qemu-system (1)

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NAME

qemu-doc - QEMU version 2.10.0 User Documentation

SYNOPSIS

qemu-system-i386 [options] [disk_image]

DESCRIPTION

The 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

-

PCI UHCI, OHCI, EHCI

or

XHCI USB

controller and a virtual

USB-1.1

hub.

is supported with up to 255 CPUs.

uses the from the Seabios project and the Plex86/Bochs

uses emulation by Tatsuyuki Satoh.

uses emulation ( <www.deinmeister.de/gusemu>) by Tibor `` Schütz.

Note that, by default,

shares (7) with parallel ports and so must be told to not have parallel ports to have working

        qemu-system-i386 dos.img -soundhw gus -parallel none

Alternatively:

        qemu-system-i386 dos.img -device gus,irq=5

Or some other unclaimed

is the chip used in Windows Sound System and products

OPTIONS

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

Standard options

-h

Display help and exit

-version

Display version information and exit

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

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

For architectures which aim to support live migration 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, hax 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.

kernel_irqchip=on|off

Controls in-kernel irqchip support for the chosen accelerator when available.

gfx_passthru=on|off

Enables

IGD GFX

passthrough support for the chosen machine when available.

vmport=on|off|auto

Enables emulation of VMWare

IO

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

kvm_shadow_mem=size

Defines the size of the

KVM

shadow

MMU.

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.

s390-squash-mcss=on|off

Enables or disables squashing subchannels into the default css. The default is off.

enforce-config-section=on|off

If enforce-config-section is set to on, force migration code to send configuration section even if the machine-type sets the migration.send-configuration property to off.

NOTE:

this parameter is deprecated. Please use -global migration.send-configuration=on|off instead.

-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, hax 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.

thread=single|multi

Controls number of

TCG

threads. When the

TCG

is multi-threaded there will be one thread per vCPU therefor taking advantage of additional host cores. The default is to enable multi-threading where both the back-end and front-ends support it and no incompatible

TCG

features have been enabled (e.g. icount/replay).

-smp [cpus=]n[,cores=cores][,threads=threads][,sockets=sockets][,maxcpus=maxcpus]

Simulate an

SMP

system with n CPUs. On the

PC

target, up to 255 CPUs are supported. On Sparc32 target, Linux limits the number of usable CPUs to 4. For the

PC

target, the number of cores per socket, the number of threads per cores and the total number of sockets can be specified. Missing values will be computed. If any on the three values is given, the total number of CPUs n can be omitted. maxcpus specifies the maximum number of hotpluggable CPUs.

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

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

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

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

Define a

NUMA

node and assign

RAM

and VCPUs to it. Set the

NUMA

distance from a source node to a destination node.

Legacy

VCPU

assignment uses cpus option where firstcpu and lastcpu are

CPU

indexes. Each cpus option represent a contiguous range of

CPU

indexes (or a single

VCPU

if lastcpu is omitted). A non-contiguous set of VCPUs can be represented by providing multiple cpus options. If cpus is omitted on all nodes, VCPUs are automatically split between them.

For example, the following option assigns VCPUs 0, 1, 2 and 5 to a

NUMA

node:

        -numa node,cpus=0-2,cpus=5

cpu option is a new alternative to cpus option which uses socket-id|core-id|thread-id properties to assign

CPU

objects to a node using topology layout properties of

CPU.

The set of properties is machine specific, and depends on used machine type/smp options. It could be queried with hotpluggable-cpus monitor command. node-id property specifies node to which

CPU

object will be assigned, it's required for node to be declared with node option before it's used with cpu option.

For example:

        -M pc \
        -smp 1,sockets=2,maxcpus=2 \
        -numa node,nodeid=0 -numa node,nodeid=1 \
        -numa cpu,node-id=0,socket-id=0 -numa cpu,node-id=1,socket-id=1

mem assigns a given

RAM

amount to a node. memdev assigns

RAM

from a given memory backend device to a node. If mem and memdev are omitted in all nodes,

RAM

is split equally between them.

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

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.

-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-i386
        -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-i386 -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-i386 -boot order=nc
        # boot from CD-ROM first, switch back to default order after reboot
        qemu-system-i386 -boot once=d
        # boot with a splash picture for 5 seconds.
        qemu-system-i386 -boot menu=on,splash=/root/boot.bmp,splash-time=5000

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

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

Sets guest startup

RAM

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

For example, the following command-line sets the guest startup

RAM

size to 1GB, creates 3 slots to hotplug additional memory and sets the maximum memory the guest can reach to 4GB:

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

If slots and maxmem are not specified, memory hotplug won't be enabled and the guest startup

RAM

will never increase.

-mem-path path

Allocate guest

RAM

from a temporarily created file in path.

-mem-prealloc

Preallocate memory when using -mem-path.

-k language

Use keyboard layout language (for example "fr" for French). This option is only needed where it is not easy to get raw

PC

keycodes (e.g. on Macs, with some X11 servers or with a

VNC

or curses display). You don't normally need to use it on PC/Linux or PC/Windows hosts.

The available layouts are:

        ar  de-ch  es  fo     fr-ca  hu  ja  mk     no  pt-br  sv
        da  en-gb  et  fr     fr-ch  is  lt  nl     pl  ru     th
        de  en-us  fi  fr-be  hr     it  lv  nl-be  pt  sl     tr

The default is "en-us".

-audio-help

Will show the audio subsystem help: list of drivers, tunable parameters.

-soundhw card1[,card2,...] or -soundhw all

Enable audio and selected sound hardware. Use 'help' to print all available sound hardware.

        qemu-system-i386 -soundhw sb16,adlib disk.img
        qemu-system-i386 -soundhw es1370 disk.img
        qemu-system-i386 -soundhw ac97 disk.img
        qemu-system-i386 -soundhw hda disk.img
        qemu-system-i386 -soundhw all disk.img
        qemu-system-i386 -soundhw help

Note that Linux's i810_audio

OSS

kernel (for

AC97

) module might require manually specifying clocking.

        modprobe i810_audio clocking=48000

-balloon none

Disable balloon device.

-balloon virtio[,addr=addr]

Enable virtio balloon device (default), optionally with

PCI

address addr.

-device driver[,prop[=value][,...]]

Add device driver. prop=value sets driver properties. Valid properties depend on the driver. To get help on possible drivers and properties, use "-device help" and "-device driver,help".

