QEMU User Documentation — QEMU documentation
QEMU User Documentation
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QEMU User Documentation
Synopsis
qemu-system-x86_64 [options] [disk_image]
Description
The QEMU PC System emulator simulates the following peripherals:
i440FX host PCI bridge and PIIX3 PCI to ISA bridge
Cirrus CLGD 5446 PCI VGA card or dummy VGA card with Bochs VESA
extensions (hardware level, including all non standard modes).
PS/2 mouse and keyboard
2 PCI IDE interfaces with hard disk and CD-ROM support
Floppy disk
PCI and ISA network adapters
Serial ports
IPMI BMC, either and internal or external one
Creative SoundBlaster 16 sound card
ENSONIQ AudioPCI ES1370 sound card
Intel 82801AA AC97 Audio compatible sound card
Intel HD Audio Controller and HDA codec
Adlib (OPL2) - Yamaha YM3812 compatible chip
Gravis Ultrasound GF1 sound card
CS4231A compatible sound card
PC speaker
PCI UHCI, OHCI, EHCI or XHCI USB controller and a virtual USB-1.1
hub.
SMP is supported with a large number of virtual CPUs (upper limit is
configuration dependent).
QEMU uses the PC BIOS from the Seabios project and the Plex86/Bochs LGPL
VGA BIOS.
QEMU uses YM3812 emulation by Tatsuyuki Satoh.
QEMU uses GUS emulation (GUSEMU32
) 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
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, nitro, nvmm, whpx, mshv or tcg can be
available. By default, tcg is used. If there is more than one
accelerator specified, the next one is used if the previous one
fails to initialize.
vmport=on|off|auto
Enables emulation of VMWare IO port, for vmmouse etc. auto says
to select the value based on accel and i8042. For accel=xen or
i8042=off the default is off otherwise the default is on.
dump-guest-core=on|off
Include guest memory in a core dump. The default is on.
mem-merge=on|off
Enables or disables memory merge support. This feature, when
supported by the host, de-duplicates identical memory pages
among VMs instances (enabled by default).
aes-key-wrap=on|off
Enables or disables AES key wrapping support on s390-ccw hosts.
This feature controls whether AES wrapping keys will be created
to allow execution of AES cryptographic functions. The default
is on.
dea-key-wrap=on|off
Enables or disables DEA key wrapping support on s390-ccw hosts.
This feature controls whether DEA wrapping keys will be created
to allow execution of DEA cryptographic functions. The default
is on.
nvdimm=on|off
Enables or disables NVDIMM support. The default is off.
memory-encryption=
Memory encryption object to use. The default is none.
hmat=on|off
Enables or disables ACPI Heterogeneous Memory Attribute Table
(HMAT) support. The default is off.
spcr=on|off
Enables or disables ACPI Serial Port Console Redirection Table
(SPCR) support. The default is on.
aux-ram-share=on|off
Allocate auxiliary guest RAM as an anonymous file that is
shareable with an external process. This option applies to
memory allocated as a side effect of creating various devices.
It does not apply to memory-backend-objects, whether explicitly
specified on the command line, or implicitly created by the -m
command line option. The default is off.
To use the cpr-transfer migration mode, you must set aux-ram-share=on.
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
512
mem
path
=/
hugetlbfs
prealloc
on
share
on
machine
memory
backend
pc
ram
512
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
512
use
canonical
path
for
ramblock
id
off
machine
memory
backend
pc
ram
512
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
128
cxl
fmw
.0
interleave
granularity
512
sgx-epc.0.memdev=
Define an SGX EPC section.
smp-cache.0.cache=cachename,smp-cache.0.topology=topologylevel
Define cache properties for SMP system.
cache=cachename
specifies the cache that the properties will be
applied on. This field is the combination of cache level and cache
type. It supports
l1d
(L1 data cache),
l1i
(L1 instruction
cache),
l2
(L2 unified cache) and
l3
(L3 unified cache).
topology=topologylevel
sets the cache topology level. It accepts
CPU topology levels including
core
module
cluster
die
socket
book
drawer
and a special value
default
. If
default
is set, then the cache topology will follow the architecture’s
default cache topology model. If another topology level is set, the cache
will be shared at corresponding CPU topology level. For example,
topology=core
makes the cache shared by all threads within a core.
The omitting cache will default to using the
default
level.
The default cache topology model for an i386 PC machine is as follows:
l1d
l1i
, and
l2
caches are per
core
, while the
l3
cache is per
die
Example:
machine
smp
cache
.0
cache
l1d
smp
cache
.0
topology
core
smp
cache
.1
cache
l1i
smp
cache
.1
topology
core
-M
as -machine.
-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, nitro, nvmm, whpx, mshv 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
1GiB/2MiB/4KiB, 32MiB/16KiB and 512MiB/64KiB for 4KiB/16KiB/64KiB
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
hyperv=on|off|auto
For the WHPX backend, determines whether to enable Hyper-V enlightenments.
On x86_64, Hyper-V enlightenments are on by default. On AArch64, they’re off
by default.
-smp
[[cpus=]n][,maxcpus=maxcpus][,drawers=drawers][,books=books][,sockets=sockets][,dies=dies][,clusters=clusters][,modules=modules][,cores=cores][,threads=threads]
Simulate a SMP system with ‘
‘ 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
sockets
cores
threads
maxcpus
The following sub-option defines a CPU topology hierarchy (2 sockets
totally on the machine, 2 dies per socket, 2 modules per die, 2 cores per
module, 2 threads per core) for PC machines which support sockets/dies
/modules/cores/threads. Some members of the option can be omitted but
their values will be automatically computed:
smp
32
sockets
dies
modules
cores
threads
maxcpus
32
The following sub-option defines a CPU topology hierarchy (2 sockets
totally on the machine, 2 clusters per socket, 2 cores per cluster,
2 threads per core) for ARM virt machines which support sockets/clusters
/cores/threads. Some members of the option can be omitted but their values
will be automatically computed:
smp
16
sockets
clusters
cores
threads
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
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
cpus
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:
pc
smp
sockets
maxcpus
numa
node
nodeid
numa
node
nodeid
numa
cpu
node
id
socket
id
numa
cpu
node
id
socket
id
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
slots
maxmem
object
memory
backend
ram
size
id
m0
object
memory
backend
ram
size
id
m1
numa
node
nodeid
memdev
m0
numa
node
nodeid
memdev
m1
initiator
smp
sockets
maxcpus
numa
cpu
node
id
socket
id
numa
cpu
node
id
socket
id
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 MiB/s, GiB/s or TiB/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 MiB/s; The processors in NUMA node 0 access
memory in NUMA node 1 with access-latency 10 nanoseconds,
access-bandwidth is 100 MiB/s. And for memory side cache information,
NUMA node 0 and 1 both have 1 level memory cache, size is 10KiB,
policy is write-back, the cache Line size is 8 bytes:
machine
hmat
on
object
memory
backend
ram
size
id
m0
object
memory
backend
ram
size
id
m1
smp
sockets
maxcpus
numa
node
nodeid
memdev
m0
numa
node
nodeid
memdev
m1
initiator
numa
cpu
node
id
socket
id
numa
cpu
node
id
socket
id
numa
hmat
lb
initiator
target
hierarchy
memory
data
type
access
latency
latency
numa
hmat
lb
initiator
target
hierarchy
memory
data
type
access
bandwidth
bandwidth
200
numa
hmat
lb
initiator
target
hierarchy
memory
data
type
access
latency
latency
10
numa
hmat
lb
initiator
target
hierarchy
memory
data
type
access
bandwidth
bandwidth
100
numa
hmat
cache
node
id
size
10
level
associativity
direct
policy
write
back
line
numa
hmat
cache
node
id
size
10
level
associativity
direct
policy
write
back
line
-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 1GiB, creates 3 slots to hotplug additional memory and sets
the maximum memory the guest can reach to 4GiB:
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.
If no audio backend is specified, QEMU will attempt to select a
default one. The
-display
option may influence which backend is
selected.
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
# 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 off.
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
dbus,id=id[,prop=value[,...]]
Creates a D-Bus backend. It must be associated with the display
(as
-display
dbus,audiodev=id
). (Since 7.0)
D-Bus specific options are:
nsamples
Number of samples per read/write (default to 480, 10ms at 48kHz)
(Since 10.0)
-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|off
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.
lan.channel=val
channel number of the fake LAN channel. It can be 0 or any
integer from 0x1 to 0xb inclusive. If set to 0, the LAN channel
is disabled, otherwise the LAN channel is enabled at the
specified channel number. The default is 0.
lan.ipaddr=addr
the ipv4 address of the BMC LAN channel.
lan.ipsrc=val
the ipv4 address source of the BMC LAN channel. It can be 0
(unspecified source), 1 (static address), 2 (DHCP), 3 (BIOS or
system software), or 4 (other source). The default is 0.
lan.macaddr=mac
the mac address of the BMC LAN channel.
lan.netmask=mask
the ipv4 subnet mask for the BMC LAN channel.
lan.defgw_ipaddr=addr
the default gateway ipv4 address for the BMC LAN channel.
lan.defgw_macaddr=mac
the default gateway mac address for the BMC LAN channel.
-device
ipmi-bmc-extern,id=id,chardev=id[,slave_addr=val]
Add a connection to an external IPMI BMC simulator. Instead of
locally emulating the BMC like the above item, instead connect to an
external entity that provides the IPMI services.
A connection is made to an external BMC simulator. If you do this,
it is strongly recommended that you use the “reconnect-ms=” chardev
option to reconnect to the simulator if the connection is lost. Note
that if this is not used carefully, it can be a security issue, as
the interface has the ability to send resets, NMIs, and power off
the VM. It’s best if QEMU makes a connection to an external
simulator running on a secure port on localhost, so neither the
simulator nor QEMU is exposed to any outside network.
See the “lanserv/README.vm” file in the OpenIPMI library for more
details on the external interface.
-device
isa-ipmi-kcs,bmc=id[,ioport=val][,irq=val]
Add a KCS IPMI interface on the ISA bus. This also adds a
corresponding ACPI and SMBIOS entries, if appropriate.
bmc=id
The BMC to connect to, one of ipmi-bmc-sim or ipmi-bmc-extern
above.
ioport=val
Define the I/O address of the interface. The default is 0xca0
for KCS.
irq=val
Define the interrupt to use. The default is 5. To disable
interrupts, set this to 0.
-device
isa-ipmi-bt,bmc=id[,ioport=val][,irq=val]
Like the KCS interface, but defines a BT interface. The default port
is 0xe4 and the default interrupt is 5.
-device
pci-ipmi-kcs,bmc=id
Add a KCS IPMI interface on the PCI bus.
bmc=id
The BMC to connect to, one of ipmi-bmc-sim or ipmi-bmc-extern above.
-device
pci-ipmi-bt,bmc=id
Like the KCS interface, but defines a BT interface on the PCI bus.
-device
intel-iommu[,option=...]
This is only supported by
-machine
q35
, which will enable Intel VT-d
emulation within the guest. It supports below options:
intremap=on|off
(default: auto)
This enables interrupt remapping feature. It’s required to enable
complete x2apic. Currently it only supports kvm kernel-irqchip modes
off
or
split
, while full kernel-irqchip is not yet supported.
