QEMU(1)

QEMU(1) QEMU QEMU(1)

NAME
qemu - QEMU User Documentation

SYNOPSIS
qemu-system-x86_64 [options] [disk_image]

DESCRIPTION
The QEMU PC System emulator simulates the following peripherals:

o i440FX host PCI bridge and PIIX3 PCI to ISA bridge

o Cirrus CLGD 5446 PCI VGA card or dummy VGA card with Bochs VESA ex-
tensions (hardware level, including all non standard modes).

o PS/2 mouse and keyboard

o 2 PCI IDE interfaces with hard disk and CD-ROM support

o Floppy disk

o PCI and ISA network adapters

o Serial ports

o IPMI BMC, either and internal or external one

o Creative SoundBlaster 16 sound card

o ENSONIQ AudioPCI ES1370 sound card

o Intel 82801AA AC97 Audio compatible sound card

o Intel HD Audio Controller and HDA codec

o Adlib (OPL2) - Yamaha YM3812 compatible chip

o Gravis Ultrasound GF1 sound card

o CS4231A compatible sound card

o PCI UHCI, OHCI, EHCI or XHCI USB controller and a virtual USB-1.1
hub.

SMP is supported with up to 255 CPUs.

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" Schutz.

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 -soundhw 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

OPTIONS
disk_image is a raw hard disk image for IDE hard disk 0. Some targets
do not need a disk image.

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 compati-
bility across releases, each release will introduce a new ver-
sioned 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, hax, hvf, 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 ac-
cel=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 mem-
ory 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.

enforce-config-section=on|off
If enforce-config-section is set to on, force migration
code to send configuration section even if the ma-
chine-type sets the migration.send-configuration property
to off. NOTE: this parameter is deprecated. Please use
-global migration.send-configuration=on|off instead.

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.

-cpu model
Select CPU model (-cpu help for list and additional feature se-
lection)

-accel name[,prop=value[,...]]
This is used to enable an accelerator. Depending on the target
architecture, kvm, xen, hax, hvf, 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.

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 therefor
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).

-smp [cpus=]n[,cores=cores][,threads=threads][,dies=dies][,sock-
ets=sockets][,maxcpus=maxcpus]
Simulate an SMP system with n CPUs. On the PC target, up to 255
CPUs are supported. On Sparc32 target, Linux limits the number
of usable CPUs to 4. For the PC target, the number of cores per
die, the number of threads per cores, the number of dies per
packages and the total number of sockets can be specified. Miss-
ing values will be computed. If any on the three values is
given, the total number of CPUs n can be omitted. maxcpus speci-
fies the maximum number of hotpluggable CPUs.

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

-numa node[,memdev=id][,cpus=firstcpu[-lastcpu]][,nodeid=node][,initia-
tor=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=hierar-
chy,data-type=tpye[,latency=lat][,bandwidth=bw]

-numa hmat-cache,node-id=node,size=size,level=level[,associativ-
ity=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 contigu-
ous range of CPU indexes (or a single VCPU if lastcpu is omit-
ted). A non-contiguous set of VCPUs can be represented by pro-
viding 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

'mem' assigns a given RAM amount to a node. 'memdev' assigns RAM
from a given memory backend device to a node. If 'mem' and
'memdev' are omitted in all nodes, RAM is split equally between
them.

'mem' and 'memdev' are mutually exclusive. Furthermore, if one
node uses 'memdev', all of them have to use it.

'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 al-
locate RAM and VCPUs respectively.

Use 'hmat-lb' to set System Locality Latency and Bandwidth In-
formation between initiator and target NUMA nodes in ACPI Het-
erogeneous Attribute Memory Table (HMAT). Initiator NUMA node
can create memory requests, usually it has one or more proces-
sors. 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 'mem-
ory', the structure represents the memory performance; if hier-
archy 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|sec-
ond-level|third-level', 'data-type' is 'access|read|write' hit
latency or 'access|read|write' hit bandwidth of the target mem-
ory 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 be-
longs. 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. associa-
tivity 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 nanosec-
onds, access-bandwidth is 200 MB/s; The processors in NUMA node
0 access memory in NUMA node 1 with access-latency 10 nanosec-
onds, 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 \
-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 dupli-
cate 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 de-
vices which are created automatically by the machine model. To
create a device which is not created automatically and set prop-
erties 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 [or-
der=drives][,once=drives][,menu=on|off][,splash=sp_name][,splash-time=sp_time][,re-
boot-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_time-
out ms when boot failed, then reboot. If rb_timeout is '-1',
guest will not reboot, qemu passes '-1' to bios by default. Cur-
rently 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 ver-
sions.

