Provided by: qemu-system-common_9.0.2+ds-4ubuntu5.2_amd64 
NAME
qemu - QEMU User Documentation
SYNOPSIS
qemu-system-x86_64 [options] [disk_image]
DESCRIPTION
The QEMU PC System emulator simulates the following peripherals:
• i440FX host PCI bridge and PIIX3 PCI to ISA bridge
• Cirrus CLGD 5446 PCI VGA card or dummy VGA card with Bochs VESA extensions (hardware level, including
all non standard modes).
• PS/2 mouse and keyboard
• 2 PCI IDE interfaces with hard disk and CD-ROM support
• Floppy disk
• PCI and ISA network adapters
• Serial ports
• IPMI BMC, either and internal or external one
• Creative SoundBlaster 16 sound card
• ENSONIQ AudioPCI ES1370 sound card
• Intel 82801AA AC97 Audio compatible sound card
• Intel HD Audio Controller and HDA codec
• Adlib (OPL2) - Yamaha YM3812 compatible chip
• Gravis Ultrasound GF1 sound card
• CS4231A compatible sound card
• PC speaker
• PCI UHCI, OHCI, EHCI or XHCI USB controller and a virtual USB-1.1 hub.
SMP is supported with up to 255 CPUs (and 4096 CPUs for PC Q35 machine).
QEMU uses the PC BIOS from the Seabios project and the Plex86/Bochs LGPL VGA BIOS.
QEMU uses YM3812 emulation by Tatsuyuki Satoh.
QEMU uses GUS emulation (GUSEMU32 http://www.deinmeister.de/gusemu/) by Tibor "TS" Schütz.
Note that, by default, GUS shares IRQ(7) with parallel ports and so QEMU must be told to not have
parallel ports to have working GUS.
qemu-system-x86_64 dos.img -device gus -parallel none
Alternatively:
qemu-system-x86_64 dos.img -device gus,irq=5
Or some other unclaimed IRQ.
CS4231A is the chip used in Windows Sound System and GUSMAX products
The PC speaker audio device can be configured using the pcspk-audiodev machine property, i.e.
qemu-system-x86_64 some.img -audiodev <backend>,id=<name> -machine pcspk-audiodev=<name>
Machine-specific options
It supports the following machine-specific options:
• x-south-bridge=PIIX3|piix4-isa (Experimental option to select a particular south bridge. Default:
PIIX3)
OPTIONS
disk_image is a raw hard disk image for IDE hard disk 0. Some targets do not need a disk image.
When dealing with options parameters as arbitrary strings containing commas, such as in "file=my,file"
and "string=a,b", it's necessary to double the commas. For instance,"-fw_cfg name=z,string=a,,b" will be
parsed as "-fw_cfg name=z,string=a,b".
Standard options
-h Display help and exit
-version
Display version information and exit
-machine [type=]name[,prop=value[,...]]
Select the emulated machine by name. Use -machine help to list available machines.
For architectures which aim to support live migration compatibility across releases, each release
will introduce a new versioned machine type. For example, the 2.8.0 release introduced machine
types "pc-i440fx-2.8" and "pc-q35-2.8" for the x86_64/i686 architectures.
To allow live migration of guests from QEMU version 2.8.0, to QEMU version 2.9.0, the 2.9.0
version must support the "pc-i440fx-2.8" and "pc-q35-2.8" machines too. To allow users live
migrating VMs to skip multiple intermediate releases when upgrading, new releases of QEMU will
support machine types from many previous versions.
Supported machine properties are:
accel=accels1[:accels2[:...]]
This is used to enable an accelerator. Depending on the target architecture, kvm, xen, hvf,
nvmm, whpx or tcg can be available. By default, tcg is used. If there is more than one
accelerator specified, the next one is used if the previous one fails to initialize.
vmport=on|off|auto
Enables emulation of VMWare IO port, for vmmouse etc. auto says to select the value based
on accel. For accel=xen the default is off otherwise the default is on.
dump-guest-core=on|off
Include guest memory in a core dump. The default is on.
mem-merge=on|off
Enables or disables memory merge support. This feature, when supported by the host,
de-duplicates identical memory pages among VMs instances (enabled by default).
aes-key-wrap=on|off
Enables or disables AES key wrapping support on s390-ccw hosts. This feature controls
whether AES wrapping keys will be created to allow execution of AES cryptographic
functions. The default is on.
dea-key-wrap=on|off
Enables or disables DEA key wrapping support on s390-ccw hosts. This feature controls
whether DEA wrapping keys will be created to allow execution of DEA cryptographic
functions. The default is on.
nvdimm=on|off
Enables or disables NVDIMM support. The default is off.
memory-encryption=
Memory encryption object to use. The default is none.
hmat=on|off
Enables or disables ACPI Heterogeneous Memory Attribute Table (HMAT) support. The default
is off.
memory-backend='id'
An alternative to legacy -mem-path and mem-prealloc options. Allows to use a memory
backend as main RAM.
For example:
-object memory-backend-file,id=pc.ram,size=512M,mem-path=/hugetlbfs,prealloc=on,share=on
-machine memory-backend=pc.ram
-m 512M
Migration compatibility note:
• as backend id one shall use value of 'default-ram-id', advertised by machine type
(available via query-machines QMP command), if migration to/from old QEMU (<5.0) is
expected.
• for machine types 4.0 and older, user shall use x-use-canonical-path-for-ramblock-id=off
backend option if migration to/from old QEMU (<5.0) is expected.
For example:
-object memory-backend-ram,id=pc.ram,size=512M,x-use-canonical-path-for-ramblock-id=off
-machine memory-backend=pc.ram
-m 512M
cxl-fmw.0.targets.0=firsttarget,cxl-fmw.0.targets.1=secondtarget,cxl-fmw.0.size=size[,cxl-fmw.0.interleave-granularity=granularity]
Define a CXL Fixed Memory Window (CFMW).
Described in the CXL 2.0 ECN: CEDT CFMWS & QTG _DSM.
They are regions of Host Physical Addresses (HPA) on a system which may be interleaved
across one or more CXL host bridges. The system software will assign particular devices
into these windows and configure the downstream Host-managed Device Memory (HDM) decoders
in root ports, switch ports and devices appropriately to meet the interleave requirements
before enabling the memory devices.
targets.X=target provides the mapping to CXL host bridges which may be identified by the id
provided in the -device entry. Multiple entries are needed to specify all the targets when
the fixed memory window represents interleaved memory. X is the target index from 0.
size=size sets the size of the CFMW. This must be a multiple of 256MiB. The region will be
aligned to 256MiB but the location is platform and configuration dependent.
interleave-granularity=granularity sets the granularity of interleave. Default 256 (bytes).
Only 256, 512, 1k, 2k, 4k, 8k and 16k granularities supported.
Example:
-machine cxl-fmw.0.targets.0=cxl.0,cxl-fmw.0.targets.1=cxl.1,cxl-fmw.0.size=128G,cxl-fmw.0.interleave-granularity=512
sgx-epc.0.memdev=@var{memid},sgx-epc.0.node=@var{numaid}
Define an SGX EPC section.
-cpu model
Select CPU model (-cpu help for list and additional feature selection)
-accel name[,prop=value[,...]]
This is used to enable an accelerator. Depending on the target architecture, kvm, xen, hvf, nvmm,
whpx or tcg can be available. By default, tcg is used. If there is more than one accelerator
specified, the next one is used if the previous one fails to initialize.
igd-passthru=on|off
When Xen is in use, this option controls whether Intel integrated graphics devices can be
passed through to the guest (default=off)
kernel-irqchip=on|off|split
Controls KVM in-kernel irqchip support. The default is full acceleration of the interrupt
controllers. On x86, split irqchip reduces the kernel attack surface, at a performance cost
for non-MSI interrupts. Disabling the in-kernel irqchip completely is not recommended
except for debugging purposes.
kvm-shadow-mem=size
Defines the size of the KVM shadow MMU.
one-insn-per-tb=on|off
Makes the TCG accelerator put only one guest instruction into each translation block. This
slows down emulation a lot, but can be useful in some situations, such as when trying to
analyse the logs produced by the -d option.
split-wx=on|off
Controls the use of split w^x mapping for the TCG code generation buffer. Some operating
systems require this to be enabled, and in such a case this will default on. On other
operating systems, this will default off, but one may enable this for testing or debugging.
tb-size=n
Controls the size (in MiB) of the TCG translation block cache.
thread=single|multi
Controls number of TCG threads. When the TCG is multi-threaded there will be one thread per
vCPU therefore taking advantage of additional host cores. The default is to enable
multi-threading where both the back-end and front-ends support it and no incompatible TCG
features have been enabled (e.g. icount/replay).
dirty-ring-size=n
When the KVM accelerator is used, it controls the size of the per-vCPU dirty page ring
buffer (number of entries for each vCPU). It should be a value that is power of two, and it
should be 1024 or bigger (but still less than the maximum value that the kernel supports).
4096 could be a good initial value if you have no idea which is the best. Set this value
to 0 to disable the feature. By default, this feature is disabled (dirty-ring-size=0).
When enabled, KVM will instead record dirty pages in a bitmap.
eager-split-size=n
KVM implements dirty page logging at the PAGE_SIZE granularity and enabling dirty-logging
on a huge-page requires breaking it into PAGE_SIZE pages in the first place. KVM on ARM
does this splitting lazily by default. There are performance benefits in doing huge-page
split eagerly, especially in situations where TLBI costs associated with break-before-make
sequences are considerable and also if guest workloads are read intensive. The size here
specifies how many pages to break at a time and needs to be a valid block size which is
1GB/2MB/4KB, 32MB/16KB and 512MB/64KB for 4KB/16KB/64KB PAGE_SIZE respectively. Be wary of
specifying a higher size as it will have an impact on the memory. By default, this feature
is disabled (eager-split-size=0).
notify-vmexit=run|internal-error|disable,notify-window=n
Enables or disables notify VM exit support on x86 host and specify the corresponding notify
window to trigger the VM exit if enabled. run option enables the feature. It does nothing
and continue if the exit happens. internal-error option enables the feature. It raises a
internal error. disable option doesn't enable the feature. This feature can mitigate the
CPU stuck issue due to event windows don't open up for a specified of time (i.e.
notify-window). Default: notify-vmexit=run,notify-window=0.
device=path
Sets the path to the KVM device node. Defaults to /dev/kvm. This option can be used to pass
the KVM device to use via a file descriptor by setting the value to /dev/fdset/NN.
-smp
[[cpus=]n][,maxcpus=maxcpus][,sockets=sockets][,dies=dies][,clusters=clusters][,cores=cores][,threads=threads]
Simulate a SMP system with 'n' CPUs initially present on the machine type board. On boards
supporting CPU hotplug, the optional 'maxcpus' parameter can be set to enable further CPUs to be
added at runtime. When both parameters are omitted, the maximum number of CPUs will be calculated
from the provided topology members and the initial CPU count will match the maximum number. When
only one of them is given then the omitted one will be set to its counterpart's value. Both
parameters may be specified, but the maximum number of CPUs must be equal to or greater than the
initial CPU count. Product of the CPU topology hierarchy must be equal to the maximum number of
CPUs. Both parameters are subject to an upper limit that is determined by the specific machine
type chosen.
To control reporting of CPU topology information, values of the topology parameters can be
specified. Machines may only support a subset of the parameters and different machines may have
different subsets supported which vary depending on capacity of the corresponding CPU targets. So
for a particular machine type board, an expected topology hierarchy can be defined through the
supported sub-option. Unsupported parameters can also be provided in addition to the sub-option,
but their values must be set as 1 in the purpose of correct parsing.
Either the initial CPU count, or at least one of the topology parameters must be specified. The
specified parameters must be greater than zero, explicit configuration like "cpus=0" is not
allowed. Values for any omitted parameters will be computed from those which are given.
For example, the following sub-option defines a CPU topology hierarchy (2 sockets totally on the
machine, 2 cores per socket, 2 threads per core) for a machine that only supports
sockets/cores/threads. Some members of the option can be omitted but their values will be
automatically computed:
-smp 8,sockets=2,cores=2,threads=2,maxcpus=8
The following sub-option defines a CPU topology hierarchy (2 sockets totally on the machine, 2
dies per socket, 2 cores per die, 2 threads per core) for PC machines which support
sockets/dies/cores/threads. Some members of the option can be omitted but their values will be
automatically computed:
-smp 16,sockets=2,dies=2,cores=2,threads=2,maxcpus=16
The following sub-option defines a CPU topology hierarchy (2 sockets totally on the machine, 2
clusters per socket, 2 cores per cluster, 2 threads per core) for ARM virt machines which support
sockets/clusters /cores/threads. Some members of the option can be omitted but their values will
be automatically computed:
-smp 16,sockets=2,clusters=2,cores=2,threads=2,maxcpus=16
Historically preference was given to the coarsest topology parameters when computing missing
values (ie sockets preferred over cores, which were preferred over threads), however, this
behaviour is considered liable to change. Prior to 6.2 the preference was sockets over cores over
threads. Since 6.2 the preference is cores over sockets over threads.
For example, the following option defines a machine board with 2 sockets of 1 core before 6.2 and
1 socket of 2 cores after 6.2:
-smp 2
Note: The cluster topology will only be generated in ACPI and exposed to guest if it's explicitly
specified in -smp.
-numa node[,mem=size][,cpus=firstcpu[-lastcpu]][,nodeid=node][,initiator=initiator]
-numa node[,memdev=id][,cpus=firstcpu[-lastcpu]][,nodeid=node][,initiator=initiator]
-numa dist,src=source,dst=destination,val=distance
-numa cpu,node-id=node[,socket-id=x][,core-id=y][,thread-id=z]
-numa hmat-lb,initiator=node,target=node,hierarchy=hierarchy,data-type=type[,latency=lat][,bandwidth=bw]
-numa hmat-cache,node-id=node,size=size,level=level[,associativity=str][,policy=str][,line=size]
Define a NUMA node and assign RAM and VCPUs to it. Set the NUMA distance from a source node to a
destination node. Set the ACPI Heterogeneous Memory Attributes for the given nodes.
Legacy VCPU assignment uses 'cpus' option where firstcpu and lastcpu are CPU indexes. Each 'cpus'
option represent a contiguous range of CPU indexes (or a single VCPU if lastcpu is omitted). A
non-contiguous set of VCPUs can be represented by providing multiple 'cpus' options. If 'cpus' is
omitted on all nodes, VCPUs are automatically split between them.
For example, the following option assigns VCPUs 0, 1, 2 and 5 to a NUMA node:
-numa node,cpus=0-2,cpus=5
'cpu' option is a new alternative to 'cpus' option which uses 'socket-id|core-id|thread-id'
properties to assign CPU objects to a node using topology layout properties of CPU. The set of
properties is machine specific, and depends on used machine type/'smp' options. It could be
queried with 'hotpluggable-cpus' monitor command. 'node-id' property specifies node to which CPU
object will be assigned, it's required for node to be declared with 'node' option before it's used
with 'cpu' option.
For example:
-M pc \
-smp 1,sockets=2,maxcpus=2 \
-numa node,nodeid=0 -numa node,nodeid=1 \
-numa cpu,node-id=0,socket-id=0 -numa cpu,node-id=1,socket-id=1
'memdev' option assigns RAM from a given memory backend device to a node. It is recommended to use
'memdev' option over legacy 'mem' option. This is because 'memdev' option provides better
performance and more control over the backend's RAM (e.g. 'prealloc' parameter of
'-memory-backend-ram' allows memory preallocation).
For compatibility reasons, legacy 'mem' option is supported in 5.0 and older machine types. Note
that 'mem' and 'memdev' are mutually exclusive. If one node uses 'memdev', the rest nodes have to
use 'memdev' option, and vice versa.
Users must specify memory for all NUMA nodes by 'memdev' (or legacy 'mem' if available). In QEMU
5.2, the support for '-numa node' without memory specified was removed.
'initiator' is an additional option that points to an initiator NUMA node that has best
performance (the lowest latency or largest bandwidth) to this NUMA node. Note that this option can
be set only when the machine property 'hmat' is set to 'on'.
Following example creates a machine with 2 NUMA nodes, node 0 has CPU. node 1 has only memory, and
its initiator is node 0. Note that because node 0 has CPU, by default the initiator of node 0 is
itself and must be itself.
-machine hmat=on \
-m 2G,slots=2,maxmem=4G \
-object memory-backend-ram,size=1G,id=m0 \
-object memory-backend-ram,size=1G,id=m1 \
-numa node,nodeid=0,memdev=m0 \
-numa node,nodeid=1,memdev=m1,initiator=0 \
-smp 2,sockets=2,maxcpus=2 \
-numa cpu,node-id=0,socket-id=0 \
-numa cpu,node-id=0,socket-id=1
source and destination are NUMA node IDs. distance is the NUMA distance from source to
destination. The distance from a node to itself is always 10. If any pair of nodes is given a
distance, then all pairs must be given distances. Although, when distances are only given in one
direction for each pair of nodes, then the distances in the opposite directions are assumed to be
the same. If, however, an asymmetrical pair of distances is given for even one node pair, then all
node pairs must be provided distance values for both directions, even when they are symmetrical.
When a node is unreachable from another node, set the pair's distance to 255.
Note that the -numa option doesn't allocate any of the specified resources, it just assigns
existing resources to NUMA nodes. This means that one still has to use the -m, -smp options to
allocate RAM and VCPUs respectively.
Use 'hmat-lb' to set System Locality Latency and Bandwidth Information between initiator and
target NUMA nodes in ACPI Heterogeneous Attribute Memory Table (HMAT). Initiator NUMA node can
create memory requests, usually it has one or more processors. Target NUMA node contains
addressable memory.
In 'hmat-lb' option, node are NUMA node IDs. hierarchy is the memory hierarchy of the target NUMA
node: if hierarchy is 'memory', the structure represents the memory performance; if hierarchy is
'first-level|second-level|third-level', this structure represents aggregated performance of memory
side caches for each domain. type of 'data-type' is type of data represented by this structure
instance: if 'hierarchy' is 'memory', 'data-type' is 'access|read|write' latency or
'access|read|write' bandwidth of the target memory; if 'hierarchy' is
'first-level|second-level|third-level', 'data-type' is 'access|read|write' hit latency or
'access|read|write' hit bandwidth of the target memory side cache.
lat is latency value in nanoseconds. bw is bandwidth value, the possible value and units are
NUM[M|G|T], mean that the bandwidth value are NUM byte per second (or MB/s, GB/s or TB/s depending
on used suffix). Note that if latency or bandwidth value is 0, means the corresponding latency or
bandwidth information is not provided.
In 'hmat-cache' option, node-id is the NUMA-id of the memory belongs. size is the size of memory
side cache in bytes. level is the cache level described in this structure, note that the cache
level 0 should not be used with 'hmat-cache' option. associativity is the cache associativity,
the possible value is 'none/direct(direct-mapped)/complex(complex cache indexing)'. policy is the
write policy. line is the cache Line size in bytes.
For example, the following options describe 2 NUMA nodes. Node 0 has 2 cpus and a ram, node 1 has
only a ram. The processors in node 0 access memory in node 0 with access-latency 5 nanoseconds,
access-bandwidth is 200 MB/s; The processors in NUMA node 0 access memory in NUMA node 1 with
access-latency 10 nanoseconds, access-bandwidth is 100 MB/s. And for memory side cache
information, NUMA node 0 and 1 both have 1 level memory cache, size is 10KB, policy is write-back,
the cache Line size is 8 bytes:
-machine hmat=on \
-m 2G \
-object memory-backend-ram,size=1G,id=m0 \
-object memory-backend-ram,size=1G,id=m1 \
-smp 2,sockets=2,maxcpus=2 \
-numa node,nodeid=0,memdev=m0 \
-numa node,nodeid=1,memdev=m1,initiator=0 \
-numa cpu,node-id=0,socket-id=0 \
-numa cpu,node-id=0,socket-id=1 \
-numa hmat-lb,initiator=0,target=0,hierarchy=memory,data-type=access-latency,latency=5 \
-numa hmat-lb,initiator=0,target=0,hierarchy=memory,data-type=access-bandwidth,bandwidth=200M \
-numa hmat-lb,initiator=0,target=1,hierarchy=memory,data-type=access-latency,latency=10 \
-numa hmat-lb,initiator=0,target=1,hierarchy=memory,data-type=access-bandwidth,bandwidth=100M \
-numa hmat-cache,node-id=0,size=10K,level=1,associativity=direct,policy=write-back,line=8 \
-numa hmat-cache,node-id=1,size=10K,level=1,associativity=direct,policy=write-back,line=8
-add-fd fd=fd,set=set[,opaque=opaque]
Add a file descriptor to an fd set. Valid options are:
fd=fd This option defines the file descriptor of which a duplicate is added to fd set. The file
descriptor cannot be stdin, stdout, or stderr.
set=set
This option defines the ID of the fd set to add the file descriptor to.
opaque=opaque
This option defines a free-form string that can be used to describe fd.