The default value is “auto”, which will be decided by the mode of
kernel-irqchip.
caching-mode=on|off
(default: off)
This enables caching mode for the VT-d emulated device. When
caching-mode is enabled, each guest DMA buffer mapping will generate an
IOTLB invalidation from the guest IOMMU driver to the vIOMMU device in
a synchronous way. It is required for
-device
vfio-pci
to work
with the VT-d device, because host assigned devices requires to setup
the DMA mapping on the host before guest DMA starts.
device-iotlb=on|off
(default: off)
This enables device-iotlb capability for the emulated VT-d device. So
far virtio/vhost should be the only real user for this parameter,
paired with ats=on configured for the device.
aw-bits=39|48
(default: 39)
This decides the address width of IOVA address space. The address
space has 39 bits width for 3-level IOMMU page tables, and 48 bits for
4-level IOMMU page tables.
Please also refer to the wiki page for general scenarios of VT-d
emulation in QEMU:
-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.
-device
arm-smmuv3,primary-bus=id[,option=...]
This is only supported by
-machine
virt
(ARM).
primary-bus=id
Accepts either the default root complex (pcie.0) or a
pxb-pcie based root complex.
accel=on|off
(default: off)
Enables guest to leverage host SMMUv3 features for acceleration.
Enabling accel configures the host SMMUv3 in nested mode to support
vfio-pci passthrough.
The following options are available when accel=on.
Note: ‘auto’ mode is not currently supported.
ril=on|off
(default: on)
Support for Range Invalidation, which allows the SMMUv3 driver to
invalidate TLB entries for a range of IOVAs at once instead of issuing
separate commands to invalidate each page. Must match with host SMMUv3
Range Invalidation support.
ats=on|off
(default: off)
Support for Address Translation Services, which enables PCIe devices to
cache address translations in their local TLB and reduce latency. Host
SMMUv3 must support ATS in order to enable this feature for the vIOMMU.
oas=val
(supported values are 44 and 48. default: 44)
Sets the Output Address Size in bits. The value set here must be less
than or equal to the host SMMUv3’s supported OAS, so that the
intermediate physical addresses (IPA) consumed by host SMMU for stage-2
translation do not exceed the host’s max supported IPA size.
ssidsize=val
(val between 0 and 20. default: 0)
Sets the Substream ID size in bits. When set to a non-zero value,
PASID capability is advertised to the vIOMMU and accelerated use cases
such as Shared Virtual Addressing (SVA) are supported.
-device
amd-iommu[,option=...]
Enables emulation of an AMD-Vi I/O Memory Management Unit (IOMMU).
Only available with
-machine
q35
, it supports the following options:
dma-remap=on|off
(default: off)
Support for DMA address translation and access permission checking for
guests attaching passthrough devices to paging domains, using the AMD v1
I/O Page Table format. This enables
-device
vfio-pci,...
to work
correctly with a guest using the DMA remapping feature of the vIOMMU.
intremap=on|off
(default: auto)
Generic x86 IOMMU functionality implemented by
amd-iommu
device.
Enables interrupt remapping feature in guests, which is also required to
enable x2apic support.
Currently only available with
kernel-irqchip=off|split
, it is
automatically enabled when either of those modes is in use, and disabled
with
kernel-irqchip=on
xtsup=on|off
(default: off)
Interrupt remapping table supports x2apic mode, enabling the use of
128-bit IRTE format with 32-bit destination field by the guest. Required
to support routing interrupts to vCPUs with APIC IDs larger than 0xff.
-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 MiB/s.
bps_max=bm,bps_rd_max=rm,bps_wr_max=wm
Specify bursts in bytes per second, either for all request types
or for reads or writes only. Bursts allow the guest I/O to spike
above the limit temporarily.
iops=i,iops_rd=r,iops_wr=w
Specify request rate limits in requests per second, either for
all request types or for reads or writes only.
iops_max=bm,iops_rd_max=rm,iops_wr_max=wm
Specify bursts in requests per second, either for all request
types or for reads or writes only. Bursts allow the guest I/O to
spike above the limit temporarily.
iops_size=is
Let every is bytes of a request count as a new request for iops
throttling purposes. Use this option to prevent guests from
circumventing iops limits by sending fewer but larger requests.
group=g
Join a throttling quota group with given name g. All drives that
are members of the same group are accounted for together. Use
this option to prevent guests from circumventing throttling
limits by using many small disks instead of a single larger
disk.
By default, the
cache.writeback=on
mode is used. It will report
data writes as completed as soon as the data is present in the host
page cache. This is safe as long as your guest OS makes sure to
correctly flush disk caches where needed. If your guest OS does not
handle volatile disk write caches correctly and your host crashes or
loses power, then the guest may experience data corruption.
For such guests, you should consider using
cache.writeback=off
This means that the host page cache will be used to read and write
data, but write notification will be sent to the guest only after
QEMU has made sure to flush each write to the disk. Be aware that
this has a major impact on performance.
When using the
-snapshot
option, unsafe caching is always used.
Copy-on-read avoids accessing the same backing file sectors
repeatedly and is useful when the backing file is over a slow
network. By default copy-on-read is off.
Instead of
-cdrom
you can use:
qemu-system-x86_64 -drive file=file,index=2,media=cdrom
Instead of
-hda
-hdb
-hdc
-hdd
, you can use:
qemu-system-x86_64 -drive file=file,index=0,media=disk
qemu-system-x86_64 -drive file=file,index=1,media=disk
qemu-system-x86_64 -drive file=file,index=2,media=disk
qemu-system-x86_64 -drive file=file,index=3,media=disk
You can open an image using pre-opened file descriptors from an fd
set:
qemu-system-x86_64 \
-add-fd fd=3,set=2,opaque="rdwr:/path/to/file" \
-add-fd fd=4,set=2,opaque="rdonly:/path/to/file" \
-drive file=/dev/fdset/2,index=0,media=disk
You can connect a CDROM to the slave of ide0:
qemu-system-x86_64 -drive file=file,if=ide,index=1,media=cdrom
If you don’t specify the “file=” argument, you define an empty
drive:
qemu-system-x86_64 -drive if=ide,index=1,media=cdrom
Instead of
-fda
-fdb
, you can use:
qemu-system-x86_64 -drive file=file,index=0,if=floppy
qemu-system-x86_64 -drive file=file,index=1,if=floppy
By default, interface is “ide” and index is automatically
incremented:
qemu-system-x86_64 -drive file=a -drive file=b
is interpreted like:
qemu-system-x86_64 -hda a -hdb b
-mtdblock
file
Use file as on-board Flash memory image.
-sd
file
Use file as SecureDigital card image.
-snapshot
Write to temporary files instead of disk image files. In this case,
the raw disk image you use is not written back. You can however
force the write back by pressing C-a s (see the
Disk Images
chapter in the System Emulation Users Guide).
Warning
snapshot is incompatible with
-blockdev
(instead use qemu-img
to manually create snapshot images to attach to your blockdev).
If you have mixed
-blockdev
and
-drive
declarations you
can use the ‘snapshot’ property on your drive declarations
instead of this global option.
-fsdev
local,id=id,path=path,security_model=security_model
[,writeout=writeout][,readonly=on][,fmode=fmode][,dmode=dmode]
[,throttling.option=value[,throttling.option=value[,...]]]
-fsdev
synth,id=id[,readonly=on]
Define a new file system device. Valid options are:
local
Accesses to the filesystem are done by QEMU.
synth
Synthetic filesystem, only used by QTests.
id=id
Specifies identifier for this device.
path=path
Specifies the export path for the file system device. Files
under this path will be available to the 9p client on the guest.
security_model=security_model
Specifies the security model to be used for this export path.
Supported security models are “passthrough”, “mapped-xattr”,
“mapped-file” and “none”. In “passthrough” security model, files
are stored using the same credentials as they are created on the
guest. This requires QEMU to run as root. In “mapped-xattr”
security model, some of the file attributes like uid, gid, mode
bits and link target are stored as file attributes. For
“mapped-file” these attributes are stored in the hidden
.virtfs_metadata directory. Directories exported by this
security model cannot interact with other unix tools. “none”
security model is same as passthrough except the sever won’t
report failures if it fails to set file attributes like
ownership. Security model is mandatory only for local fsdriver.
writeout=writeout
This is an optional argument. The only supported value is
“immediate”. This means that host page cache will be used to
read and write data but write notification will be sent to the
guest only when the data has been reported as written by the
storage subsystem.
readonly=on
Enables exporting 9p share as a readonly mount for guests. By
default read-write access is given.
fmode=fmode
Specifies the default mode for newly created files on the host.
Works only with security models “mapped-xattr” and
“mapped-file”.
dmode=dmode
Specifies the default mode for newly created directories on the
host. Works only with security models “mapped-xattr” and
“mapped-file”.
throttling.bps-total=b,throttling.bps-read=r,throttling.bps-write=w
Specify bandwidth throttling limits in bytes per second, either
for all request types or for reads or writes only.
throttling.bps-total-max=bm,bps-read-max=rm,bps-write-max=wm
Specify bursts in bytes per second, either for all request types
or for reads or writes only. Bursts allow the guest I/O to spike
above the limit temporarily.
throttling.iops-total=i,throttling.iops-read=r,
throttling.iops-write=w
Specify request rate limits in requests per second, either for
all request types or for reads or writes only.
throttling.iops-total-max=im,throttling.iops-read-max=irm,
throttling.iops-write-max=iwm
Specify bursts in requests per second, either for all request
types or for reads or writes only. Bursts allow the guest I/O to
spike above the limit temporarily.
throttling.iops-size=is
Let every is bytes of a request count as a new request for iops
throttling purposes.
-fsdev option is used along with -device driver “virtio-9p-…”.
-device
virtio-9p-type,fsdev=id,mount_tag=mount_tag
Options for virtio-9p-… driver are:
type
Specifies the variant to be used. Supported values are “pci”,
“ccw” or “device”, depending on the machine type.
fsdev=id
Specifies the id value specified along with -fsdev option.
mount_tag=mount_tag
Specifies the tag name to be used by the guest to mount this
export point.
-virtfs
local,path=path,mount_tag=mount_tag
,security_model=security_model[,writeout=writeout][,readonly=on]
[,fmode=fmode][,dmode=dmode][,multidevs=multidevs]
-virtfs
synth,mount_tag=mount_tag
Define a new virtual filesystem device and expose it to the guest using
a virtio-9p-device (a.k.a. 9pfs), which essentially means that a certain
directory on host is made directly accessible by guest as a pass-through
file system by using the 9P network protocol for communication between
host and guests, if desired even accessible, shared by several guests
simultaneously.
Note that
-virtfs
is actually just a convenience shortcut for its
generalized form
-fsdev
-device
virtio-9p-pci
The general form of pass-through file system options are:
local
Accesses to the filesystem are done by QEMU.
synth
Synthetic filesystem, only used by QTests.
id=id
Specifies identifier for the filesystem device
path=path
Specifies the export path for the file system device. Files
under this path will be available to the 9p client on the guest.
security_model=security_model
Specifies the security model to be used for this export path.
