest object, which can be used to provide the guest memory encryption support on AMD processors.

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

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

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

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

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

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

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

    e.g to launch a SEV guest

        # qemu-system-x86_64 \
            ...... \
            -object sev-guest,id=sev0,cbitpos=47,reduced-phys-bits=1 \
            -machine ...,memory-encryption=sev0 \
            .....

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

    Create an authorization object that will control access to network services.

    The `identity` parameter is identifies the user and its format depends on the network service that authorization object is associated with. For authorizing based on TLS x509 certificates, the 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 a x509 distinguished name would look like:

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

    Note the use of quotes due to the x509 distinguished name containing whitespace, and escaping of ‘,’.

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

    Create an authorization object that will control access to network services.

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

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

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

    When checking access the object will iterate over all the rules and the first rule to match will have its `policy` value returned as the result. If no rules match, then the default `policy` value is returned.

    The rules can either be an exact string match, or they can use the simple UNIX glob pattern matching to allow wildcards to be used.

    If `refresh` is set to true the file will be monitored and automatically reloaded whenever its content changes.

    As with the `authz-simple` object, the format of the identity strings being matched depends on the network service, but is 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`

    Create an authorization object that will control access to network services.

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

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

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

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

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

    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. This can become a scalability bottleneck. IOThreads allow device emulation and I/O to run on other host CPUs.

    The `id` parameter is a unique ID that will be used to reference this IOThread from `-device ...,iothread=id`. Multiple devices can be assigned to an IOThread. Note that not all devices support an `iothread` parameter.

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

    IOThreads use an adaptive polling algorithm to reduce event loop latency. Instead of entering a blocking system call to monitor file descriptors and then pay the cost of being woken up when an event occurs, the polling algorithm spins waiting for events for a short time. The algorithm’s default parameters are suitable for many cases but can be adjusted based on knowledge of the workload and/or host device latency.

    The `poll-max-ns` parameter is the maximum number of nanoseconds to busy wait for events. Polling can be disabled by setting this value to 0.

    The `poll-grow` parameter is the multiplier used to increase the polling time when the algorithm detects it is missing events due to not polling long enough.

    The `poll-shrink` parameter is the divisor used to decrease the polling time when the algorithm detects it is spending too long polling without encountering events.

    The `aio-max-batch` parameter is the maximum number of requests in a batch for the AIO engine, 0 means that the engine will use its default.

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

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

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

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

    Target system display

  2

    Monitor

  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.

During emulation, if you are using a character backend multiplexer (which is the default if you are 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

## Notes

In addition to using normal file images for the emulated storage devices, QEMU can also use networked resources such as iSCSI devices. These are specified using a special URL syntax.

`iSCSI`

  iSCSI support allows QEMU to access iSCSI resources directly and use as images for the guest storage. Both disk and cdrom images are supported.

  Syntax for specifying iSCSI LUNs is “iscsi://<target-ip>[:<port>]/<target-iqn>/<lun>”

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

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

  Example (without authentication):

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

  Example (CHAP username/password via URL):

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

  Example (CHAP username/password via environment variables):

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

`NBD`

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

  Syntax for specifying a NBD device using TCP, in preferred URI form: “nbd://<server-ip>[:<port>]/[<export>]”

  Syntax for specifying a NBD device using Unix Domain Sockets; remember that ‘?’ is a shell glob character and may need quoting: “nbd+unix:///[<export>]?socket=<domain-socket>”

  Older syntax that is also recognized: “nbd:<server-ip>:<port>[:exportname=<export>]”

  Syntax for specifying a NBD device using Unix Domain Sockets “nbd:unix:<domain-socket>[:exportname=<export>]”

  Example for TCP

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

  Example for Unix Domain Sockets

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

`SSH`

  QEMU supports SSH (Secure Shell) access to remote disks.

  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.

`GlusterFS`

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

  Syntax for specifying a VM disk image on GlusterFS volume is

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

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

  Example

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

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

  See also http://www.gluster.org.

`HTTP/HTTPS/FTP/FTPS`

  QEMU supports read-only access to files accessed over http(s) and ftp(s).

  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.