You can open an image using pre-opened file descriptors from an fd set:
qemu-system-x86_64 \
-add-fd fd=3,set=2,opaque="rdwr:/path/to/file" \
-add-fd fd=4,set=2,opaque="rdonly:/path/to/file" \
-drive file=/dev/fdset/2,index=0,media=disk
-set group.id.arg=value
Set parameter arg for item id of type group
-global driver.prop=value
-global driver=driver,property=property,value=value
Set default value of driver's property prop to value, e.g.:
qemu-system-x86_64 -global ide-hd.physical_block_size=4096 disk-image.img
In particular, you can use this to set driver properties for devices which are created
automatically by the machine model. To create a device which is not created automatically and set
properties on it, use -device.
-global driver.prop=value is shorthand for -global driver=driver,property=prop,value=value. The
longhand syntax works even when driver contains a dot.
-boot
[order=drives][,once=drives][,menu=on|off][,splash=sp_name][,splash-time=sp_time][,reboot-timeout=rb_timeout][,strict=on|off]
Specify boot order drives as a string of drive letters. Valid drive letters depend on the target
architecture. The x86 PC uses: a, b (floppy 1 and 2), c (first hard disk), d (first CD-ROM), n-p
(Etherboot from network adapter 1-4), hard disk boot is the default. To apply a particular boot
order only on the first startup, specify it via once. Note that the order or once parameter should
not be used together with the bootindex property of devices, since the firmware implementations
normally do not support both at the same time.
Interactive boot menus/prompts can be enabled via menu=on as far as firmware/BIOS supports them.
The default is non-interactive boot.
A splash picture could be passed to bios, enabling user to show it as logo, when option
splash=sp_name is given and menu=on, If firmware/BIOS supports them. Currently Seabios for X86
system support it. limitation: The splash file could be a jpeg file or a BMP file in 24 BPP
format(true color). The resolution should be supported by the SVGA mode, so the recommended is
320x240, 640x480, 800x640.
A timeout could be passed to bios, guest will pause for rb_timeout ms when boot failed, then
reboot. If rb_timeout is '-1', guest will not reboot, qemu passes '-1' to bios by default.
Currently Seabios for X86 system support it.
Do strict boot via strict=on as far as firmware/BIOS supports it. This only effects when boot
priority is changed by bootindex options. The default is non-strict boot.
# try to boot from network first, then from hard disk
qemu-system-x86_64 -boot order=nc
# boot from CD-ROM first, switch back to default order after reboot
qemu-system-x86_64 -boot once=d
# boot with a splash picture for 5 seconds.
qemu-system-x86_64 -boot menu=on,splash=/root/boot.bmp,splash-time=5000
Note: The legacy format '-boot drives' is still supported but its use is discouraged as it may be
removed from future versions.
-m [size=]megs[,slots=n,maxmem=size]
Sets guest startup RAM size to megs megabytes. Default is 128 MiB. Optionally, a suffix of "M" or
"G" can be used to signify a value in megabytes or gigabytes respectively. Optional pair slots,
maxmem could be used to set amount of hotpluggable memory slots and maximum amount of memory. Note
that maxmem must be aligned to the page size.
For example, the following command-line sets the guest startup RAM size to 1GB, creates 3 slots to
hotplug additional memory and sets the maximum memory the guest can reach to 4GB:
qemu-system-x86_64 -m 1G,slots=3,maxmem=4G
If slots and maxmem are not specified, memory hotplug won't be enabled and the guest startup RAM
will never increase.
-mem-path path
Allocate guest RAM from a temporarily created file in path.
-mem-prealloc
Preallocate memory when using -mem-path.
-k language
Use keyboard layout language (for example fr for French). This option is only needed where it is
not easy to get raw PC keycodes (e.g. on Macs, with some X11 servers or with a VNC or curses
display). You don't normally need to use it on PC/Linux or PC/Windows hosts.
The available layouts are:
ar de-ch es fo fr-ca hu ja mk no pt-br sv
da en-gb et fr fr-ch is lt nl pl ru th
de en-us fi fr-be hr it lv nl-be pt sl tr
The default is en-us.
-audio [driver=]driver[,model=value][,prop[=value][,...]]
If the model option is specified, -audio is a shortcut for configuring both the guest audio
hardware and the host audio backend in one go. The guest hardware model can be set with
model=modelname. Use model=help to list the available device types.
The following two example do exactly the same, to show how -audio can be used to shorten the
command line length:
qemu-system-x86_64 -audiodev pa,id=pa -device sb16,audiodev=pa
qemu-system-x86_64 -audio pa,model=sb16
If the model option is not specified, -audio is used to configure a default audio backend that
will be used whenever the audiodev property is not set on a device or machine. In particular,
-audio none ensures that no audio is produced even for machines that have embedded sound hardware.
In both cases, the driver option is the same as with the corresponding -audiodev option below.
Use driver=help to list the available drivers.
-audiodev [driver=]driver,id=id[,prop[=value][,...]]
Adds a new audio backend driver identified by id. There are global and driver specific properties.
Some values can be set differently for input and output, they're marked with in|out.. You can set
the input's property with in.prop and the output's property with out.prop. For example:
-audiodev alsa,id=example,in.frequency=44110,out.frequency=8000
-audiodev alsa,id=example,out.channels=1 # leaves in.channels unspecified
NOTE: parameter validation is known to be incomplete, in many cases specifying an invalid option
causes QEMU to print an error message and continue emulation without sound.
Valid global options are:
id=identifier
Identifies the audio backend.
timer-period=period
Sets the timer period used by the audio subsystem in microseconds. Default is 10000 (10
ms).
in|out.mixing-engine=on|off
Use QEMU's mixing engine to mix all streams inside QEMU and convert audio formats when not
supported by the backend. When off, fixed-settings must be off too. Note that disabling
this option means that the selected backend must support multiple streams and the audio
formats used by the virtual cards, otherwise you'll get no sound. It's not recommended to
disable this option unless you want to use 5.1 or 7.1 audio, as mixing engine only supports
mono and stereo audio. Default is on.
in|out.fixed-settings=on|off
Use fixed settings for host audio. When off, it will change based on how the guest opens
the sound card. In this case you must not specify frequency, channels or format. Default is
on.
in|out.frequency=frequency
Specify the frequency to use when using fixed-settings. Default is 44100Hz.
in|out.channels=channels
Specify the number of channels to use when using fixed-settings. Default is 2 (stereo).
in|out.format=format
Specify the sample format to use when using fixed-settings. Valid values are: s8, s16,
s32, u8, u16, u32, f32. Default is s16.
in|out.voices=voices
Specify the number of voices to use. Default is 1.
in|out.buffer-length=usecs
Sets the size of the buffer in microseconds.
-audiodev none,id=id[,prop[=value][,...]]
Creates a dummy backend that discards all outputs. This backend has no backend specific
properties.
-audiodev alsa,id=id[,prop[=value][,...]]
Creates backend using the ALSA. This backend is only available on Linux.
ALSA specific options are:
in|out.dev=device
Specify the ALSA device to use for input and/or output. Default is default.
in|out.period-length=usecs
Sets the period length in microseconds.
in|out.try-poll=on|off
Attempt to use poll mode with the device. Default is on.
threshold=threshold
Threshold (in microseconds) when playback starts. Default is 0.
-audiodev coreaudio,id=id[,prop[=value][,...]]
Creates a backend using Apple's Core Audio. This backend is only available on Mac OS and only
supports playback.
Core Audio specific options are:
in|out.buffer-count=count
Sets the count of the buffers.
-audiodev dsound,id=id[,prop[=value][,...]]
Creates a backend using Microsoft's DirectSound. This backend is only available on Windows and
only supports playback.
DirectSound specific options are:
latency=usecs
Add extra usecs microseconds latency to playback. Default is 10000 (10 ms).
-audiodev oss,id=id[,prop[=value][,...]]
Creates a backend using OSS. This backend is available on most Unix-like systems.
OSS specific options are:
in|out.dev=device
Specify the file name of the OSS device to use. Default is /dev/dsp.
in|out.buffer-count=count
Sets the count of the buffers.
in|out.try-poll=on|of
Attempt to use poll mode with the device. Default is on.
try-mmap=on|off
Try using memory mapped device access. Default is off.
exclusive=on|off
Open the device in exclusive mode (vmix won't work in this case). Default is off.
dsp-policy=policy
Sets the timing policy (between 0 and 10, where smaller number means smaller latency but
higher CPU usage). Use -1 to use buffer sizes specified by buffer and buffer-count. This
option is ignored if you do not have OSS 4. Default is 5.
-audiodev pa,id=id[,prop[=value][,...]]
Creates a backend using PulseAudio. This backend is available on most systems.
PulseAudio specific options are:
server=server
Sets the PulseAudio server to connect to.
in|out.name=sink
Use the specified source/sink for recording/playback.
in|out.latency=usecs
Desired latency in microseconds. The PulseAudio server will try to honor this value but
actual latencies may be lower or higher.
-audiodev pipewire,id=id[,prop[=value][,...]]
Creates a backend using PipeWire. This backend is available on most systems.
PipeWire specific options are:
in|out.latency=usecs
Desired latency in microseconds.
in|out.name=sink
Use the specified source/sink for recording/playback.
in|out.stream-name
Specify the name of pipewire stream.
-audiodev sdl,id=id[,prop[=value][,...]]
Creates a backend using SDL. This backend is available on most systems, but you should use your
platform's native backend if possible.
SDL specific options are:
in|out.buffer-count=count
Sets the count of the buffers.
-audiodev sndio,id=id[,prop[=value][,...]]
Creates a backend using SNDIO. This backend is available on OpenBSD and most other Unix-like
systems.
Sndio specific options are:
in|out.dev=device
Specify the sndio device to use for input and/or output. Default is default.
in|out.latency=usecs
Sets the desired period length in microseconds.
-audiodev spice,id=id[,prop[=value][,...]]
Creates a backend that sends audio through SPICE. This backend requires -spice and automatically
selected in that case, so usually you can ignore this option. This backend has no backend specific
properties.
-audiodev wav,id=id[,prop[=value][,...]]
Creates a backend that writes audio to a WAV file.
Backend specific options are:
path=path
Write recorded audio into the specified file. Default is qemu.wav.
-device driver[,prop[=value][,...]]
Add device driver. prop=value sets driver properties. Valid properties depend on the driver. To
get help on possible drivers and properties, use -device help and -device driver,help.
Some drivers are:
-device ipmi-bmc-sim,id=id[,prop[=value][,...]]
Add an IPMI BMC. This is a simulation of a hardware management interface processor that normally
sits on a system. It provides a watchdog and the ability to reset and power control the system.
You need to connect this to an IPMI interface to make it useful
The IPMI slave address to use for the BMC. The default is 0x20. This address is the BMC's address
on the I2C network of management controllers. If you don't know what this means, it is safe to
ignore it.
id=id The BMC id for interfaces to use this device.
slave_addr=val
Define slave address to use for the BMC. The default is 0x20.
sdrfile=file
file containing raw Sensor Data Records (SDR) data. The default is none.
fruareasize=val
size of a Field Replaceable Unit (FRU) area. The default is 1024.
frudatafile=file
file containing raw Field Replaceable Unit (FRU) inventory data. The default is none.
guid=uuid
value for the GUID for the BMC, in standard UUID format. If this is set, get "Get GUID"
command to the BMC will return it. Otherwise "Get GUID" will return an error.
-device ipmi-bmc-extern,id=id,chardev=id[,slave_addr=val]
Add a connection to an external IPMI BMC simulator. Instead of locally emulating the BMC like the
above item, instead connect to an external entity that provides the IPMI services.
A connection is made to an external BMC simulator. If you do this, it is strongly recommended that
you use the "reconnect=" chardev option to reconnect to the simulator if the connection is lost.
Note that if this is not used carefully, it can be a security issue, as the interface has the
ability to send resets, NMIs, and power off the VM. It's best if QEMU makes a connection to an
external simulator running on a secure port on localhost, so neither the simulator nor QEMU is
exposed to any outside network.
See the "lanserv/README.vm" file in the OpenIPMI library for more details on the external
interface.
-device isa-ipmi-kcs,bmc=id[,ioport=val][,irq=val]
Add a KCS IPMI interface on the ISA bus. This also adds a corresponding ACPI and SMBIOS entries,
if appropriate.
bmc=id The BMC to connect to, one of ipmi-bmc-sim or ipmi-bmc-extern above.
ioport=val
Define the I/O address of the interface. The default is 0xca0 for KCS.
irq=val
Define the interrupt to use. The default is 5. To disable interrupts, set this to 0.
-device isa-ipmi-bt,bmc=id[,ioport=val][,irq=val]
Like the KCS interface, but defines a BT interface. The default port is 0xe4 and the default
interrupt is 5.
-device pci-ipmi-kcs,bmc=id
Add a KCS IPMI interface on the PCI bus.
bmc=id The BMC to connect to, one of ipmi-bmc-sim or ipmi-bmc-extern above.
-device pci-ipmi-bt,bmc=id
Like the KCS interface, but defines a BT interface on the PCI bus.
-device intel-iommu[,option=...]
This is only supported by -machine q35, which will enable Intel VT-d emulation within the guest.
It supports below options:
intremap=on|off (default: auto)
This enables interrupt remapping feature. It's required to enable complete x2apic.
Currently it only supports kvm kernel-irqchip modes off or split, while full kernel-irqchip
is not yet supported. The default value is "auto", which will be decided by the mode of
kernel-irqchip.
caching-mode=on|off (default: off)
This enables caching mode for the VT-d emulated device. When caching-mode is enabled, each
guest DMA buffer mapping will generate an IOTLB invalidation from the guest IOMMU driver to
the vIOMMU device in a synchronous way. It is required for -device vfio-pci to work with
the VT-d device, because host assigned devices requires to setup the DMA mapping on the
host before guest DMA starts.
device-iotlb=on|off (default: off)
This enables device-iotlb capability for the emulated VT-d device. So far virtio/vhost
should be the only real user for this parameter, paired with ats=on configured for the
device.
aw-bits=39|48 (default: 39)
This decides the address width of IOVA address space. The address space has 39 bits width
for 3-level IOMMU page tables, and 48 bits for 4-level IOMMU page tables.
Please also refer to the wiki page for general scenarios of VT-d emulation in QEMU: ‐
https://wiki.qemu.org/Features/VT-d.
-device virtio-iommu-pci[,option=...]
This is only supported by -machine q35 (x86_64) and -machine virt (ARM). It supports below
options:
granule=val (possible values are 4k, 8k, 16k, 64k and host; default: host)
This decides the default granule to be be exposed by the virtio-iommu. If host, the granule
matches the host page size.
aw-bits=val (val between 32 and 64, default depends on machine)
This decides the address width of the IOVA address space.
-name name
Sets the name of the guest. This name will be displayed in the SDL window caption. The name will
also be used for the VNC server. Also optionally set the top visible process name in Linux. Naming
of individual threads can also be enabled on Linux to aid debugging.
-uuid uuid
Set system UUID.
Block device options
The QEMU block device handling options have a long history and have gone through several iterations as
the feature set and complexity of the block layer have grown. Many online guides to QEMU often reference
older and deprecated options, which can lead to confusion.
The most explicit way to describe disks is to use a combination of -device to specify the hardware device
and -blockdev to describe the backend. The device defines what the guest sees and the backend describes
how QEMU handles the data. It is the only guaranteed stable interface for describing block devices and as
such is recommended for management tools and scripting.
The -drive option combines the device and backend into a single command line option which is a more human
friendly. There is however no interface stability guarantee although some older board models still need
updating to work with the modern blockdev forms.
Older options like -hda are essentially macros which expand into -drive options for various drive
interfaces. The original forms bake in a lot of assumptions from the days when QEMU was emulating a
legacy PC, they are not recommended for modern configurations.
-fda file
-fdb file
Use file as floppy disk 0/1 image (see the Disk Images chapter in the System Emulation Users
Guide).
-hda file
-hdb file
-hdc file
-hdd file
Use file as hard disk 0, 1, 2 or 3 image on the default bus of the emulated machine (this is for
example the IDE bus on most x86 machines, but it can also be SCSI, virtio or something else on
other target architectures). See also the Disk Images chapter in the System Emulation Users Guide.
-cdrom file
Use file as CD-ROM image on the default bus of the emulated machine (which is IDE1 master on x86,
so you cannot use -hdc and -cdrom at the same time there). On systems that support it, you can use
the host CD-ROM by using /dev/cdrom as filename.
-blockdev option[,option[,option[,...]]]
Define a new block driver node. Some of the options apply to all block drivers, other options are
only accepted for a specific block driver. See below for a list of generic options and options for
the most common block drivers.
Options that expect a reference to another node (e.g. file) can be given in two ways. Either you
specify the node name of an already existing node (file=node-name), or you define a new node
inline, adding options for the referenced node after a dot (file.filename=path,file.aio=native).
A block driver node created with -blockdev can be used for a guest device by specifying its node
name for the drive property in a -device argument that defines a block device.
Valid options for any block driver node:
driver Specifies the block driver to use for the given node.
node-name
This defines the name of the block driver node by which it will be referenced later.
The name must be unique, i.e. it must not match the name of a different block driver
node, or (if you use -drive as well) the ID of a drive.
If no node name is specified, it is automatically generated. The generated node
name is not intended to be predictable and changes between QEMU invocations. For the
top level, an explicit node name must be specified.
read-only
Open the node read-only. Guest write attempts will fail.
Note that some block drivers support only read-only access, either generally or in
certain configurations. In this case, the default value read-only=off does not work
and the option must be specified explicitly.
auto-read-only
If auto-read-only=on is set, QEMU may fall back to read-only usage even when
read-only=off is requested, or even switch between modes as needed, e.g. depending
on whether the image file is writable or whether a writing user is attached to the
node.
force-share
Override the image locking system of QEMU by forcing the node to utilize weaker
shared access for permissions where it would normally request exclusive access. When
there is the potential for multiple instances to have the same file open (whether
this invocation of QEMU is the first or the second instance), both instances must
permit shared access for the second instance to succeed at opening the file.
Enabling force-share=on requires read-only=on.
cache.direct
The host page cache can be avoided with cache.direct=on. This will attempt to do
disk IO directly to the guest's memory. QEMU may still perform an internal copy of
the data.
cache.no-flush
In case you don't care about data integrity over host failures, you can use
cache.no-flush=on. This option tells QEMU that it never needs to write any data to
the disk but can instead keep things in cache. If anything goes wrong, like your
host losing power, the disk storage getting disconnected accidentally, etc. your
image will most probably be rendered unusable.
discard=discard
discard is one of "ignore" (or "off") or "unmap" (or "on") and controls whether
discard (also known as trim or unmap) requests are ignored or passed to the
filesystem. Some machine types may not support discard requests.
detect-zeroes=detect-zeroes
detect-zeroes is "off", "on" or "unmap" and enables the automatic conversion of
plain zero writes by the OS to driver specific optimized zero write commands. You
may even choose "unmap" if discard is set to "unmap" to allow a zero write to be
converted to an unmap operation.
Driver-specific options for file
This is the protocol-level block driver for accessing regular files.
filename
The path to the image file in the local filesystem
aio Specifies the AIO backend (threads/native/io_uring, default: threads)
locking
Specifies whether the image file is protected with Linux OFD / POSIX locks. The
default is to use the Linux Open File Descriptor API if available, otherwise no lock
is applied. (auto/on/off, default: auto)
Example:
-blockdev driver=file,node-name=disk,filename=disk.img
Driver-specific options for raw
This is the image format block driver for raw images. It is usually stacked on top of a
protocol level block driver such as file.
file Reference to or definition of the data source block driver node (e.g. a file driver
node)
Example 1:
-blockdev driver=file,node-name=disk_file,filename=disk.img
-blockdev driver=raw,node-name=disk,file=disk_file
Example 2:
-blockdev driver=raw,node-name=disk,file.driver=file,file.filename=disk.img
Driver-specific options for qcow2
This is the image format block driver for qcow2 images. It is usually stacked on top of a
protocol level block driver such as file.
file Reference to or definition of the data source block driver node (e.g. a file driver
node)
backing
Reference to or definition of the backing file block device (default is taken from
the image file). It is allowed to pass null here in order to disable the default
backing file.
lazy-refcounts
Whether to enable the lazy refcounts feature (on/off; default is taken from the
image file)
cache-size
The maximum total size of the L2 table and refcount block caches in bytes (default:
the sum of l2-cache-size and refcount-cache-size)
l2-cache-size
The maximum size of the L2 table cache in bytes (default: if cache-size is not
specified - 32M on Linux platforms, and 8M on non-Linux platforms; otherwise, as
large as possible within the cache-size, while permitting the requested or the
minimal refcount cache size)
refcount-cache-size
The maximum size of the refcount block cache in bytes (default: 4 times the cluster
size; or if cache-size is specified, the part of it which is not used for the L2
cache)
cache-clean-interval
Clean unused entries in the L2 and refcount caches. The interval is in seconds. The
default value is 600 on supporting platforms, and 0 on other platforms. Setting it
to 0 disables this feature.
pass-discard-request
Whether discard requests to the qcow2 device should be forwarded to the data source
(on/off; default: on if discard=unmap is specified, off otherwise)
pass-discard-snapshot
Whether discard requests for the data source should be issued when a snapshot
operation (e.g. deleting a snapshot) frees clusters in the qcow2 file (on/off;
default: on)
pass-discard-other
Whether discard requests for the data source should be issued on other occasions
where a cluster gets freed (on/off; default: off)
discard-no-unref
When enabled, data clusters will remain preallocated when they are no longer used,
e.g. because they are discarded or converted to zero clusters. As usual, whether the
old data is discarded or kept on the protocol level (i.e. in the image file) depends
on the setting of the pass-discard-request option. Keeping the clusters preallocated
prevents qcow2 fragmentation that would otherwise be caused by freeing and
re-allocating them later. Besides potential performance degradation, such
fragmentation can lead to increased allocation of clusters past the end of the image
file, resulting in image files whose file length can grow much larger than their
guest disk size would suggest. If image file length is of concern (e.g. when
storing qcow2 images directly on block devices), you should consider enabling this
option.
overlap-check
Which overlap checks to perform for writes to the image (none/constant/cached/all;
default: cached). For details or finer granularity control refer to the QAPI
documentation of blockdev-add.