-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 key-
codes (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-help
Will show the -audiodev equivalent of the currently specified
(deprecated) environment variables.

-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 mi-
croseconds. 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 back-
end. 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-set-
tings. 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 buf-
fer-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 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. This backend has no backend specific properties.

-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 usu-
ally 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.

-soundhw card1[,card2,...] or -soundhw all
Enable audio and selected sound hardware. Use 'help' to print
all available sound hardware. For example:

qemu_system-x86_64 -soundhw sb16,adlib disk.img
qemu_system-x86_64 -soundhw es1370 disk.img
qemu_system-x86_64 -soundhw ac97 disk.img
qemu_system-x86_64 -soundhw hda disk.img
qemu_system-x86_64 -soundhw all disk.img
qemu_system-x86_64 -soundhw help

Note that Linux's i810_audio OSS kernel (for AC97) module might
require manually specifying clocking.

modprobe i810_audio clocking=48000

-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[,slave_addr=val][,sdrfile=file][,furarea-
size=val][,furdatafile=file][,guid=uuid]
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 sys-
tem. 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 manage-
ment 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) inven-
tory data. The default is none.

guid=uuid
value for the GUID for the BMC, in standard UUID format.
If this is set, get "Get GUID" command to the BMC will
return it. Otherwise "Get GUID" will return an error.

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

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

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 interafce on the ISA bus. This also adds a corre-
sponding 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.

-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
-fda file

-fdb file
Use file as floppy disk 0/1 image (see disk_005fimages).

-hda file

-hdb file

-hdc file

-hdd file
Use file as hard disk 0, 1, 2 or 3 image (see disk_005fimages).

-cdrom file
Use file as CD-ROM image (you cannot use -hdc and -cdrom at the
same time). 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 op-
tions 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 al-
ready 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 in-
tended 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 re-
quested, 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 forc-
ing the node to utilize weaker shared access for
permissions where it would normally request exclu-
sive access. When there is the potential for mul-
tiple 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.di-
rect=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 los-
ing 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 en-
ables 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, de-
fault: 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, oth-
erwise 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 ref-
count 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 clus-
ter gets freed (on/off; default: off)

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 block-
dev-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 short-
cut for defining the corresponding -blockdev and -device op-
tions.

-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 disk_005fim-
ages) 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 us-
ing 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 is connected the drive 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 -block-
dev), 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", or "native" and selects between pthread
based disk I/O and native Linux AIO.

format=format
Specify which disk format will be used rather than de-
tecting 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 er-
ror 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 re-
quest 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, ei-
ther 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 re-
quest 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 cir-
cumventing 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 re-
peatedly and is useful when the backing file is over a slow net-
work. 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 incre-
mented:

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.

-pflash file
Use file as a parallel flash 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 disk_005fim-
ages).

-fsdev local,id=id,path=path,security_model=security_model [,write-
out=writeout][,readonly][,fmode=fmode][,dmode=dmode] [,throttling.op-
tion=value[,throttling.option=value[,...]]]

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

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

-fsdev synth,id=id[,readonly]
Define a new file system device. Valid options are:

local Accesses to the filesystem are done by QEMU.

proxy Accesses to the filesystem are done by
virtfs-proxy-helper(1).

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 at-
tributes 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
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 de-
scriptor 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,throt-
tling.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 re-
quest 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, throt-
tling.iops-write=w
Specify request rate limits in requests per second, ei-
ther 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 re-
quest 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 op-
tion.

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=secu-
rity_model[,writeout=writeout][,readonly]
[,fmode=fmode][,dmode=dmode][,multidevs=multidevs]

-virtfs proxy,socket=socket,mount_tag=mount_tag [,writeout=write-
out][,readonly]

-virtfs proxy,sock_fd=sock_fd,mount_tag=mount_tag [,writeout=write-
out][,readonly]

-virtfs synth,mount_tag=mount_tag
Define a new filesystem device and expose it to the guest using
a virtio-9p-device. The general form of a Virtual File system
pass-through options are:

local Accesses to the filesystem are done by QEMU.

proxy Accesses to the filesystem are done by
virtfs-proxy-helper(1).

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.

readonly
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 de-
vice 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 mul-
tiple 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 colli-
sions. Remapping inodes in such use cases is required be-
cause 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, how-
ever 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 ac-
cess operations (e.g. readdir() would still return en-
tries from other devices).

-iscsi Configure iSCSI session parameters.

USB 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. Note that this option is deprecated,
please use -device usb-... instead. See usb_005fdevices.

mouse Virtual Mouse. This will override the PS/2 mouse emula-
tion 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.