Some drivers are:

-device ipmi-bmc-sim,id=id[,slave_addr=val][,sdrfile=file][,furareasize=val][,furdatafile=file]

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.

bmc=id

The

BMC

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

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.

-device ipmi-bmc-extern,id=id,chardev=id[,slave_addr=val]

Add a connection to an external

IPMI BMC

simulator. Instead of locally emulating the

BMC

like the above item, instead connect to an external entity that provides the

IPMI

services.

A connection is made to an external

BMC

simulator. If you do this, it is strongly recommended that you use the ``reconnect='' chardev option to reconnect to the simulator if the connection is lost. Note that if this is not used carefully, it can be a security issue, as the interface has the ability to send resets, NMIs, and power off the

VM.

It's best if

QEMU

makes a connection to an external simulator running on a secure port on localhost, so neither the simulator nor

QEMU

is exposed to any outside network.

See the ``lanserv/README.vm'' file in the OpenIPMI library for more details on the external interface.

-device isa-ipmi-kcs,bmc=id[,ioport=val][,irq=val]

Add a

KCS IPMI

interafce 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.

-name name

Sets the name of the guest. This name will be displayed in the

SDL

window caption. The name will also be used for the

VNC

server. Also optionally set the top visible process name in Linux. Naming of individual threads can also be enabled on Linux to aid debugging.

-uuid uuid

Set system

UUID.

Block device options

-fda file

-fdb file

Use file as floppy disk 0/1 image.

-hda file

-hdb file

-hdc file

-hdd file

Use file as hard disk 0, 1, 2 or 3 image.

-cdrom file

Use file as CD-ROM image (you cannot use -hdc and -cdrom at the same time). You can use the host CD-ROM by using /dev/cdrom as filename.

-blockdev option[,option[,option[,...]]]

Define a new block driver node. Some of the options apply to all block drivers, other options are only accepted for a specific block driver. See below for a list of generic options and 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.

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, default: threads)

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 an empty string 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: 1048576 bytes or 8 clusters, whichever is larger)

l2-cache-size

The maximum size of the L2 table cache in bytes (default: 4/5 of the total cache size)

refcount-cache-size

The maximum size of the refcount block cache in bytes (default: 1/5 of the total cache size)

cache-clean-interval

Clean unused entries in the L2 and refcount caches. The interval is in seconds. The default value is 0 and it 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)

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

media=media

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

cyls=c,heads=h,secs=s[,trans=t]

These options have the same definition as they have in -hdachs. These parameters are deprecated, use the corresponding parameters of "-device" instead.

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'', or ``native'' and selects between pthread based disk I/O and native Linux

AIO.

format=format

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

serial=serial

This option specifies the serial number to assign to the device. This parameter is deprecated, use the corresponding parameter of "-device" instead.

addr=addr

Specify the controller's

PCI

address (if=virtio only). This parameter is deprecated, use the corresponding parameter of "-device" instead.

werror=action,rerror=action

Specify which action to take on write and read errors. Valid actions are: ``ignore'' (ignore the error and try to continue), ``stop'' (pause

QEMU

), ``report'' (report the error to the guest), ``enospc'' (pause

QEMU

only if the host disk is full; report the error to the guest otherwise). The default setting is werror=enospc and rerror=report.

copy-on-read=copy-on-read

copy-on-read is ``on'' or ``off'' and enables whether to copy read backing file sectors into the image file.

bps=b,bps_rd=r,bps_wr=w

Specify bandwidth throttling limits in bytes per second, either for all request types or for reads or writes only. Small values can lead to timeouts or hangs inside the guest. A safe minimum for disks is 2 MB/s.

bps_max=bm,bps_rd_max=rm,bps_wr_max=wm

Specify bursts in bytes per second, either for all request types or for reads or writes only. Bursts allow the guest I/O to spike above the limit temporarily.

iops=i,iops_rd=r,iops_wr=w

Specify request rate limits in requests per second, either for all request types or for reads or writes only.

iops_max=bm,iops_rd_max=rm,iops_wr_max=wm

Specify bursts in requests per second, either for all request types or for reads or writes only. Bursts allow the guest I/O to spike above the limit temporarily.

iops_size=is

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

group=g

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

By default, the cache.writeback=on mode is used. It will report data writes as completed as soon as the data is present in the host page cache. This is safe as long as your guest

OS

makes sure to correctly flush disk caches where needed. If your guest

OS

does not handle volatile disk write caches correctly and your host crashes or loses power, then the guest may experience data corruption.

For such guests, you should consider using cache.writeback=off. This means that the host page cache will be used to read and write data, but write notification will be sent to the guest only after

QEMU

has made sure to flush each write to the disk. Be aware that this has a major impact on performance.

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

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

Instead of -cdrom you can use:

        qemu-system-i386 -drive file=file,index=2,media=cdrom

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

        qemu-system-i386 -drive file=file,index=0,media=disk
        qemu-system-i386 -drive file=file,index=1,media=disk
        qemu-system-i386 -drive file=file,index=2,media=disk
        qemu-system-i386 -drive file=file,index=3,media=disk

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

        qemu-system-i386
        -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-i386 -drive file=file,if=ide,index=1,media=cdrom

If you don't specify the ``file='' argument, you define an empty drive:

        qemu-system-i386 -drive if=ide,index=1,media=cdrom

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

        qemu-system-i386 -drive file=file,index=0,if=floppy
        qemu-system-i386 -drive file=file,index=1,if=floppy

By default, interface is ``ide'' and index is automatically incremented:

        qemu-system-i386 -drive file=a -drive file=b"

is interpreted like:

        qemu-system-i386 -hda a -hdb b

-mtdblock file

Use file as on-board Flash memory image.

-sd file

Use file as SecureDigital card image.

-pflash file

Use file as a parallel flash image.

-snapshot

Write to temporary files instead of disk image files. In this case, the raw disk image you use is not written back. You can however force the write back by pressing C-a s.

-hdachs c,h,s,[,t]

Force hard disk 0 physical geometry (1 <= c <= 16383, 1 <= h <= 16, 1 <= s <= 63) and optionally force the

BIOS

translation mode (t=none, lba or auto). Usually

QEMU

can guess all those parameters. This option is deprecated, please use "-device ide-hd,cyls=c,heads=h,secs=s,..." instead.