Example 1:
-blockdev driver=file,node-name=my_file,filename=/tmp/disk.qcow2
-blockdev driver=qcow2,node-name=hda,file=my_file,overlap-check=none,cache-size=16777216
Example 2:
-blockdev driver=qcow2,node-name=disk,file.driver=http,file.filename=http://example.com/image.qcow2
Driver-specific options for other drivers
Please refer to the QAPI documentation of the blockdev-add QMP command.
-drive option[,option[,option[,...]]]
Define a new drive. This includes creating a block driver node (the backend) as well as a guest
device, and is mostly a shortcut for defining the corresponding -blockdev and -device options.
-drive accepts all options that are accepted by -blockdev. In addition, it knows the following
options:
file=file
This option defines which disk image (see the Disk Images chapter in the System Emulation
Users Guide) to use with this drive. If the filename contains comma, you must double it
(for instance, "file=my,,file" to use file "my,file").
Special files such as iSCSI devices can be specified using protocol specific URLs. See the
section for "Device URL Syntax" for more information.
if=interface
This option defines on which type on interface the drive is connected. Available types are:
ide, scsi, sd, mtd, floppy, pflash, virtio, none.
bus=bus,unit=unit
These options define where is connected the drive by defining the bus number and the unit
id.
index=index
This option defines where the drive is connected by using an index in the list of available
connectors of a given interface type.
media=media
This option defines the type of the media: disk or cdrom.
snapshot=snapshot
snapshot is "on" or "off" and controls snapshot mode for the given drive (see -snapshot).
cache=cache
cache is "none", "writeback", "unsafe", "directsync" or "writethrough" and controls how the
host cache is used to access block data. This is a shortcut that sets the cache.direct and
cache.no-flush options (as in -blockdev), and additionally cache.writeback, which provides
a default for the write-cache option of block guest devices (as in -device). The modes
correspond to the following settings:
┌─────────────┬─────────────────┬──────────────┬────────────────┐
│ │ cache.writeback │ cache.direct │ cache.no-flush │
├─────────────┼─────────────────┼──────────────┼────────────────┤
│writeback │ on │ off │ off │
├─────────────┼─────────────────┼──────────────┼────────────────┤
│none │ on │ on │ off │
├─────────────┼─────────────────┼──────────────┼────────────────┤
│writethrough │ off │ off │ off │
├─────────────┼─────────────────┼──────────────┼────────────────┤
│directsync │ off │ on │ off │
├─────────────┼─────────────────┼──────────────┼────────────────┤
│unsafe │ on │ off │ on │
└─────────────┴─────────────────┴──────────────┴────────────────┘
The default mode is cache=writeback.
aio=aio
aio is "threads", "native", or "io_uring" and selects between pthread based disk I/O,
native Linux AIO, or Linux io_uring API.
format=format
Specify which disk format will be used rather than detecting the format. Can be used to
specify format=raw to avoid interpreting an untrusted format header.
werror=action,rerror=action
Specify which action to take on write and read errors. Valid actions are: "ignore" (ignore
the error and try to continue), "stop" (pause QEMU), "report" (report the error to the
guest), "enospc" (pause QEMU only if the host disk is full; report the error to the guest
otherwise). The default setting is werror=enospc and rerror=report.
copy-on-read=copy-on-read
copy-on-read is "on" or "off" and enables whether to copy read backing file sectors into
the image file.
bps=b,bps_rd=r,bps_wr=w
Specify bandwidth throttling limits in bytes per second, either for all request types or
for reads or writes only. Small values can lead to timeouts or hangs inside the guest. A
safe minimum for disks is 2 MB/s.
bps_max=bm,bps_rd_max=rm,bps_wr_max=wm
Specify bursts in bytes per second, either for all request types or for reads or writes
only. Bursts allow the guest I/O to spike above the limit temporarily.
iops=i,iops_rd=r,iops_wr=w
Specify request rate limits in requests per second, either for all request types or for
reads or writes only.
iops_max=bm,iops_rd_max=rm,iops_wr_max=wm
Specify bursts in requests per second, either for all request types or for reads or writes
only. Bursts allow the guest I/O to spike above the limit temporarily.
iops_size=is
Let every is bytes of a request count as a new request for iops throttling purposes. Use
this option to prevent guests from circumventing iops limits by sending fewer but larger
requests.
group=g
Join a throttling quota group with given name g. All drives that are members of the same
group are accounted for together. Use this option to prevent guests from circumventing
throttling limits by using many small disks instead of a single larger disk.
By default, the cache.writeback=on mode is used. It will report data writes as completed as soon
as the data is present in the host page cache. This is safe as long as your guest OS makes sure to
correctly flush disk caches where needed. If your guest OS does not handle volatile disk write
caches correctly and your host crashes or loses power, then the guest may experience data
corruption.
For such guests, you should consider using cache.writeback=off. This means that the host page
cache will be used to read and write data, but write notification will be sent to the guest only
after QEMU has made sure to flush each write to the disk. Be aware that this has a major impact on
performance.
When using the -snapshot option, unsafe caching is always used.
Copy-on-read avoids accessing the same backing file sectors repeatedly and is useful when the
backing file is over a slow network. By default copy-on-read is off.
Instead of -cdrom you can use:
qemu-system-x86_64 -drive file=file,index=2,media=cdrom
Instead of -hda, -hdb, -hdc, -hdd, you can use:
qemu-system-x86_64 -drive file=file,index=0,media=disk
qemu-system-x86_64 -drive file=file,index=1,media=disk
qemu-system-x86_64 -drive file=file,index=2,media=disk
qemu-system-x86_64 -drive file=file,index=3,media=disk
You can open an image using pre-opened file descriptors from an fd set:
qemu-system-x86_64 \
-add-fd fd=3,set=2,opaque="rdwr:/path/to/file" \
-add-fd fd=4,set=2,opaque="rdonly:/path/to/file" \
-drive file=/dev/fdset/2,index=0,media=disk
You can connect a CDROM to the slave of ide0:
qemu-system-x86_64 -drive file=file,if=ide,index=1,media=cdrom
If you don't specify the "file=" argument, you define an empty drive:
qemu-system-x86_64 -drive if=ide,index=1,media=cdrom
Instead of -fda, -fdb, you can use:
qemu-system-x86_64 -drive file=file,index=0,if=floppy
qemu-system-x86_64 -drive file=file,index=1,if=floppy
By default, interface is "ide" and index is automatically incremented:
qemu-system-x86_64 -drive file=a -drive file=b
is interpreted like:
qemu-system-x86_64 -hda a -hdb b
-mtdblock file
Use file as on-board Flash memory image.
-sd file
Use file as SecureDigital card image.
-snapshot
Write to temporary files instead of disk image files. In this case, the raw disk image you use is
not written back. You can however force the write back by pressing C-a s (see the Disk Images
chapter in the System Emulation Users Guide).
WARNING:
snapshot is incompatible with -blockdev (instead use qemu-img to manually create snapshot
images to attach to your blockdev). If you have mixed -blockdev and -drive declarations you
can use the 'snapshot' property on your drive declarations instead of this global option.
-fsdev local,id=id,path=path,security_model=security_model
[,writeout=writeout][,readonly=on][,fmode=fmode][,dmode=dmode]
[,throttling.option=value[,throttling.option=value[,...]]]
-fsdev proxy,id=id,socket=socket[,writeout=writeout][,readonly=on]
-fsdev proxy,id=id,sock_fd=sock_fd[,writeout=writeout][,readonly=on]
-fsdev synth,id=id[,readonly=on]
Define a new file system device. Valid options are:
local Accesses to the filesystem are done by QEMU.
proxy Accesses to the filesystem are done by virtfs-proxy-helper(1). This option is deprecated
(since QEMU 8.1) and will be removed in a future version of QEMU. Use local instead.
synth Synthetic filesystem, only used by QTests.
id=id Specifies identifier for this device.
path=path
Specifies the export path for the file system device. Files under this path will be
available to the 9p client on the guest.
security_model=security_model
Specifies the security model to be used for this export path. Supported security models
are "passthrough", "mapped-xattr", "mapped-file" and "none". In "passthrough" security
model, files are stored using the same credentials as they are created on the guest. This
requires QEMU to run as root. In "mapped-xattr" security model, some of the file attributes
like uid, gid, mode bits and link target are stored as file attributes. For "mapped-file"
these attributes are stored in the hidden .virtfs_metadata directory. Directories exported
by this security model cannot interact with other unix tools. "none" security model is same
as passthrough except the sever won't report failures if it fails to set file attributes
like ownership. Security model is mandatory only for local fsdriver. Other fsdrivers (like
proxy) don't take security model as a parameter.
writeout=writeout
This is an optional argument. The only supported value is "immediate". This means that host
page cache will be used to read and write data but write notification will be sent to the
guest only when the data has been reported as written by the storage subsystem.
readonly=on
Enables exporting 9p share as a readonly mount for guests. By default read-write access is
given.
socket=socket
Enables proxy filesystem driver to use passed socket file for communicating with
virtfs-proxy-helper(1).
sock_fd=sock_fd
Enables proxy filesystem driver to use passed socket descriptor for communicating with
virtfs-proxy-helper(1). Usually a helper like libvirt will create socketpair and pass one
of the fds as sock_fd.
fmode=fmode
Specifies the default mode for newly created files on the host. Works only with security
models "mapped-xattr" and "mapped-file".
dmode=dmode
Specifies the default mode for newly created directories on the host. Works only with
security models "mapped-xattr" and "mapped-file".
throttling.bps-total=b,throttling.bps-read=r,throttling.bps-write=w
Specify bandwidth throttling limits in bytes per second, either for all request types or
for reads or writes only.
throttling.bps-total-max=bm,bps-read-max=rm,bps-write-max=wm
Specify bursts in bytes per second, either for all request types or for reads or writes
only. Bursts allow the guest I/O to spike above the limit temporarily.
throttling.iops-total=i,throttling.iops-read=r, throttling.iops-write=w
Specify request rate limits in requests per second, either for all request types or for
reads or writes only.
throttling.iops-total-max=im,throttling.iops-read-max=irm, throttling.iops-write-max=iwm
Specify bursts in requests per second, either for all request types or for reads or writes
only. Bursts allow the guest I/O to spike above the limit temporarily.
throttling.iops-size=is
Let every is bytes of a request count as a new request for iops throttling purposes.
-fsdev option is used along with -device driver "virtio-9p-...".
-device virtio-9p-type,fsdev=id,mount_tag=mount_tag
Options for virtio-9p-... driver are:
type Specifies the variant to be used. Supported values are "pci", "ccw" or "device", depending
on the machine type.
fsdev=id
Specifies the id value specified along with -fsdev option.
mount_tag=mount_tag
Specifies the tag name to be used by the guest to mount this export point.
-virtfs local,path=path,mount_tag=mount_tag
,security_model=security_model[,writeout=writeout][,readonly=on]
[,fmode=fmode][,dmode=dmode][,multidevs=multidevs]
-virtfs proxy,socket=socket,mount_tag=mount_tag [,writeout=writeout][,readonly=on]
-virtfs proxy,sock_fd=sock_fd,mount_tag=mount_tag [,writeout=writeout][,readonly=on]
-virtfs synth,mount_tag=mount_tag
Define a new virtual filesystem device and expose it to the guest using a virtio-9p-device (a.k.a.
9pfs), which essentially means that a certain directory on host is made directly accessible by
guest as a pass-through file system by using the 9P network protocol for communication between
host and guests, if desired even accessible, shared by several guests simultaneously.
Note that -virtfs is actually just a convenience shortcut for its generalized form -fsdev -device
virtio-9p-pci.
The general form of pass-through file system options are:
local Accesses to the filesystem are done by QEMU.
proxy Accesses to the filesystem are done by virtfs-proxy-helper(1). This option is deprecated
(since QEMU 8.1) and will be removed in a future version of QEMU. Use local instead.
synth Synthetic filesystem, only used by QTests.
id=id Specifies identifier for the filesystem device
path=path
Specifies the export path for the file system device. Files under this path will be
available to the 9p client on the guest.
security_model=security_model
Specifies the security model to be used for this export path. Supported security models
are "passthrough", "mapped-xattr", "mapped-file" and "none". In "passthrough" security
model, files are stored using the same credentials as they are created on the guest. This
requires QEMU to run as root. In "mapped-xattr" security model, some of the file attributes
like uid, gid, mode bits and link target are stored as file attributes. For "mapped-file"
these attributes are stored in the hidden .virtfs_metadata directory. Directories exported
by this security model cannot interact with other unix tools. "none" security model is same
as passthrough except the sever won't report failures if it fails to set file attributes
like ownership. Security model is mandatory only for local fsdriver. Other fsdrivers (like
proxy) don't take security model as a parameter.
writeout=writeout
This is an optional argument. The only supported value is "immediate". This means that host
page cache will be used to read and write data but write notification will be sent to the
guest only when the data has been reported as written by the storage subsystem.
readonly=on
Enables exporting 9p share as a readonly mount for guests. By default read-write access is
given.
socket=socket
Enables proxy filesystem driver to use passed socket file for communicating with
virtfs-proxy-helper(1). Usually a helper like libvirt will create socketpair and pass one
of the fds as sock_fd.
sock_fd
Enables proxy filesystem driver to use passed 'sock_fd' as the socket descriptor for
interfacing with virtfs-proxy-helper(1).
fmode=fmode
Specifies the default mode for newly created files on the host. Works only with security
models "mapped-xattr" and "mapped-file".
dmode=dmode
Specifies the default mode for newly created directories on the host. Works only with
security models "mapped-xattr" and "mapped-file".
mount_tag=mount_tag
Specifies the tag name to be used by the guest to mount this export point.
multidevs=multidevs
Specifies how to deal with multiple devices being shared with a 9p export. Supported
behaviours are either "remap", "forbid" or "warn". The latter is the default behaviour on
which virtfs 9p expects only one device to be shared with the same export, and if more than
one device is shared and accessed via the same 9p export then only a warning message is
logged (once) by qemu on host side. In order to avoid file ID collisions on guest you
should either create a separate virtfs export for each device to be shared with guests
(recommended way) or you might use "remap" instead which allows you to share multiple
devices with only one export instead, which is achieved by remapping the original inode
numbers from host to guest in a way that would prevent such collisions. Remapping inodes in
such use cases is required because the original device IDs from host are never passed and
exposed on guest. Instead all files of an export shared with virtfs always share the same
device id on guest. So two files with identical inode numbers but from actually different
devices on host would otherwise cause a file ID collision and hence potential misbehaviours
on guest. "forbid" on the other hand assumes like "warn" that only one device is shared by
the same export, however it will not only log a warning message but also deny access to
additional devices on guest. Note though that "forbid" does currently not block all
possible file access operations (e.g. readdir() would still return entries from other
devices).
-iscsi Configure iSCSI session parameters.
USB convenience options
-usb Enable USB emulation on machine types with an on-board USB host controller (if not enabled by
default). Note that on-board USB host controllers may not support USB 3.0. In this case -device
qemu-xhci can be used instead on machines with PCI.
-usbdevice devname
Add the USB device devname, and enable an on-board USB controller if possible and necessary (just
like it can be done via -machine usb=on). Note that this option is mainly intended for the user's
convenience only. More fine-grained control can be achieved by selecting a USB host controller (if
necessary) and the desired USB device via the -device option instead. For example, instead of
using -usbdevice mouse it is possible to use -device qemu-xhci -device usb-mouse to connect the
USB mouse to a USB 3.0 controller instead (at least on machines that support PCI and do not have
an USB controller enabled by default yet). For more details, see the chapter about Connecting USB
devices in the System Emulation Users Guide. Possible devices for devname are:
braille
Braille device. This will use BrlAPI to display the braille output on a real or fake device
(i.e. it also creates a corresponding braille chardev automatically beside the usb-braille
USB device).
keyboard
Standard USB keyboard. Will override the PS/2 keyboard (if present).
mouse Virtual Mouse. This will override the PS/2 mouse emulation when activated.
tablet Pointer device that uses absolute coordinates (like a touchscreen). This means QEMU is able
to report the mouse position without having to grab the mouse. Also overrides the PS/2
mouse emulation when activated.
wacom-tablet
Wacom PenPartner USB tablet.
Display options
-display type
Select type of display to use. Use -display help to list the available display types. Valid values
for type are
spice-app[,gl=on|off]
Start QEMU as a Spice server and launch the default Spice client application. The Spice
server will redirect the serial consoles and QEMU monitors. (Since 4.0)
dbus Export the display over D-Bus interfaces. (Since 7.0)
The connection is registered with the "org.qemu" name (and queued when already owned).
addr=<dbusaddr> : D-Bus bus address to connect to.
p2p=yes|no : Use peer-to-peer connection, accepted via QMP add_client.
gl=on|off|core|es : Use OpenGL for rendering (the D-Bus interface will share framebuffers
with DMABUF file descriptors).
sdl Display video output via SDL (usually in a separate graphics window; see the SDL
documentation for other possibilities). Valid parameters are:
grab-mod=<mods> : Used to select the modifier keys for toggling the mouse grabbing in
conjunction with the "g" key. <mods> can be either lshift-lctrl-lalt or rctrl.
gl=on|off|core|es : Use OpenGL for displaying
show-cursor=on|off : Force showing the mouse cursor
window-close=on|off : Allow to quit qemu with window close button
gtk Display video output in a GTK window. This interface provides drop-down menus and other UI
elements to configure and control the VM during runtime. Valid parameters are:
full-screen=on|off : Start in fullscreen mode
gl=on|off : Use OpenGL for displaying
grab-on-hover=on|off : Grab keyboard input on mouse hover
show-tabs=on|off (Display the tab bar for switching between the)
various graphical interfaces (e.g. VGA and virtual console character devices) by
default.
show-cursor=on|off : Force showing the mouse cursor
window-close=on|off : Allow to quit qemu with window close button
show-menubar=on|off : Display the main window menubar, defaults to "on"
zoom-to-fit=on|off (Expand video output to the window size,)
defaults to "off"
curses[,charset=<encoding>]
Display video output via curses. For graphics device models which support a text mode, QEMU
can display this output using a curses/ncurses interface. Nothing is displayed when the
graphics device is in graphical mode or if the graphics device does not support a text
mode. Generally only the VGA device models support text mode. The font charset used by the
guest can be specified with the charset option, for example charset=CP850 for IBM CP850
encoding. The default is CP437.
cocoa Display video output in a Cocoa window. Mac only. This interface provides drop-down menus
and other UI elements to configure and control the VM during runtime. Valid parameters are:
full-grab=on|off (Capture all key presses, including system combos.)
This requires accessibility permissions, since it performs a global grab on key
events. (default: off) See ‐
https://support.apple.com/en-in/guide/mac-help/mh32356/mac
swap-opt-cmd=on|off (Swap the Option and Command keys so that their)
key codes match their position on non-Mac keyboards and you can use Meta/Super and
Alt where you expect them. (default: off)
show-cursor=on|off : Force showing the mouse cursor
left-command-key=on|off : Disable forwarding left command key to host
full-screen=on|off : Start in fullscreen mode
zoom-to-fit=on|off (Expand video output to the window size,)
defaults to "off"
egl-headless[,rendernode=<file>]
Offload all OpenGL operations to a local DRI device. For any graphical display, this
display needs to be paired with either VNC or SPICE displays.
vnc=<display>
Start a VNC server on display <display>
none Do not display video output. The guest will still see an emulated graphics card, but its
output will not be displayed to the QEMU user. This option differs from the -nographic
option in that it only affects what is done with video output; -nographic also changes the
destination of the serial and parallel port data.