Supported security models are “passthrough”, “mapped-xattr”,
“mapped-file” and “none”. In “passthrough” security model, files
are stored using the same credentials as they are created on the
guest. This requires QEMU to run as root. In “mapped-xattr”
security model, some of the file attributes like uid, gid, mode
bits and link target are stored as file attributes. For
“mapped-file” these attributes are stored in the hidden
.virtfs_metadata directory. Directories exported by this
security model cannot interact with other unix tools. “none”
security model is same as passthrough except the sever won’t
report failures if it fails to set file attributes like
ownership. Security model is mandatory only for local fsdriver.
writeout=writeout
This is an optional argument. The only supported value is
“immediate”. This means that host page cache will be used to
read and write data but write notification will be sent to the
guest only when the data has been reported as written by the
storage subsystem.
readonly=on
Enables exporting 9p share as a readonly mount for guests. By
default read-write access is given.
fmode=fmode
Specifies the default mode for newly created files on the host.
Works only with security models “mapped-xattr” and
“mapped-file”.
dmode=dmode
Specifies the default mode for newly created directories on the
host. Works only with security models “mapped-xattr” and
“mapped-file”.
mount_tag=mount_tag
Specifies the tag name to be used by the guest to mount this
export point.
multidevs=remap|forbid|warn
Specifies how to deal with multiple devices being shared with
the same 9p export in order to avoid file ID collisions on guest.
Supported behaviours are either “remap” (default), “forbid” or
“warn”.
remap
: assumes the possibility that more than one device is
shared with the same 9p export. Therefore inode numbers from host
are remapped for guest in a way that would prevent file ID
collisions on guest. Remapping inodes in such 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 severe misbehaviours on guest.
warn
: virtfs 9p expects only one device to be shared with
the same export. If however 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. No further action is performed
in this case that would prevent file ID collisions on guest. This
could thus lead to severe misbehaviours in this case like wrong
files being accessed and data corruption on the exported tree.
forbid
: assumes like “warn” that only one device is shared
by the same 9p 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. This may also influence the default
audio backend selection.
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)
If no audio backend is specified and the dbus display backend is
specified, the dbus audio backend is used by default.
The connection is registered with the “org.qemu” name (and queued when
already owned).
addr=
: 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=
: Used to select the modifier keys for toggling
the mouse grabbing in conjunction with the “g” key.
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=
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
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=
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=
Start a VNC server on 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=
Set the TCP port spice is listening on for plaintext channels.
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=
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=
Set the TCP port spice is listening on for encrypted channels.
x509-dir=
Set the x509 file directory. Expects same filenames as -vnc
$display,x509=$dir
x509-key-file=
x509-key-password=
x509-cert-file=
x509-cacert-file=
x509-dh-key-file=
The x509 file names can also be configured individually.
tls-ciphers=
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.
video-codec=
Provide the preferred codec the Spice server should use with the
Gstreamer encoder. This option is only relevant when gl=on is
specified. If no codec is provided, then the codec gstreamer:h264
would be used as default. And, for the case where gl=off, the
default codec to be used is determined by the Spice server.
max-refresh-rate=rate
Provide the maximum refresh rate (or FPS) at which the encoding
requests should be sent to the Spice server. Default would be 30.
gl=on|off
Enable/disable OpenGL context. Default is off.
rendernode=
DRM render node for OpenGL rendering. If not specified, it will
pick the first available. (Since 2.9)
-vga
type
Select type of VGA card to emulate. Valid values for type are
cirrus
Cirrus Logic GD5446 Video card. All Windows versions starting
from Windows 95 should recognize and use this graphic card. For
optimal performances, use 16 bit color depth in the guest and
the host OS. (This card was the default before QEMU 2.2)
std
Standard VGA card with Bochs VBE extensions. If your guest OS
supports the VESA 2.0 VBE extensions (e.g. Windows XP) and if
you want to use high resolution modes (>= 1280x1024x16) then you
should use this option. (This card is the default since QEMU
2.2)
vmware
VMWare SVGA-II compatible adapter. Use it if you have
sufficiently recent XFree86/XOrg server or Windows guest with a
driver for this card.
qxl
QXL paravirtual graphic card. It is VGA compatible (including
VESA 2.0 VBE support). Works best with qxl guest drivers
installed though. Recommended choice when using the spice
protocol.
tcx
(sun4m only) Sun TCX framebuffer. This is the default
framebuffer for sun4m machines and offers both 8-bit and 24-bit
colour depths at a fixed resolution of 1024x768.
cg3
(sun4m only) Sun cgthree framebuffer. This is a simple 8-bit
framebuffer for sun4m machines available in both 1024x768
(OpenBIOS) and 1152x900 (OBP) resolutions aimed at people
wishing to run older Solaris versions.
virtio
Virtio VGA card.
none
Disable VGA card.
-full-screen
Start in full screen.
-g
width
height
[x
depth
Set the initial graphical resolution and depth (PPC, SPARC only).
For PPC the default is 800x600x32.
For SPARC with the TCX graphics device, the default is 1024x768x8
with the option of 1024x768x24. For cgthree, the default is
1024x768x8 with the option of 1152x900x8 for people who wish to use
OBP.
-vnc
display[,option[,option[,...]]]
Normally, if QEMU is compiled with graphical window support, it
displays output such as guest graphics, guest console, and the QEMU
monitor in a window. With this option, you can have QEMU listen on
VNC display display and redirect the VGA display over the VNC
session. It is very useful to enable the usb tablet device when
using this option (option
-device
usb-tablet
). When using the
VNC display, you must use the
-k
parameter to set the keyboard
layout if you are not using en-us. Valid syntax for the display is
to=L
With this option, QEMU will try next available VNC displays,
until the number L, if the originally defined “-vnc display” is
not available, e.g. port 5900+display is already used by another
application. By default, to=0.
host:d
TCP connections will only be allowed from host on display d. By
convention the TCP port is 5900+d. Optionally, host can be
omitted in which case the server will accept connections from
any host.
unix:path
Connections will be allowed over UNIX domain sockets where path
is the location of a unix socket to listen for connections on.
none
VNC is initialized but not started. The monitor
change
command can be used to later start the VNC server.
Following the display value there may be one or more option flags
separated by commas. Valid options are
reverse=on|off
Connect to a listening VNC client via a “reverse” connection.
The client is specified by the display. For reverse network
connections (host:d,``reverse``), the d argument is a TCP port
number, not a display number.
websocket=on|off
Opens an additional TCP listening port dedicated to VNC
Websocket connections. If a bare websocket option is given, the
Websocket port is 5700+display. An alternative port can be
specified with the syntax
websocket
=port.
If host is specified connections will only be allowed from this
host. It is possible to control the websocket listen address
independently, using the syntax
websocket
=host:port.
Websocket could be allowed over UNIX domain socket, using the syntax
websocket
=unix:path, where path is the location of a unix socket
to listen for connections on.
If no TLS credentials are provided, the websocket connection
runs in unencrypted mode. If TLS credentials are provided, the
websocket connection requires encrypted client connections.
password=on|off
Require that password based authentication is used for client
connections.
The password must be set separately using the
set_password
command in the
QEMU Monitor
. The
syntax to change your password is:
set_password
where
either “vnc” or “spice”.
If you would like to change
should use
expire_password
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
expire.
password-secret=
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
eno1 UP 50:54:00:00:00:42
Currently, the PCI device has to be attached to the root bus.
Network options
-nic
[tap|passt|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
passt,id=str[,option][,...]
Configure a passt network backend which requires no administrator
privilege to run. Valid options are:
id=id
Assign symbolic name for use in monitor commands.
path=file
Filename of the passt program to run. If it is not provided,
passt command will be started with the help of the PATH environment
variable.
quiet=on|off
By default,
quiet=on
to disable informational message from
passt.
quiet=on
is passed as
--quiet
to passt.
vhost-user=on|off
By default,
vhost-user=off
and QEMU uses the stream network
backend to communicate with passt. If
vhost-user=on
, passt is
started with
--vhost-user
and QEMU uses the vhost-user network
backend to communicate with passt.
@mtu
Assign MTU via DHCP/NDP
address
IPv4 or IPv6 address
netmask
IPv4 mask
mac
source MAC address
gateway
IPv4 or IPv6 address as gateway
interface
Interface for addresses and routes
outbound
Bind to address as outbound source
outbound-if4
Bind to outbound interface for IPv4
outbound-if6
Bind to outbound interface for IPv6
dns
IPv4 or IPv6 address as DNS
Search domains
fqdn
FQDN to configure client with
dhcp-dns
Enable/disable DNS list in DHCP/DHCPv6/NDP
dhcp-search
Enable/disable list in DHCP/DHCPv6/NDP
map-host-loopback
Address to refer to host
map-guest-addr
Addr to translate to guest’s address
dns-forward
Forward DNS queries sent to
dns-host
Host nameserver to direct queries to
tcp
Enable/disable TCP
udp
Enable/disable UDP
icmp
Enable/disable ICMP
dhcp
Enable/disable DHCP
ndp
Enable/disable NDP
dhcpv6
Enable/disable DHCPv6
ra
Enable/disable route advertisements
freebind
Bind to any address for forwarding
ipv4
Enable/disable IPv4
ipv6
Enable/disable IPv6
tcp-ports
TCP ports to forward
udp-ports
UDP ports to forward
param=string
string
will be passed to passt as a command line parameter,
we can have multiple occurrences of the
param
parameter to
pass multiple parameters to passt.
For instance, to pass
--trace
--log=trace.log
qemu-system-x86_64 -nic passt,param=--trace,param=--log=trace.log
-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|unix]:[[hostaddr]:hostport|hostpath]-[guestaddr]:guestport
Redirect incoming TCP, UDP or UNIX 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.
To redirect host unix socket /tmp/vm to guest tcp socket 23 use
following:
# on the host
qemu-system-x86_64 -nic user,hostfwd=unix:/tmp/vm-:23
guestfwd=[tcp]:server:port-dev
guestfwd=[tcp]:server:port-cmd:command
Forward guest TCP connections to the IP address server on port
port to the character device dev or to a program executed by
cmd:command which gets spawned for each connection. This option
can be given multiple times.
You can either use a chardev directly and have that one used
throughout QEMU’s lifetime, like in the following example:
# open 10.10.1.1:4321 on bootup, connect 10.0.2.100:1234 to it whenever
# the guest accesses it
qemu-system-x86_64 -nic user,guestfwd=tcp:10.0.2.100:1234-
tcp:10.10.1.1:4321
Or you can execute a command on every TCP connection established
by the guest, so that QEMU behaves similar to an inetd process
for that virtual server:
# call "netcat 10.10.1.1 4321" on every TCP connection to 10.0.2.100:1234
# and connect the TCP stream to its stdin/stdout
qemu-system-x86_64 -nic 'user,id=n1,guestfwd=tcp:10.0.2.100:1234-cmd:netcat 10.10.1.1 4321'
-netdev
tap,id=id[,fd=h][,ifname=name][,script=file][,downscript=dfile][,br=bridge][,helper=helper]
Configure a host TAP network backend with ID id.
Use the network script file to configure it and the network script
dfile to deconfigure it. If name is not provided, the OS
automatically provides one. The default network configure script is
/etc/qemu-ifup
and the default network deconfigure script is
/etc/qemu-ifdown
. Use
script=no
or
downscript=no
to
disable script execution.
If running QEMU as an unprivileged user, use the network helper
to configure the TAP interface and attach it to the bridge.
The default network helper executable is
/path/to/qemu-bridge-helper
and the default bridge device is
br0
fd
=h can be used to specify the handle of an already opened
host TAP interface.