-fsdev fsdriver,id=id,path=path,[security_model=security_model][,writeout=writeout][,readonly][,socket=socket|sock_fd=sock_fd][,fmode=fmode][,dmode=dmode]

Define a new file system device. Valid options are:

fsdriver

This option specifies the fs driver backend to use. Currently ``local'', ``handle'' and ``proxy'' file system drivers are supported.

id=id

Specifies identifier for this device

path=path

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

security_model=security_model

Specifies the security model to be used for this export path. Supported security models are ``passthrough'', ``mapped-xattr'', ``mapped-file'' and ``none''. In ``passthrough'' security model, files are stored using the same credentials as they are created on the guest. This requires

QEMU

to run as root. In ``mapped-xattr'' security model, some of the file attributes like uid, gid, mode bits and link target are stored as file attributes. For ``mapped-file'' these attributes are stored in the hidden .virtfs_metadata directory. Directories exported by this security model cannot interact with other unix tools. ``none'' security model is same as passthrough except the sever won't report failures if it fails to set file attributes like ownership. Security model is mandatory only for local fsdriver. Other fsdrivers (like handle, proxy) don't take security model as a parameter.

writeout=writeout

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

readonly

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

socket=socket

Enables proxy filesystem driver to use passed socket file for communicating with virtfs-proxy-helper

sock_fd=sock_fd

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

fmode=fmode

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

dmode=dmode

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

-fsdev option is used along with -device driver ``virtio-9p-pci''.

-device virtio-9p-pci,fsdev=id,mount_tag=mount_tag

Options for virtio-9p-pci driver are:

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 fsdriver[,path=path],mount_tag=mount_tag[,security_model=security_model][,writeout=writeout][,readonly][,socket=socket|sock_fd=sock_fd][,fmode=fmode][,dmode=dmode]

The general form of a Virtual File system pass-through options are:

fsdriver

This option specifies the fs driver backend to use. Currently ``local'', ``handle'' and ``proxy'' file system drivers are supported.

id=id

Specifies identifier for this device

path=path

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

security_model=security_model

Specifies the security model to be used for this export path. Supported security models are ``passthrough'', ``mapped-xattr'', ``mapped-file'' and ``none''. In ``passthrough'' security model, files are stored using the same credentials as they are created on the guest. This requires

QEMU

to run as root. In ``mapped-xattr'' security model, some of the file attributes like uid, gid, mode bits and link target are stored as file attributes. For ``mapped-file'' these attributes are stored in the hidden .virtfs_metadata directory. Directories exported by this security model cannot interact with other unix tools. ``none'' security model is same as passthrough except the sever won't report failures if it fails to set file attributes like ownership. Security model is mandatory only for local fsdriver. Other fsdrivers (like handle, proxy) don't take security model as a parameter.

writeout=writeout

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

readonly

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

socket=socket

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

sock_fd

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

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''.

-virtfs_synth

Create synthetic file system image

options

-usb

Enable the

USB

driver (if it is not used by default yet).

-usbdevice devname

Add the

USB

device devname. Note that this option is deprecated, please use "-device usb-..." instead.

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.

disk:[format=format]:file

Mass storage device based on file. The optional format argument will be used rather than detecting the format. Can be used to specify "format=raw" to avoid interpreting an untrusted format header.

host:bus.addr

Pass through the host device identified by bus.addr (Linux only).

host:vendor_id:product_id

Pass through the host device identified by vendor_id:product_id (Linux only).

serial:[vendorid=vendor_id][,productid=product_id]:dev

Serial converter to host character device dev, see "-serial" for the available devices.

braille

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

net:options

Network adapter that supports

CDC

ethernet and

RNDIS

protocols.

Display options

-display type

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

sdl

Display video output via

SDL

(usually in a separate graphics window; see the

SDL

documentation for other possibilities).

curses

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.

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.

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.

vnc

Start a

VNC

server on display <arg>

-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.

-curses

Normally, if

QEMU

is compiled with graphical window support, it displays output such as guest graphics, guest console, and the

QEMU

monitor in a window. With this option,

QEMU

can display the

VGA

output when in text mode using a curses/ncurses interface. Nothing is displayed in graphical mode.

-no-frame

Do not use decorations for

SDL

windows and start them using the whole available screen space. This makes the using

QEMU

in a dedicated desktop workspace more convenient.

-alt-grab

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

-ctrl-grab

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

-no-quit

Disable

SDL

window close capability.

-sdl

Enable

SDL.

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

Enable the spice remote desktop protocol. Valid options are

port=<nr>

Set the

TCP

port spice is listening on for plaintext channels.

addr=<addr>

Set the

IP

address spice is listening on. Default is any address.

ipv4

ipv6

unix

Force using the specified

IP

version.

password=<secret>

Set the password you need to authenticate.

sasl

Require that the client use

SASL

to authenticate with the spice. The exact choice of authentication method used is controlled from the system / user's

SASL

configuration file for the 'qemu' service. This is typically found in /etc/sasl2/qemu.conf. If running

QEMU

as an unprivileged user, an environment variable

SASL_CONF_PATH

can be used to make it search alternate locations for the service config. While some

SASL

auth methods can also provide data encryption (eg

GSSAPI

), it is recommended that

SASL

always be combined with the 'tls' and 'x509' settings to enable use of

SSL

and server certificates. This ensures a data encryption preventing compromise of authentication credentials.

disable-ticketing

Allow client connects without authentication.

disable-copy-paste

Disable copy paste between the client and the guest.

disable-agent-file-xfer

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

tls-port=<nr>

Set the

TCP

port spice is listening on for encrypted channels.

x509-dir=<dir>

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

x509-key-file=<file>

x509-key-password=<file>

x509-cert-file=<file>

x509-cacert-file=<file>

x509-dh-key-file=<file>

The x509 file names can also be configured individually.

tls-ciphers=<list>

Specify which ciphers to use.

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

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

Force specific channel to be used with or without

TLS

encryption. The options can be specified multiple times to configure multiple channels. The special name ``default'' can be used to set the default mode. For channels which are not explicitly forced into one mode the spice client is allowed to pick tls/plaintext as he pleases.

image-compression=[auto_glz|auto_lz|quic|glz|lz|off]

Configure image compression (lossless). Default is auto_glz.

jpeg-wan-compression=[auto|never|always]

zlib-glz-wan-compression=[auto|never|always]

Configure wan image compression (lossy for slow links). Default is auto.

streaming-video=[off|all|filter]

Configure video stream detection. Default is off.

agent-mouse=[on|off]

Enable/disable passing mouse events via vdagent. Default is on.

playback-compression=[on|off]

Enable/disable audio stream compression (using celt 0.5.1). Default is on.

seamless-migration=[on|off]

Enable/disable spice seamless migration. Default is off.

gl=[on|off]

Enable/disable OpenGL context. Default is off.

rendernode=<file>

DRM

render node for OpenGL rendering. If not specified, it will pick the first available. (Since 2.9)

-portrait

Rotate graphical output 90 deg left (only

PXA LCD

).