-nographic
Normally, if QEMU is compiled with graphical window support, it displays output such as guest
graphics, guest console, and the QEMU monitor in a window. With this option, you can totally
disable graphical output so that QEMU is a simple command line application. The emulated serial
port is redirected on the console and muxed with the monitor (unless redirected elsewhere
explicitly). Therefore, you can still use QEMU to debug a Linux kernel with a serial console. Use
C-a h for help on switching between the console and monitor.
-spice option[,option[,...]]
Enable the spice remote desktop protocol. Valid options are
port=<nr>
Set the TCP port spice is listening on for plaintext channels.
addr=<addr>
Set the IP address spice is listening on. Default is any address.
ipv4=on|off; ipv6=on|off; unix=on|off
Force using the specified IP version.
password-secret=<secret-id>
Set the ID of the secret object containing the password you need to authenticate.
sasl=on|off
Require that the client use SASL to authenticate with the spice. The exact choice of
authentication method used is controlled from the system / user's SASL configuration file
for the 'qemu' service. This is typically found in /etc/sasl2/qemu.conf. If running QEMU as
an unprivileged user, an environment variable SASL_CONF_PATH can be used to make it search
alternate locations for the service config. While some SASL auth methods can also provide
data encryption (eg GSSAPI), it is recommended that SASL always be combined with the 'tls'
and 'x509' settings to enable use of SSL and server certificates. This ensures a data
encryption preventing compromise of authentication credentials.
disable-ticketing=on|off
Allow client connects without authentication.
disable-copy-paste=on|off
Disable copy paste between the client and the guest.
disable-agent-file-xfer=on|off
Disable spice-vdagent based file-xfer between the client and the guest.
tls-port=<nr>
Set the TCP port spice is listening on for encrypted channels.
x509-dir=<dir>
Set the x509 file directory. Expects same filenames as -vnc $display,x509=$dir
x509-key-file=<file>; x509-key-password=<file>; x509-cert-file=<file>; x509-cacert-file=<file>;
x509-dh-key-file=<file>
The x509 file names can also be configured individually.
tls-ciphers=<list>
Specify which ciphers to use.
tls-channel=[main|display|cursor|inputs|record|playback];
plaintext-channel=[main|display|cursor|inputs|record|playback]
Force specific channel to be used with or without TLS encryption. The options can be
specified multiple times to configure multiple channels. The special name "default" can be
used to set the default mode. For channels which are not explicitly forced into one mode
the spice client is allowed to pick tls/plaintext as he pleases.
image-compression=[auto_glz|auto_lz|quic|glz|lz|off]
Configure image compression (lossless). Default is auto_glz.
jpeg-wan-compression=[auto|never|always]; zlib-glz-wan-compression=[auto|never|always]
Configure wan image compression (lossy for slow links). Default is auto.
streaming-video=[off|all|filter]
Configure video stream detection. Default is off.
agent-mouse=[on|off]
Enable/disable passing mouse events via vdagent. Default is on.
playback-compression=[on|off]
Enable/disable audio stream compression (using celt 0.5.1). Default is on.
seamless-migration=[on|off]
Enable/disable spice seamless migration. Default is off.
gl=[on|off]
Enable/disable OpenGL context. Default is off.
rendernode=<file>
DRM render node for OpenGL rendering. If not specified, it will pick the first available.
(Since 2.9)
-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. Windows XP) and if you want to use high resolution modes (>= 1280x1024x16)
then you should use this option. (This card is the default since QEMU 2.2)
vmware VMWare SVGA-II compatible adapter. Use it if you have sufficiently recent XFree86/XOrg
server or Windows guest with a driver for this card.
qxl QXL paravirtual graphic card. It is VGA compatible (including VESA 2.0 VBE support). Works
best with qxl guest drivers installed though. Recommended choice when using the spice
protocol.
tcx (sun4m only) Sun TCX framebuffer. This is the default framebuffer for sun4m machines and
offers both 8-bit and 24-bit colour depths at a fixed resolution of 1024x768.
cg3 (sun4m only) Sun cgthree framebuffer. This is a simple 8-bit framebuffer for sun4m machines
available in both 1024x768 (OpenBIOS) and 1152x900 (OBP) resolutions aimed at people
wishing to run older Solaris versions.
virtio Virtio VGA card.
none Disable VGA card.
-full-screen
Start in full screen.
-g widthxheight[xdepth]
Set the initial graphical resolution and depth (PPC, SPARC only).
For PPC the default is 800x600x32.
For SPARC with the TCX graphics device, the default is 1024x768x8 with the option of 1024x768x24.
For cgthree, the default is 1024x768x8 with the option of 1152x900x8 for people who wish to use
OBP.
-vnc display[,option[,option[,...]]]
Normally, if QEMU is compiled with graphical window support, it displays output such as guest
graphics, guest console, and the QEMU monitor in a window. With this option, you can have QEMU
listen on VNC display display and redirect the VGA display over the VNC session. It is very useful
to enable the usb tablet device when using this option (option -device usb-tablet). When using the
VNC display, you must use the -k parameter to set the keyboard layout if you are not using en-us.
Valid syntax for the display is
to=L With this option, QEMU will try next available VNC displays, until the number L, if the
originally defined "-vnc display" is not available, e.g. port 5900+display is already used
by another application. By default, to=0.
host:d TCP connections will only be allowed from host on display d. By convention the TCP port is
5900+d. Optionally, host can be omitted in which case the server will accept connections
from any host.
unix:path
Connections will be allowed over UNIX domain sockets where path is the location of a unix
socket to listen for connections on.
none VNC is initialized but not started. The monitor change command can be used to later start
the VNC server.
Following the display value there may be one or more option flags separated by commas. Valid
options are
reverse=on|off
Connect to a listening VNC client via a "reverse" connection. The client is specified by
the display. For reverse network connections (host:d,``reverse``), the d argument is a TCP
port number, not a display number.
websocket=on|off
Opens an additional TCP listening port dedicated to VNC Websocket connections. If a bare
websocket option is given, the Websocket port is 5700+display. An alternative port can be
specified with the syntax websocket=port.
If host is specified connections will only be allowed from this host. It is possible to
control the websocket listen address independently, using the syntax websocket=host:port.
If no TLS credentials are provided, the websocket connection runs in unencrypted mode. If
TLS credentials are provided, the websocket connection requires encrypted client
connections.
password=on|off
Require that password based authentication is used for client connections.
The password must be set separately using the set_password command in the QEMU Monitor. The
syntax to change your password is: set_password <protocol> <password> where <protocol>
could be either "vnc" or "spice".
If you would like to change <protocol> password expiration, you should use expire_password
<protocol> <expiration-time> where expiration time could be one of the following options:
now, never, +seconds or UNIX time of expiration, e.g. +60 to make password expire in 60
seconds, or 1335196800 to make password expire on "Mon Apr 23 12:00:00 EDT 2012" (UNIX time
for this date and time).
You can also use keywords "now" or "never" for the expiration time to allow <protocol>
password to expire immediately or never expire.
password-secret=<secret-id>
Require that password based authentication is used for client connections, using the
password provided by the secret object identified by secret-id.
tls-creds=ID
Provides the ID of a set of TLS credentials to use to secure the VNC server. They will
apply to both the normal VNC server socket and the websocket socket (if enabled). Setting
TLS credentials will cause the VNC server socket to enable the VeNCrypt auth mechanism. The
credentials should have been previously created using the -object tls-creds argument.
tls-authz=ID
Provides the ID of the QAuthZ authorization object against which the client's x509
distinguished name will validated. This object is only resolved at time of use, so can be
deleted and recreated on the fly while the VNC server is active. If missing, it will
default to denying access.
sasl=on|off
Require that the client use SASL to authenticate with the VNC server. The exact choice of
authentication method used is controlled from the system / user's SASL configuration file
for the 'qemu' service. This is typically found in /etc/sasl2/qemu.conf. If running QEMU as
an unprivileged user, an environment variable SASL_CONF_PATH can be used to make it search
alternate locations for the service config. While some SASL auth methods can also provide
data encryption (eg GSSAPI), it is recommended that SASL always be combined with the 'tls'
and 'x509' settings to enable use of SSL and server certificates. This ensures a data
encryption preventing compromise of authentication credentials. See the VNC security
section in the System Emulation Users Guide for details on using SASL authentication.
sasl-authz=ID
Provides the ID of the QAuthZ authorization object against which the client's SASL username
will validated. This object is only resolved at time of use, so can be deleted and
recreated on the fly while the VNC server is active. If missing, it will default to denying
access.
acl=on|off
Legacy method for enabling authorization of clients against the x509 distinguished name and
SASL username. It results in the creation of two authz-list objects with IDs of
vnc.username and vnc.x509dname. The rules for these objects must be configured with the HMP
ACL commands.
This option is deprecated and should no longer be used. The new sasl-authz and tls-authz
options are a replacement.
lossy=on|off
Enable lossy compression methods (gradient, JPEG, ...). If this option is set, VNC client
may receive lossy framebuffer updates depending on its encoding settings. Enabling this
option can save a lot of bandwidth at the expense of quality.
non-adaptive=on|off
Disable adaptive encodings. Adaptive encodings are enabled by default. An adaptive encoding
will try to detect frequently updated screen regions, and send updates in these regions
using a lossy encoding (like JPEG). This can be really helpful to save bandwidth when
playing videos. Disabling adaptive encodings restores the original static behavior of
encodings like Tight.
share=[allow-exclusive|force-shared|ignore]
Set display sharing policy. 'allow-exclusive' allows clients to ask for exclusive access.
As suggested by the rfb spec this is implemented by dropping other connections. Connecting
multiple clients in parallel requires all clients asking for a shared session (vncviewer:
-shared switch). This is the default. 'force-shared' disables exclusive client access.
Useful for shared desktop sessions, where you don't want someone forgetting specify -shared
disconnect everybody else. 'ignore' completely ignores the shared flag and allows everybody
connect unconditionally. Doesn't conform to the rfb spec but is traditional QEMU behavior.
key-delay-ms
Set keyboard delay, for key down and key up events, in milliseconds. Default is 10.
Keyboards are low-bandwidth devices, so this slowdown can help the device and guest to keep
up and not lose events in case events are arriving in bulk. Possible causes for the latter
are flaky network connections, or scripts for automated testing.
audiodev=audiodev
Use the specified audiodev when the VNC client requests audio transmission. When not using
an -audiodev argument, this option must be omitted, otherwise is must be present and
specify a valid audiodev.
power-control=on|off
Permit the remote client to issue shutdown, reboot or reset power control requests.
i386 target only
-win2k-hack
Use it when installing Windows 2000 to avoid a disk full bug. After Windows 2000 is installed, you
no longer need this option (this option slows down the IDE transfers). Synonym of -global
ide-device.win2k-install-hack=on.
-no-fd-bootchk
Disable boot signature checking for floppy disks in BIOS. May be needed to boot from old floppy
disks. Synonym of -m fd-bootchk=off.
-acpitable [sig=str][,rev=n][,oem_id=str][,oem_table_id=str][,oem_rev=n]
[,asl_compiler_id=str][,asl_compiler_rev=n][,data=file1[:file2]...]
Add ACPI table with specified header fields and context from specified files. For file=, take
whole ACPI table from the specified files, including all ACPI headers (possible overridden by
other options). For data=, only data portion of the table is used, all header information is
specified in the command line. If a SLIC table is supplied to QEMU, then the SLIC's oem_id and
oem_table_id fields will override the same in the RSDT and the FADT (a.k.a. FACP), in order to
ensure the field matches required by the Microsoft SLIC spec and the ACPI spec.
-smbios file=binary
Load SMBIOS entry from binary file.
-smbios type=0[,vendor=str][,version=str][,date=str][,release=%d.%d][,uefi=on|off]
Specify SMBIOS type 0 fields
-smbios
type=1[,manufacturer=str][,product=str][,version=str][,serial=str][,uuid=uuid][,sku=str][,family=str]
Specify SMBIOS type 1 fields
-smbios type=2[,manufacturer=str][,product=str][,version=str][,serial=str][,asset=str][,location=str]
Specify SMBIOS type 2 fields
-smbios type=3[,manufacturer=str][,version=str][,serial=str][,asset=str][,sku=str]
Specify SMBIOS type 3 fields
-smbios
type=4[,sock_pfx=str][,manufacturer=str][,version=str][,serial=str][,asset=str][,part=str][,processor-family=%d][,processor-id=%d]
Specify SMBIOS type 4 fields
-smbios
type=9[,slot_designation=str][,slot_type=%d][,slot_data_bus_width=%d][,current_usage=%d][,slot_length=%d][,slot_id=%d][,slot_characteristics1=%d][,slot_characteristics12=%d][,pci_device=str]
Specify SMBIOS type 9 fields
-smbios type=11[,value=str][,path=filename]
Specify SMBIOS type 11 fields
This argument can be repeated multiple times, and values are added in the order they are parsed.
Applications intending to use OEM strings data are encouraged to use their application name as a
prefix for the value string. This facilitates passing information for multiple applications
concurrently.
The value=str syntax provides the string data inline, while the path=filename syntax loads data
from a file on disk. Note that the file is not permitted to contain any NUL bytes.
Both the value and path options can be repeated multiple times and will be added to the SMBIOS
table in the order in which they appear.
Note that on the x86 architecture, the total size of all SMBIOS tables is limited to 65535 bytes.
Thus the OEM strings data is not suitable for passing large amounts of data into the guest.
Instead it should be used as a indicator to inform the guest where to locate the real data set,
for example, by specifying the serial ID of a block device.
An example passing three strings is
-smbios type=11,value=cloud-init:ds=nocloud-net;s=http://10.10.0.1:8000/,\
value=anaconda:method=http://dl.fedoraproject.org/pub/fedora/linux/releases/25/x86_64/os,\
path=/some/file/with/oemstringsdata.txt
In the guest OS this is visible with the dmidecode command
$ dmidecode -t 11
Handle 0x0E00, DMI type 11, 5 bytes
OEM Strings
String 1: cloud-init:ds=nocloud-net;s=http://10.10.0.1:8000/
String 2: anaconda:method=http://dl.fedoraproject.org/pub/fedora/linux/releases/25/x86_64/os
String 3: myapp:some extra data
-smbios
type=17[,loc_pfx=str][,bank=str][,manufacturer=str][,serial=str][,asset=str][,part=str][,speed=%d]
Specify SMBIOS type 17 fields
-smbios type=41[,designation=str][,kind=str][,instance=%d][,pcidev=str]
Specify SMBIOS type 41 fields
This argument can be repeated multiple times. Its main use is to allow network interfaces be
created as enoX on Linux, with X being the instance number, instead of the name depending on the
interface position on the PCI bus.
Here is an example of use:
-netdev user,id=internet \
-device virtio-net-pci,mac=50:54:00:00:00:42,netdev=internet,id=internet-dev \
-smbios type=41,designation='Onboard LAN',instance=1,kind=ethernet,pcidev=internet-dev
In the guest OS, the device should then appear as eno1:
..parsed-literal:
$ ip -brief l
lo UNKNOWN 00:00:00:00:00:00 <LOOPBACK,UP,LOWER_UP>
eno1 UP 50:54:00:00:00:42 <BROADCAST,MULTICAST,UP,LOWER_UP>
Currently, the PCI device has to be attached to the root bus.
Network options
-nic [tap|bridge|user|l2tpv3|vde|netmap|af-xdp|vhost-user|socket][,...][,mac=macaddr][,model=mn]
This option is a shortcut for configuring both the on-board (default) guest NIC hardware and the
host network backend in one go. The host backend options are the same as with the corresponding
-netdev options below. The guest NIC model can be set with model=modelname. Use model=help to list
the available device types. The hardware MAC address can be set with mac=macaddr.
The following two example do exactly the same, to show how -nic can be used to shorten the command
line length:
qemu-system-x86_64 -netdev user,id=n1,ipv6=off -device e1000,netdev=n1,mac=52:54:98:76:54:32
qemu-system-x86_64 -nic user,ipv6=off,model=e1000,mac=52:54:98:76:54:32
-nic none
Indicate that no network devices should be configured. It is used to override the default
configuration (default NIC with "user" host network backend) which is activated if no other
networking options are provided.
-netdev user,id=id[,option][,option][,...]
Configure user mode host network backend which requires no administrator privilege to run. Valid
options are:
id=id Assign symbolic name for use in monitor commands.
ipv4=on|off and ipv6=on|off
Specify that either IPv4 or IPv6 must be enabled. If neither is specified both protocols
are enabled.
net=addr[/mask]
Set IP network address the guest will see. Optionally specify the netmask, either in the
form a.b.c.d or as number of valid top-most bits. Default is 10.0.2.0/24.
host=addr
Specify the guest-visible address of the host. Default is the 2nd IP in the guest network,
i.e. x.x.x.2.
ipv6-net=addr[/int]
Set IPv6 network address the guest will see (default is fec0::/64). The network prefix is
given in the usual hexadecimal IPv6 address notation. The prefix size is optional, and is
given as the number of valid top-most bits (default is 64).
ipv6-host=addr
Specify the guest-visible IPv6 address of the host. Default is the 2nd IPv6 in the guest
network, i.e. xxxx::2.
restrict=on|off
If this option is enabled, the guest will be isolated, i.e. it will not be able to contact
the host and no guest IP packets will be routed over the host to the outside. This option
does not affect any explicitly set forwarding rules.
hostname=name
Specifies the client hostname reported by the built-in DHCP server.
dhcpstart=addr
Specify the first of the 16 IPs the built-in DHCP server can assign. Default is the 15th to
31st IP in the guest network, i.e. x.x.x.15 to x.x.x.31.
dns=addr
Specify the guest-visible address of the virtual nameserver. The address must be different
from the host address. Default is the 3rd IP in the guest network, i.e. x.x.x.3.
ipv6-dns=addr
Specify the guest-visible address of the IPv6 virtual nameserver. The address must be
different from the host address. Default is the 3rd IP in the guest network, i.e. xxxx::3.
dnssearch=domain
Provides an entry for the domain-search list sent by the built-in DHCP server. More than
one domain suffix can be transmitted by specifying this option multiple times. If
supported, this will cause the guest to automatically try to append the given domain
suffix(es) in case a domain name can not be resolved.
Example:
qemu-system-x86_64 -nic user,dnssearch=mgmt.example.org,dnssearch=example.org
domainname=domain
Specifies the client domain name reported by the built-in DHCP server.
tftp=dir
When using the user mode network stack, activate a built-in TFTP server. The files in dir
will be exposed as the root of a TFTP server. The TFTP client on the guest must be
configured in binary mode (use the command bin of the Unix TFTP client). The built-in TFTP
server is read-only; it does not implement any command for writing files. QEMU will not
write to this directory.
tftp-server-name=name
In BOOTP reply, broadcast name as the "TFTP server name" (RFC2132 option 66). This can be
used to advise the guest to load boot files or configurations from a different server than
the host address.
bootfile=file
When using the user mode network stack, broadcast file as the BOOTP filename. In
conjunction with tftp, this can be used to network boot a guest from a local directory.
Example (using pxelinux):
qemu-system-x86_64 -hda linux.img -boot n -device e1000,netdev=n1 \
-netdev user,id=n1,tftp=/path/to/tftp/files,bootfile=/pxelinux.0
smb=dir[,smbserver=addr]
When using the user mode network stack, activate a built-in SMB server so that Windows OSes
can access to the host files in dir transparently. The IP address of the SMB server can be
set to addr. By default the 4th IP in the guest network is used, i.e. x.x.x.4.
In the guest Windows OS, the line:
10.0.2.4 smbserver
must be added in the file C:\WINDOWS\LMHOSTS (for windows 9x/Me) or
C:\WINNT\SYSTEM32\DRIVERS\ETC\LMHOSTS (Windows NT/2000).
Then dir can be accessed in \\smbserver\qemu.
Note that a SAMBA server must be installed on the host OS.
hostfwd=[tcp|udp]:[hostaddr]:hostport-[guestaddr]:guestport
Redirect incoming TCP or UDP connections to the host port hostport to the guest IP address
guestaddr on guest port guestport. If guestaddr is not specified, its value is x.x.x.15
(default first address given by the built-in DHCP server). By specifying hostaddr, the rule
can be bound to a specific host interface. If no connection type is set, TCP is used. This
option can be given multiple times.
For example, to redirect host X11 connection from screen 1 to guest screen 0, use the
following:
# on the host
qemu-system-x86_64 -nic user,hostfwd=tcp:127.0.0.1:6001-:6000
# this host xterm should open in the guest X11 server
xterm -display :1
To redirect telnet connections from host port 5555 to telnet port on the guest, use the
following:
# on the host
qemu-system-x86_64 -nic user,hostfwd=tcp::5555-:23
telnet localhost 5555
Then when you use on the host telnet localhost 5555, you connect to the guest telnet
server.
guestfwd=[tcp]:server:port-dev; guestfwd=[tcp]:server:port-cmd:command
Forward guest TCP connections to the IP address server on port port to the character device
dev or to a program executed by cmd:command which gets spawned for each connection. This
option can be given multiple times.
