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

This is used to enable an accelerator. Depending on the target architecture, kvm, xen, hvf, nvmm, whpx or tcg can be available. By default, tcg is used. If there is more than one accelerator specified, the next one is used if the previous one fails to initialize.

vmport=on|off|auto

Enables emulation of VMWare IO port, for vmmouse etc. auto says to select the value based on accel. For accel=xen the default is off otherwise the default is on.

dump-guest-core=on|off

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

mem-merge=on|off

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

aes-key-wrap=on|off

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

dea-key-wrap=on|off

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

nvdimm=on|off

Enables or disables NVDIMM support. The default is off.

memory-encryption=

Memory encryption object to use. The default is none.

hmat=on|off

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

memory-backend='id'

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

For example:

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

Migration compatibility note:

For example:

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

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

Define a CXL Fixed Memory Window (CFMW).

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

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

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

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

interleave-granularity=granularity sets the granularity of interleave. Default 256KiB. Only 256KiB, 512KiB, 1024KiB, 2048KiB 4096KiB, 8192KiB and 16384KiB granularities supported.

Example:

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

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.

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.

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.

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.

in|out.buffer-count=count

Sets the count of the buffers.

latency=usecs

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

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.

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.

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.

in|out.buffer-count=count

Sets the count of the buffers.

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.

path=path

Write recorded audio into the specified file. Default is qemu.wav.

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.

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.

bmc=id

The BMC to connect to, one of ipmi-bmc-sim or ipmi-bmc-extern above.

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.

Valid options for any block driver node:

Driver-specific options for file

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

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.

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.

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.

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.

local

Accesses to the filesystem are done by QEMU.

proxy

Accesses to the filesystem are done by virtfs-proxy-helper(1). This option is deprecated (since QEMU 8.1) and will be removed in a future version of QEMU. Use local instead.

synth

Synthetic filesystem, only used by QTests.

id=id

Specifies 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. Other fsdrivers (like proxy) don't take security model as a parameter.

writeout=writeout

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

readonly=on

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

socket=socket

Enables proxy filesystem driver to use passed socket file for communicating with virtfs-proxy-helper(1).

sock_fd=sock_fd

Enables proxy filesystem driver to use passed socket descriptor for communicating with virtfs-proxy-helper(1). Usually a helper like libvirt will create socketpair and pass one of the fds as sock_fd.

fmode=fmode

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

dmode=dmode

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

throttling.bps-total=b,throttling.bps-read=r,throttling.bps-write=w

Specify bandwidth throttling limits in bytes per second, either for all request types or for reads or writes only.

throttling.bps-total-max=bm,bps-read-max=rm,bps-write-max=wm

Specify bursts in bytes per second, either for all request types or for reads or writes only. Bursts 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.

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.

local

Accesses to the filesystem are done by QEMU.

proxy

Accesses to the filesystem are done by virtfs-proxy-helper(1). This option is deprecated (since QEMU 8.1) and will be removed in a future version of QEMU. Use local instead.

synth

Synthetic filesystem, only used by QTests.

id=id

Specifies 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. Other fsdrivers (like proxy) don't take security model as a parameter.

writeout=writeout

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

readonly=on

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

socket=socket

Enables proxy filesystem driver to use passed socket file for communicating with virtfs-proxy-helper(1). Usually a helper like libvirt will create socketpair and pass one of the fds as sock_fd.

sock_fd

Enables proxy filesystem driver to use passed 'sock_fd' as the socket descriptor for interfacing with virtfs-proxy-helper(1).

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).

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.

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-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"

curses[,charset=<encoding>]

Display video output via curses. For graphics device models which support a text mode, QEMU can display this output using a curses/ncurses interface. Nothing is displayed when the graphics device is in graphical mode or if the graphics device does not support a text mode. Generally only the VGA device models support text mode. The font charset used by the guest can be specified with the charset option, for example charset=CP850 for IBM CP850 encoding. The default is CP437.

cocoa

Display video output in a Cocoa window. Mac only. This interface provides drop-down menus and other UI elements to configure and control the VM during runtime. Valid parameters are:

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

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

egl-headless[,rendernode=<file>]

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

vnc=<display>

Start a VNC server on display <display>

none

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.

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)

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.

to=L

With this option, QEMU will try next available VNC displays, until the number L, if the origianlly 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.

reverse=on|off

Connect to a listening VNC client via a "reverse" connection. The client is specified by the display. For reverse network connections (host:d,``reverse``), the d argument is a TCP port number, not a display number.

websocket=on|off

Opens an additional TCP listening port dedicated to VNC Websocket connections. If a bare websocket option is given, the Websocket port is 5700+display. An alternative port can be specified with the syntax websocket=port.

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

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

password=on|off

Require that password based authentication is used for client connections.

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

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.