-rotate deg

Rotate graphical output some deg left (only

PXA LCD

).

-vga type

Select type of

VGA

card to emulate. Valid values for type are

cirrus

Cirrus Logic

GD5446

Video card. All Windows versions starting from Windows 95 should recognize and use this graphic card. For optimal performances, use 16 bit color depth in the guest and the host

OS.

(This card was the default before

QEMU 2.2

)

std

Standard

VGA

card with Bochs

VBE

extensions. If your guest

OS

supports the

VESA 2.0 VBE

extensions (e.g. Windows

XP

) and if you want to use high resolution modes (>= 1280x1024x16) then you should use this option. (This card is the default since

QEMU 2.2

)

vmware

VMWare SVGA-II compatible adapter. Use it if you have sufficiently recent XFree86/XOrg server or Windows guest with a driver for this card.

qxl

QXL

paravirtual graphic card. It is

VGA

compatible (including

VESA 2.0 VBE

support). Works best with qxl guest drivers installed though. Recommended choice when using the spice protocol.

tcx

(sun4m only) Sun

TCX

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

cg3

(sun4m only) Sun cgthree framebuffer. This is a simple 8-bit framebuffer for sun4m machines available in both 1024x768 (OpenBIOS) and 1152x900 (

OBP

) resolutions aimed at people wishing to run older Solaris versions.

virtio

Virtio

VGA

card.

none

Disable

VGA

card.

-full-screen

Start in full screen.

-g widthxheight[xdepth]

Set the initial graphical resolution and depth (

PPC, SPARC

only).

-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 origianlly defined "-vnc display" is not available, e.g. port 5900+display is already used by another application. By default, to=0.

host:d

TCP

connections will only be allowed from host on display d. By convention the

TCP

port is 5900+d. Optionally, host can be omitted in which case the server will accept connections from any host.

unix:path

Connections will be allowed over

UNIX

domain sockets where path is the location of a unix socket to listen for connections on.

none

VNC

is initialized but not started. The monitor "change" command can be used to later start the

VNC

server.

Following the display value there may be one or more option flags separated by commas. Valid options are

reverse

Connect to a listening

VNC

client via a ``reverse'' 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

Opens an additional

TCP

listening port dedicated to

VNC

Websocket connections. If a bare websocket option is given, the Websocket port is 5700+display. An alternative port can be specified with the syntax "websocket"=port.

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

If no

TLS

credentials are provided, the websocket connection runs in unencrypted mode. If

TLS

credentials are provided, the websocket connection requires encrypted client connections.

password

Require that password based authentication is used for client connections.

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

If you would like to change <protocol> password expiration, you should use "expire_password <protocol> <expiration-time>" where expiration time could be one of the following options: now, never, +seconds or

UNIX

time of expiration, e.g. +60 to make password expire in 60 seconds, or 1335196800 to make password expire on ``Mon Apr 23 12:00:00

EDT 2012''

(

UNIX

time for this date and time).

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

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.

The tls-creds parameter obsoletes the tls, x509, and x509verify options, and as such it is not permitted to set both new and old type options at the same time.

tls

Require that client use

TLS

when communicating with the

VNC

server. This uses anonymous

TLS

credentials so is susceptible to a man-in-the-middle attack. It is recommended that this option be combined with either the x509 or x509verify options.

This option is now deprecated in favor of using the tls-creds argument.

x509=/path/to/certificate/dir

Valid if tls is specified. Require that x509 credentials are used for negotiating the

TLS

session. The server will send its x509 certificate to the client. It is recommended that a password be set on the

VNC

server to provide authentication of the client when this is used. The path following this option specifies where the x509 certificates are to be loaded from. See the vnc_security section for details on generating certificates.

This option is now deprecated in favour of using the tls-creds argument.

x509verify=/path/to/certificate/dir

Valid if tls is specified. Require that x509 credentials are used for negotiating the

TLS

session. The server will send its x509 certificate to the client, and request that the client send its own x509 certificate. The server will validate the client's certificate against the

CA

certificate, and reject clients when validation fails. If the certificate authority is trusted, this is a sufficient authentication mechanism. You may still wish to set a password on the

VNC

server as a second authentication layer. The path following this option specifies where the x509 certificates are to be loaded from. See the vnc_security section for details on generating certificates.

This option is now deprecated in favour of using the tls-creds argument.

sasl

Require that the client use

SASL

to authenticate with the

VNC

server. The exact choice of authentication method used is controlled from the system / user's

SASL

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 for details on using

SASL

authentication.

acl

Turn on access control lists for checking of the x509 client certificate and

SASL

party. For x509 certs, the

ACL

check is made against the certificate's distinguished name. This is something that looks like "C=GB,O=ACME,L=Boston,CN=bob". For

SASL

party, the

ACL

check is made against the username, which depending on the

SASL

plugin, may include a realm component, eg "bob" or "bob@EXAMPLE.COM". When the acl flag is set, the initial access list will be empty, with a "deny" policy. Thus no one will be allowed to use the

VNC

server until the ACLs have been loaded. This can be achieved using the "acl" monitor command.

lossy

Enable lossy compression methods (gradient,

JPEG, ...

). If this option is set,

VNC

client may receive lossy framebuffer updates depending on its encoding settings. Enabling this option can save a lot of bandwidth at the expense of quality.

non-adaptive

Disable adaptive encodings. Adaptive encodings are 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.

i386 target only

-win2k-hack

Use it when installing Windows 2000 to avoid a disk full bug. After Windows 2000 is installed, you no longer need this option (this option slows down the

IDE

transfers).

-no-fd-bootchk

Disable boot signature checking for floppy disks in

BIOS.

May be needed to boot from old floppy disks.

-no-acpi

Disable

ACPI

(Advanced Configuration and Power Interface) support. Use it if your guest

OS

complains about

ACPI

problems (

PC

target machine only).

-no-hpet

Disable

HPET

support.