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

Display options
-display type
Select type of display to use. This option is a replacement for
the old style -sdl/-curses/... options. Use -display help to
list the available display types. Valid values for type are

sdl Display video output via SDL (usually in a separate
graphics window; see the SDL documentation for other pos-
sibilities).

curses Display video output via curses. For graphics device mod-
els which support a text mode, QEMU can display this out-
put using a curses/ncurses interface. Nothing is dis-
played when the graphics device is in graphical mode or
if the graphics device does not support a text mode. Gen-
erally 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.

none Do not display video output. The guest will still see an
emulated graphics card, but its output will not be dis-
played 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 destina-
tion of the serial and parallel port data.

gtk Display video output in a GTK window. This interface pro-
vides drop-down menus and other UI elements to configure
and control the VM during runtime.

vnc Start a VNC server on display <arg>

egl-headless
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.

spice-app
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)

-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 dis-
able graphical output so that QEMU is a simple command line ap-
plication. The emulated serial port is redirected on the con-
sole and muxed with the monitor (unless redirected elsewhere ex-
plicitly). 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.

-curses
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, QEMU can display the
VGA output when in text mode using a curses/ncurses interface.
Nothing is displayed in graphical mode.

-alt-grab
Use Ctrl-Alt-Shift to grab mouse (instead of Ctrl-Alt). Note
that this also affects the special keys (for fullscreen, moni-
tor-mode switching, etc).

-ctrl-grab
Use Right-Ctrl to grab mouse (instead of Ctrl-Alt). Note that
this also affects the special keys (for fullscreen, monitor-mode
switching, etc).

-no-quit
Disable SDL window close capability.

-sdl Enable SDL.

-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; ipv6; unix
Force using the specified IP version.

password=<secret>
Set the password you need to authenticate.

sasl 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
Allow client connects without authentication.

disable-copy-paste
Disable copy paste between the client and the guest.

disable-agent-file-xfer
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.

jpeg-wan-compression=[auto|never|always]; zlib-glz-wan-compres-
sion=[auto|never|always]
Configure wan image compression (lossy for slow links).
Default is auto.

streaming-video=[off|all|filter]
Configure video stream detection. Default is off.

agent-mouse=[on|off]
Enable/disable passing mouse events via vdagent. Default
is on.

playback-compression=[on|off]
Enable/disable audio stream compression (using celt
0.5.1). Default is on.

seamless-migration=[on|off]
Enable/disable spice seamless migration. Default is off.

gl=[on|off]
Enable/disable OpenGL context. Default is off.

rendernode=<file>
DRM render node for OpenGL rendering. If not specified,
it will pick the first available. (Since 2.9)

-portrait
Rotate graphical output 90 deg left (only PXA LCD).

-rotate deg
Rotate graphical output some deg left (only PXA LCD).

-vga type
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. Win-
dows 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 (in-
cluding VESA 2.0 VBE support). Works best with qxl guest
drivers installed though. Recommended choice when using
the spice protocol.

tcx (sun4m only) Sun TCX framebuffer. This is the default
framebuffer for sun4m machines and offers both 8-bit and
24-bit colour depths at a fixed resolution of 1024x768.

cg3 (sun4m only) Sun cgthree framebuffer. This is a simple
8-bit framebuffer for sun4m machines available in both
1024x768 (OpenBIOS) and 1152x900 (OBP) resolutions aimed
at people wishing to run older Solaris versions.

virtio Virtio VGA card.

none Disable VGA card.

-full-screen
Start in full screen.

-g widthxheight[xdepth]
Set the initial graphical resolution and depth (PPC, SPARC
only).

For PPC the default is 800x600x32.

For SPARC with the TCX graphics device, the default is
1024x768x8 with the option of 1024x768x24. For cgthree, the de-
fault 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 de-
vice 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 dis-
plays, 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 con-
nections 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
Connect to a listening VNC client via a "reverse" connec-
tion. The client is specified by the display. For re-
verse network connections (host:d,``reverse``), the d ar-
gument is a TCP port number, not a display number.

websocket
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 web-
socket=host:port.

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

password
Require that password based authentication is used for
client connections.

The password must be set separately using the set_pass-
word command in the pcsys_005fmonitor. The syntax to
change your password is: set_password <protocol> <pass-
word> where <protocol> could be either "vnc" or "spice".