You can either use a chardev directly and have that one used throughout QEMU's lifetime,
like in the following example:
# open 10.10.1.1:4321 on bootup, connect 10.0.2.100:1234 to it whenever
# the guest accesses it
qemu-system-x86_64 -nic user,guestfwd=tcp:10.0.2.100:1234-tcp:10.10.1.1:4321
Or you can execute a command on every TCP connection established by the guest, so that QEMU
behaves similar to an inetd process for that virtual server:
# call "netcat 10.10.1.1 4321" on every TCP connection to 10.0.2.100:1234
# and connect the TCP stream to its stdin/stdout
qemu-system-x86_64 -nic 'user,id=n1,guestfwd=tcp:10.0.2.100:1234-cmd:netcat 10.10.1.1 4321'
-netdev tap,id=id[,fd=h][,ifname=name][,script=file][,downscript=dfile][,br=bridge][,helper=helper]
Configure a host TAP network backend with ID id.
Use the network script file to configure it and the network script dfile to deconfigure it. If
name is not provided, the OS automatically provides one. The default network configure script is
/etc/qemu-ifup and the default network deconfigure script is /etc/qemu-ifdown. Use script=no or
downscript=no to disable script execution.
If running QEMU as an unprivileged user, use the network helper to configure the TAP interface and
attach it to the bridge. The default network helper executable is
/usr/lib/qemu/qemu-bridge-helper and the default bridge device is br0.
fd=h can be used to specify the handle of an already opened host TAP interface.
Examples:
#launch a QEMU instance with the default network script
qemu-system-x86_64 linux.img -nic tap
#launch a QEMU instance with two NICs, each one connected
#to a TAP device
qemu-system-x86_64 linux.img \
-netdev tap,id=nd0,ifname=tap0 -device e1000,netdev=nd0 \
-netdev tap,id=nd1,ifname=tap1 -device rtl8139,netdev=nd1
#launch a QEMU instance with the default network helper to
#connect a TAP device to bridge br0
qemu-system-x86_64 linux.img -device virtio-net-pci,netdev=n1 \
-netdev tap,id=n1,"helper=/usr/lib/qemu/qemu-bridge-helper"
-netdev bridge,id=id[,br=bridge][,helper=helper]
Connect a host TAP network interface to a host bridge device.
Use the network helper helper to configure the TAP interface and attach it to the bridge. The
default network helper executable is /usr/lib/qemu/qemu-bridge-helper and the default bridge
device is br0.
Examples:
#launch a QEMU instance with the default network helper to
#connect a TAP device to bridge br0
qemu-system-x86_64 linux.img -netdev bridge,id=n1 -device virtio-net,netdev=n1
#launch a QEMU instance with the default network helper to
#connect a TAP device to bridge qemubr0
qemu-system-x86_64 linux.img -netdev bridge,br=qemubr0,id=n1 -device virtio-net,netdev=n1
-netdev socket,id=id[,fd=h][,listen=[host]:port][,connect=host:port]
This host network backend can be used to connect the guest's network to another QEMU virtual
machine using a TCP socket connection. If listen is specified, QEMU waits for incoming connections
on port (host is optional). connect is used to connect to another QEMU instance using the listen
option. fd=h specifies an already opened TCP socket.
Example:
# launch a first QEMU instance
qemu-system-x86_64 linux.img \
-device e1000,netdev=n1,mac=52:54:00:12:34:56 \
-netdev socket,id=n1,listen=:1234
# connect the network of this instance to the network of the first instance
qemu-system-x86_64 linux.img \
-device e1000,netdev=n2,mac=52:54:00:12:34:57 \
-netdev socket,id=n2,connect=127.0.0.1:1234
-netdev socket,id=id[,fd=h][,mcast=maddr:port[,localaddr=addr]]
Configure a socket host network backend to share the guest's network traffic with another QEMU
virtual machines using a UDP multicast socket, effectively making a bus for every QEMU with same
multicast address maddr and port. NOTES:
1. Several QEMU can be running on different hosts and share same bus (assuming correct multicast
setup for these hosts).
2. mcast support is compatible with User Mode Linux (argument ethN=mcast), see ‐
http://user-mode-linux.sf.net.
3. Use fd=h to specify an already opened UDP multicast socket.
Example:
# launch one QEMU instance
qemu-system-x86_64 linux.img \
-device e1000,netdev=n1,mac=52:54:00:12:34:56 \
-netdev socket,id=n1,mcast=230.0.0.1:1234
# launch another QEMU instance on same "bus"
qemu-system-x86_64 linux.img \
-device e1000,netdev=n2,mac=52:54:00:12:34:57 \
-netdev socket,id=n2,mcast=230.0.0.1:1234
# launch yet another QEMU instance on same "bus"
qemu-system-x86_64 linux.img \
-device e1000,netdev=n3,mac=52:54:00:12:34:58 \
-netdev socket,id=n3,mcast=230.0.0.1:1234
Example (User Mode Linux compat.):
# launch QEMU instance (note mcast address selected is UML's default)
qemu-system-x86_64 linux.img \
-device e1000,netdev=n1,mac=52:54:00:12:34:56 \
-netdev socket,id=n1,mcast=239.192.168.1:1102
# launch UML
/path/to/linux ubd0=/path/to/root_fs eth0=mcast
Example (send packets from host's 1.2.3.4):
qemu-system-x86_64 linux.img \
-device e1000,netdev=n1,mac=52:54:00:12:34:56 \
-netdev socket,id=n1,mcast=239.192.168.1:1102,localaddr=1.2.3.4
-netdev
l2tpv3,id=id,src=srcaddr,dst=dstaddr[,srcport=srcport][,dstport=dstport],txsession=txsession[,rxsession=rxsession][,ipv6=on|off][,udp=on|off][,cookie64][,counter][,pincounter][,txcookie=txcookie][,rxcookie=rxcookie][,offset=offset]
Configure a L2TPv3 pseudowire host network backend. L2TPv3 (RFC3931) is a popular protocol to
transport Ethernet (and other Layer 2) data frames between two systems. It is present in routers,
firewalls and the Linux kernel (from version 3.3 onwards).
This transport allows a VM to communicate to another VM, router or firewall directly.
src=srcaddr
source address (mandatory)
dst=dstaddr
destination address (mandatory)
udp select udp encapsulation (default is ip).
srcport=srcport
source udp port.
dstport=dstport
destination udp port.
ipv6 force v6, otherwise defaults to v4.
rxcookie=rxcookie; txcookie=txcookie
Cookies are a weak form of security in the l2tpv3 specification. Their function is mostly
to prevent misconfiguration. By default they are 32 bit.
cookie64
Set cookie size to 64 bit instead of the default 32
counter=off
Force a 'cut-down' L2TPv3 with no counter as in draft-mkonstan-l2tpext-keyed-ipv6-tunnel-00
pincounter=on
Work around broken counter handling in peer. This may also help on networks which have
packet reorder.
offset=offset
Add an extra offset between header and data
For example, to attach a VM running on host 4.3.2.1 via L2TPv3 to the bridge br-lan on the remote
Linux host 1.2.3.4:
# Setup tunnel on linux host using raw ip as encapsulation
# on 1.2.3.4
ip l2tp add tunnel remote 4.3.2.1 local 1.2.3.4 tunnel_id 1 peer_tunnel_id 1 \
encap udp udp_sport 16384 udp_dport 16384
ip l2tp add session tunnel_id 1 name vmtunnel0 session_id \
0xFFFFFFFF peer_session_id 0xFFFFFFFF
ifconfig vmtunnel0 mtu 1500
ifconfig vmtunnel0 up
brctl addif br-lan vmtunnel0
# on 4.3.2.1
# launch QEMU instance - if your network has reorder or is very lossy add ,pincounter
qemu-system-x86_64 linux.img -device e1000,netdev=n1 \
-netdev l2tpv3,id=n1,src=4.2.3.1,dst=1.2.3.4,udp,srcport=16384,dstport=16384,rxsession=0xffffffff,txsession=0xffffffff,counter
-netdev vde,id=id[,sock=socketpath][,port=n][,group=groupname][,mode=octalmode]
Configure VDE backend to connect to PORT n of a vde switch running on host and listening for
incoming connections on socketpath. Use GROUP groupname and MODE octalmode to change default
ownership and permissions for communication port. This option is only available if QEMU has been
compiled with vde support enabled.
Example:
# launch vde switch
vde_switch -F -sock /tmp/myswitch
# launch QEMU instance
qemu-system-x86_64 linux.img -nic vde,sock=/tmp/myswitch
-netdev
af-xdp,id=str,ifname=name[,mode=native|skb][,force-copy=on|off][,queues=n][,start-queue=m][,inhibit=on|off][,sock-fds=x:y:...:z]
Configure AF_XDP backend to connect to a network interface 'name' using AF_XDP socket. A specific
program attach mode for a default XDP program can be forced with 'mode', defaults to best-effort,
where the likely most performant mode will be in use. Number of queues 'n' should generally match
the number or queues in the interface, defaults to 1. Traffic arriving on non-configured device
queues will not be delivered to the network backend.
# set number of queues to 4
ethtool -L eth0 combined 4
# launch QEMU instance
qemu-system-x86_64 linux.img -device virtio-net-pci,netdev=n1 \
-netdev af-xdp,id=n1,ifname=eth0,queues=4
'start-queue' option can be specified if a particular range of queues [m, m + n] should be in use.
For example, this is may be necessary in order to use certain NICs in native mode. Kernel allows
the driver to create a separate set of XDP queues on top of regular ones, and only these queues
can be used for AF_XDP sockets. NICs that work this way may also require an additional traffic
redirection with ethtool to these special queues.
# set number of queues to 1
ethtool -L eth0 combined 1
# redirect all the traffic to the second queue (id: 1)
# note: drivers may require non-empty key/mask pair.
ethtool -N eth0 flow-type ether \
dst 00:00:00:00:00:00 m FF:FF:FF:FF:FF:FE action 1
ethtool -N eth0 flow-type ether \
dst 00:00:00:00:00:01 m FF:FF:FF:FF:FF:FE action 1
# launch QEMU instance
qemu-system-x86_64 linux.img -device virtio-net-pci,netdev=n1 \
-netdev af-xdp,id=n1,ifname=eth0,queues=1,start-queue=1
XDP program can also be loaded externally. In this case 'inhibit' option should be set to 'on'
and 'sock-fds' provided with file descriptors for already open but not bound XDP sockets already
added to a socket map for corresponding queues. One socket per queue.
qemu-system-x86_64 linux.img -device virtio-net-pci,netdev=n1 \
-netdev af-xdp,id=n1,ifname=eth0,queues=3,inhibit=on,sock-fds=15:16:17
-netdev vhost-user,chardev=id[,vhostforce=on|off][,queues=n]
Establish a vhost-user netdev, backed by a chardev id. The chardev should be a unix domain socket
backed one. The vhost-user uses a specifically defined protocol to pass vhost ioctl replacement
messages to an application on the other end of the socket. On non-MSIX guests, the feature can be
forced with vhostforce. Use 'queues=n' to specify the number of queues to be created for
multiqueue vhost-user.
Example:
qemu -m 512 -object memory-backend-file,id=mem,size=512M,mem-path=/hugetlbfs,share=on \
-numa node,memdev=mem \
-chardev socket,id=chr0,path=/path/to/socket \
-netdev type=vhost-user,id=net0,chardev=chr0 \
-device virtio-net-pci,netdev=net0
-netdev vhost-vdpa[,vhostdev=/path/to/dev][,vhostfd=h]
Establish a vhost-vdpa netdev.
vDPA device is a device that uses a datapath which complies with the virtio specifications with a
vendor specific control path. vDPA devices can be both physically located on the hardware or
emulated by software.
-netdev hubport,id=id,hubid=hubid[,netdev=nd]
Create a hub port on the emulated hub with ID hubid.
The hubport netdev lets you connect a NIC to a QEMU emulated hub instead of a single netdev.
Alternatively, you can also connect the hubport to another netdev with ID nd by using the
netdev=nd option.
-net nic[,netdev=nd][,macaddr=mac][,model=type] [,name=name][,addr=addr][,vectors=v]
Legacy option to configure or create an on-board (or machine default) Network Interface Card(NIC)
and connect it either to the emulated hub with ID 0 (i.e. the default hub), or to the netdev nd.
If model is omitted, then the default NIC model associated with the machine type is used. Note
that the default NIC model may change in future QEMU releases, so it is highly recommended to
always specify a model. Optionally, the MAC address can be changed to mac, the device address set
to addr (PCI cards only), and a name can be assigned for use in monitor commands. Optionally, for
PCI cards, you can specify the number v of MSI-X vectors that the card should have; this option
currently only affects virtio cards; set v = 0 to disable MSI-X. If no -net option is specified, a
single NIC is created. QEMU can emulate several different models of network card. Use -net
nic,model=help for a list of available devices for your target.
-net user|tap|bridge|socket|l2tpv3|vde[,...][,name=name]
Configure a host network backend (with the options corresponding to the same -netdev option) and
connect it to the emulated hub 0 (the default hub). Use name to specify the name of the hub port.
Character device options
The general form of a character device option is:
-chardev backend,id=id[,mux=on|off][,options]
Backend is one of: null, socket, udp, msmouse, vc, ringbuf, file, pipe, console, serial, pty,
stdio, braille, parallel, spicevmc, spiceport. The specific backend will determine the applicable
options.
Use -chardev help to print all available chardev backend types.
All devices must have an id, which can be any string up to 127 characters long. It is used to
uniquely identify this device in other command line directives.
A character device may be used in multiplexing mode by multiple front-ends. Specify mux=on to
enable this mode. A multiplexer is a "1:N" device, and here the "1" end is your specified chardev
backend, and the "N" end is the various parts of QEMU that can talk to a chardev. If you create a
chardev with id=myid and mux=on, QEMU will create a multiplexer with your specified ID, and you
can then configure multiple front ends to use that chardev ID for their input/output. Up to four
different front ends can be connected to a single multiplexed chardev. (Without multiplexing
enabled, a chardev can only be used by a single front end.) For instance you could use this to
allow a single stdio chardev to be used by two serial ports and the QEMU monitor:
-chardev stdio,mux=on,id=char0 \
-mon chardev=char0,mode=readline \
-serial chardev:char0 \
-serial chardev:char0
You can have more than one multiplexer in a system configuration; for instance you could have a
TCP port multiplexed between UART 0 and UART 1, and stdio multiplexed between the QEMU monitor and
a parallel port:
-chardev stdio,mux=on,id=char0 \
-mon chardev=char0,mode=readline \
-parallel chardev:char0 \
-chardev tcp,...,mux=on,id=char1 \
-serial chardev:char1 \
-serial chardev:char1
When you're using a multiplexed character device, some escape sequences are interpreted in the
input. See the chapter about Keys in the character backend multiplexer in the System Emulation
Users Guide for more details.
Note that some other command line options may implicitly create multiplexed character backends;
for instance -serial mon:stdio creates a multiplexed stdio backend connected to the serial port
and the QEMU monitor, and -nographic also multiplexes the console and the monitor to stdio.
There is currently no support for multiplexing in the other direction (where a single QEMU front
end takes input and output from multiple chardevs).
Every backend supports the logfile option, which supplies the path to a file to record all data
transmitted via the backend. The logappend option controls whether the log file will be truncated
or appended to when opened.
The available backends are:
-chardev null,id=id
A void device. This device will not emit any data, and will drop any data it receives. The null
backend does not take any options.
-chardev socket,id=id[,TCP options or unix
options][,server=on|off][,wait=on|off][,telnet=on|off][,websocket=on|off][,reconnect=seconds][,tls-creds=id][,tls-authz=id]
Create a two-way stream socket, which can be either a TCP or a unix socket. A unix socket will be
created if path is specified. Behaviour is undefined if TCP options are specified for a unix
socket.
server=on|off specifies that the socket shall be a listening socket.
wait=on|off specifies that QEMU should not block waiting for a client to connect to a listening
socket.
telnet=on|off specifies that traffic on the socket should interpret telnet escape sequences.
websocket=on|off specifies that the socket uses WebSocket protocol for communication.
reconnect sets the timeout for reconnecting on non-server sockets when the remote end goes away.
qemu will delay this many seconds and then attempt to reconnect. Zero disables reconnecting, and
is the default.
tls-creds requests enablement of the TLS protocol for encryption, and specifies the id of the TLS
credentials to use for the handshake. The credentials must be previously created with the -object
tls-creds argument.
tls-auth provides the ID of the QAuthZ authorization object against which the client's x509
distinguished name will be validated. This object is only resolved at time of use, so can be
deleted and recreated on the fly while the chardev server is active. If missing, it will default
to denying access.
TCP and unix socket options are given below:
TCP options: port=port[,host=host][,to=to][,ipv4=on|off][,ipv6=on|off][,nodelay=on|off]
host for a listening socket specifies the local address to be bound. For a connecting
socket species the remote host to connect to. host is optional for listening sockets. If
not specified it defaults to 0.0.0.0.
port for a listening socket specifies the local port to be bound. For a connecting socket
specifies the port on the remote host to connect to. port can be given as either a port
number or a service name. port is required.
to is only relevant to listening sockets. If it is specified, and port cannot be bound,
QEMU will attempt to bind to subsequent ports up to and including to until it succeeds. to
must be specified as a port number.
ipv4=on|off and ipv6=on|off specify that either IPv4 or IPv6 must be used. If neither is
specified the socket may use either protocol.
nodelay=on|off disables the Nagle algorithm.
unix options: path=path[,abstract=on|off][,tight=on|off]
path specifies the local path of the unix socket. path is required. abstract=on|off
specifies the use of the abstract socket namespace, rather than the filesystem. Optional,
defaults to false. tight=on|off sets the socket length of abstract sockets to their
minimum, rather than the full sun_path length. Optional, defaults to true.
-chardev
udp,id=id[,host=host],port=port[,localaddr=localaddr][,localport=localport][,ipv4=on|off][,ipv6=on|off]
Sends all traffic from the guest to a remote host over UDP.
host specifies the remote host to connect to. If not specified it defaults to localhost.
port specifies the port on the remote host to connect to. port is required.
localaddr specifies the local address to bind to. If not specified it defaults to 0.0.0.0.
localport specifies the local port to bind to. If not specified any available local port will be
used.
ipv4=on|off and ipv6=on|off specify that either IPv4 or IPv6 must be used. If neither is
specified the device may use either protocol.
-chardev msmouse,id=id
Forward QEMU's emulated msmouse events to the guest. msmouse does not take any options.
-chardev vc,id=id[[,width=width][,height=height]][[,cols=cols][,rows=rows]]
Connect to a QEMU text console. vc may optionally be given a specific size.
width and height specify the width and height respectively of the console, in pixels.
cols and rows specify that the console be sized to fit a text console with the given dimensions.
-chardev ringbuf,id=id[,size=size]
Create a ring buffer with fixed size size. size must be a power of two and defaults to 64K.
-chardev file,id=id,path=path[,input-path=input-path]
Log all traffic received from the guest to a file.
path specifies the path of the file to be opened. This file will be created if it does not already
exist, and overwritten if it does. path is required.
If input-path is specified, this is the path of a second file which will be used for input. If
input-path is not specified, no input will be available from the chardev.
Note that input-path is not supported on Windows hosts.
-chardev pipe,id=id,path=path
Create a two-way connection to the guest. The behaviour differs slightly between Windows hosts and
other hosts:
On Windows, a single duplex pipe will be created at \\.pipe\path.
On other hosts, 2 pipes will be created called path.in and path.out. Data written to path.in will
be received by the guest. Data written by the guest can be read from path.out. QEMU will not
create these fifos, and requires them to be present.
path forms part of the pipe path as described above. path is required.
-chardev console,id=id
Send traffic from the guest to QEMU's standard output. console does not take any options.
console is only available on Windows hosts.
-chardev serial,id=id,path=path
Send traffic from the guest to a serial device on the host.
On Unix hosts serial will actually accept any tty device, not only serial lines.
path specifies the name of the serial device to open.
-chardev pty,id=id
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 includes exiting QEMU with the key
sequence Control-c. This option is enabled by default, use signal=off to disable it.
-chardev braille,id=id
Connect to a local BrlAPI server. braille does not take any options.
-chardev parallel,id=id,path=path
parallel is only available on Linux, FreeBSD and DragonFlyBSD
hosts.
Connect to a local parallel port.
path specifies the path to the parallel port device. path is required.
-chardev spicevmc,id=id,debug=debug,name=name
spicevmc is only available when spice support is built in.
debug debug level for spicevmc
name name of spice channel to connect to
Connect to a spice virtual machine channel, such as vdiport.
-chardev spiceport,id=id,debug=debug,name=name
spiceport is only available when spice support is built in.
debug debug level for spicevmc
name name of spice port to connect to
Connect to a spice port, allowing a Spice client to handle the traffic identified by a name
(preferably a fqdn).
TPM device options
The general form of a TPM device option is:
-tpmdev backend,id=id[,options]
The specific backend type will determine the applicable options. The -tpmdev option creates the
TPM backend and requires a -device option that specifies the TPM frontend interface model.