-acpitable [sig=str][,rev=n][,oem_id=str][,oem_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][,family=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]

Specify

SMBIOS

type 4 fields

-smbios type=17[,loc_pfx=str][,bank=str][,manufacturer=str][,serial=str][,asset=str][,part=str][,speed=%d]

Specify

SMBIOS

type 17 fields

Network options

-net nic[,vlan=n][,macaddr=mac][,model=type] [,name=name][,addr=addr][,vectors=v]

Create a new Network Interface Card and connect it to

VLAN

n (n = 0 is the default). The

NIC

is an e1000 by default on the

PC

target. 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. Valid values for type are "virtio", "i82551", "i82557b", "i82559er", "ne2k_pci", "ne2k_isa", "pcnet", "rtl8139", "e1000", "smc91c111", "lance" and "mcf_fec". Not all devices are supported on all targets. Use "-net nic,model=help" for a list of available devices for your target.

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

-net user[,option][,option][,...]

Use the user mode network stack which requires no administrator privilege to run. Valid options are:

vlan=n

Connect user mode stack to

VLAN

n (n = 0 is the default).

id=id

name=name

Assign symbolic name for use in monitor commands.

ipv4 and ipv6 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 -net user,dnssearch=mgmt.example.org,dnssearch=example.org [...]

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).

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-i386 -hda linux.img -boot n -net user,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. QEMU

was tested successfully with smbd versions from Red Hat 9, Fedora Core 3 and OpenSUSE 11.x.

hostfwd=[tcp|udp]:[hostaddr]:hostport-[guestaddr]:guestport

Redirect incoming

TCP

or

UDP

connections to the host port hostport to the guest

IP

address guestaddr on guest port guestport. If guestaddr is not specified, its value is x.x.x.15 (default first address given by the built-in

DHCP

server). By specifying hostaddr, the rule can be bound to a specific host interface. If no connection type is set,

TCP

is used. This option can be given multiple times.

For example, to redirect host X11 connection from screen 1 to guest screen 0, use the following:

        # on the host
        qemu-system-i386 -net 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-i386 -net user,hostfwd=tcp::5555-:23 [...]
        telnet localhost 5555

Then when you use on the host "telnet localhost 5555", you connect to the guest telnet server.

guestfwd=[tcp]:server:port-dev

guestfwd=[tcp]:server:port-cmd:command

Forward guest

TCP

connections to the

IP

address server on port port to the character device dev or to a program executed by cmd:command which gets spawned for each connection. This option can be given multiple times.

You can either use a chardev directly and have that one used throughout

QEMU

's lifetime, like in the following example:

        # open 10.10.1.1:4321 on bootup, connect 10.0.2.100:1234 to it whenever
        # the guest accesses it
        qemu -net 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 -net 'user,guestfwd=tcp:10.0.2.100:1234-cmd:netcat 10.10.1.1 4321'

Note: Legacy stand-alone options -tftp, -bootp, -smb and -redir are still processed and applied to -net user. Mixing them with the new configuration syntax gives undefined results. Their use for new applications is discouraged as they will be removed from future versions.

-netdev tap,id=id[,fd=h][,ifname=name][,script=file][,downscript=dfile][,br=bridge][,helper=helper]

-net tap[,vlan=n][,name=name][,fd=h][,ifname=name][,script=file][,downscript=dfile][,br=bridge][,helper=helper]

Connect the host

TAP

network interface name to

VLAN

n.

Use the network script file to configure it and the network script dfile to deconfigure it. If name is not provided, the

OS

automatically provides one. The default network configure script is /etc/qemu-ifup and the default network deconfigure script is /etc/qemu-ifdown. Use script=no or downscript=no to disable script execution.

If running

QEMU

as an unprivileged user, use the network helper helper to configure the

TAP

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

fd=h can be used to specify the handle of an already opened host

TAP

interface.

Examples:

        #launch a QEMU instance with the default network script
        qemu-system-i386 linux.img -net nic -net tap

        
        #launch a QEMU instance with two NICs, each one connected
        #to a TAP device
        qemu-system-i386 linux.img \
        -net nic,vlan=0 -net tap,vlan=0,ifname=tap0 \
        -net nic,vlan=1 -net tap,vlan=1,ifname=tap1

        
        #launch a QEMU instance with the default network helper to
        #connect a TAP device to bridge br0
        qemu-system-i386 linux.img \
        -net nic -net tap,"helper=/path/to/qemu-bridge-helper"

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

-net bridge[,vlan=n][,name=name][,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-i386 linux.img -net bridge -net nic,model=virtio

        
        #launch a QEMU instance with the default network helper to
        #connect a TAP device to bridge qemubr0
        qemu-system-i386 linux.img -net bridge,br=qemubr0 -net nic,model=virtio

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

-net socket[,vlan=n][,name=name][,fd=h] [,listen=[host]:port][,connect=host:port]

Connect the

VLAN

n to a remote

VLAN

in 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-i386 linux.img \
        -net nic,macaddr=52:54:00:12:34:56 \
        -net socket,listen=:1234
        # connect the VLAN 0 of this instance to the VLAN 0
        # of the first instance
        qemu-system-i386 linux.img \
        -net nic,macaddr=52:54:00:12:34:57 \
        -net socket,connect=127.0.0.1:1234

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

-net socket[,vlan=n][,name=name][,fd=h][,mcast=maddr:port[,localaddr=addr]]

Create a

VLAN

n shared with another

QEMU

virtual machines using a

UDP

multicast socket, effectively making a bus for every

QEMU

with same multicast address maddr and port.

NOTES:

1.

Several

QEMU

can be running on different hosts and share same bus (assuming correct multicast setup for these hosts).

2.

mcast support is compatible with User Mode Linux (argument ethN=mcast), see <user-mode-linux.sf.net>.

3.

Use fd=h to specify an already opened

UDP

multicast socket.