Examples:
#launch a QEMU instance with the default network script
qemu-system-x86_64 linux.img -nic tap
#launch a QEMU instance with two NICs, each one connected
#to a TAP device
qemu-system-x86_64 linux.img \
-netdev tap,id=nd0,ifname=tap0 -device e1000,netdev=nd0 \
-netdev tap,id=nd1,ifname=tap1 -device rtl8139,netdev=nd1
#launch a QEMU instance with the default network helper to
#connect a TAP device to bridge br0
qemu-system-x86_64 linux.img -device virtio-net-pci,netdev=n1 \
-netdev tap,id=n1,"helper=/path/to/qemu-bridge-helper"
-netdev
bridge,id=id[,br=bridge][,helper=helper]
Connect a host TAP network interface to a host bridge device.
Use the network helper helper to configure the TAP interface and
attach it to the bridge. The default network helper executable is
/path/to/qemu-bridge-helper
and the default bridge device is
br0
Examples:
#launch a QEMU instance with the default network helper to
#connect a TAP device to bridge br0
qemu-system-x86_64 linux.img -netdev bridge,id=n1 -device virtio-net,netdev=n1
#launch a QEMU instance with the default network helper to
#connect a TAP device to bridge qemubr0
qemu-system-x86_64 linux.img -netdev bridge,br=qemubr0,id=n1 -device virtio-net,netdev=n1
-netdev
socket,id=id[,fd=h][,listen=[host]:port][,connect=host:port]
This host network backend can be used to connect the guest’s network
to another QEMU virtual machine using a TCP socket connection. If
listen
is specified, QEMU waits for incoming connections on port
(host is optional).
connect
is used to connect to another QEMU
instance using the
listen
option.
fd
=h specifies an
already opened TCP socket.
Example:
# launch a first QEMU instance
qemu-system-x86_64 linux.img \
-device e1000,netdev=n1,mac=52:54:00:12:34:56 \
-netdev socket,id=n1,listen=:1234
# connect the network of this instance to the network of the first instance
qemu-system-x86_64 linux.img \
-device e1000,netdev=n2,mac=52:54:00:12:34:57 \
-netdev socket,id=n2,connect=127.0.0.1:1234
-netdev
socket,id=id[,fd=h][,mcast=maddr:port[,localaddr=addr]]
Configure a socket host network backend to share the guest’s network
traffic with another QEMU virtual machines using a UDP multicast
socket, effectively making a bus for every QEMU with same multicast
address maddr and port. NOTES:
Several QEMU can be running on different hosts and share same bus
(assuming correct multicast setup for these hosts).
mcast support is compatible with User Mode Linux (argument
ethN=mcast
), see
Use
fd=h
to specify an already opened UDP multicast socket.
Example:
# launch one QEMU instance
qemu-system-x86_64 linux.img \
-device e1000,netdev=n1,mac=52:54:00:12:34:56 \
-netdev socket,id=n1,mcast=230.0.0.1:1234
# launch another QEMU instance on same "bus"
qemu-system-x86_64 linux.img \
-device e1000,netdev=n2,mac=52:54:00:12:34:57 \
-netdev socket,id=n2,mcast=230.0.0.1:1234
# launch yet another QEMU instance on same "bus"
qemu-system-x86_64 linux.img \
-device e1000,netdev=n3,mac=52:54:00:12:34:58 \
-netdev socket,id=n3,mcast=230.0.0.1:1234
Example (User Mode Linux compat.):
# launch QEMU instance (note mcast address selected is UML's default)
qemu-system-x86_64 linux.img \
-device e1000,netdev=n1,mac=52:54:00:12:34:56 \
-netdev socket,id=n1,mcast=239.192.168.1:1102
# launch UML
/path/to/linux ubd0=/path/to/root_fs eth0=mcast
Example (send packets from host’s 1.2.3.4):
qemu-system-x86_64 linux.img \
-device e1000,netdev=n1,mac=52:54:00:12:34:56 \
-netdev socket,id=n1,mcast=239.192.168.1:1102,localaddr=1.2.3.4
-netdev
stream,id=str[,server=on|off],addr.type=inet,addr.host=host,addr.port=port[,to=maxport][,numeric=on|off][,keep-alive=on|off][,mptcp=on|off][,addr.ipv4=on|off][,addr.ipv6=on|off][,reconnect-ms=milliseconds]
Configure a network backend to connect to another QEMU virtual machine or a proxy using a TCP/IP socket.
server=on|off
if
on
create a server socket
addr.host=host,addr.port=port
socket address to listen on (server=on) or connect to (server=off)
to=maxport
if present, this is range of possible addresses, with port between
port
and
maxport
numeric=on|off
if
on
host
and
port
are guaranteed to be numeric, otherwise a name resolution should be attempted (default:
off
keep-alive=on|off
enable keep-alive when connecting to this socket. Not supported for passive sockets.
mptcp=on|off
enable multipath TCP
ipv4=on|off
whether to accept IPv4 addresses, default to try both IPv4 and IPv6
ipv6=on|off
whether to accept IPv6 addresses, default to try both IPv4 and IPv6
reconnect-ms=milliseconds
for a client socket, if a socket is disconnected, then attempt a reconnect after the given number of milliseconds.
Setting this to zero disables this function. (default: 0)
Example (two guests connected using a TCP/IP socket):
# first VM
qemu-system-x86_64 linux.img \
-device virtio-net,netdev=net0,mac=52:54:00:12:34:56 \
-netdev stream,id=net0,server=on,addr.type=inet,addr.host=localhost,addr.port=1234
# second VM
qemu-system-x86_64 linux.img \
-device virtio-net,netdev=net0,mac=52:54:00:12:34:57 \
-netdev stream,id=net0,server=off,addr.type=inet,addr.host=localhost,addr.port=1234,reconnect-ms=5000
-netdev
stream,id=str[,server=on|off],addr.type=unix,addr.path=path[,abstract=on|off][,tight=on|off][,reconnect-ms=milliseconds]
Configure a network backend to connect to another QEMU virtual machine or a proxy using a stream oriented unix domain socket.
server=on|off
if
on
create a server socket
addr.path=path
filesystem path to use
abstract=on|off
if
on
, this is a Linux abstract socket address.
tight=on|off
if false, pad an abstract socket address with enough null bytes to make it fill struct sockaddr_un member sun_path.
reconnect-ms=milliseconds
for a client socket, if a socket is disconnected, then attempt a reconnect after the given number of milliseconds.
Setting this to zero disables this function. (default: 0)
Example (using passt as a replacement of -netdev user):
# start passt server as a non privileged user
passt
UNIX domain socket bound at /tmp/passt_1.socket
# start QEMU to connect to passt
qemu-system-x86_64 linux.img \
-device virtio-net,netdev=net0 \
-netdev stream,id=net0,server=off,addr.type=unix,addr.path=/tmp/passt_1.socket
Example (two guests connected using a stream oriented unix domain socket):
# first VM
qemu-system-x86_64 linux.img \
-device virtio-net,netdev=net0,mac=52:54:00:12:34:56 \
netdev stream,id=net0,server=on,addr.type=unix,addr.path=/tmp/qemu0
# second VM
qemu-system-x86_64 linux.img \
-device virtio-net,netdev=net0,mac=52:54:00:12:34:57 \
-netdev stream,id=net0,server=off,addr.type=unix,addr.path=/tmp/qemu0,reconnect-ms=5000
-netdev
stream,id=str[,server=on|off],addr.type=fd,addr.str=file-descriptor[,reconnect-ms=milliseconds]
Configure a network backend to connect to another QEMU virtual machine or a proxy using a stream oriented socket file descriptor.
server=on|off
if
on
create a server socket
addr.str=file-descriptor
file descriptor number to use as a socket
reconnect-ms=milliseconds
for a client socket, if a socket is disconnected, then attempt a reconnect after the given number of milliseconds.
Setting this to zero disables this function. (default: 0)
-netdev
dgram,id=str,remote.type=inet,remote.host=maddr,remote.port=port[,local.type=inet,local.host=addr]
Configure a network backend to connect to a multicast address.
remote.host=maddr,remote.port=port
multicast address
local.host=addr
specify the host address to send packets from
Example:
# launch one QEMU instance
qemu-system-x86_64 linux.img \
-device virtio-net,netdev=net0,mac=52:54:00:12:34:56 \
-netdev dgram,id=net0,remote.type=inet,remote.host=224.0.0.1,remote.port=1234
# launch another QEMU instance on same "bus"
qemu-system-x86_64 linux.img \
-device virtio-net,netdev=net0,mac=52:54:00:12:34:57 \
-netdev dgram,id=net0,remote.type=inet,remote.host=224.0.0.1,remote.port=1234
# launch yet another QEMU instance on same "bus"
qemu-system-x86_64 linux.img \
-device virtio-net,netdev=net0,mac=52:54:00:12:34:58 \
-netdev dgram,id=net0,remote.type=inet,remote.host=224.0.0.1,remote.port=1234
-netdev
dgram,id=str,remote.type=inet,remote.host=maddr,remote.port=port[,local.type=fd,local.str=file-descriptor]
Configure a network backend to connect to a multicast address using a UDP socket file descriptor.
remote.host=maddr,remote.port=port
multicast address
local.str=file-descriptor
File descriptor to use to send packets
-netdev
dgram,id=str,local.type=inet,local.host=addr,local.port=port[,remote.type=inet,remote.host=addr,remote.port=port]
Configure a network backend to connect to another QEMU virtual
machine or a proxy using a datagram oriented unix domain socket.
local.host=addr,local.port=port
IP address to use to send the packets from
remote.host=addr,remote.port=port
Destination IP address
Example (two guests connected using an UDP/IP socket):
# first VM
qemu-system-x86_64 linux.img \
-device virtio-net,netdev=net0,mac=52:54:00:12:34:56 \
-netdev dgram,id=net0,local.type=inet,local.host=localhost,local.port=1234,remote.type=inet,remote.host=localhost,remote.port=1235
# second VM
qemu-system-x86_64 linux.img \
-device virtio-net,netdev=net0,mac=52:54:00:12:34:56 \
-netdev dgram,id=net0,local.type=inet,local.host=localhost,local.port=1235,remote.type=inet,remote.host=localhost,remote.port=1234
-netdev
dgram,id=str,local.type=unix,local.path=path[,remote.type=unix,remote.path=path]
Configure a network backend to connect to another QEMU virtual
machine or a proxy using a datagram oriented unix socket.
local.path=path
filesystem path to use to bind the socket
remote.path=path
filesystem path to use as a destination (see sendto(2))
Example (two guests connected using an UDP/UNIX socket):
# first VM
qemu-system-x86_64 linux.img \
-device virtio-net,netdev=net0,mac=52:54:00:12:34:56 \
-netdev dgram,id=net0,local.type=unix,local.path=/tmp/qemu0,remote.type=unix,remote.path=/tmp/qemu1
# second VM
qemu-system-x86_64 linux.img \
-device virtio-net,netdev=net0,mac=52:54:00:12:34:57 \
-netdev dgram,id=net0,local.type=unix,local.path=/tmp/qemu1,remote.type=unix,remote.path=/tmp/qemu0
-netdev
dgram,id=str,local.type=fd,local.str=file-descriptor
Configure a network backend to connect to another QEMU virtual
machine or a proxy using a datagram oriented socket file descriptor.
local.str=file-descriptor
File descriptor to use to send packets
-netdev
l2tpv3,id=id,src=srcaddr,dst=dstaddr[,srcport=srcport][,dstport=dstport],txsession=txsession[,rxsession=rxsession][,ipv6=on|off][,udp=on|off][,cookie64=on|off][,counter=on|off][,pincounter=on|off][,txcookie=txcookie][,rxcookie=rxcookie][,offset=offset]
Configure a L2TPv3 pseudowire host network backend. L2TPv3 (RFC3931)
is a popular protocol to transport Ethernet (and other Layer 2) data
frames between two systems. It is present in routers, firewalls and
the Linux kernel (from version 3.3 onwards).