Use -tpmdev help to print all available TPM backend types.
The available backends are:
-tpmdev passthrough,id=id,path=path,cancel-path=cancel-path
(Linux-host only) Enable access to the host's TPM using the passthrough driver.
path specifies the path to the host's TPM device, i.e., on a Linux host this would be /dev/tpm0.
path is optional and by default /dev/tpm0 is used.
cancel-path specifies the path to the host TPM device's sysfs entry allowing for cancellation of
an ongoing TPM command. cancel-path is optional and by default QEMU will search for the sysfs
entry to use.
Some notes about using the host's TPM with the passthrough driver:
The TPM device accessed by the passthrough driver must not be used by any other application on the
host.
Since the host's firmware (BIOS/UEFI) has already initialized the TPM, the VM's firmware
(BIOS/UEFI) will not be able to initialize the TPM again and may therefore not show a TPM-specific
menu that would otherwise allow the user to configure the TPM, e.g., allow the user to
enable/disable or activate/deactivate the TPM. Further, if TPM ownership is released from within a
VM then the host's TPM will get disabled and deactivated. To enable and activate the TPM again
afterwards, the host has to be rebooted and the user is required to enter the firmware's menu to
enable and activate the TPM. If the TPM is left disabled and/or deactivated most TPM commands will
fail.
To create a passthrough TPM use the following two options:
-tpmdev passthrough,id=tpm0 -device tpm-tis,tpmdev=tpm0
Note that the -tpmdev id is tpm0 and is referenced by tpmdev=tpm0 in the device option.
-tpmdev emulator,id=id,chardev=dev
(Linux-host only) Enable access to a TPM emulator using Unix domain socket based chardev backend.
chardev specifies the unique ID of a character device backend that provides connection to the
software TPM server.
To create a TPM emulator backend device with chardev socket backend:
-chardev socket,id=chrtpm,path=/tmp/swtpm-sock -tpmdev emulator,id=tpm0,chardev=chrtpm -device tpm-tis,tpmdev=tpm0
Boot Image or Kernel specific
There are broadly 4 ways you can boot a system with QEMU.
• specify a firmware and let it control finding a kernel
• specify a firmware and pass a hint to the kernel to boot
• direct kernel image boot
• manually load files into the guest's address space
The third method is useful for quickly testing kernels but as there is no firmware to pass configuration
information to the kernel the hardware must either be probeable, the kernel built for the exact
configuration or passed some configuration data (e.g. a DTB blob) which tells the kernel what drivers it
needs. This exact details are often hardware specific.
The final method is the most generic way of loading images into the guest address space and used mostly
for bare metal type development where the reset vectors of the processor are taken into account.
For x86 machines and some other architectures -bios will generally do the right thing with whatever it is
given. For other machines the more strict -pflash option needs an image that is sized for the flash
device for the given machine type.
Please see the QEMU System Emulator Targets section of the manual for more detailed documentation.
-bios file
Set the filename for the BIOS.
-pflash file
Use file as a parallel flash image.
The kernel options were designed to work with Linux kernels although other things (like hypervisors) can
be packaged up as a kernel executable image. The exact format of a executable image is usually
architecture specific.
The way in which the kernel is started (what address it is loaded at, what if any information is passed
to it via CPU registers, the state of the hardware when it is started, and so on) is also architecture
specific. Typically it follows the specification laid down by the Linux kernel for how kernels for that
architecture must be started.
-kernel bzImage
Use bzImage as kernel image. The kernel can be either a Linux kernel or in multiboot format.
-append cmdline
Use cmdline as kernel command line
-initrd file
Use file as initial ram disk.
-initrd "file1 arg=foo,file2"
This syntax is only available with multiboot.
Use file1 and file2 as modules and pass arg=foo as parameter to the first module. Commas can be
provided in module parameters by doubling them on the command line to escape them:
-initrd "bzImage earlyprintk=xen,,keep root=/dev/xvda1,initrd.img"
Multiboot only. Use bzImage as the first module with "earlyprintk=xen,keep root=/dev/xvda1" as its
command line, and initrd.img as the second module.
-dtb file
Use file as a device tree binary (dtb) image and pass it to the kernel on boot.
Finally you can also manually load images directly into the address space of the guest. This is most
useful for developers who already know the layout of their guest and take care to ensure something sane
will happen when the reset vector executes.
The generic loader can be invoked by using the loader device:
-device loader,addr=<addr>,data=<data>,data-len=<data-len>[,data-be=<data-be>][,cpu-num=<cpu-num>]
there is also the guest loader which operates in a similar way but tweaks the DTB so a hypervisor loaded
via -kernel can find where the guest image is:
-device guest-loader,addr=<addr>[,kernel=<path>,[bootargs=<arguments>]][,initrd=<path>]
Debug/Expert options
-compat [deprecated-input=@var{input-policy}][,deprecated-output=@var{output-policy}]
Set policy for handling deprecated management interfaces (experimental):
deprecated-input=accept (default)
Accept deprecated commands and arguments
deprecated-input=reject
Reject deprecated commands and arguments
deprecated-input=crash
Crash on deprecated commands and arguments
deprecated-output=accept (default)
Emit deprecated command results and events
deprecated-output=hide
Suppress deprecated command results and events
Limitation: covers only syntactic aspects of QMP.
-compat [unstable-input=@var{input-policy}][,unstable-output=@var{output-policy}]
Set policy for handling unstable management interfaces (experimental):
unstable-input=accept (default)
Accept unstable commands and arguments
unstable-input=reject
Reject unstable commands and arguments
unstable-input=crash
Crash on unstable commands and arguments
unstable-output=accept (default)
Emit unstable command results and events
unstable-output=hide
Suppress unstable command results and events
Limitation: covers only syntactic aspects of QMP.
-fw_cfg [name=]name,file=file
Add named fw_cfg entry with contents from file file. If the filename contains comma, you must
double it (for instance, "file=my,,file" to use file "my,file").
-fw_cfg [name=]name,string=str
Add named fw_cfg entry with contents from string str. If the string contains comma, you must
double it (for instance, "string=my,,string" to use file "my,string").
The terminating NUL character of the contents of str will not be included as part of the fw_cfg
item data. To insert contents with embedded NUL characters, you have to use the file parameter.
The fw_cfg entries are passed by QEMU through to the guest.
Example:
-fw_cfg name=opt/com.mycompany/blob,file=./my_blob.bin
creates an fw_cfg entry named opt/com.mycompany/blob with contents from ./my_blob.bin.
-serial dev
Redirect the virtual serial port to host character device dev. The default device is vc in
graphical mode and stdio in non graphical mode.
This option can be used several times to simulate multiple serial ports.
You can use -serial none to suppress the creation of default serial devices.
Available character devices are:
vc[:WxH]
Virtual console. Optionally, a width and height can be given in pixel with
vc:800x600
It is also possible to specify width or height in characters:
vc:80Cx24C
pty [Linux only] Pseudo TTY (a new PTY is automatically allocated)
none No device is allocated. Note that for machine types which emulate systems where a serial
device is always present in real hardware, this may be equivalent to the null option, in
that the serial device is still present but all output is discarded. For boards where the
number of serial ports is truly variable, this suppresses the creation of the device.
null A guest will see the UART or serial device as present in the machine, but all output is
discarded, and there is no input. Conceptually equivalent to redirecting the output to
/dev/null.
chardev:id
Use a named character device defined with the -chardev option.
/dev/XXX
[Linux only] Use host tty, e.g. /dev/ttyS0. The host serial port parameters are set
according to the emulated ones.
/dev/parportN
[Linux only, parallel port only] Use host parallel port N. Currently SPP and EPP parallel
port features can be used.
file:filename
Write output to filename. No character can be read.
stdio [Unix only] standard input/output
pipe:filename
name pipe filename
COMn [Windows only] Use host serial port n
udp:[remote_host]:remote_port[@[src_ip]:src_port]
This implements UDP Net Console. When remote_host or src_ip are not specified they default
to 0.0.0.0. When not using a specified src_port a random port is automatically chosen.
If you just want a simple readonly console you can use netcat or nc, by starting QEMU with:
-serial udp::4555 and nc as: nc -u -l -p 4555. Any time QEMU writes something to that port
it will appear in the netconsole session.
If you plan to send characters back via netconsole or you want to stop and start QEMU a lot
of times, you should have QEMU use the same source port each time by using something like
-serial udp::4555@:4556 to QEMU. Another approach is to use a patched version of netcat
which can listen to a TCP port and send and receive characters via udp. If you have a
patched version of netcat which activates telnet remote echo and single char transfer, then
you can use the following options to set up a netcat redirector to allow telnet on port
5555 to access the QEMU port.
QEMU Options:
-serial udp::4555@:4556
netcat options:
-u -P 4555 -L 0.0.0.0:4556 -t -p 5555 -I -T
telnet options:
localhost 5555
tcp:[host]:port[,server=on|off][,wait=on|off][,nodelay=on|off][,reconnect=seconds]
The TCP Net Console has two modes of operation. It can send the serial I/O to a location or
wait for a connection from a location. By default the TCP Net Console is sent to host at
the port. If you use the server=on option QEMU will wait for a client socket application to
connect to the port before continuing, unless the wait=on|off option was specified. The
nodelay=on|off option disables the Nagle buffering algorithm. The reconnect=on option only
applies if server=no is set, if the connection goes down it will attempt to reconnect at
the given interval. If host is omitted, 0.0.0.0 is assumed. Only one TCP connection at a
time is accepted. You can use telnet=on to connect to the corresponding character device.
Example to send tcp console to 192.168.0.2 port 4444
-serial tcp:192.168.0.2:4444
Example to listen and wait on port 4444 for connection
-serial tcp::4444,server=on
Example to not wait and listen on ip 192.168.0.100 port 4444
-serial tcp:192.168.0.100:4444,server=on,wait=off
telnet:host:port[,server=on|off][,wait=on|off][,nodelay=on|off]
The telnet protocol is used instead of raw tcp sockets. The options work the same as if you
had specified -serial tcp. The difference is that the port acts like a telnet server or
client using telnet option negotiation. This will also allow you to send the MAGIC_SYSRQ
sequence if you use a telnet that supports sending the break sequence. Typically in unix
telnet you do it with Control-] and then type "send break" followed by pressing the enter
key.
websocket:host:port,server=on[,wait=on|off][,nodelay=on|off]
The WebSocket protocol is used instead of raw tcp socket. The port acts as a WebSocket
server. Client mode is not supported.
unix:path[,server=on|off][,wait=on|off][,reconnect=seconds]
A unix domain socket is used instead of a tcp socket. The option works the same as if you
had specified -serial tcp except the unix domain socket path is used for connections.
mon:dev_string
This is a special option to allow the monitor to be multiplexed onto another serial port.
The monitor is accessed with key sequence of Control-a and then pressing c. dev_string
should be any one of the serial devices specified above. An example to multiplex the
monitor onto a telnet server listening on port 4444 would be:
-serial mon:telnet::4444,server=on,wait=off
When the monitor is multiplexed to stdio in this way, Ctrl+C will not terminate QEMU any
more but will be passed to the guest instead.
braille
Braille device. This will use BrlAPI to display the braille output on a real or fake
device.
msmouse
Three button serial mouse. Configure the guest to use Microsoft protocol.
-parallel dev
Redirect the virtual parallel port to host device dev (same devices as the serial port). On Linux
hosts, /dev/parportN can be used to use hardware devices connected on the corresponding host
parallel port.
This option can be used several times to simulate up to 3 parallel ports.
Use -parallel none to disable all parallel ports.
-monitor dev
Redirect the monitor to host device dev (same devices as the serial port). The default device is
vc in graphical mode and stdio in non graphical mode. Use -monitor none to disable the default
monitor.
-qmp dev
Like -monitor but opens in 'control' mode. For example, to make QMP available on localhost port
4444:
-qmp tcp:localhost:4444,server=on,wait=off
Not all options are configurable via this syntax; for maximum flexibility use the -mon option and
an accompanying -chardev.
-qmp-pretty dev
Like -qmp but uses pretty JSON formatting.
-mon [chardev=]name[,mode=readline|control][,pretty[=on|off]]
Set up a monitor connected to the chardev name. QEMU supports two monitors: the Human Monitor
Protocol (HMP; for human interaction), and the QEMU Monitor Protocol (QMP; a JSON RPC-style
protocol). The default is HMP; mode=control selects QMP instead. pretty is only valid when
mode=control, turning on JSON pretty printing to ease human reading and debugging.
For example:
-chardev socket,id=mon1,host=localhost,port=4444,server=on,wait=off \
-mon chardev=mon1,mode=control,pretty=on
enables the QMP monitor on localhost port 4444 with pretty-printing.
-debugcon dev
Redirect the debug console to host device dev (same devices as the serial port). The debug console
is an I/O port which is typically port 0xe9; writing to that I/O port sends output to this device.
The default device is vc in graphical mode and stdio in non graphical mode.
-pidfile file
Store the QEMU process PID in file. It is useful if you launch QEMU from a script.
--preconfig
Pause QEMU for interactive configuration before the machine is created, which allows querying and
configuring properties that will affect machine initialization. Use QMP command 'x-exit-preconfig'
to exit the preconfig state and move to the next state (i.e. run guest if -S isn't used or pause
the second time if -S is used). This option is experimental.
-S Do not start CPU at startup (you must type 'c' in the monitor).
-overcommit mem-lock=on|off
-overcommit cpu-pm=on|off
Run qemu with hints about host resource overcommit. The default is to assume that host overcommits
all resources.
Locking qemu and guest memory can be enabled via mem-lock=on (disabled by default). This works
when host memory is not overcommitted and reduces the worst-case latency for guest.
Guest ability to manage power state of host cpus (increasing latency for other processes on the
same host cpu, but decreasing latency for guest) can be enabled via cpu-pm=on (disabled by
default). This works best when host CPU is not overcommitted. When used, host estimates of CPU
cycle and power utilization will be incorrect, not taking into account guest idle time.
-gdb dev
Accept a gdb connection on device dev (see the GDB usage chapter in the System Emulation Users
Guide). Note that this option does not pause QEMU execution -- if you want QEMU to not start the
guest until you connect with gdb and issue a continue command, you will need to also pass the -S
option to QEMU.
The most usual configuration is to listen on a local TCP socket:
-gdb tcp::3117
but you can specify other backends; UDP, pseudo TTY, or even stdio are all reasonable use cases.
For example, a stdio connection allows you to start QEMU from within gdb and establish the
connection via a pipe:
(gdb) target remote | exec qemu-system-x86_64 -gdb stdio ...
-s Shorthand for -gdb tcp::1234, i.e. open a gdbserver on TCP port 1234 (see the GDB usage chapter in
the System Emulation Users Guide).
-d item1[,...]
Enable logging of specified items. Use '-d help' for a list of log items.
-D logfile
Output log in logfile instead of to stderr
-dfilter range1[,...]
Filter debug output to that relevant to a range of target addresses. The filter spec can be
either start+size, start-size or start..end where start end and size are the addresses and sizes
required. For example:
-dfilter 0x8000..0x8fff,0xffffffc000080000+0x200,0xffffffc000060000-0x1000
Will dump output for any code in the 0x1000 sized block starting at 0x8000 and the 0x200 sized
block starting at 0xffffffc000080000 and another 0x1000 sized block starting at
0xffffffc00005f000.
-seed number
Force the guest to use a deterministic pseudo-random number generator, seeded with number. This
does not affect crypto routines within the host.
-L path
Set the directory for the BIOS, VGA BIOS and keymaps.
To list all the data directories, use -L help.
-enable-kvm
Enable KVM full virtualization support. This option is only available if KVM support is enabled
when compiling.
-xen-domid id
Specify xen guest domain id (XEN only).
-xen-attach
Attach to existing xen domain. libxl will use this when starting QEMU (XEN only). Restrict set of
available xen operations to specified domain id (XEN only).
-no-reboot
Exit instead of rebooting.
-no-shutdown
Don't exit QEMU on guest shutdown, but instead only stop the emulation. This allows for instance
switching to monitor to commit changes to the disk image.
-action event=action
The action parameter serves to modify QEMU's default behavior when certain guest events occur. It
provides a generic method for specifying the same behaviors that are modified by the -no-reboot
and -no-shutdown parameters.
Examples:
-action panic=none -action reboot=shutdown,shutdown=pause -device i6300esb -action watchdog=pause
-loadvm file
Start right away with a saved state (loadvm in monitor)
-daemonize
Daemonize the QEMU process after initialization. QEMU will not detach from standard IO until it is
ready to receive connections on any of its devices. This option is a useful way for external
programs to launch QEMU without having to cope with initialization race conditions.
-option-rom file
Load the contents of file as an option ROM. This option is useful to load things like EtherBoot.
-rtc [base=utc|localtime|datetime][,clock=host|rt|vm][,driftfix=none|slew]
Specify base as utc or localtime to let the RTC start at the current UTC or local time,
respectively. localtime is required for correct date in MS-DOS or Windows. To start at a specific
point in time, provide datetime in the format 2006-06-17T16:01:21 or 2006-06-17. The default base
is UTC.
By default the RTC is driven by the host system time. This allows using of the RTC as accurate
reference clock inside the guest, specifically if the host time is smoothly following an accurate
external reference clock, e.g. via NTP. If you want to isolate the guest time from the host, you
can set clock to rt instead, which provides a host monotonic clock if host support it. To even
prevent the RTC from progressing during suspension, you can set clock to vm (virtual clock).
'clock=vm' is recommended especially in icount mode in order to preserve determinism; however,
note that in icount mode the speed of the virtual clock is variable and can in general differ from
the host clock.
Enable driftfix (i386 targets only) if you experience time drift problems, specifically with
Windows' ACPI HAL. This option will try to figure out how many timer interrupts were not processed
by the Windows guest and will re-inject them.
-icount
[shift=N|auto][,align=on|off][,sleep=on|off][,rr=record|replay,rrfile=filename[,rrsnapshot=snapshot]]
Enable virtual instruction counter. The virtual cpu will execute one instruction every 2^N ns of
virtual time. If auto is specified then the virtual cpu speed will be automatically adjusted to
keep virtual time within a few seconds of real time.
Note that while this option can give deterministic behavior, it does not provide cycle accurate
emulation. Modern CPUs contain superscalar out of order cores with complex cache hierarchies. The
number of instructions executed often has little or no correlation with actual performance.
When the virtual cpu is sleeping, the virtual time will advance at default speed unless sleep=on
is specified. With sleep=on, the virtual time will jump to the next timer deadline instantly
whenever the virtual cpu goes to sleep mode and will not advance if no timer is enabled. This
behavior gives deterministic execution times from the guest point of view. The default if icount
is enabled is sleep=off. sleep=on cannot be used together with either shift=auto or align=on.
align=on will activate the delay algorithm which will try to synchronise the host clock and the
virtual clock. The goal is to have a guest running at the real frequency imposed by the shift
option. Whenever the guest clock is behind the host clock and if align=on is specified then we
print a message to the user to inform about the delay. Currently this option does not work when
shift is auto. Note: The sync algorithm will work for those shift values for which the guest clock
runs ahead of the host clock. Typically this happens when the shift value is high (how high
depends on the host machine). The default if icount is enabled is align=off.
When the rr option is specified deterministic record/replay is enabled. The rrfile= option must
also be provided to specify the path to the replay log. In record mode data is written to this
file, and in replay mode it is read back. If the rrsnapshot option is given then it specifies a
VM snapshot name. In record mode, a new VM snapshot with the given name is created at the start of
execution recording. In replay mode this option specifies the snapshot name used to load the
initial VM state.
-watchdog-action action
The action controls what QEMU will do when the watchdog timer expires. The default is reset
(forcefully reset the guest). Other possible actions are: shutdown (attempt to gracefully
shutdown the guest), poweroff (forcefully poweroff the guest), inject-nmi (inject a NMI into the
guest), pause (pause the guest), debug (print a debug message and continue), or none (do nothing).
Note that the shutdown action requires that the guest responds to ACPI signals, which it may not
be able to do in the sort of situations where the watchdog would have expired, and thus
-watchdog-action shutdown is not recommended for production use.
Examples:
-device i6300esb -watchdog-action pause
-echr numeric_ascii_value
Change the escape character used for switching to the monitor when using monitor and serial
sharing. The default is 0x01 when using the -nographic option. 0x01 is equal to pressing
Control-a. You can select a different character from the ascii control keys where 1 through 26 map
to Control-a through Control-z. For instance you could use the either of the following to change
the escape character to Control-t.
-echr 0x14; -echr 20
-incoming tcp:[host]:port[,to=maxport][,ipv4=on|off][,ipv6=on|off]
-incoming rdma:host:port[,ipv4=on|off][,ipv6=on|off]
Prepare for incoming migration, listen on a given tcp port.
-incoming unix:socketpath
Prepare for incoming migration, listen on a given unix socket.
-incoming fd:fd
Accept incoming migration from a given file descriptor.
-incoming file:filename[,offset=offset]
Accept incoming migration from a given file starting at offset. offset allows the common size
suffixes, or a 0x prefix, but not both.