Example:

        # launch one QEMU instance
        qemu-system-i386 linux.img \
        -net nic,macaddr=52:54:00:12:34:56 \
        -net socket,mcast=230.0.0.1:1234
        # launch another QEMU instance on same "bus"
        qemu-system-i386 linux.img \
        -net nic,macaddr=52:54:00:12:34:57 \
        -net socket,mcast=230.0.0.1:1234
        # launch yet another QEMU instance on same "bus"
        qemu-system-i386 linux.img \
        -net nic,macaddr=52:54:00:12:34:58 \
        -net socket,mcast=230.0.0.1:1234

Example (User Mode Linux compat.):

        # launch QEMU instance (note mcast address selected
        # is UML's default)
        qemu-system-i386 linux.img \
        -net nic,macaddr=52:54:00:12:34:56 \
        -net socket,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-i386 linux.img \
        -net nic,macaddr=52:54:00:12:34:56 \
        -net socket,mcast=239.192.168.1:1102,localaddr=1.2.3.4

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

-net l2tpv3[,vlan=n][,name=name],src=srcaddr,dst=dstaddr[,srcport=srcport][,dstport=dstport],txsession=txsession[,rxsession=rxsession][,ipv6][,udp][,cookie64][,counter][,pincounter][,txcookie=txcookie][,rxcookie=rxcookie][,offset=offset]

Connect

VLAN

n to L2TPv3 pseudowire. L2TPv3 (

RFC3391

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

This transport allows a

VM

to communicate to another

VM,

router or firewall directly.

src=srcaddr

source address (mandatory)

dst=dstaddr

destination address (mandatory)

udp

select udp encapsulation (default is ip).

srcport=srcport

source udp port.

dstport=dstport

destination udp port.

ipv6

force v6, otherwise defaults to v4.

rxcookie=rxcookie

txcookie=txcookie

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

cookie64

Set cookie size to 64 bit instead of the default 32

counter=off

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

pincounter=on

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

offset=offset

Add an extra offset between header and data

For example, to attach a

VM

running on host 4.3.2.1 via L2TPv3 to the bridge br-lan on the remote Linux host 1.2.3.4:

        # Setup tunnel on linux host using raw ip as encapsulation
        # on 1.2.3.4
        ip l2tp add tunnel remote 4.3.2.1 local 1.2.3.4 tunnel_id 1 peer_tunnel_id 1 \
        encap udp udp_sport 16384 udp_dport 16384
        ip l2tp add session tunnel_id 1 name vmtunnel0 session_id \
        0xFFFFFFFF peer_session_id 0xFFFFFFFF
        ifconfig vmtunnel0 mtu 1500
        ifconfig vmtunnel0 up
        brctl addif br-lan vmtunnel0
        
        
        # on 4.3.2.1
        # launch QEMU instance - if your network has reorder or is very lossy add ,pincounter
        
        qemu-system-i386 linux.img -net nic -net l2tpv3,src=4.2.3.1,dst=1.2.3.4,udp,srcport=16384,dstport=16384,rxsession=0xffffffff,txsession=0xffffffff,counter

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

-net vde[,vlan=n][,name=name][,sock=socketpath] [,port=n][,group=groupname][,mode=octalmode]

Connect

VLAN

n 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-i386 linux.img -net nic -net vde,sock=/tmp/myswitch

-netdev hubport,id=id,hubid=hubid

Create a hub port on

QEMU

``vlan'' hubid.

The hubport netdev lets you connect a

NIC

to a

QEMU

``vlan'' instead of a single netdev. "-net" and "-device" with parameter vlan create the required hub automatically.

-netdev vhost-user,chardev=id[,vhostforce=on|off][,queues=n]

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

Example:

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

-net dump[,vlan=n][,file=file][,len=len]

Dump network traffic on

VLAN

n to file file (qemu-vlan0.pcap by default). 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. Note: For devices created with '-netdev', use '-object filter-dump,...' instead.

-net none

Indicate that no network devices should be configured. It is used to override the default configuration (-net nic -net user) which is activated if no -net options are provided.

Character device options

The general form of a character device option is:

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

Backend is one of: null, socket, udp, msmouse, vc, ringbuf, file, pipe, console, serial, pty, stdio, braille, tty, parallel, parport, spicevmc. spiceport. The specific backend will 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.

Note that some other command line options may implicitly create multiplexed character backends; for instance -serial mon:stdio creates a multiplexed stdio backend connected to the serial port and the

QEMU

monitor, and -nographic also multiplexes the console and the monitor to stdio.

There is currently no support for multiplexing in the other direction (where a single

QEMU

front end takes input and output from multiple chardevs).

Every backend supports the logfile option, which supplies the path to a file to record all data transmitted via the backend. The logappend option controls whether the log file will be truncated or appended to when opened.

Further options to each backend are described below.

-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] [,nowait] [,telnet] [,reconnect=seconds] [,tls-creds=id]

Create a two-way stream socket, which can be either a

TCP

or a unix socket. A unix socket will be created if path is specified. Behaviour is undefined if

TCP

options are specified for a unix socket.

server specifies that the socket shall be a listening socket.

nowait specifies that

QEMU

should not block waiting for a client to connect to a listening socket.

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

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

tls-creds requests enablement of the

TLS

protocol for encryption, and specifies the id of the

TLS

credentials to use for the handshake. The credentials must be previously created with the -object tls-creds argument.

TCP

and unix socket options are given below:

TCP

options: port=port [,host=host] [,to=to] [,ipv4] [,ipv6] [,nodelay]

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

nodelay disables the Nagle algorithm.

unix options: path=path

path specifies the local path of the unix socket. path is required.

-chardev udp ,id=id [,host=host] ,port=port [,localaddr=localaddr] [,localport=localport] [,ipv4] [,ipv6]

Sends all traffic from the guest to a remote host over

UDP.

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

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

localaddr specifies the local address to bind to. If not 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 and ipv6 specify that either IPv4 or IPv6 must be used. If neither is specified the device may use either protocol.

-chardev msmouse ,id=id

Forward

QEMU

's emulated msmouse events to the guest. msmouse does not take any options.

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

Connect to a

QEMU

text console. vc may optionally be given a specific size.

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

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

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

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

-chardev file ,id=id ,path=path

Log all traffic received from the guest to a file.

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

-chardev pipe ,id=id ,path=path

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

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

On other hosts, 2 pipes will be created called path.in and path.out. Data written to path.in will be received by the guest. Data written by the guest can be read from path.out.

QEMU

will not create these fifos, and requires them to be present.

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

-chardev console ,id=id

Send traffic from the guest to

QEMU

's standard output. console does not take any options.

console is only available on Windows hosts.

-chardev serial ,id=id ,path=path

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

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

path specifies the name of the serial device to open.

-chardev pty ,id=id

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

pty is not available on Windows hosts.

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

Connect to standard input and standard output of the

QEMU

process.

signal controls if signals are enabled on the terminal, that includes exiting

QEMU

with the key sequence Control-c. This option is enabled by default, use signal=off to disable it.

-chardev braille ,id=id

Connect to a local BrlAPI server. braille does not take any options.

-chardev tty ,id=id ,path=path

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

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

-chardev parallel ,id=id ,path=path

-chardev parport ,id=id ,path=path

parallel is only available on Linux, FreeBSD and DragonFlyBSD hosts.