This transport allows a VM to communicate to another VM, router or
firewall directly.
src=srcaddr
source address (mandatory)
dst=dstaddr
destination address (mandatory)
udp=on
select udp encapsulation (default is ip).
srcport=srcport
source udp port.
dstport=dstport
destination udp port.
ipv6=on
force v6, otherwise defaults to v4.
rxcookie=rxcookie
txcookie=txcookie
Cookies are a weak form of security in the l2tpv3 specification.
Their function is mostly to prevent misconfiguration. By default
they are 32 bit.
cookie64=on
Set cookie size to 64 bit instead of the default 32
counter=off
Force a ‘cut-down’ L2TPv3 with no counter as in
draft-mkonstan-l2tpext-keyed-ipv6-tunnel-00
pincounter=on
Work around broken counter handling in peer. This may also help
on networks which have packet reorder.
offset=offset
Add an extra offset between header and data
For example, to attach a VM running on host 4.3.2.1 via L2TPv3 to
the bridge br-lan on the remote Linux host 1.2.3.4:
# Setup tunnel on linux host using raw ip as encapsulation
# on 1.2.3.4
ip l2tp add tunnel remote 4.3.2.1 local 1.2.3.4 tunnel_id 1 peer_tunnel_id 1 \
encap udp udp_sport 16384 udp_dport 16384
ip l2tp add session tunnel_id 1 name vmtunnel0 session_id \
0xFFFFFFFF peer_session_id 0xFFFFFFFF
ifconfig vmtunnel0 mtu 1500
ifconfig vmtunnel0 up
brctl addif br-lan vmtunnel0
# on 4.3.2.1
# launch QEMU instance - if your network has reorder or is very lossy add ,pincounter
qemu-system-x86_64 linux.img -device e1000,netdev=n1 \
-netdev l2tpv3,id=n1,src=4.2.3.1,dst=1.2.3.4,udp=on,srcport=16384,dstport=16384,rxsession=0xffffffff,txsession=0xffffffff,counter=on
-netdev
vde,id=id[,sock=socketpath][,port=n][,group=groupname][,mode=octalmode]
Configure VDE backend to connect to PORT n of a vde switch running
on host and listening for incoming connections on socketpath. Use
GROUP groupname and MODE octalmode to change default ownership and
permissions for communication port. This option is only available if
QEMU has been compiled with vde support enabled.
Example:
# launch vde switch
vde_switch -F -sock /tmp/myswitch
# launch QEMU instance
qemu-system-x86_64 linux.img -nic vde,sock=/tmp/myswitch
-netdev
af-xdp,id=str,ifname=name[,mode=native|skb][,force-copy=on|off][,queues=n][,start-queue=m][,inhibit=on|off][,sock-fds=x:y:...:z][,map-path=/path/to/socket/map][,map-start-index=i]
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’. Either ‘sock-fds’ or ‘map-path’ can be used with
‘inhibit’ enabled. ‘sock-fds’ can be 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
For the ‘inhibit’ option set to ‘on’ used together with ‘map-path’ it is
expected that the XDP program with the socket map is already loaded on
the networking device and the map pinned into BPF file system. The path
to the pinned map is then passed to QEMU which then creates the file
descriptors and inserts them into the existing socket map.
qemu-system-x86_64 linux.img -device virtio-net-pci,netdev=n1 \
-netdev af-xdp,id=n1,ifname=eth0,queues=2,inhibit=on,map-path=/sys/fs/bpf/xsks_map
Additionally, ‘map-start-index’ can be used to specify the start offset
for insertion into the socket map. The combination of ‘map-path’ and
‘sock-fds’ together is not supported.
-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
512
object
memory
backend
file
id
mem
size
512
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|passt|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
hub
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.
If you need to aggregate data in the opposite direction (where one
QEMU frontend interface receives input and output from multiple
backend chardev devices), please refer to the paragraph below
regarding chardev
hub
aggregator device configuration.
Every backend supports the
logfile
option, which supplies the
path to a file to record all data transmitted via the backend. The
logappend
option controls whether the log file will be truncated
or appended to when opened.
The available backends are:
-chardev
null,id=id
A void device. This device will not emit any data, and will drop any
data it receives. The null backend does not take any options.
-chardev
socket,id=id[,TCP
options
or
unix
options][,server=on|off][,wait=on|off][,telnet=on|off][,websocket=on|off][,reconnect-ms=milliseconds][,tls-creds=id][,tls-authz=id]
Create a two-way stream socket, which can be either a TCP or a unix
socket. A unix socket will be created if
path
is specified.
Behaviour is undefined if TCP options are specified for a unix
socket.
server=on|off
specifies that the socket shall be a listening socket.
wait=on|off
specifies that QEMU should not block waiting for a client
to connect to a listening socket.
telnet=on|off
specifies that traffic on the socket should interpret
telnet escape sequences.
websocket=on|off
specifies that the socket uses WebSocket protocol for
communication.
reconnect-ms
sets the timeout for reconnecting on non-server
sockets when the remote end goes away. qemu will delay this many
milliseconds and then attempt to reconnect. Zero disables reconnecting,
and is the default.
tls-creds
requests enablement of the TLS protocol for
encryption, and specifies the id of the TLS credentials to use for
the handshake. The credentials must be previously created with the
-object
tls-creds
argument.
tls-auth
provides the ID of the QAuthZ authorization object
against which the client’s x509 distinguished name will be
validated. This object is only resolved at time of use, so can be
deleted and recreated on the fly while the chardev server is active.
If missing, it will default to denying access.
TCP and unix socket options are given below:
TCP
options:
port=port[,host=host][,to=to][,ipv4=on|off][,ipv6=on|off][,nodelay=on|off]
host
for a listening socket specifies the local address to
be bound. For a connecting socket species the remote host to
connect to.
host
is optional for listening sockets. If not
specified it defaults to
0.0.0.0
port
for a listening socket specifies the local port to be
bound. For a connecting socket specifies the port on the remote
host to connect to.
port
can be given as either a port
number or a service name.
port
is required.
to
is only relevant to listening sockets. If it is
specified, and
port
cannot be bound, QEMU will attempt to
bind to subsequent ports up to and including
to
until it
succeeds.
to
must be specified as a port number.
ipv4=on|off
and
ipv6=on|off
specify that either IPv4
or IPv6 must be used. If neither is specified the socket may
use either protocol.
nodelay=on|off
disables the Nagle algorithm.
unix
options:
path=path[,abstract=on|off][,tight=on|off]
path
specifies the local path of the unix socket.
path
is required.
abstract=on|off
specifies the use of the abstract socket namespace,
rather than the filesystem. Optional, defaults to false.
tight=on|off
sets the socket length of abstract sockets to their minimum,
rather than the full sun_path length. Optional, defaults to true.
-chardev
udp,id=id[,host=host],port=port[,localaddr=localaddr][,localport=localport][,ipv4=on|off][,ipv6=on|off]
Sends all traffic from the guest to a remote host over UDP.
host
specifies the remote host to connect to. If not specified
it defaults to
localhost
port
specifies the port on the remote host to connect to.
port
is required.
localaddr
specifies the local address to bind to. If not
specified it defaults to
0.0.0.0
localport
specifies the local port to bind to. If not specified
any available local port will be used.
ipv4=on|off
and
ipv6=on|off
specify that either IPv4 or IPv6 must be used.
If neither is specified the device may use either protocol.
-chardev
msmouse,id=id
Forward QEMU’s emulated msmouse events to the guest.
msmouse
does not take any options.
-chardev
hub,id=id,chardevs.0=id[,chardevs.N=id]
Explicitly create chardev backend hub device with the possibility
to aggregate input from multiple backend devices and forward it to
a single frontend device. Additionally,
hub
device takes the
output from the frontend device and sends it back to all the
connected backend devices. This allows for seamless interaction
between different backend devices and a single frontend
interface. Aggregation supported for up to 4 chardev
devices. (Since 10.0)
For example, the following is a use case of 2 backend devices:
virtual console
vc0
and a pseudo TTY
pty0
connected to
a single virtio hvc console frontend device with a hub
hub0
help. Virtual console renders text to an image, which can be
shared over the VNC protocol. In turn, pty backend provides
bidirectional communication to the virtio hvc console over the
pseudo TTY file. The example configuration can be as follows:
chardev
pty
path
=/
tmp
pty
id
pty0
chardev
vc
id
vc0
chardev
hub
id
hub0
chardevs
.0
pty0
chardevs
.1
vc0
device
virtconsole
chardev
hub0
vnc
0.0.0.0
Once QEMU starts VNC client and any TTY emulator can be used to
control a single hvc console:
# Start TTY emulator
tio
tmp
pty
# Start VNC client and switch to virtual console Ctrl-Alt-2
vncviewer
Several frontend devices is not supported. Stacking of multiplexers
and hub devices is not supported as well.
-chardev
vc,id=id[[,width=width][,height=height]][[,cols=cols][,rows=rows]]
Connect to a QEMU text console.
vc
may optionally be given a
specific size.
width
and
height
specify the width and height respectively
of the console, in pixels.
cols
and
rows
specify that the console be sized to fit a
text console with the given dimensions.
-chardev
ringbuf,id=id[,size=size]
Create a ring buffer with fixed size
size
. size must be a power
of two and defaults to
64K
-chardev
file,id=id,path=path[,input-path=input-path]
Log all traffic received from the guest to a file.
path
specifies the path of the file to be opened. This file will
be created if it does not already exist, and overwritten if it does.
path
is required.
If
input-path
is specified, this is the path of a second file
which will be used for input. If
input-path
is not specified,
no input will be available from the chardev.
Note that
input-path
is not supported on Windows hosts.
-chardev
pipe,id=id,path=path
Create a two-way connection to the guest. The behaviour differs
slightly between Windows hosts and other hosts:
On Windows, a single duplex pipe will be created at
\\.pipe\path
On other hosts, 2 pipes will be created called
path.in
and
path.out
. Data written to
path.in
will be received by the
guest. Data written by the guest can be read from
path.out
. QEMU
will not create these fifos, and requires them to be present.
path
forms part of the pipe path as described above.
path
is
required.
-chardev
console,id=id
Send traffic from the guest to QEMU’s standard output.
console
does not take any options.
console
is only available on Windows hosts.
-chardev
serial,id=id,path=path
Send traffic from the guest to a serial device on the host.
On Unix hosts serial will actually accept any tty device, not only
serial lines.
path
specifies the name of the serial device to open.
-chardev
pty,id=id[,path=path]
Create a new pseudo-terminal on the host and connect to it.
pty
is not available on Windows hosts.
If
path
is specified, QEMU will create a symbolic link at
that location which points to the new PTY device.
This avoids having to make QMP or HMP monitor queries to find out
what the new PTY device path is.