If you would like to change <protocol> password expira-
tion, you should use expire_password <protocol> <expira-
tion-time> where expiration time could be one of the fol-
lowing options: now, never, +seconds or UNIX time of ex-
piration, 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 expi-
ration time to allow <protocol> password to expire imme-
diately or never expire.

tls-creds=ID
Provides the ID of a set of TLS credentials to use to se-
cure 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 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 configu-
ration file for the 'qemu' service. This is typically
found in /etc/sasl2/qemu.conf. If running QEMU as an un-
privileged 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_005fsecurity sec-
tion 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 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 com-
mands.

This option is deprecated and should no longer be used.
The new sasl-authz and tls-authz options are a replace-
ment.

lossy 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
Disable adaptive encodings. Adaptive encodings are en-
abled 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 origi-
nal 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 connec-
tions. 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 desk-
top sessions, where you don't want someone forgetting
specify -shared disconnect everybody else. 'ignore' com-
pletely ignores the shared flag and allows everybody con-
nect 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 arriv-
ing 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.

i386 target only
-win2k-hack
Use it when installing Windows 2000 to avoid a disk full bug.
After Windows 2000 is installed, you no longer need this option
(this option slows down the IDE transfers).

-no-fd-bootchk
Disable boot signature checking for floppy disks in BIOS. May be
needed to boot from old floppy disks.

-no-acpi
Disable ACPI (Advanced Configuration and Power Interface) sup-
port. Use it if your guest OS complains about ACPI problems (PC
target machine only).

-no-hpet
Disable HPET support.

-acpitable [sig=str][,rev=n][,oem_id=str][,oem_ta-
ble_id=str][,oem_rev=n] [,asl_compiler_id=str][,asl_com-
piler_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 spec-
ified 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 re-
quired 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][,re-
lease=%d.%d][,uefi=on|off]
Specify SMBIOS type 0 fields

-smbios type=1[,manufacturer=str][,product=str][,version=str][,se-
rial=str][,uuid=uuid][,sku=str][,family=str]
Specify SMBIOS type 1 fields

-smbios type=2[,manufacturer=str][,product=str][,version=str][,se-
rial=str][,asset=str][,location=str]
Specify SMBIOS type 2 fields

-smbios type=3[,manufacturer=str][,version=str][,serial=str][,as-
set=str][,sku=str]
Specify SMBIOS type 3 fields

-smbios type=4[,sock_pfx=str][,manufacturer=str][,version=str][,se-
rial=str][,asset=str][,part=str]
Specify SMBIOS type 4 fields

-smbios type=17[,loc_pfx=str][,bank=str][,manufacturer=str][,se-
rial=str][,asset=str][,part=str][,speed=%d]
Specify SMBIOS type 17 fields

Network options
-nic
[tap|bridge|user|l2tpv3|vde|netmap|vhost-user|socket][,...][,mac=macaddr][,model=mn]
This option is a shortcut for configuring both the on-board (de-
fault) guest NIC hardware and the host network backend in one
go. The host backend options are the same as with the corre-
sponding -netdev options below. The guest NIC model can be set
with model=modelname. Use model=help to list the available de-
vice 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 net-
working options are provided.

-netdev user,id=id[,option][,option][,...]
Configure user mode host network backend which requires no ad-
ministrator 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 nei-
ther 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 op-
tional, 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. De-
fault 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 name-
server. The address must be different from the host ad-
dress. Default is the 3rd IP in the guest network, i.e.
x.x.x.3.

ipv6-dns=addr
Specify the guest-visible address of the IPv6 virtual
nameserver. The address must be different from the host
address. Default is the 3rd IP in the guest network,
i.e. xxxx::3.

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

Example:

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

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

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

tftp-server-name=name
In 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; guest-
fwd=[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 ex-
ecuted by cmd:command which gets spawned for each connec-
tion. 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 es-
tablished 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][,down-
script=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
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 con-
nection. If listen is specified, QEMU waits for incoming connec-
tions 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 l2tpv3,id=id,src=srcaddr,dst=dstaddr[,srcport=srcport][,dst-
port=dstport],txsession=txsession[,rxsession=rxses-
sion][,ipv6][,udp][,cookie64][,counter][,pincounter][,txcookie=tx-
cookie][,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 on-
wards).

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 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 speci-
fication. Their function is mostly to prevent misconfig-
uration. By default they are 32 bit.

cookie64
Set cookie size to 64 bit instead of the default 32

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

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

offset=offset
Add an extra offset between header and data

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

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

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

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

-netdev vde,id=id[,sock=socketpath][,port=n][,group=group-
name][,mode=octalmode]
Configure VDE backend to connect to PORT n of a vde switch run-
ning on host and listening for incoming connections on socket-
path. 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 en-
abled.