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-kvm -nic user,dnssearch=mgmt.example.org,dnssearch=example.org

domainname=domain

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

tftp=dir

When using the user mode network stack, activate a built-in TFTP server. The files in dir will be exposed as the root of a TFTP server. The TFTP client on the guest must be configured in binary mode (use the command bin of the Unix TFTP client).

tftp-server-name=name

In 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-kvm -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-kvm -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-kvm -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-kvm -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-kvm -nic  'user,id=n1,guestfwd=tcp:10.0.2.100:1234-cmd:netcat 10.10.1.1 4321'

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.

src=srcaddr

source address (mandatory)

dst=dstaddr

destination address (mandatory)

udp

select udp encapsulation (default is ip).

srcport=srcport

source udp port.

dstport=dstport

destination udp port.

ipv6

force v6, otherwise defaults to v4.

rxcookie=rxcookie; txcookie=txcookie

Cookies are a weak form of security in the l2tpv3 specification. Their function is mostly to prevent misconfiguration. By default they are 32 bit.

cookie64

Set cookie size to 64 bit instead of the default 32

counter=off

Force a 'cut-down' L2TPv3 with no counter as in draft-mkonstan-l2tpext-keyed-ipv6-tunnel-00

pincounter=on

Work around broken counter handling in peer. This may also help on networks which have packet reorder.

offset=offset

Add an extra offset between header and data

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.

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.

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

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

vc[:WxH]

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

vc:800x600

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

vc:80Cx24C

pty

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

none

No device is allocated.

null

void device

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.

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

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

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

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

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

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

unix:path[,server=on|off][,wait=on|off][,reconnect=seconds]

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

mon:dev_string

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

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

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

braille

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

msmouse

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

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.

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

file=file

Load the given plugin from a shared library file.

argname=argvalue

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

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.

-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.

The share is also required for pvrdma devices due to limitations in the RDMA API provided by Linux.

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:

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 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-kvm \


    -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,script=/etc/qemu-ifup,downscript=/etc/qemu-ifdown
-device e1000,id=e0,netdev=hn0,mac=52:a4:00:12:78:66
-chardev socket,id=mirror0,host=3.3.3.3,port=9003,server=on,wait=off
-chardev socket,id=compare1,host=3.3.3.3,port=9004,server=on,wait=off
-chardev socket,id=compare0,host=3.3.3.3,port=9001,server=on,wait=off
-chardev socket,id=compare0-0,host=3.3.3.3,port=9001
-chardev socket,id=compare_out,host=3.3.3.3,port=9005,server=on,wait=off
-chardev socket,id=compare_out0,host=3.3.3.3,port=9005
-object iothread,id=iothread1
-object filter-mirror,id=m0,netdev=hn0,queue=tx,outdev=mirror0
-object filter-redirector,netdev=hn0,id=redire0,queue=rx,indev=compare_out
-object filter-redirector,netdev=hn0,id=redire1,queue=rx,outdev=compare0
-object colo-compare,id=comp0,primary_in=compare0-0,secondary_in=compare1,outdev=compare_out0,iothread=iothread1
secondary:
-netdev tap,id=hn0,vhost=off,script=/etc/qemu-ifup,down script=/etc/qemu-ifdown
-device e1000,netdev=hn0,mac=52:a4:00:12:78:66
-chardev socket,id=red0,host=3.3.3.3,port=9003
-chardev socket,id=red1,host=3.3.3.3,port=9004
-object filter-redirector,id=f1,netdev=hn0,queue=tx,indev=red0
-object filter-redirector,id=f2,netdev=hn0,queue=rx,outdev=red1
Xen COLO
primary:
-netdev tap,id=hn0,vhost=off,script=/etc/qemu-ifup,downscript=/etc/qemu-ifdown
-device e1000,id=e0,netdev=hn0,mac=52:a4:00:12:78:66
-chardev socket,id=mirror0,host=3.3.3.3,port=9003,server=on,wait=off
-chardev socket,id=compare1,host=3.3.3.3,port=9004,server=on,wait=off
-chardev socket,id=compare0,host=3.3.3.3,port=9001,server=on,wait=off
-chardev socket,id=compare0-0,host=3.3.3.3,port=9001
-chardev socket,id=compare_out,host=3.3.3.3,port=9005,server=on,wait=off
-chardev socket,id=compare_out0,host=3.3.3.3,port=9005
-chardev socket,id=notify_way,host=3.3.3.3,port=9009,server=on,wait=off
-object filter-mirror,id=m0,netdev=hn0,queue=tx,outdev=mirror0
-object filter-redirector,netdev=hn0,id=redire0,queue=rx,indev=compare_out
-object filter-redirector,netdev=hn0,id=redire1,queue=rx,outdev=compare0
-object iothread,id=iothread1
-object colo-compare,id=comp0,primary_in=compare0-0,secondary_in=compare1,outdev=compare_out0,notify_dev=nofity_way,iothread=iothread1
secondary:
-netdev tap,id=hn0,vhost=off,script=/etc/qemu-ifup,down script=/etc/qemu-ifdown
-device e1000,netdev=hn0,mac=52:a4:00:12:78:66
-chardev socket,id=red0,host=3.3.3.3,port=9003
-chardev socket,id=red1,host=3.3.3.3,port=9004
-object filter-redirector,id=f1,netdev=hn0,queue=tx,indev=red0
-object filter-redirector,id=f2,netdev=hn0,queue=rx,outdev=red1

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-kvm \


  [...] \


      -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-kvm \


  [...] \


      -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-kvm -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-kvm \


    -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-kvm \


    ...... \


    -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-kvm \


    ... \


    -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-kvm \


    ... \


    -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-kvm \


    ... \


    -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

1

Target system display

2

Monitor

3

Serial port