Note that while QEMU will remove the symlink when it exits
gracefully, it will not do so in case of crashes or on certain
startup errors. It is recommended that the user checks and removes
the symlink after QEMU terminates to account for this.
-chardev
stdio,id=id[,signal=on|off]
Connect to standard input and standard output of the QEMU process.
signal
controls if signals are enabled on the terminal, that
includes exiting QEMU with the key sequence Control-c. This option
is enabled by default, use
signal=off
to disable it.
-chardev
braille,id=id
Connect to a local BrlAPI server.
braille
does not take any
options.
-chardev
parallel,id=id,path=path
parallel
is only available on Linux, FreeBSD and DragonFlyBSD
hosts.
Connect to a local parallel port.
path
specifies the path to the parallel port device.
path
is
required.
-chardev
spicevmc,id=id,debug=debug,name=name
spicevmc
is only available when spice support is built in.
debug
debug level for spicevmc
name
name of spice channel to connect to
Connect to a spice virtual machine channel, such as vdiport.
-chardev
spiceport,id=id,debug=debug,name=name
spiceport
is only available when spice support is built in.
debug
debug level for spicevmc
name
name of spice port to connect to
Connect to a spice port, allowing a Spice client to handle the
traffic identified by a name (preferably a fqdn).
TPM device options
The general form of a TPM device option is:
-tpmdev
backend,id=id[,options]
The specific backend type will determine the applicable options. The
-tpmdev
option creates the TPM backend and requires a
-device
option that specifies the TPM frontend interface model.
Use
-tpmdev
help
to print all available TPM backend types.
The available backends are:
-tpmdev
passthrough,id=id,path=path,cancel-path=cancel-path
(Linux-host only) Enable access to the host’s TPM using the
passthrough driver.
path
specifies the path to the host’s TPM device, i.e., on a
Linux host this would be
/dev/tpm0
path
is optional and by
default
/dev/tpm0
is used.
cancel-path
specifies the path to the host TPM device’s sysfs
entry allowing for cancellation of an ongoing TPM command.
cancel-path
is optional and by default QEMU will search for the
sysfs entry to use.
Some notes about using the host’s TPM with the passthrough driver:
The TPM device accessed by the passthrough driver must not be used
by any other application on the host.
Since the host’s firmware (BIOS/UEFI) has already initialized the
TPM, the VM’s firmware (BIOS/UEFI) will not be able to initialize
the TPM again and may therefore not show a TPM-specific menu that
would otherwise allow the user to configure the TPM, e.g., allow the
user to enable/disable or activate/deactivate the TPM. Further, if
TPM ownership is released from within a VM then the host’s TPM will
get disabled and deactivated. To enable and activate the TPM again
afterwards, the host has to be rebooted and the user is required to
enter the firmware’s menu to enable and activate the TPM. If the TPM
is left disabled and/or deactivated most TPM commands will fail.
To create a passthrough TPM use the following two options:
tpmdev
passthrough
id
tpm0
device
tpm
tis
tpmdev
tpm0
Note that the
-tpmdev
id is
tpm0
and is referenced by
tpmdev=tpm0
in the device option.
-tpmdev
emulator,id=id,chardev=dev
(Linux-host only) Enable access to a TPM emulator using Unix domain
socket based chardev backend.
chardev
specifies the unique ID of a character device backend
that provides connection to the software TPM server.
To create a TPM emulator backend device with chardev socket backend:
chardev
socket
id
chrtpm
path
=/
tmp
swtpm
sock
tpmdev
emulator
id
tpm0
chardev
chrtpm
device
tpm
tis
tpmdev
tpm0
Boot Image or Kernel specific
There are broadly 4 ways you can boot a system with QEMU.
specify a firmware and let it control finding a kernel
specify a firmware and pass a hint to the kernel to boot
direct kernel image boot
manually load files into the guest’s address space
The third method is useful for quickly testing kernels but as there is
no firmware to pass configuration information to the kernel the
hardware must either be probeable, the kernel built for the exact
configuration or passed some configuration data (e.g. a DTB blob)
which tells the kernel what drivers it needs. This exact details are
often hardware specific.
The final method is the most generic way of loading images into the
guest address space and used mostly for
bare
metal
type
development where the reset vectors of the processor are taken into
account.
For x86 machines and some other architectures
-bios
will generally
do the right thing with whatever it is given. For other machines the
more strict
-pflash
option needs an image that is sized for the
flash device for the given machine type.
Please see the
QEMU System Emulator Targets
section of the manual for
more detailed documentation.
-bios
file
Set the filename for the BIOS.
-pflash
file
Use file as a parallel flash image.
The kernel options were designed to work with Linux kernels although
other things (like hypervisors) can be packaged up as a kernel
executable image. The exact format of a executable image is usually
architecture specific.
The way in which the kernel is started (what address it is loaded at,
what if any information is passed to it via CPU registers, the state
of the hardware when it is started, and so on) is also architecture
specific. Typically it follows the specification laid down by the
Linux kernel for how kernels for that architecture must be started.
-kernel
bzImage
Use bzImage as kernel image. The kernel can be either a Linux kernel
or in multiboot format.
-shim
shim.efi
Use ‘shim.efi’ to boot the kernel
-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=
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=
Debug/Expert options
-compat
[deprecated-input=
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=
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
800
x600
It is also possible to specify width or height in characters:
vc
80
Cx24C
pty[:path]
[Linux only] Pseudo TTY (a new PTY is automatically allocated).
If
path
is specified, QEMU will create a symbolic link at
that location which points to the new PTY device.
This avoids having to make QMP or HMP monitor queries to find
out what the new PTY device path is.
Note that while QEMU will remove the symlink when it exits
gracefully, it will not do so in case of crashes or on certain
startup errors. It is recommended that the user checks and
removes the symlink after QEMU terminates to account for this.
none
No device is allocated. Note that for machine types which
emulate systems where a serial device is always present in
real hardware, this may be equivalent to the
null
option,
in that the serial device is still present but all output
is discarded. For boards where the number of serial ports is
truly variable, this suppresses the creation of the device.
null
A guest will see the UART or serial device as present in the
machine, but all output is discarded, and there is no input.
Conceptually equivalent to redirecting the output to
/dev/null
chardev:id
Use a named character device defined with the
-chardev
option.
/dev/XXX
[Linux only] Use host tty, e.g.
/dev/ttyS0
. The host serial
port parameters are set according to the emulated ones.
/dev/parportN
[Linux only, parallel port only] Use host parallel port N.
Currently SPP and EPP parallel port features can be used.
file:filename
Write output to filename. No character can be read.
stdio
[Unix only] standard input/output
pipe:filename
name pipe filename
COMn
[Windows only] Use host serial port n
udp:[remote_host]:remote_port[@[src_ip]:src_port]
This implements UDP Net Console. When remote_host or src_ip
are not specified they default to
0.0.0.0
. When not using a
specified src_port a random port is automatically chosen.
If you just want a simple readonly console you can use
netcat
or
nc
, by starting QEMU with:
-serial
udp::4555
and nc as:
nc
-u
-l
-p
4555
. Any time
QEMU writes something to that port it will appear in the
netconsole session.
If you plan to send characters back via netconsole or you want
to stop and start QEMU a lot of times, you should have QEMU use
the same source port each time by using something like
-serial
udp::4555@:4556
to QEMU. Another approach is to use a patched
version of netcat which can listen to a TCP port and send and
receive characters via udp. If you have a patched version of
netcat which activates telnet remote echo and single char
transfer, then you can use the following options to set up a
netcat redirector to allow telnet on port 5555 to access the
QEMU port.
QEMU
Options:
-serial udp::4555@:4556
netcat
options:
-u -P 4555 -L 0.0.0.0:4556 -t -p 5555 -I -T
telnet
options:
localhost 5555
tcp:[host]:port[,server=on|off][,wait=on|off][,nodelay=on|off][,reconnect-ms=milliseconds]
The TCP Net Console has two modes of operation. It can send the
serial I/O to a location or wait for a connection from a
location. By default the TCP Net Console is sent to host at the
port. If you use the
server=on
option QEMU will wait for a client
socket application to connect to the port before continuing,
unless the
wait=on|off
option was specified. The
nodelay=on|off
option disables the Nagle buffering algorithm. The
reconnect-ms
option only applies if
server=no
is set, if the connection goes
down it will attempt to reconnect at the given interval. If host
is omitted, 0.0.0.0 is assumed. Only one TCP connection at a
time is accepted. You can use
telnet=on
to connect to the
corresponding character device.
Example
to
send
tcp
console
to
192.168.0.2
port
4444
-serial
tcp:192.168.0.2:4444
Example
to
listen
and
wait
on
port
4444
for
connection
-serial
tcp::4444,server=on
Example
to
not
wait
and
listen
on
ip
192.168.0.100
port
4444
-serial
tcp:192.168.0.100:4444,server=on,wait=off
telnet:host:port[,server=on|off][,wait=on|off][,nodelay=on|off]
The telnet protocol is used instead of raw tcp sockets. The
options work the same as if you had specified
-serial
tcp
The difference is that the port acts like a telnet server or
client using telnet option negotiation. This will also allow you
to send the MAGIC_SYSRQ sequence if you use a telnet that
supports sending the break sequence. Typically in unix telnet
you do it with Control-] and then type “send break” followed by
pressing the enter key.
websocket:host:port,server=on[,wait=on|off][,nodelay=on|off]
The WebSocket protocol is used instead of raw tcp socket. The
port acts as a WebSocket server. Client mode is not supported.
unix:path[,server=on|off][,wait=on|off][,reconnect-ms=milliseconds]
A unix domain socket is used instead of a tcp socket. The option
works the same as if you had specified
-serial
tcp
except
the unix domain socket path is used for connections.
mon:dev_string
This is a special option to allow the monitor to be multiplexed
onto another serial port. The monitor is accessed with key
sequence of Control-a and then pressing c. dev_string should be
any one of the serial devices specified above. An example to
multiplex the monitor onto a telnet server listening on port
4444 would be:
-serial
mon:telnet::4444,server=on,wait=off
When the monitor is multiplexed to stdio in this way, Ctrl+C
will not terminate QEMU any more but will be passed to the guest
instead.
braille
Braille device. This will use BrlAPI to display the braille
output on a real or fake device.
msmouse
Three button serial mouse. Configure the guest to use Microsoft
protocol.
-parallel
dev
Redirect the virtual parallel port to host device dev (same devices
as the serial port). On Linux hosts,
/dev/parportN
can be used
to use hardware devices connected on the corresponding host parallel
port.
This option can be used several times to simulate up to 3 parallel
ports.
Use
-parallel
none
to disable all parallel ports.
-monitor
dev
Redirect the monitor to host device dev (same devices as the serial
port). The default device is
vc
in graphical mode and
stdio
in non graphical mode. Use
-monitor
none
to disable the default
monitor.
-qmp
dev
Like
-monitor
but opens in ‘control’ mode. For example, to make
QMP available on localhost port 4444:
qmp
tcp
localhost
4444
server
on
wait
off
Not all options are configurable via this syntax; for maximum
flexibility use the
-mon
option and an accompanying
-chardev
-qmp-pretty
dev
Like
-qmp
but uses pretty JSON formatting.