Connect to a local parallel port.

path specifies the path to the parallel port device. path is 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).

Device

Syntax

In addition to using normal file images for the emulated storage devices,

can also use networked resources such as iSCSI devices. These are specified using a special syntax.

iSCSI

iSCSI support allows

QEMU

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

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

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

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

Example (without authentication):

        qemu-system-i386 -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-i386 -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-i386 -drive file=iscsi://192.0.2.1/iqn.2001-04.com.example/1

iSCSI support is an optional feature of

QEMU

and only available when compiled and linked against libiscsi.

iSCSI parameters such as username and password can also be specified via a configuration file. See qemu-doc for more information and examples.

NBD

QEMU

supports

NBD

(Network Block Devices) both using

TCP

protocol as well as Unix Domain Sockets.

Syntax for specifying a

NBD

device using

TCP

``nbd:<server-ip>:<port>[:exportname=<export>]''

Syntax for specifying a

NBD

device using Unix Domain Sockets ``nbd:unix:<domain-socket>[:exportname=<export>]''

Example for

TCP

        qemu-system-i386 --drive file=nbd:192.0.2.1:30000

Example for Unix Domain Sockets

        qemu-system-i386 --drive file=nbd:unix:/tmp/nbd-socket

SSH

QEMU

supports

SSH

(Secure Shell) access to remote disks.

Examples:

        qemu-system-i386 -drive file=ssh://user@host/path/to/disk.img
        qemu-system-i386 -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.

Sheepdog

Sheepdog is a distributed storage system for

QEMU. QEMU

supports using either local sheepdog devices or remote networked devices.

Syntax for specifying a sheepdog device

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

Example

        qemu-system-i386 --drive file=sheepdog://192.0.2.1:30000/MyVirtualMachine

See also <sheepdog.github.io/sheepdog>.

GlusterFS

GlusterFS is a user space distributed file system.

QEMU

supports the use of GlusterFS volumes for hosting

VM

disk images using

TCP,

Unix Domain Sockets and

RDMA

transport protocols.

Syntax for specifying a

VM

disk image on GlusterFS volume is

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

Example

        URI:
        qemu-system-x86_64 --drive file=gluster://192.0.2.1/testvol/a.img,
                                       file.debug=9,file.logfile=/var/log/qemu-gluster.log
        
        JSON:
        qemu-system-x86_64 'json:{"driver":"qcow2",
                                  "file":{"driver":"gluster",
                                           "volume":"testvol","path":"a.img",
                                           "debug":9,"logfile":"/var/log/qemu-gluster.log",
                                           "server":[{"type":"tcp","host":"1.2.3.4","port":24007},
                                                     {"type":"unix","socket":"/var/run/glusterd.socket"}]}}'
        qemu-system-x86_64 -drive driver=qcow2,file.driver=gluster,file.volume=testvol,file.path=/path/a.img,
                                              file.debug=9,file.logfile=/var/log/qemu-gluster.log,
                                              file.server.0.type=tcp,file.server.0.host=1.2.3.4,file.server.0.port=24007,
                                              file.server.1.type=unix,file.server.1.socket=/var/run/glusterd.socket

See also <www.gluster.org>.

HTTP/HTTPS/FTP/FTPS

QEMU

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

Syntax using a single filename:

        <protocol>://[<username>[:<password>]@]<host>/<path>

where:

protocol

'http', 'https', 'ftp', or 'ftps'.

username

Optional username for authentication to the remote server.

password

Optional password for authentication to the remote server.

host

Address of the remote server.

path

Path on the remote server, including any query string.

The following options are also supported:

url

The full

URL

when passing options to the driver explicitly.

readahead

The amount of data to read ahead with each range request to the remote server. This value may optionally have the suffix 'T', 'G', 'M', 'K', 'k' or 'b'. If it does not have a suffix, it will be assumed to be in bytes. The value must be a multiple of 512 bytes. It defaults to 256k.

sslverify

Whether to verify the remote server's certificate when connecting over

SSL.

It can have the value 'on' or 'off'. It defaults to 'on'.

cookie

Send this cookie (it can also be a list of cookies separated by ';') with each outgoing request. Only supported when using protocols such as

HTTP

which support cookies, otherwise ignored.

timeout

Set the timeout in seconds of the

CURL

connection. This timeout is the time that

CURL

waits for a response from the remote server to get the size of the image to be downloaded. If not set, the default timeout of 5 seconds is used.

Note that when passing options to qemu explicitly, driver is the value of <protocol>.

Example: boot from a remote Fedora 20 live

ISO

image

        qemu-system-x86_64 --drive media=cdrom,file=dl.fedoraproject.org/pub/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=dl.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":"dl.fedoraproject.org/pub/fedora/linux/releases/20/Images/x86_64/Fedora-x86_64-20-20131211.1-sda.qcow2",, "file.readahead":"64k"}' /tmp/Fedora-x86_64-20-20131211.1-sda.qcow2
        
        qemu-system-x86_64 -drive file=/tmp/Fedora-x86_64-20-20131211.1-sda.qcow2,copy-on-read=on

Example: boot from an image stored on a VMware vSphere server with a self-signed certificate using a local overlay for writes, a readahead of 64k and a timeout of 10 seconds.

        qemu-img create -f qcow2 -o backing_file='json:{"file.driver":"https",, "file.url":"user:password@vsphere.example.com/folder/test/test-flat.vmdk?dcPath=Datacenter&dsName=datastore1",, "file.sslverify":"off",, "file.readahead":"64k",, "file.timeout":10}' /tmp/test.qcow2
        
        qemu-system-x86_64 -drive file=/tmp/test.qcow2

Bluetooth(R) options

-bt hci[...]

Defines the function of the corresponding Bluetooth

HCI.

-bt options are matched with the HCIs present in the chosen machine type. For example when emulating a machine with only one

HCI

built into it, only the first "-bt hci[...]" option is valid and defines the

HCI

's logic. The Transport Layer is decided by the machine type. Currently the machines "n800" and "n810" have one

HCI

and all other machines have none.

The following three types are recognized:

-bt hci,null

(default) The corresponding Bluetooth

HCI

assumes no internal logic and will not respond to any

HCI

commands or emit events.

-bt hci,host[:id]

("bluez" only) The corresponding

HCI

passes commands / events to / from the physical

HCI

identified by the name id (default: "hci0") on the computer running

QEMU.

Only available on "bluez" capable systems like Linux.