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 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 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 de-
fault) 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. Option-
ally, for PCI cards, you can specify the number v of MSI-X vec-
tors that the card should have; this option currently only af-
fects virtio cards; set v = 0 to disable MSI-X. If no -net op-
tion 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, tty, parallel,
parport, spicevmc, spiceport. The specific backend will deter-
mine 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 moni-
tor:

-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 configura-
tion; for instance you could have a TCP port multiplexed between
UART 0 and UART 1, and stdio multiplexed between the QEMU moni-
tor 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 mux_005fkeys.

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 con-
sole and the monitor to stdio.

There is currently no support for multiplexing in the other di-
rection (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 trun-
cated 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 op-
tions.

-chardev socket,id=id[,TCP options or unix op-
tions][,server][,nowait][,telnet][,websocket][,reconnect=sec-
onds][,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 specifies that the socket shall be a listening socket.

nowait specifies that QEMU should not block waiting for a client
to connect to a listening socket.

telnet specifies that traffic on the socket should interpret
telnet escape sequences.

websocket specifies that the socket uses WebSocket protocol for
communication.

reconnect sets the timeout for reconnecting on non-server sock-
ets when the remote end goes away. qemu will delay this many
seconds and then attempt to reconnect. Zero disables reconnect-
ing, and is the default.

tls-creds requests enablement of the TLS protocol for encryp-
tion, 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 vali-
dated. This object is only resolved at time of use, so can be
deleted and recreated on the fly while the chardev server is ac-
tive. 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][,ipv6][,node-
lay]
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 sock-
ets. 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 ei-
ther a port number or a service name. port is required.

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

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

nodelay disables the Nagle algorithm.

unix options: path=path
path specifies the local path of the unix socket. path is
required.

-chardev udp,id=id[,host=host],port=port[,localaddr=localaddr][,local-
port=localport][,ipv4][,ipv6]
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 speci-
fied 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 and ipv6 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
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.

-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 re-
quired.

-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
Create a new pseudo-terminal on the host and connect to it. pty
does not take any options.

pty is not available on Windows hosts.

-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 in-
cludes 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 op-
tions.

-chardev tty,id=id,path=path
tty is only available on Linux, Sun, FreeBSD, NetBSD, OpenBSD
and DragonFlyBSD hosts. It is an alias for serial.

path specifies the path to the tty. path is required.

-chardev parallel,id=id,path=path

-chardev parport,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 re-
quired.

-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 -de-
vice 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 de-
fault /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. can-
cel-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 ini-
tialize 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 re-
booted 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 tp-
mdev=tpm0 in the device option.

-tpmdev emulator,id=id,chardev=dev
(Linux-host only) Enable access to a TPM emulator using Unix do-
main 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

Linux/Multiboot boot specific
When using these options, you can use a given Linux or Multiboot kernel
without installing it in the disk image. It can be useful for easier
testing of various kernels.

-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.

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

Debug/Expert options
-fw_cfg [name=]name,file=file
Add named fw_cfg entry with contents from file file.

-fw_cfg [name=]name,string=str
Add named fw_cfg entry with contents from string str.

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 parame-
ter.

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 con-
tents 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 up to 4 serial
ports.

Use -serial none to disable all serial ports.

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 charac-
ters:

vc:80Cx24C

pty [Linux only] Pseudo TTY (a new PTY is automatically allo-
cated)

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 se-
rial 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 automati-
cally 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 some-
thing to that port it will appear in the netconsole ses-
sion.

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 acti-
vates 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][,nowait][,nodelay][,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 connec-
tion from a location. By default the TCP Net Console is
sent to host at the port. If you use the server option
QEMU will wait for a client socket application to connect
to the port before continuing, unless the nowait option
was specified. The nodelay option disables the Nagle
buffering algorithm. The reconnect option only applies if
noserver is set, if the connection goes down it will at-
tempt 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 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

Example to not wait and listen on ip 192.168.0.100 port
4444
-serial tcp:192.168.0.100:4444,server,nowait

telnet:host:port[,server][,nowait][,nodelay]
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 se-
quence. Typically in unix telnet you do it with Control-]
and then type "send break" followed by pressing the enter
key.

websocket:host:port,server[,nowait][,nodelay]
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][,nowait][,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 connec-
tions.

mon:dev_string
This is a special option to allow the monitor to be mul-
tiplexed onto another serial port. The monitor is ac-
cessed 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,nowait

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 Mi-
crosoft protocol.

-parallel dev
Redirect the virtual parallel port to host device dev (same de-
vices 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 paral-
lel ports.

Use -parallel none to disable all parallel ports.

-monitor dev
Redirect the monitor to host device dev (same devices as the se-
rial 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.

-qmp-pretty dev
Like -qmp but uses pretty JSON formatting.