-mon
[chardev=]name[,mode=readline|control][,pretty=on|off]
Set up a monitor connected to the chardev
name
QEMU supports two monitors: the Human Monitor Protocol
(HMP; for human interaction), and the QEMU Monitor Protocol
(QMP; a JSON RPC-style protocol).
The default is HMP;
mode=control
selects QMP instead.
pretty
is only valid when
mode=control
turning on JSON pretty printing to ease
human reading and debugging.
For example:
chardev
socket
id
mon1
host
localhost
port
4444
server
on
wait
off
mon
chardev
mon1
mode
control
pretty
on
enables the QMP monitor on localhost port 4444 with pretty-printing.
-debugcon
dev
Redirect the debug console to host device dev (same devices as the
serial port). The debug console is an I/O port which is typically
port 0xe9; writing to that I/O port sends output to this device. The
default device is
vc
in graphical mode and
stdio
in non
graphical mode.
-pidfile
file
Store the QEMU process PID in file. It is useful if you launch QEMU
from a script.
--preconfig
Pause QEMU for interactive configuration before the machine is
created, which allows querying and configuring properties that will
affect machine initialization. Use QMP command ‘x-exit-preconfig’ to
exit the preconfig state and move to the next state (i.e. run guest
if -S isn’t used or pause the second time if -S is used). This
option is experimental.
-S
Do not start CPU at startup (you must type ‘c’ in the monitor).
-overcommit
mem-lock=on|off|on-fault
-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
or
mem-lock=on-fault
(disabled by default). This works when
host memory is not overcommitted and reduces the worst-case latency for
guest. The on-fault option is better for reducing the memory footprint
since it makes allocations lazy, but the pages still get locked in place
once faulted by the guest or QEMU. Note that the two options are mutually
exclusive.
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
.0
x8fff
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=off
is specified. With
sleep=off
, 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=on
sleep=off
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
The -incoming option specifies the migration channel for an incoming
migration. It may be used multiple times to specify multiple
migration channel types. The channel type is specified in
or is ‘main’ for all other forms of -incoming. If multiple -incoming
options are specified for a channel type, the last one takes precedence.
-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
Accept incoming migration on the migration channel. For the syntax
of
MigrationChannel
Examples:
incoming
'{"channel-type": "main",
"addr"
"transport"
"socket"
"type"
"unix"
"path"
"my.sock"
}}
incoming
main
addr
transport
socket
addr
type
unix
addr
path
my
sock
-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.
-prom-env
variable=value
Set OpenBIOS nvram variable to given value (PPC, SPARC only).
qemu
system
sparc
prom
env
'auto-boot?=false'
prom
env
'boot-device=sd(0,2,0):d'
prom
env
'boot-args=linux single'
qemu
system
ppc
prom
env
'auto-boot?=false'
prom
env
'boot-device=hd:2,\yaboot'
prom
env
'boot-args=conf=hd:2,\yaboot.conf'
-semihosting
Enable
Semihosting
mode (ARM, M68K, Xtensa, MIPS, RISC-V only).
Warning
Note that this allows guest direct access to the host filesystem, so
should only be used with a trusted guest OS.
See the -semihosting-config option documentation for further
information about the facilities this enables.
-semihosting-config
[enable=on|off][,target=native|gdb|auto][,chardev=id][,userspace=on|off][,arg=str[,...]]
Enable and configure
Semihosting
(ARM, M68K, Xtensa, MIPS, RISC-V
only).
Warning
Note that this allows guest direct access to the host filesystem, so
should only be used with a trusted guest OS.
target=native|gdb|auto
Defines where the semihosting calls will be addressed, to QEMU
native
) or to GDB (
gdb
). The default is
auto
, which
means
gdb
during debug sessions and
native
otherwise.
chardev=str1
Send the output to a chardev backend output for native or auto
output when not in gdb
userspace=on|off
Allows code running in guest userspace to access the semihosting
interface. The default is that only privileged guest code can
make semihosting calls. Note that setting
userspace=on
should
only be used if all guest code is trusted (for example, in
bare-metal test case code).
arg=str1,arg=str2,...
Allows the user to pass input arguments, and can be used
multiple times to build up a list. The old-style
-kernel
-append
method of passing a command line is
still supported for backward compatibility. If both the
--semihosting-config
arg
and the
-kernel
-append
are
specified, the former is passed to semihosting as it always
takes precedence.
-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][,exit-with-parent=on|off][,user=username|uid:gid]
Set QEMU process lifecycle options.
async-teardown=on
enables asynchronous teardown. A new process called
“cleanup/
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
user=...
exit-with-parent=on
causes QEMU to exit if the parent process of
QEMU exits. This can be used when QEMU runs a captive appliance,
where the lifetime of the appliance is scoped to the parent process.
In case the parent process crashes, QEMU is still cleaned up.
This only works on Linux, FreeBSD and macOS platforms.
user=username
or
user=uid:gid
can be used to drop root privileges
before starting guest execution. QEMU will use the
setuid
and
setgid
system calls to switch to the specified identity. Note that the
user=username
syntax will also apply the full set of supplementary
groups for the user, whereas the
user=uid:gid
will use only the
gid
group.
-msg
[timestamp=on|off][,guest-name=on|off]
Control error message format.
timestamp=on|off
Prefix messages with a timestamp. Default is off.
guest-name=on|off
Prefix messages with guest name but only if -name guest option is set
otherwise the option is ignored. Default is off.
-dump-vmstate
file
Dump json-encoded vmstate information for current machine type to
file in file
-enable-sync-profile
Enable synchronization profiling.
-perfmap
Generate a map file for Linux perf tools that will allow basic profiling
information to be broken down into basic blocks.
-jitdump
Generate a dump file for Linux perf tools that maps basic blocks to symbol
names, line numbers and JITted code.
Generic object creation
-object
typename[,prop1=value1,...]
Create a new object of type typename setting properties in the order
they are specified. Note that the ‘id’ property must be set. These
objects are placed in the ‘/objects’ path.
-object
memory-backend-file,id=id,size=size,mem-path=dir,share=on|off,discard-data=on|off,merge=on|off,dump=on|off,prealloc=on|off,host-nodes=host-nodes,policy=default|preferred|bind|interleave,align=align,offset=offset,readonly=on|off,rom=on|off|auto
Creates a memory file backend object, which can be used to back
the guest RAM with huge pages.
The
id
parameter is a unique ID that will be used to
reference this memory region in other parameters, e.g.
-numa
-device
nvdimm
, etc.
The
size
option provides the size of the memory region, and
accepts common suffixes, e.g.
500M
The
mem-path
provides the path to either a shared memory or
huge page filesystem mount.
The
share
boolean option determines whether the memory
region is marked as private to QEMU, or shared. The latter
allows a co-operating external process to access the QEMU memory
region.
Setting share=on might affect the ability to configure NUMA
bindings for the memory backend under some circumstances, see
Documentation/vm/numa_memory_policy.txt on the Linux kernel
source tree for additional details.
Setting the
discard-data
boolean option to on indicates that
file contents can be destroyed when QEMU exits, to avoid
unnecessarily flushing data to the backing file. Note that
discard-data
is only an optimization, and QEMU might not
discard file contents if it aborts unexpectedly or is terminated
using SIGKILL.
The
merge
boolean option enables memory merge, also known as
MADV_MERGEABLE, so that Kernel Samepage Merging will consider
the pages for memory deduplication.
Setting the
dump
boolean option to off excludes the memory
from core dumps. This feature is also known as MADV_DONTDUMP.
The
prealloc
boolean option enables memory preallocation.
The
host-nodes
option binds the memory range to a list of
NUMA host nodes.
The
policy
option sets the NUMA policy to one of the
following values:
default
default host policy
preferred
prefer the given host node list for allocation
bind
restrict memory allocation to the given host node list
interleave
interleave memory allocations across the given host node
list
The
align
option specifies the base address alignment when
QEMU mmap(2)
mem-path
, and accepts common suffixes, eg
2M
. Some backend store specified by
mem-path
requires an
alignment different than the default one used by QEMU, eg the
device DAX /dev/dax0.0 requires 2M alignment rather than 4K. In
such cases, users can specify the required alignment via this
option.
The
offset
option specifies the offset into the target file
that the region starts at. You can use this parameter to back
multiple regions with a single file.
The
pmem
option specifies whether the backing file specified
by
mem-path
is in host persistent memory that can be
accessed using the SNIA NVM programming model (e.g. Intel
NVDIMM). If
pmem
is set to ‘on’, QEMU will take necessary
operations to guarantee the persistence of its own writes to
mem-path
(e.g. in vNVDIMM label emulation and live
migration). Also, we will map the backend-file with MAP_SYNC
flag, which ensures the file metadata is in sync for
mem-path
in case of host crash or a power failure. MAP_SYNC
requires support from both the host kernel (since Linux kernel
4.15) and the filesystem of
mem-path
mounted with DAX
option.
The
readonly
option specifies whether the backing file is opened
read-only or read-write (default).
The
rom
option specifies whether to create Read Only Memory
(ROM) that cannot be modified by the VM. Any write attempts to such
ROM will be denied. Most use cases want proper RAM instead of ROM.
However, selected use cases, like R/O NVDIMMs, can benefit from
ROM. If set to
on
, create ROM; if set to
off
, create
writable RAM; if set to
auto
(default), the value of the
readonly
option is used. This option is primarily helpful when
we want to have writable RAM in configurations that would
traditionally create ROM before the
rom
option was introduced:
VM templating, where we want to open a file readonly
readonly=on
) and mark the memory to be private for QEMU
share=off
). For this use case, we need writable RAM instead
of ROM, and want to also set
rom=off
-object
memory-backend-ram,id=id,merge=on|off,dump=on|off,share=on|off,prealloc=on|off,size=size,host-nodes=host-nodes,policy=default|preferred|bind|interleave
Creates a memory backend object, which can be used to back the
guest RAM. Memory backend objects offer more control than the
-m
option that is traditionally used to define guest RAM.
Please refer to
memory-backend-file
for a description of the
options.
-object
memory-backend-memfd,id=id,merge=on|off,dump=on|off,share=on|off,prealloc=on|off,size=size,host-nodes=host-nodes,policy=default|preferred|bind|interleave,seal=on|off,hugetlb=on|off,hugetlbsize=size
Creates an anonymous memory file backend object, which allows
QEMU to share the memory with an external process (e.g. when
using vhost-user). The memory is allocated with memfd and
optional sealing. (Linux only)
The
seal
option creates a sealed-file, that will block
further resizing the memory (‘on’ by default).
The
hugetlb
option specify the file to be created resides in
the hugetlbfs filesystem (since Linux 4.14). Used in conjunction
with the
hugetlb
option, the
hugetlbsize
option specify
the hugetlb page size on systems that support multiple hugetlb
page sizes (it must be a power of 2 value supported by the
system).
In some versions of Linux, the
hugetlb
option is
incompatible with the
seal
option (requires at least Linux
4.16).
Please refer to
memory-backend-file
for a description of the
other options.
The
share
boolean option is on by default with memfd.
-object
memory-backend-shm,id=id,merge=on|off,dump=on|off,share=on|off,prealloc=on|off,size=size,host-nodes=host-nodes,policy=default|preferred|bind|interleave
Creates a POSIX shared memory backend object, which allows
QEMU to share the memory with an external process (e.g. when
using vhost-user).
memory-backend-shm
is a more portable and less featureful version
of
memory-backend-memfd
. It can then be used in any POSIX system,
especially when memfd is not supported.