-incoming exec:cmdline
Accept incoming migration as an output from specified external command.
-incoming defer
Wait for the URI to be specified via migrate_incoming. The monitor can be used to change settings
(such as migration parameters) prior to issuing the migrate_incoming to allow the migration to
begin.
-only-migratable
Only allow migratable devices. Devices will not be allowed to enter an unmigratable state.
-nodefaults
Don't create default devices. Normally, QEMU sets the default devices like serial port, parallel
port, virtual console, monitor device, VGA adapter, floppy and CD-ROM drive and others. The
-nodefaults option will disable all those default devices.
-runas user
Immediately before starting guest execution, drop root privileges, switching to the specified
user.
-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, RISC-V only).
WARNING:
Note that this allows guest direct access to the host filesystem, so should only be used with a
trusted guest OS.
See the -semihosting-config option documentation for further information about the facilities this
enables.
-semihosting-config
[enable=on|off][,target=native|gdb|auto][,chardev=id][,userspace=on|off][,arg=str[,...]]
Enable and configure Semihosting (ARM, M68K, Xtensa, MIPS, Nios II, RISC-V only).
WARNING:
Note that this allows guest direct access to the host filesystem, so should only be used with a
trusted guest OS.
target=native|gdb|auto
Defines where the semihosting calls will be addressed, to QEMU (native) or to GDB (gdb).
The default is auto, which means gdb during debug sessions and native otherwise.
chardev=str1
Send the output to a chardev backend output for native or auto output when not in gdb
userspace=on|off
Allows code running in guest userspace to access the semihosting interface. The default is
that only privileged guest code can make semihosting calls. Note that setting userspace=on
should only be used if all guest code is trusted (for example, in bare-metal test case
code).
arg=str1,arg=str2,...
Allows the user to pass input arguments, and can be used multiple times to build up a list.
The old-style -kernel/-append method of passing a command line is still supported for
backward compatibility. If both the --semihosting-config arg and the -kernel/-append are
specified, the former is passed to semihosting as it always takes precedence.
-old-param
Old param mode (ARM only).
-sandbox arg[,obsolete=string][,elevateprivileges=string][,spawn=string][,resourcecontrol=string]
Enable Seccomp mode 2 system call filter. 'on' will enable syscall filtering and 'off' will
disable it. The default is 'off'.
obsolete=string
Enable Obsolete system calls
elevateprivileges=string
Disable set*uid|gid system calls
spawn=string
Disable *fork and execve
resourcecontrol=string
Disable process affinity and schedular priority
-readconfig file
Read device configuration from file. This approach is useful when you want to spawn QEMU process
with many command line options but you don't want to exceed the command line character limit.
-no-user-config
The -no-user-config option makes QEMU not load any of the user-provided config files on
sysconfdir.
-trace [[enable=]pattern][,events=file][,file=file]
Specify tracing options.
[enable=]PATTERN
Immediately enable events matching PATTERN (either event name or a globbing pattern). This
option is only available if QEMU has been compiled with the simple, log or ftrace tracing
backend. To specify multiple events or patterns, specify the -trace option multiple times.
Use -trace help to print a list of names of trace points.
events=FILE
Immediately enable events listed in FILE. The file must contain one event name (as listed in
the trace-events-all file) per line; globbing patterns are accepted too. This option is only
available if QEMU has been compiled with the simple, log or ftrace tracing backend.
file=FILE
Log output traces to FILE. This option is only available if QEMU has been compiled with the
simple tracing backend.
-plugin file=file[,argname=argvalue]
Load a plugin.
file=file
Load the given plugin from a shared library file.
argname=argvalue
Argument passed to the plugin. (Can be given multiple times.)
-run-with [async-teardown=on|off][,chroot=dir]
Set QEMU process lifecycle options.
async-teardown=on enables asynchronous teardown. A new process called "cleanup/<QEMU_PID>" will be
created at startup sharing the address space with the main QEMU process, using clone. It will wait
for the main QEMU process to terminate completely, and then exit. This allows QEMU to terminate
very quickly even if the guest was huge, leaving the teardown of the address space to the cleanup
process. Since the cleanup process shares the same cgroups as the main QEMU process, accounting is
performed correctly. This only works if the cleanup process is not forcefully killed with SIGKILL
before the main QEMU process has terminated completely.
chroot=dir can be used for doing a chroot to the specified directory immediately before starting
the guest execution. This is especially useful in combination with -runas.
-msg [timestamp[=on|off]][,guest-name[=on|off]]
Control error message format.
timestamp=on|off
Prefix messages with a timestamp. Default is off.
guest-name=on|off
Prefix messages with guest name but only if -name guest option is set otherwise the option
is ignored. Default is off.
-dump-vmstate file
Dump json-encoded vmstate information for current machine type to file in file
-enable-sync-profile
Enable synchronization profiling.
-perfmap
Generate a map file for Linux perf tools that will allow basic profiling information to be broken
down into basic blocks.
-jitdump
Generate a dump file for Linux perf tools that maps basic blocks to symbol names, line numbers and
JITted code.
Generic object creation
-object typename[,prop1=value1,...]
Create a new object of type typename setting properties in the order they are specified. Note that
the 'id' property must be set. These objects are placed in the '/objects' path.
-object
memory-backend-file,id=id,size=size,mem-path=dir,share=on|off,discard-data=on|off,merge=on|off,dump=on|off,prealloc=on|off,host-nodes=host-nodes,policy=default|preferred|bind|interleave,align=align,offset=offset,readonly=on|off,rom=on|off|auto
Creates a memory file backend object, which can be used to back the guest RAM with huge
pages.
The id parameter is a unique ID that will be used to reference this memory region in other
parameters, e.g. -numa, -device nvdimm, etc.
The size option provides the size of the memory region, and accepts common suffixes, e.g.
500M.
The mem-path provides the path to either a shared memory or huge page filesystem mount.
The share boolean option determines whether the memory region is marked as private to QEMU,
or shared. The latter allows a co-operating external process to access the QEMU memory
region.
The share is also required for pvrdma devices due to limitations in the RDMA API provided
by Linux.
Setting share=on might affect the ability to configure NUMA bindings for the memory backend
under some circumstances, see Documentation/vm/numa_memory_policy.txt on the Linux kernel
source tree for additional details.
Setting the discard-data boolean option to on indicates that file contents can be destroyed
when QEMU exits, to avoid unnecessarily flushing data to the backing file. Note that
discard-data is only an optimization, and QEMU might not discard file contents if it aborts
unexpectedly or is terminated using SIGKILL.
The merge boolean option enables memory merge, also known as MADV_MERGEABLE, so that Kernel
Samepage Merging will consider the pages for memory deduplication.
Setting the dump boolean option to off excludes the memory from core dumps. This feature is
also known as MADV_DONTDUMP.
The prealloc boolean option enables memory preallocation.
The host-nodes option binds the memory range to a list of NUMA host nodes.
The policy option sets the NUMA policy to one of the following values:
default
default host policy
preferred
prefer the given host node list for allocation
bind restrict memory allocation to the given host node list
interleave
interleave memory allocations across the given host node list
The align option specifies the base address alignment when QEMU mmap(2) mem-path, and
accepts common suffixes, eg 2M. Some backend store specified by mem-path requires an
alignment different than the default one used by QEMU, eg the device DAX /dev/dax0.0
requires 2M alignment rather than 4K. In such cases, users can specify the required
alignment via this option.
The offset option specifies the offset into the target file that the region starts at. You
can use this parameter to back multiple regions with a single file.
The pmem option specifies whether the backing file specified by mem-path is in host
persistent memory that can be accessed using the SNIA NVM programming model (e.g. Intel
NVDIMM). If pmem is set to 'on', QEMU will take necessary operations to guarantee the
persistence of its own writes to mem-path (e.g. in vNVDIMM label emulation and live
migration). Also, we will map the backend-file with MAP_SYNC flag, which ensures the file
metadata is in sync for mem-path in case of host crash or a power failure. MAP_SYNC
requires support from both the host kernel (since Linux kernel 4.15) and the filesystem of
mem-path mounted with DAX option.
The readonly option specifies whether the backing file is opened read-only or read-write
(default).
The rom option specifies whether to create Read Only Memory (ROM) that cannot be modified
by the VM. Any write attempts to such ROM will be denied. Most use cases want proper RAM
instead of ROM. However, selected use cases, like R/O NVDIMMs, can benefit from ROM. If
set to on, create ROM; if set to off, create writable RAM; if set to auto (default), the
value of the readonly option is used. This option is primarily helpful when we want to have
writable RAM in configurations that would traditionally create ROM before the rom option
was introduced: VM templating, where we want to open a file readonly (readonly=on) and mark
the memory to be private for QEMU (share=off). For this use case, we need writable RAM
instead of ROM, and want to also set rom=off.
-object
memory-backend-ram,id=id,merge=on|off,dump=on|off,share=on|off,prealloc=on|off,size=size,host-nodes=host-nodes,policy=default|preferred|bind|interleave
Creates a memory backend object, which can be used to back the guest RAM. Memory backend
objects offer more control than the -m option that is traditionally used to define guest
RAM. Please refer to memory-backend-file for a description of the options.
-object
memory-backend-memfd,id=id,merge=on|off,dump=on|off,share=on|off,prealloc=on|off,size=size,host-nodes=host-nodes,policy=default|preferred|bind|interleave,seal=on|off,hugetlb=on|off,hugetlbsize=size
Creates an anonymous memory file backend object, which allows QEMU to share the memory with
an external process (e.g. when using vhost-user). The memory is allocated with memfd and
optional sealing. (Linux only)
The seal option creates a sealed-file, that will block further resizing the memory ('on' by
default).
The hugetlb option specify the file to be created resides in the hugetlbfs filesystem
(since Linux 4.14). Used in conjunction with the hugetlb option, the hugetlbsize option
specify the hugetlb page size on systems that support multiple hugetlb page sizes (it must
be a power of 2 value supported by the system).
In some versions of Linux, the hugetlb option is incompatible with the seal option
(requires at least Linux 4.16).
Please refer to memory-backend-file for a description of the other options.
The share boolean option is on by default with memfd.
-object iommufd,id=id[,fd=fd]
Creates an iommufd backend which allows control of DMA mapping through the /dev/iommu
device.
The id parameter is a unique ID which frontends (such as vfio-pci of vdpa) will use to
connect with the iommufd backend.
The fd parameter is an optional pre-opened file descriptor resulting from /dev/iommu
opening. Usually the iommufd is shared across all subsystems, bringing the benefit of
centralized reference counting.
-object rng-builtin,id=id
Creates a random number generator backend which obtains entropy from QEMU builtin
functions. The id parameter is a unique ID that will be used to reference this entropy
backend from the virtio-rng device. By default, the virtio-rng device uses this RNG
backend.
-object rng-random,id=id,filename=/dev/random
Creates a random number generator backend which obtains entropy from a device on the host.
The id parameter is a unique ID that will be used to reference this entropy backend from
the virtio-rng device. The filename parameter specifies which file to obtain entropy from
and if omitted defaults to /dev/urandom.
-object rng-egd,id=id,chardev=chardevid
Creates a random number generator backend which obtains entropy from an external daemon
running on the host. The id parameter is a unique ID that will be used to reference this
entropy backend from the virtio-rng device. The chardev parameter is the unique ID of a
character device backend that provides the connection to the RNG daemon.
-object tls-creds-anon,id=id,endpoint=endpoint,dir=/path/to/cred/dir,verify-peer=on|off
Creates a TLS anonymous credentials object, which can be used to provide TLS support on
network backends. The id parameter is a unique ID which network backends will use to access
the credentials. The endpoint is either server or client depending on whether the QEMU
network backend that uses the credentials will be acting as a client or as a server. If
verify-peer is enabled (the default) then once the handshake is completed, the peer
credentials will be verified, though this is a no-op for anonymous credentials.
The dir parameter tells QEMU where to find the credential files. For server endpoints,
this directory may contain a file dh-params.pem providing diffie-hellman parameters to use
for the TLS server. If the file is missing, QEMU will generate a set of DH parameters at
startup. This is a computationally expensive operation that consumes random pool entropy,
so it is recommended that a persistent set of parameters be generated upfront and saved.
-object tls-creds-psk,id=id,endpoint=endpoint,dir=/path/to/keys/dir[,username=username]
Creates a TLS Pre-Shared Keys (PSK) credentials object, which can be used to provide TLS
support on network backends. The id parameter is a unique ID which network backends will
use to access the credentials. The endpoint is either server or client depending on whether
the QEMU network backend that uses the credentials will be acting as a client or as a
server. For clients only, username is the username which will be sent to the server. If
omitted it defaults to "qemu".
The dir parameter tells QEMU where to find the keys file. It is called "dir/keys.psk" and
contains "username:key" pairs. This file can most easily be created using the GnuTLS
psktool program.
For server endpoints, dir may also contain a file dh-params.pem providing diffie-hellman
parameters to use for the TLS server. If the file is missing, QEMU will generate a set of
DH parameters at startup. This is a computationally expensive operation that consumes
random pool entropy, so it is recommended that a persistent set of parameters be generated
up front and saved.
-object
tls-creds-x509,id=id,endpoint=endpoint,dir=/path/to/cred/dir,priority=priority,verify-peer=on|off,passwordid=id
Creates a TLS anonymous credentials object, which can be used to provide TLS support on
network backends. The id parameter is a unique ID which network backends will use to access
the credentials. The endpoint is either server or client depending on whether the QEMU
network backend that uses the credentials will be acting as a client or as a server. If
verify-peer is enabled (the default) then once the handshake is completed, the peer
credentials will be verified. With x509 certificates, this implies that the clients must be
provided with valid client certificates too.
The dir parameter tells QEMU where to find the credential files. For server endpoints,
this directory may contain a file dh-params.pem providing diffie-hellman parameters to use
for the TLS server. If the file is missing, QEMU will generate a set of DH parameters at
startup. This is a computationally expensive operation that consumes random pool entropy,
so it is recommended that a persistent set of parameters be generated upfront and saved.
For x509 certificate credentials the directory will contain further files providing the
x509 certificates. The certificates must be stored in PEM format, in filenames ca-cert.pem,
ca-crl.pem (optional), server-cert.pem (only servers), server-key.pem (only servers),
client-cert.pem (only clients), and client-key.pem (only clients).
For the server-key.pem and client-key.pem files which contain sensitive private keys, it is
possible to use an encrypted version by providing the passwordid parameter. This provides
the ID of a previously created secret object containing the password for decryption.
The priority parameter allows to override the global default priority used by gnutls. This
can be useful if the system administrator needs to use a weaker set of crypto priorities
for QEMU without potentially forcing the weakness onto all applications. Or conversely if
one wants wants a stronger default for QEMU than for all other applications, they can do
this through this parameter. Its format is a gnutls priority string as described at ‐
https://gnutls.org/manual/html_node/Priority-Strings.html.
-object tls-cipher-suites,id=id,priority=priority
Creates a TLS cipher suites object, which can be used to control the TLS cipher/protocol
algorithms that applications are permitted to use.
The id parameter is a unique ID which frontends will use to access the ordered list of
permitted TLS cipher suites from the host.
The priority parameter allows to override the global default priority used by gnutls. This
can be useful if the system administrator needs to use a weaker set of crypto priorities
for QEMU without potentially forcing the weakness onto all applications. Or conversely if
one wants wants a stronger default for QEMU than for all other applications, they can do
this through this parameter. Its format is a gnutls priority string as described at ‐
https://gnutls.org/manual/html_node/Priority-Strings.html.
An example of use of this object is to control UEFI HTTPS Boot. The tls-cipher-suites
object exposes the ordered list of permitted TLS cipher suites from the host side to the
guest firmware, via fw_cfg. The list is represented as an array of IANA_TLS_CIPHER objects.
The firmware uses the IANA_TLS_CIPHER array for configuring guest-side TLS.
In the following example, the priority at which the host-side policy is retrieved is given
by the priority property. Given that QEMU uses GNUTLS, priority=@SYSTEM may be used to
refer to /etc/crypto-policies/back-ends/gnutls.config.
# qemu-system-x86_64 \
-object tls-cipher-suites,id=mysuite0,priority=@SYSTEM \
-fw_cfg name=etc/edk2/https/ciphers,gen_id=mysuite0
-object
filter-buffer,id=id,netdev=netdevid,interval=t[,queue=all|rx|tx][,status=on|off][,position=head|tail|id=<id>][,insert=behind|before]
Interval t can't be 0, this filter batches the packet delivery: all packets arriving in a
given interval on netdev netdevid are delayed until the end of the interval. Interval is in
microseconds. status is optional that indicate whether the netfilter is on (enabled) or off
(disabled), the default status for netfilter will be 'on'.
queue all|rx|tx is an option that can be applied to any netfilter.
all: the filter is attached both to the receive and the transmit queue of the netdev
(default).
rx: the filter is attached to the receive queue of the netdev, where it will receive
packets sent to the netdev.
tx: the filter is attached to the transmit queue of the netdev, where it will receive
packets sent by the netdev.
position head|tail|id=<id> is an option to specify where the filter should be inserted in
the filter list. It can be applied to any netfilter.
head: the filter is inserted at the head of the filter list, before any existing filters.
tail: the filter is inserted at the tail of the filter list, behind any existing filters
(default).
id=<id>: the filter is inserted before or behind the filter specified by <id>, see the
insert option below.
insert behind|before is an option to specify where to insert the new filter relative to the
one specified with position=id=<id>. It can be applied to any netfilter.
before: insert before the specified filter.
behind: insert behind the specified filter (default).
-object
filter-mirror,id=id,netdev=netdevid,outdev=chardevid,queue=all|rx|tx[,vnet_hdr_support][,position=head|tail|id=<id>][,insert=behind|before]
filter-mirror on netdev netdevid,mirror net packet to chardevchardevid, if it has the
vnet_hdr_support flag, filter-mirror will mirror packet with vnet_hdr_len.
-object
filter-redirector,id=id,netdev=netdevid,indev=chardevid,outdev=chardevid,queue=all|rx|tx[,vnet_hdr_support][,position=head|tail|id=<id>][,insert=behind|before]
filter-redirector on netdev netdevid,redirect filter's net packet to chardev chardevid,and
redirect indev's packet to filter.if it has the vnet_hdr_support flag, filter-redirector
will redirect packet with vnet_hdr_len. Create a filter-redirector we need to differ outdev
id from indev id, id can not be the same. we can just use indev or outdev, but at least one
of indev or outdev need to be specified.
-object
filter-rewriter,id=id,netdev=netdevid,queue=all|rx|tx,[vnet_hdr_support][,position=head|tail|id=<id>][,insert=behind|before]
Filter-rewriter is a part of COLO project.It will rewrite tcp packet to secondary from
primary to keep secondary tcp connection,and rewrite tcp packet to primary from secondary
make tcp packet can be handled by client.if it has the vnet_hdr_support flag, we can parse
packet with vnet header.
usage: colo secondary: -object filter-redirector,id=f1,netdev=hn0,queue=tx,indev=red0
-object filter-redirector,id=f2,netdev=hn0,queue=rx,outdev=red1 -object
filter-rewriter,id=rew0,netdev=hn0,queue=all
-object
filter-dump,id=id,netdev=dev[,file=filename][,maxlen=len][,position=head|tail|id=<id>][,insert=behind|before]
Dump the network traffic on netdev dev to the file specified by filename. At most len bytes
(64k by default) per packet are stored. The file format is libpcap, so it can be analyzed
with tools such as tcpdump or Wireshark.
-object
colo-compare,id=id,primary_in=chardevid,secondary_in=chardevid,outdev=chardevid,iothread=id[,vnet_hdr_support][,notify_dev=id][,compare_timeout=@var{ms}][,expired_scan_cycle=@var{ms}][,max_queue_size=@var{size}]
Colo-compare gets packet from primary_in chardevid and secondary_in, then compare whether
the payload of primary packet and secondary packet are the same. If same, it will output
primary packet to out_dev, else it will notify COLO-framework to do checkpoint and send
primary packet to out_dev. In order to improve efficiency, we need to put the task of
comparison in another iothread. If it has the vnet_hdr_support flag, colo compare will
send/recv packet with vnet_hdr_len. The compare_timeout=@var{ms} determines the maximum
time of the colo-compare hold the packet. The expired_scan_cycle=@var{ms} is to set the
period of scanning expired primary node network packets. The max_queue_size=@var{size} is
to set the max compare queue size depend on user environment. If user want to use Xen
COLO, need to add the notify_dev to notify Xen colo-frame to do checkpoint.
COLO-compare must be used with the help of filter-mirror, filter-redirector and
filter-rewriter.