-mon [chardev=]name[,mode=readline|control][,pretty[=on|off]]
Setup monitor on chardev name. pretty turns on JSON pretty
printing easing human reading and debugging.

-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 typ-
ically port 0xe9; writing to that I/O port sends output to this
device. The default device is vc in graphical mode and stdio in
non graphical mode.

-pidfile file
Store the QEMU process PID in file. It is useful if you launch
QEMU from a script.

-singlestep
Run the emulation in single step mode.

--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-pre-
config' 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).

-realtime mlock=on|off
Run qemu with realtime features. mlocking qemu and guest memory
can be enabled via mlock=on (enabled by default).

-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 over-
committed and reduces the worst-case latency for guest. This is
equivalent to realtime.

Guest ability to manage power state of host cpus (increasing la-
tency for other processes on the same host cpu, but decreasing
latency for guest) can be enabled via cpu-pm=on (disabled by de-
fault). 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 gdb_005fusage). 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 connec-
tion 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 gdb_005fusage).

-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 ad-
dresses. 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 gen-
erator, 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.

-bios file
Set the filename for the BIOS.

-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 em-
ulation. This allows for instance switching to monitor to commit
changes to the disk image.

-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 initializa-
tion race conditions.

-option-rom file
Load the contents of file as an option ROM. This option is use-
ful to load things like EtherBoot.

-rtc [base=utc|localtime|datetime][,clock=host|rt|vm][,drift-
fix=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 al-
lows 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 recom-
mended especially in icount mode in order to preserve determin-
ism; 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][,rr=record|replay,rrfile=filename,rrsnap-
shot=snapshot]
Enable virtual instruction counter. The virtual cpu will execute
one instruction every 2^N ns of virtual time. If auto is speci-
fied then the virtual cpu speed will be automatically adjusted
to keep virtual time within a few seconds of real time.

When the virtual cpu is sleeping, the virtual time will advance
at default speed unless sleep=on|off is specified. With
sleep=on|off, the virtual time will jump to the next timer dead-
line instantly whenever the virtual cpu goes to sleep mode and
will not advance if no timer is enabled. This behavior give de-
terministic execution times from the guest point of view.

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 cor-
relation with actual performance.

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 in-
form 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).

When rr option is specified deterministic record/replay is en-
abled. Replay log is written into filename file in record mode
and read from this file in replay mode.

Option rrsnapshot is used to create new vm snapshot named snap-
shot at the start of execution recording. In replay mode this
option is used to load the initial VM state.

-watchdog model
Create a virtual hardware watchdog device. Once enabled (by a
guest action), the watchdog must be periodically polled by an
agent inside the guest or else the guest will be restarted.
Choose a model for which your guest has drivers.

The model is the model of hardware watchdog to emulate. Use
-watchdog help to list available hardware models. Only one
watchdog can be enabled for a guest.

The following models may be available:

ib700 iBASE 700 is a very simple ISA watchdog with a single
timer.

i6300esb
Intel 6300ESB I/O controller hub is a much more feature-
ful PCI-based dual-timer watchdog.

diag288
A virtual watchdog for s390x backed by the diagnose 288
hypercall (currently KVM only).

-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:

-watchdog i6300esb -watchdog-action pause; -watchdog ib700

-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 Con-
trol-a. You can select a different character from the ascii con-
trol 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

-show-cursor
Show cursor.

-tb-size n
Set TCG translation block cache size. Deprecated, use '-accel
tcg,tb-size=n' instead.

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

-incoming rdma:host:port[,ipv4][,ipv6]
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 filedescriptor.

-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 moni-
tor can be used to change settings (such as migration parame-
ters) prior to issuing the migrate_incoming to allow the migra-
tion 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, moni-
tor device, VGA adapter, floppy and CD-ROM drive and others. The
-nodefaults option will disable all those default devices.

-chroot dir
Immediately before starting guest execution, chroot to the spec-
ified directory. Especially useful in combination with -runas.

-runas user
Immediately before starting guest execution, drop root privi-
leges, switching to the specified user.

-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, Nios II only).

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

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

-semihosting-config [enable=on|off][,target=na-
tive|gdb|auto][,chardev=id][,arg=str[,...]]
Enable and configure semihosting (ARM, M68K, Xtensa, MIPS, Nios
II only).

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

On Arm this implements the standard semihosting API, version
2.0.

On M68K this implements the "ColdFire GDB" interface used by
libgloss.

Xtensa semihosting provides basic file IO calls, such as
open/read/write/seek/select. Tensilica baremetal libc for ISS
and linux platform "sim" use this interface.