Please refer to
memory-backend-file
for a description of the
options.
The
share
boolean option is on by default with shm. Setting it to
off will cause a failure during allocation because it is not supported
by this backend.
-object
iommufd,id=id[,fd=fd]
Creates an iommufd backend which allows control of DMA mapping
through the
/dev/iommu
device.
The
id
parameter is a unique ID which frontends (such as
vfio-pci of vdpa) will use to connect with the iommufd backend.
The
fd
parameter is an optional pre-opened file descriptor
resulting from
/dev/iommu
opening. Usually the iommufd is shared
across all subsystems, bringing the benefit of centralized
reference counting.
-object
rng-builtin,id=id
Creates a random number generator backend which obtains entropy
from QEMU builtin functions. The
id
parameter is a unique ID
that will be used to reference this entropy backend from the
virtio-rng
device. By default, the
virtio-rng
device
uses this RNG backend.
-object
rng-random,id=id,filename=/dev/random
Creates a random number generator backend which obtains entropy
from a device on the host. The
id
parameter is a unique ID
that will be used to reference this entropy backend from the
virtio-rng
device. The
filename
parameter specifies
which file to obtain entropy from and if omitted defaults to
/dev/urandom
-object
rng-egd,id=id,chardev=chardevid
Creates a random number generator backend which obtains entropy
from an external daemon running on the host. The
id
parameter is a unique ID that will be used to reference this
entropy backend from the
virtio-rng
device. The
chardev
parameter is the unique ID of a character device backend that
provides the connection to the RNG daemon.
-object
tls-creds-anon,id=id,endpoint=endpoint,dir=/path/to/cred/dir,verify-peer=on|off
Creates a TLS anonymous credentials object, which can be used to
provide TLS support on network backends. The
id
parameter is
a unique ID which network backends will use to access the
credentials. The
endpoint
is either
server
or
client
depending on whether the QEMU network backend that uses the
credentials will be acting as a client or as a server. If
verify-peer
is enabled (the default) then once the handshake
is completed, the peer credentials will be verified, though this
is a no-op for anonymous credentials.
The dir parameter tells QEMU where to find the credential files.
For server endpoints, this directory may contain a file
dh-params.pem providing diffie-hellman parameters to use for the
TLS server. If the file is missing, QEMU will generate a set of
DH parameters at startup. This is a computationally expensive
operation that consumes random pool entropy, so it is
recommended that a persistent set of parameters be generated
upfront and saved.
-object
tls-creds-psk,id=id,endpoint=endpoint,dir=/path/to/keys/dir[,username=username]
Creates a TLS Pre-Shared Keys (PSK) credentials object, which
can be used to provide TLS support on network backends. The
id
parameter is a unique ID which network backends will use
to access the credentials. The
endpoint
is either
server
or
client
depending on whether the QEMU network backend that
uses the credentials will be acting as a client or as a server.
For clients only,
username
is the username which will be
sent to the server. If omitted it defaults to “qemu”.
The dir parameter tells QEMU where to find the keys file. It is
called “dir/keys.psk” and contains “username:key” pairs. This
file can most easily be created using the GnuTLS
psktool
program.
For server endpoints, dir may also contain a file dh-params.pem
providing diffie-hellman parameters to use for the TLS server.
If the file is missing, QEMU will generate a set of DH
parameters at startup. This is a computationally expensive
operation that consumes random pool entropy, so it is
recommended that a persistent set of parameters be generated up
front and saved.
-object
tls-creds-x509,id=id,endpoint=endpoint,dir=/path/to/cred/dir,priority=priority,verify-peer=on|off,passwordid=id
Creates a TLS anonymous credentials object, which can be used to
provide TLS support on network backends. The
id
parameter is
a unique ID which network backends will use to access the
credentials. The
endpoint
is either
server
or
client
depending on whether the QEMU network backend that uses the
credentials will be acting as a client or as a server. If
verify-peer
is enabled (the default) then once the handshake
is completed, the peer credentials will be verified. With x509
certificates, this implies that the clients must be provided
with valid client certificates too.
The dir parameter tells QEMU where to find the credential files.
For server endpoints, this directory may contain a file
dh-params.pem providing diffie-hellman parameters to use for the
TLS server. If the file is missing, QEMU will generate a set of
DH parameters at startup. This is a computationally expensive
operation that consumes random pool entropy, so it is
recommended that a persistent set of parameters be generated
upfront and saved.
For x509 certificate credentials the directory will contain
further files providing the x509 certificates. The certificates
must be stored in PEM format, in filenames ca-cert.pem,
ca-crl.pem (optional), server-cert.pem (only servers),
server-key.pem (only servers), client-cert.pem (only clients),
and client-key.pem (only clients).
For the server-key.pem and client-key.pem files which contain
sensitive private keys, it is possible to use an encrypted
version by providing the passwordid parameter. This provides the
ID of a previously created
secret
object containing the
password for decryption.
The priority parameter allows to override the global default
priority used by gnutls. This can be useful if the system
administrator needs to use a weaker set of crypto priorities for
QEMU without potentially forcing the weakness onto all
applications. Or conversely if one wants wants a stronger
default for QEMU than for all other applications, they can do
this through this parameter. Its format is a gnutls priority
string as described at
-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
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=
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=
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=
: the filter is inserted before or behind the filter
specified by
insert behind|before is an option to specify where to insert
the new filter relative to the one specified with
position=id=
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=
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=
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=
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=
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=
Colo-compare gets packets from the chardev backends specified by
primary_in
and
secondary_in
, and compares whether the payloads
of the primary packet and the secondary packet are the same.
If they match, it will output the primary packet to the chardev
backend specified by
outdev
; otherwise it will notify COLO-framework
to do a checkpoint and send the primary packet to
outdev
In order to improve efficiency, we need to put the task of comparison in
another iothread; the
iothread
option specifies that iothread object
(which your commandline should create).
The
vnet_hdr_support
flag tells
colo compare to pass the vnet header length when it sends and receives packets.
The
compare_timeout
option sets the maximum time that
colo-compare will hold the packet for, in ms.
The
expired_scan_cycle
option sets the period of scanning expired
primary node network packets, in ms.
The
max_queue_size
option sets the max compare queue size.
If you want to use Xen COLO, you need to specify
notify_dev
to
tell colo-compare how to notify Xen colo-frame to do a 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
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
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
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
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=$(
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
igvm-cfg,file=file
Create an IGVM configuration object that defines the initial state
of the guest using a file in that conforms to the Independent Guest
Virtual Machine (IGVM) file format.
This is currently only supported by
-machine
q35
and
-machine
pc
The
file
parameter is used to specify the IGVM file to load.
When provided, the IGVM file is used to populate the initial
memory of the virtual machine and, depending on the platform, can
define the initial processor state, memory map and parameters.
The IGVM file is expected to contain the firmware for the virtual
machine, therefore an
igvm-cfg
object cannot be provided along
with other ways of specifying firmware, such as the
-bios
parameter on x86 machines.
e.g to launch a machine providing the firmware in an IGVM file
# qemu-system-x86_64 \
...... \
-object igvm-cfg,id=igvm0,file=bios.igvm \
-machine ...,igvm-cfg=igvm0 \
.....
-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
Example
London
ST
London
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.
Multiplexer Keys
Key Sequence
Action
Ctrl
Alt
Toggle full screen
Ctrl
Alt
Enlarge the screen
Ctrl
Alt
Shrink the screen
Ctrl
Alt
Restore the screen’s un-scaled dimensions
Ctrl
Alt
Switch to virtual console ‘n’. Standard console mappings are:
: Target system display
: Monitor
: Serial port
Ctrl
Alt
Toggle mouse and keyboard grab.
In the virtual consoles, you can use
Ctrl
Up
Ctrl
Down
Ctrl
PageUp
and
Ctrl
PageDown
to move in the back log.
During emulation, if you are using a character backend multiplexer
(which is the default if you are using
-nographic
) then several
commands are available via an escape sequence. These key sequences all
start with an escape character, which is
Ctrl
by default, but can be
changed with
-echr
. The list below assumes you’re using the default.
Multiplexer Keys
Key Sequence
Action
Ctrl
Print this help
Ctrl
Exit emulator
Ctrl
Save disk data back to file (if -snapshot)
Ctrl
Toggle console timestamps
Ctrl
Send break (magic sysrq in Linux)
Ctrl
Rotate between the frontends connected to the multiplexer (usually this switches between the monitor and the console)
Ctrl
Ctrl
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://
By default qemu will use the iSCSI initiator-name
‘iqn.2008-11.org.linux-kvm[:
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://
Syntax for specifying a NBD device using Unix Domain Sockets;
remember that ‘?’ is a shell glob character and may need quoting:
“nbd+unix:///[
Older syntax that is also recognized:
“nbd:
Syntax for specifying a NBD device using Unix Domain Sockets
“nbd:unix:
Example for TCP
qemu-system-x86_64 --drive file=nbd:192.0.2.1:30000
Example for Unix Domain Sockets
qemu-system-x86_64 --drive file=nbd:unix:/tmp/nbd-socket
SSH
QEMU supports SSH (Secure Shell) access to remote disks.
Examples:
qemu-system-x86_64 -drive file=ssh://user@host/path/to/disk.img
qemu-system-x86_64 -drive file.driver=ssh,file.user=user,file.host=host,file.port=22,file.path=/path/to/disk.img
Currently authentication must be done using ssh-agent. Other
authentication methods may be supported in future.
GlusterFS
GlusterFS is a user space distributed file system. QEMU supports the
use of GlusterFS volumes for hosting VM disk images using TCP and Unix
Domain Sockets transport protocols.
Syntax for specifying a VM disk image on GlusterFS volume is
URI:
gluster[+type]://[host[:port]]/volume/path[?socket=...][,debug=N][,logfile=...]
JSON:
'json:{"driver":"qcow2","file":{"driver":"gluster","volume":"testvol","path":"a.img","debug":N,"logfile":"...",
"server":[{"type":"tcp","host":"...","port":"..."},
{"type":"unix","socket":"..."}]}}'
Example
URI:
qemu-system-x86_64 --drive file=gluster://192.0.2.1/testvol/a.img,
file.debug=9,file.logfile=/var/log/qemu-gluster.log
JSON:
qemu-system-x86_64 'json:{"driver":"qcow2",
"file":{"driver":"gluster",
"volume":"testvol","path":"a.img",
"debug":9,"logfile":"/var/log/qemu-gluster.log",
"server":[{"type":"tcp","host":"1.2.3.4","port":24007},
{"type":"unix","socket":"/var/run/glusterd.socket"}]}}'
qemu-system-x86_64 -drive driver=qcow2,file.driver=gluster,file.volume=testvol,file.path=/path/a.img,
file.debug=9,file.logfile=/var/log/qemu-gluster.log,
file.server.0.type=tcp,file.server.0.host=1.2.3.4,file.server.0.port=24007,
file.server.1.type=unix,file.server.1.socket=/var/run/glusterd.socket
See also
HTTP/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’.
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.
force-range
Don’t issue a HEAD HTTP request to discover if the http server
server supports range requests and rely only on GET requests. This
is especially useful for S3 presigned URLs where HEAD requests
are unauthorized. It defaults to ‘false’.
Note that when passing options to qemu explicitly,
driver
is the
value of
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":"
",, "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":"
",, "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.