KVM COLO
primary:
-netdev tap,id=hn0,vhost=off
-device e1000,id=e0,netdev=hn0,mac=52:a4:00:12:78:66
-chardev socket,id=mirror0,host=3.3.3.3,port=9003,server=on,wait=off
-chardev socket,id=compare1,host=3.3.3.3,port=9004,server=on,wait=off
-chardev socket,id=compare0,host=3.3.3.3,port=9001,server=on,wait=off
-chardev socket,id=compare0-0,host=3.3.3.3,port=9001
-chardev socket,id=compare_out,host=3.3.3.3,port=9005,server=on,wait=off
-chardev socket,id=compare_out0,host=3.3.3.3,port=9005
-object iothread,id=iothread1
-object filter-mirror,id=m0,netdev=hn0,queue=tx,outdev=mirror0
-object filter-redirector,netdev=hn0,id=redire0,queue=rx,indev=compare_out
-object filter-redirector,netdev=hn0,id=redire1,queue=rx,outdev=compare0
-object colo-compare,id=comp0,primary_in=compare0-0,secondary_in=compare1,outdev=compare_out0,iothread=iothread1
secondary:
-netdev tap,id=hn0,vhost=off
-device e1000,netdev=hn0,mac=52:a4:00:12:78:66
-chardev socket,id=red0,host=3.3.3.3,port=9003
-chardev socket,id=red1,host=3.3.3.3,port=9004
-object filter-redirector,id=f1,netdev=hn0,queue=tx,indev=red0
-object filter-redirector,id=f2,netdev=hn0,queue=rx,outdev=red1
Xen COLO
primary:
-netdev tap,id=hn0,vhost=off
-device e1000,id=e0,netdev=hn0,mac=52:a4:00:12:78:66
-chardev socket,id=mirror0,host=3.3.3.3,port=9003,server=on,wait=off
-chardev socket,id=compare1,host=3.3.3.3,port=9004,server=on,wait=off
-chardev socket,id=compare0,host=3.3.3.3,port=9001,server=on,wait=off
-chardev socket,id=compare0-0,host=3.3.3.3,port=9001
-chardev socket,id=compare_out,host=3.3.3.3,port=9005,server=on,wait=off
-chardev socket,id=compare_out0,host=3.3.3.3,port=9005
-chardev socket,id=notify_way,host=3.3.3.3,port=9009,server=on,wait=off
-object filter-mirror,id=m0,netdev=hn0,queue=tx,outdev=mirror0
-object filter-redirector,netdev=hn0,id=redire0,queue=rx,indev=compare_out
-object filter-redirector,netdev=hn0,id=redire1,queue=rx,outdev=compare0
-object iothread,id=iothread1
-object colo-compare,id=comp0,primary_in=compare0-0,secondary_in=compare1,outdev=compare_out0,notify_dev=notify_way,iothread=iothread1
secondary:
-netdev tap,id=hn0,vhost=off
-device e1000,netdev=hn0,mac=52:a4:00:12:78:66
-chardev socket,id=red0,host=3.3.3.3,port=9003
-chardev socket,id=red1,host=3.3.3.3,port=9004
-object filter-redirector,id=f1,netdev=hn0,queue=tx,indev=red0
-object filter-redirector,id=f2,netdev=hn0,queue=rx,outdev=red1
If you want to know the detail of above command line, you can read the colo-compare git
log.
-object cryptodev-backend-builtin,id=id[,queues=queues]
Creates a cryptodev backend which executes crypto operations from the QEMU cipher APIs. The
id parameter is a unique ID that will be used to reference this cryptodev backend from the
virtio-crypto device. The queues parameter is optional, which specify the queue number of
cryptodev backend, the default of queues is 1.
# qemu-system-x86_64 \
[...] \
-object cryptodev-backend-builtin,id=cryptodev0 \
-device virtio-crypto-pci,id=crypto0,cryptodev=cryptodev0 \
[...]
-object cryptodev-vhost-user,id=id,chardev=chardevid[,queues=queues]
Creates a vhost-user cryptodev backend, backed by a chardev chardevid. The id parameter is
a unique ID that will be used to reference this cryptodev backend from the virtio-crypto
device. The chardev should be a unix domain socket backed one. The vhost-user uses a
specifically defined protocol to pass vhost ioctl replacement messages to an application on
the other end of the socket. The queues parameter is optional, which specify the queue
number of cryptodev backend for multiqueue vhost-user, the default of queues is 1.
# qemu-system-x86_64 \
[...] \
-chardev socket,id=chardev0,path=/path/to/socket \
-object cryptodev-vhost-user,id=cryptodev0,chardev=chardev0 \
-device virtio-crypto-pci,id=crypto0,cryptodev=cryptodev0 \
[...]
-object secret,id=id,data=string,format=raw|base64[,keyid=secretid,iv=string]
-object secret,id=id,file=filename,format=raw|base64[,keyid=secretid,iv=string]
Defines a secret to store a password, encryption key, or some other sensitive data. The
sensitive data can either be passed directly via the data parameter, or indirectly via the
file parameter. Using the data parameter is insecure unless the sensitive data is
encrypted.
The sensitive data can be provided in raw format (the default), or base64. When encoded as
JSON, the raw format only supports valid UTF-8 characters, so base64 is recommended for
sending binary data. QEMU will convert from which ever format is provided to the format it
needs internally. eg, an RBD password can be provided in raw format, even though it will be
base64 encoded when passed onto the RBD sever.
For added protection, it is possible to encrypt the data associated with a secret using the
AES-256-CBC cipher. Use of encryption is indicated by providing the keyid and iv
parameters. The keyid parameter provides the ID of a previously defined secret that
contains the AES-256 decryption key. This key should be 32-bytes long and be base64
encoded. The iv parameter provides the random initialization vector used for encryption of
this particular secret and should be a base64 encrypted string of the 16-byte IV.
The simplest (insecure) usage is to provide the secret inline
# qemu-system-x86_64 -object secret,id=sec0,data=letmein,format=raw
The simplest secure usage is to provide the secret via a file
# printf "letmein" > mypasswd.txt # QEMU_SYSTEM_MACRO -object
secret,id=sec0,file=mypasswd.txt,format=raw
For greater security, AES-256-CBC should be used. To illustrate usage, consider the openssl
command line tool which can encrypt the data. Note that when encrypting, the plaintext must
be padded to the cipher block size (32 bytes) using the standard PKCS#5/6 compatible
padding algorithm.
First a master key needs to be created in base64 encoding:
# openssl rand -base64 32 > key.b64
# KEY=$(base64 -d key.b64 | hexdump -v -e '/1 "%02X"')
Each secret to be encrypted needs to have a random initialization vector generated. These
do not need to be kept secret
# openssl rand -base64 16 > iv.b64
# IV=$(base64 -d iv.b64 | hexdump -v -e '/1 "%02X"')
The secret to be defined can now be encrypted, in this case we're telling openssl to base64
encode the result, but it could be left as raw bytes if desired.
# SECRET=$(printf "letmein" |
openssl enc -aes-256-cbc -a -K $KEY -iv $IV)
When launching QEMU, create a master secret pointing to key.b64 and specify that to be used
to decrypt the user password. Pass the contents of iv.b64 to the second secret
# qemu-system-x86_64 \
-object secret,id=secmaster0,format=base64,file=key.b64 \
-object secret,id=sec0,keyid=secmaster0,format=base64,\
data=$SECRET,iv=$(<iv.b64)
-object
sev-guest,id=id,cbitpos=cbitpos,reduced-phys-bits=val,[sev-device=string,policy=policy,handle=handle,dh-cert-file=file,session-file=file,kernel-hashes=on|off]
Create a Secure Encrypted Virtualization (SEV) guest object, which can be used to provide
the guest memory encryption support on AMD processors.
When memory encryption is enabled, one of the physical address bit (aka the C-bit) is
utilized to mark if a memory page is protected. The cbitpos is used to provide the C-bit
position. The C-bit position is Host family dependent hence user must provide this value.
On EPYC, the value should be 47.
When memory encryption is enabled, we loose certain bits in physical address space. The
reduced-phys-bits is used to provide the number of bits we loose in physical address space.
Similar to C-bit, the value is Host family dependent. On EPYC, a guest will lose a maximum
of 1 bit, so the value should be 1.
The sev-device provides the device file to use for communicating with the SEV firmware
running inside AMD Secure Processor. The default device is '/dev/sev'. If hardware supports
memory encryption then /dev/sev devices are created by CCP driver.
The policy provides the guest policy to be enforced by the SEV firmware and restrict what
configuration and operational commands can be performed on this guest by the hypervisor.
The policy should be provided by the guest owner and is bound to the guest and cannot be
changed throughout the lifetime of the guest. The default is 0.
If guest policy allows sharing the key with another SEV guest then handle can be use to
provide handle of the guest from which to share the key.
The dh-cert-file and session-file provides the guest owner's Public Diffie-Hillman key
defined in SEV spec. The PDH and session parameters are used for establishing a
cryptographic session with the guest owner to negotiate keys used for attestation. The file
must be encoded in base64.
The kernel-hashes adds the hashes of given kernel/initrd/ cmdline to a designated guest
firmware page for measured Linux boot with -kernel. The default is off. (Since 6.2)
e.g to launch a SEV guest
# qemu-system-x86_64 \
...... \
-object sev-guest,id=sev0,cbitpos=47,reduced-phys-bits=1 \
-machine ...,memory-encryption=sev0 \
.....
-object authz-simple,id=id,identity=string
Create an authorization object that will control access to network services.
The identity parameter is identifies the user and its format depends on the network service
that authorization object is associated with. For authorizing based on TLS x509
certificates, the identity must be the x509 distinguished name. Note that care must be
taken to escape any commas in the distinguished name.
An example authorization object to validate a x509 distinguished name would look like:
# qemu-system-x86_64 \
... \
-object 'authz-simple,id=auth0,identity=CN=laptop.example.com,,O=Example Org,,L=London,,ST=London,,C=GB' \
...
Note the use of quotes due to the x509 distinguished name containing whitespace, and
escaping of ','.
-object authz-listfile,id=id,filename=path,refresh=on|off
Create an authorization object that will control access to network services.
The filename parameter is the fully qualified path to a file containing the access control
list rules in JSON format.
An example set of rules that match against SASL usernames might look like:
{
"rules": [
{ "match": "fred", "policy": "allow", "format": "exact" },
{ "match": "bob", "policy": "allow", "format": "exact" },
{ "match": "danb", "policy": "deny", "format": "glob" },
{ "match": "dan*", "policy": "allow", "format": "exact" },
],
"policy": "deny"
}
When checking access the object will iterate over all the rules and the first rule to match
will have its policy value returned as the result. If no rules match, then the default
policy value is returned.
The rules can either be an exact string match, or they can use the simple UNIX glob pattern
matching to allow wildcards to be used.
If refresh is set to true the file will be monitored and automatically reloaded whenever
its content changes.
As with the authz-simple object, the format of the identity strings being matched depends
on the network service, but is usually a TLS x509 distinguished name, or a SASL username.
An example authorization object to validate a SASL username would look like:
# qemu-system-x86_64 \
... \
-object authz-simple,id=auth0,filename=/etc/qemu/vnc-sasl.acl,refresh=on \
...
-object authz-pam,id=id,service=string
Create an authorization object that will control access to network services.
The service parameter provides the name of a PAM service to use for authorization. It
requires that a file /etc/pam.d/service exist to provide the configuration for the account
subsystem.
An example authorization object to validate a TLS x509 distinguished name would look like:
# qemu-system-x86_64 \
... \
-object authz-pam,id=auth0,service=qemu-vnc \
...
There would then be a corresponding config file for PAM at /etc/pam.d/qemu-vnc that
contains:
account requisite pam_listfile.so item=user sense=allow \
file=/etc/qemu/vnc.allow
Finally the /etc/qemu/vnc.allow file would contain the list of x509 distinguished names
that are permitted access
CN=laptop.example.com,O=Example Home,L=London,ST=London,C=GB
-object
iothread,id=id,poll-max-ns=poll-max-ns,poll-grow=poll-grow,poll-shrink=poll-shrink,aio-max-batch=aio-max-batch
Creates a dedicated event loop thread that devices can be assigned to. This is known as an
IOThread. By default device emulation happens in vCPU threads or the main event loop
thread. This can become a scalability bottleneck. IOThreads allow device emulation and I/O
to run on other host CPUs.
The id parameter is a unique ID that will be used to reference this IOThread from -device
...,iothread=id. Multiple devices can be assigned to an IOThread. Note that not all
devices support an iothread parameter.
The query-iothreads QMP command lists IOThreads and reports their thread IDs so that the
user can configure host CPU pinning/affinity.
IOThreads use an adaptive polling algorithm to reduce event loop latency. Instead of
entering a blocking system call to monitor file descriptors and then pay the cost of being
woken up when an event occurs, the polling algorithm spins waiting for events for a short
time. The algorithm's default parameters are suitable for many cases but can be adjusted
based on knowledge of the workload and/or host device latency.
The poll-max-ns parameter is the maximum number of nanoseconds to busy wait for events.
Polling can be disabled by setting this value to 0.
The poll-grow parameter is the multiplier used to increase the polling time when the
algorithm detects it is missing events due to not polling long enough.
The poll-shrink parameter is the divisor used to decrease the polling time when the
algorithm detects it is spending too long polling without encountering events.
The aio-max-batch parameter is the maximum number of requests in a batch for the AIO
engine, 0 means that the engine will use its default.
The IOThread parameters can be modified at run-time using the qom-set command (where
iothread1 is the IOThread's id):
(qemu) qom-set /objects/iothread1 poll-max-ns 100000
During the graphical emulation, you can use special key combinations from the following table to change
modes. By default the modifier is Ctrl-Alt (used in the table below) which can be changed with -display
suboption mod= where appropriate. For example, -display sdl, grab-mod=lshift-lctrl-lalt changes the
modifier key to Ctrl-Alt-Shift, while -display sdl,grab-mod=rctrl changes it to the right Ctrl key.
Ctrl-Alt-f
Toggle full screen
Ctrl-Alt-+
Enlarge the screen
Ctrl-Alt--
Shrink the screen
Ctrl-Alt-u
Restore the screen's un-scaled dimensions
Ctrl-Alt-n
Switch to virtual console 'n'. Standard console mappings are:
1 Target system display
2 Monitor
3 Serial port
Ctrl-Alt-g
Toggle mouse and keyboard grab.
In the virtual consoles, you can use Ctrl-Up, Ctrl-Down, Ctrl-PageUp and Ctrl-PageDown to move in the
back log.
During emulation, if you are using a character backend multiplexer (which is the default if you are using
-nographic) then several commands are available via an escape sequence. These key sequences all start
with an escape character, which is Ctrl-a by default, but can be changed with -echr. The list below
assumes you're using the default.
Ctrl-a h
Print this help
Ctrl-a x
Exit emulator
Ctrl-a s
Save disk data back to file (if -snapshot)
Ctrl-a t
Toggle console timestamps
Ctrl-a b
Send break (magic sysrq in Linux)
Ctrl-a c
Rotate between the frontends connected to the multiplexer (usually this switches between the
monitor and the console)
Ctrl-a Ctrl-a
Send the escape character to the frontend
NOTES
In addition to using normal file images for the emulated storage devices, QEMU can also use networked
resources such as iSCSI devices. These are specified using a special URL syntax.
iSCSI iSCSI support allows QEMU to access iSCSI resources directly and use as images for the guest
storage. Both disk and cdrom images are supported.
Syntax for specifying iSCSI LUNs is "iscsi://<target-ip>[:<port>]/<target-iqn>/<lun>"
By default qemu will use the iSCSI initiator-name 'iqn.2008-11.org.linux-kvm[:<name>]' but this
can also be set from the command line or a configuration file.
Since version QEMU 2.4 it is possible to specify a iSCSI request timeout to detect stalled
requests and force a reestablishment of the session. The timeout is specified in seconds. The
default is 0 which means no timeout. Libiscsi 1.15.0 or greater is required for this feature.
Example (without authentication):
qemu-system-x86_64 -iscsi initiator-name=iqn.2001-04.com.example:my-initiator \
-cdrom iscsi://192.0.2.1/iqn.2001-04.com.example/2 \
-drive file=iscsi://192.0.2.1/iqn.2001-04.com.example/1
Example (CHAP username/password via URL):
qemu-system-x86_64 -drive file=iscsi://user%password@192.0.2.1/iqn.2001-04.com.example/1
Example (CHAP username/password via environment variables):
LIBISCSI_CHAP_USERNAME="user" \
LIBISCSI_CHAP_PASSWORD="password" \
qemu-system-x86_64 -drive file=iscsi://192.0.2.1/iqn.2001-04.com.example/1
NBD QEMU supports NBD (Network Block Devices) both using TCP protocol as well as Unix Domain Sockets.
With TCP, the default port is 10809.
Syntax for specifying a NBD device using TCP, in preferred URI form:
"nbd://<server-ip>[:<port>]/[<export>]"
Syntax for specifying a NBD device using Unix Domain Sockets; remember that '?' is a shell glob
character and may need quoting: "nbd+unix:///[<export>]?socket=<domain-socket>"
Older syntax that is also recognized: "nbd:<server-ip>:<port>[:exportname=<export>]"
Syntax for specifying a NBD device using Unix Domain Sockets
"nbd:unix:<domain-socket>[:exportname=<export>]"
Example for TCP
qemu-system-x86_64 --drive file=nbd:192.0.2.1:30000
Example for Unix Domain Sockets
qemu-system-x86_64 --drive file=nbd:unix:/tmp/nbd-socket
SSH QEMU supports SSH (Secure Shell) access to remote disks.
Examples:
qemu-system-x86_64 -drive file=ssh://user@host/path/to/disk.img
qemu-system-x86_64 -drive file.driver=ssh,file.user=user,file.host=host,file.port=22,file.path=/path/to/disk.img
Currently authentication must be done using ssh-agent. Other authentication methods may be
supported in future.
GlusterFS
GlusterFS is a user space distributed file system. QEMU supports the use of GlusterFS volumes for
hosting VM disk images using TCP, 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
See also http://www.gluster.org.
HTTP/HTTPS/FTP/FTPS
QEMU supports read-only access to files accessed over http(s) and ftp(s).
Syntax using a single filename:
<protocol>://[<username>[:<password>]@]<host>/<path>
where:
protocol
'http', 'https', 'ftp', or 'ftps'.
username
Optional username for authentication to the remote server.
password
Optional password for authentication to the remote server.
host Address of the remote server.
path Path on the remote server, including any query string.
The following options are also supported:
url The full URL when passing options to the driver explicitly.
readahead
The amount of data to read ahead with each range request to the remote server. This value
may optionally have the suffix 'T', 'G', 'M', 'K', 'k' or 'b'. If it does not have a
suffix, it will be assumed to be in bytes. The value must be a multiple of 512 bytes. It
defaults to 256k.
sslverify
Whether to verify the remote server's certificate when connecting over SSL. It can have the
value 'on' or 'off'. It defaults to 'on'.
cookie Send this cookie (it can also be a list of cookies separated by ';') with each outgoing
request. Only supported when using protocols such as HTTP which support cookies, otherwise
ignored.
timeout
Set the timeout in seconds of the CURL connection. This timeout is the time that CURL waits
for a response from the remote server to get the size of the image to be downloaded. If not
set, the default timeout of 5 seconds is used.
Note that when passing options to qemu explicitly, driver is the value of <protocol>.
Example: boot from a remote Fedora 20 live ISO image
qemu-system-x86_64 --drive media=cdrom,file=https://archives.fedoraproject.org/pub/archive/fedora/linux/releases/20/Live/x86_64/Fedora-Live-Desktop-x86_64-20-1.iso,readonly
qemu-system-x86_64 --drive media=cdrom,file.driver=http,file.url=http://archives.fedoraproject.org/pub/fedora/linux/releases/20/Live/x86_64/Fedora-Live-Desktop-x86_64-20-1.iso,readonly
Example: boot from a remote Fedora 20 cloud image using a local overlay for writes, copy-on-read,
and a readahead of 64k
qemu-img create -f qcow2 -o backing_file='json:{"file.driver":"http",, "file.url":"http://archives.fedoraproject.org/pub/archive/fedora/linux/releases/20/Images/x86_64/Fedora-x86_64-20-20131211.1-sda.qcow2",, "file.readahead":"64k"}' /tmp/Fedora-x86_64-20-20131211.1-sda.qcow2
qemu-system-x86_64 -drive file=/tmp/Fedora-x86_64-20-20131211.1-sda.qcow2,copy-on-read=on
Example: boot from an image stored on a VMware vSphere server with a self-signed certificate using
a local overlay for writes, a readahead of 64k and a timeout of 10 seconds.
qemu-img create -f qcow2 -o backing_file='json:{"file.driver":"https",, "file.url":"https://user:password@vsphere.example.com/folder/test/test-flat.vmdk?dcPath=Datacenter&dsName=datastore1",, "file.sslverify":"off",, "file.readahead":"64k",, "file.timeout":10}' /tmp/test.qcow2
qemu-system-x86_64 -drive file=/tmp/test.qcow2
SEE ALSO
The HTML documentation of QEMU for more precise information and Linux user mode emulator invocation.
AUTHOR
Fabrice Bellard
COPYRIGHT
2025, The QEMU Project Developers