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

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 -ker-
nel/-append method of passing a command line is still
supported for backward compatibility. If both the --semi-
hosting-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][,elevateprivi-
leges=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 op-
tions but you don't want to exceed the command line character
limit.

-writeconfig file
Write device configuration to file. The file can be either file-
name to save command line and device configuration into file or
dash -) character to print the output to stdout. This can be
later used as input file for -readconfig option.

-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 avail-
able 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 back-
end.

-plugin file=file[,arg=string]
Load a plugin.

file=file
Load the given plugin from a shared library file.

arg=string
Argument string passed to the plugin. (Can be given mul-
tiple times.)

-enable-fips
Enable FIPS 140-2 compliance mode.

-msg timestamp[=on|off]
Control error message format.

timestamp=on|off
Prefix messages with a timestamp. 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.

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.

The id parameter is a unique ID that will be used to ref-
erence this memory region when configuring the -numa ar-
gument.

The size option provides the size of the memory region,
and accepts common suffixes, eg 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 lat-
ter allows a co-operating external process to access the
QEMU memory region.

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

Setting share=on might affect the ability to configure
NUMA bindings for the memory backend under some circum-
stances, 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 mem-
ory 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 fol-
lowing 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 re-
quired alignment via this option.

The pmem option specifies whether the backing file speci-
fied 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 mi-
gration). 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.

-object memory-back-
end-ram,id=id,merge=on|off,dump=on|off,share=on|off,preal-
loc=on|off,size=size,host-nodes=host-nodes,policy=default|pre-
ferred|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-back-
end-memfd,id=id,merge=on|off,dump=on|off,share=on|off,preal-
loc=on|off,size=size,host-nodes=host-nodes,policy=default|pre-
ferred|bind|interleave,seal=on|off,hugetlb=on|off,hugetlb-
size=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 op-
tion specify the hugetlb page size on systems that sup-
port 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 incom-
patible 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 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 vir-
tio-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 parame-
ter 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 refer-
ence 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=end-
point,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 ran-
dom pool entropy, so it is recommended that a persistent
set of parameters be generated upfront and saved.

-object tls-creds-psk,id=id,endpoint=end-
point,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 back-
ends. The id parameter is a unique ID which network back-
ends 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=end-
point,dir=/path/to/cred/dir,priority=priority,ver-
ify-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 cer-
tificates too.

For x509 certificate credentials the directory will con-
tain 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 ob-
ject containing the password for decryption.

The priority parameter allows to override the global de-
fault 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 weak-
ness onto all applications. Or conversely if one wants
wants a stronger default for QEMU than for all other ap-
plications, 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 filter-buffer,id=id,netdev=netdevid,inter-
val=t[,queue=all|rx|tx][,status=on|off][,posi-
tion=head|tail|id=<id>][,insert=behind|before]
Interval t can't be 0, this filter batches the packet de-
livery: all packets arriving in a given interval on net-
dev netdevid are delayed until the end of the interval.
Interval is in microseconds. status is optional that in-
dicate whether the netfilter is on (enabled) or off (dis-
abled), 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 fil-
ter specified by <id>, see the insert option below.

insert behind|before is an option to specify where to in-
sert 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=charde-
vid,queue=all|rx|tx[,vnet_hdr_support][,posi-
tion=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=charde-
vid,outdev=chardevid,queue=all|rx|tx[,vnet_hdr_support][,posi-
tion=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=netde-
vid,queue=all|rx|tx,[vnet_hdr_support][,posi-
tion=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-redirec-
tor,id=f1,netdev=hn0,queue=tx,indev=red0 -object fil-
ter-redirector,id=f2,netdev=hn0,queue=rx,outdev=red1 -ob-
ject filter-rewriter,id=rew0,netdev=hn0,queue=all

-object filter-dump,id=id,netdev=dev[,file=file-
name][,maxlen=len][,position=head|tail|id=<id>][,insert=be-
hind|before]
Dump the network traffic on netdev dev to the file speci-
fied 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,sec-
ondary_in=chardevid,outdev=chardevid,iothread=id[,vnet_hdr_sup-
port][,notify_dev=id][,compare_timeout=@var{ms}][,ex-
pired_scan_cycle=@var{ms}
Colo-compare gets packet from primary_inchardevid and
secondary_inchardevid, than compare primary packet with
secondary packet. If the packets are same, we will output
primary packet to outdevchardevid, else we will notify
colo-frame do checkpoint and send primary packet to out-
devchardevid. In order to improve efficiency, we need to
put the task of comparison in another thread. If it has
the vnet_hdr_support flag, colo compare will send/recv
packet with vnet_hdr_len. Then compare_timeout=@var{ms}
determines the maximum delay colo-compare wait for the
packet. The expired_scan_cycle=@var{ms} to set the pe-
riod of scanning expired primary node network packets.
If you want to use Xen COLO, will need the notify_dev to
notify Xen colo-frame to do checkpoint.

we must use it with the help of filter-mirror and fil-
ter-redirector.

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,nowait
-chardev socket,id=compare1,host=3.3.3.3,port=9004,server,nowait
-chardev socket,id=compare0,host=3.3.3.3,port=9001,server,nowait
-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,nowait
-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,nowait
-chardev socket,id=compare1,host=3.3.3.3,port=9004,server,nowait
-chardev socket,id=compare0,host=3.3.3.3,port=9001,server,nowait
-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,nowait
-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,nowait
-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

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
opreation 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 parame-
ter is optional, which specify the queue number of cryp-
todev 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=charde-
vid[,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=se-
cretid,iv=string]

-object secret,id=id,file=filename,format=raw|base64[,keyid=se-
cretid,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 inse-
cure unless the sensitive data is encrypted.

The sensitive data can be provided in raw format (the de-
fault), or base64. When encoded as JSON, the raw format
only supports valid UTF-8 characters, so base64 is recom-
mended for sending binary data. QEMU will convert from
which ever format is provided to the format it needs in-
ternally. eg, an RBD password can be provided in raw for-
mat, 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 de-
cryption key. This key should be 32-bytes long and be
base64 encoded. The iv parameter provides the random ini-
tialization 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 il-
lustrate 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 al-
gorithm.

First a master key needs to be created in base64 encod-
ing:

# 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 ini-
tialization 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 se-
cret

# 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,re-
duced-phys-bits=val,[sev-device=string,policy=policy,handle=han-
dle,dh-cert-file=file,session-file=file]
Create a Secure Encrypted Virtualization (SEV) guest ob-
ject, which can be used to provide the guest memory en-
cryption 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 mem-
ory page is protected. The cbitpos is used to provide the
C-bit position. The C-bit position is Host family depen-
dent 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 ad-
dress space. Similar to C-bit, the value is Host family
dependent. On EPYC, the value should be 5.

The sev-device provides the device file to use for commu-
nicating 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 cre-
ated by CCP driver.

The policy provides the guest policy to be enforced by
the SEV firmware and restrict what configuration and op-
erational 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.

e.g to launch a SEV guest

# qemu_system-x86_64 ......
-object sev-guest,id=sev0,cbitpos=47,reduced-phys-bits=5 -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 distin-
guished name. Note that care must be taken to escape any
commas in the distinguished name.

An example authorization object to validate a x509 dis-
tinguished 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=yes|no
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 iden-
tity strings being matched depends on the network ser-
vice, but is usually a TLS x509 distinguished name, or a
SASL username.

An example authorization object to validate a SASL user-
name would look like:

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

-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 distingished names that are permitted access

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

-object io-
thread,id=id,poll-max-ns=poll-max-ns,poll-grow=poll-grow,poll-shrink=poll-shrink
Creates a dedicated event loop thread that devices can be
assigned to. This is known as an IOThread. By default de-
vice 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 ref-
erence this IOThread from -device ...,iothread=id. Mul-
tiple devices can be assigned to an IOThread. Note that
not all devices support an iothread parameter.

The query-iothreads QMP command lists IOThreads and re-
ports 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 algo-
rithm spins waiting for events for a short time. The al-
gorithm'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 dis-
abled by setting this value to 0.

The poll-grow parameter is the multiplier used to in-
crease 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 spend-
ing too long polling without encountering events.

The polling 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 to
change modes. The default key mappings are shown below, but if you use
-alt-grab then the modifier is Ctrl-Alt-Shift (instead of Ctrl-Alt) and
if you use -ctrl-grab then the modifier is the right Ctrl key (instead
of Ctrl-Alt):

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
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 com-
mands 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 (usu-
ally 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 de-
vices, 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://<tar-
get-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 re-
quired 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 proto-
col 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 quot-
ing: "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 au-
thentication methods may be supported in future.

Sheepdog
Sheepdog is a distributed storage system for QEMU. QEMU supports
using either local sheepdog devices or remote networked devices.

Syntax for specifying a sheepdog device

sheepdog[+tcp|+unix]://[host:port]/vdiname[?socket=path][#snapid|#tag]

Example

qemu-system-x86_64 --drive file=sheepdog://192.0.2.1:30000/MyVirtualMachine

See also https://sheepdog.github.io/sheepdog/.

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

Syntax for specifying a VM disk image on 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