-bt hci[,vlan=n]

Add a virtual, standard

HCI

that will participate in the Bluetooth scatternet n (default 0). Similarly to -net VLANs, devices inside a bluetooth network n can only communicate with other devices in the same network (scatternet).

-bt vhci[,vlan=n]

(Linux-host only) Create a

HCI

in scatternet n (default 0) attached to the host bluetooth stack instead of to the emulated target. This allows the host and target machines to participate in a common scatternet and communicate. Requires the Linux "vhci" driver installed. Can be used as following:

        qemu-system-i386 [...OPTIONS...] -bt hci,vlan=5 -bt vhci,vlan=5

-bt device:dev[,vlan=n]

Emulate a bluetooth device dev and place it in network n (default 0).

QEMU

can only emulate one type of bluetooth devices currently:

keyboard

Virtual wireless keyboard implementing the

HIDP

bluetooth profile.

device options

The general form of a

device option is:

-tpmdev backend ,id=id [,options]

Backend type must be: passthrough.

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.

Options to each backend are described below.

Use 'help' to print all available

TPM

backend types.

        qemu -tpmdev help

-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.

Linux/Multiboot boot specific

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

-kernel bzImage

Use bzImage as kernel image. The kernel can be either a Linux kernel or in multiboot format.

-append cmdline

Use cmdline as kernel command line

-initrd file

Use file as initial ram disk.

-initrd file1 arg=foo,file2

This syntax is only available with multiboot.

Use file1 and file2 as modules and pass arg=foo as parameter to the first module.

-dtb file

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

Debug/Expert options

-fw_cfg [name=]name,file=file

Add named fw_cfg entry with contents from file file.

-fw_cfg [name=]name,string=str

Add named fw_cfg entry with contents from string str.

The terminating

NUL

character of the contents of str will not be included as part of the fw_cfg item data. To insert contents with embedded

NUL

characters, you have to use the file 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 up to 4 serial ports.

Use "-serial none" to disable all serial ports.

Available character devices are:

vc[:WxH]

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

        vc:800x600

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

        vc:80Cx24C

pty

[Linux only] Pseudo

TTY

(a new

PTY

is automatically allocated)

none

No device is allocated.

null

void device

chardev:id

Use a named character device defined with the "-chardev" option.

/dev/XXX

[Linux only] Use host tty, e.g. /dev/ttyS0. The host serial port parameters are set according to the emulated ones.

/dev/parportN

[Linux only, parallel port only] Use host parallel port N. Currently

SPP

and

EPP

parallel port features can be used.

file:filename

Write output to filename. No character can be read.

stdio

[Unix only] standard input/output

pipe:filename

name pipe filename

COM

n

[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][,nowait][,nodelay][,reconnect=seconds]

The

TCP

Net Console has two modes of operation. It can send the serial I/O to a location or wait for a connection from a location. By default the

TCP

Net Console is sent to host at the port. If you use the server option

QEMU

will wait for a client socket application to connect to the port before continuing, unless the "nowait" option was specified. The "nodelay" option disables the Nagle buffering algorithm. The "reconnect" option only applies if noserver is set, if the connection goes down it will 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" to connect to the corresponding character device.

Example to send tcp console to 192.168.0.2 port 4444

-serial tcp:192.168.0.2:4444

Example to listen and wait on port 4444 for connection

-serial tcp::4444,server

Example to not wait and listen on ip 192.168.0.100 port 4444

-serial tcp:192.168.0.100:4444,server,nowait

telnet:host:port[,server][,nowait][,nodelay]

The telnet protocol is used instead of raw tcp sockets. The options work the same as if you had specified "-serial tcp". The difference is that the port acts like a telnet server or client using telnet option negotiation. This will also allow you to send the

MAGIC_SYSRQ

sequence if you use a telnet that supports sending the break sequence. Typically in unix telnet you do it with Control-] and then type ``send break'' followed by pressing the enter key.

unix:path[,server][,nowait][,reconnect=seconds]

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

When the monitor is multiplexed to stdio in this way, Ctrl+C will not terminate

QEMU

any more but will be passed to the guest instead.

braille

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

msmouse

Three button serial mouse. Configure the guest to use 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.

-qmp-pretty dev

Like -qmp but uses pretty

JSON

formatting.

-mon [chardev=]name[,mode=readline|control]

Setup monitor on chardev name.

-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.

-singlestep

Run the emulation in single step mode.

-S

Do not start

CPU

at startup (you must type 'c' in the monitor).

-realtime mlock=on|off

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

-gdb dev

Wait for gdb connection on device dev. Typical connections will likely be TCP-based, but also

UDP,

pseudo

TTY,

or even stdio are reasonable use case. The latter is allowing to start

QEMU

from within gdb and establish the connection via a pipe:

        (gdb) target remote | exec qemu-system-i386 -gdb stdio ...

-s

Shorthand for -gdb tcp::1234, i.e. open a gdbserver on

TCP

port 1234.

-d item1[,...]

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

-D logfile

Output log in logfile instead of to stderr

-dfilter range1[,...]

Filter debug output to that relevant to a range of target addresses. The filter spec can be either start+size, start-size or start..end where start end and size are the addresses and sizes required. For example:

        -dfilter 0x8000..0x8fff,0xffffffc000080000+0x200,0xffffffc000060000-0x1000

Will dump output for any code in the 0x1000 sized block starting at 0x8000 and the 0x200 sized block starting at 0xffffffc000080000 and another 0x1000 sized block starting at 0xffffffc00005f000.

-L path

Set the directory for the

BIOS, VGA BIOS

and keymaps.

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

-bios file

Set the filename for the

BIOS.

-enable-kvm

Enable

KVM

full virtualization support. This option is only available if

KVM

support is enabled when compiling.

-enable-hax

Enable

HAX

(Hardware-based Acceleration eXecution) support. This option is only available if

HAX

support is enabled when compiling.

HAX

is only applicable to

MAC

and Windows platform, and thus does not conflict with

KVM.

-xen-domid id

Specify xen guest domain id (

XEN

only).

-xen-create

Create domain using xen hypercalls, bypassing xend. Warning: should not be used when xend is in use (

XEN

only).

-xen-attach

Attach to existing xen domain. xend 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.

-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|date][,clock=host|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 date 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. To even prevent it from progressing during suspension, you can set it to "vm".

Enable driftfix (i386 targets only) if you experience time drift problems, specifically with Windows'

ACPI HAL.

This option will try to figure out how many timer interrupts were not processed by the Windows guest and will re-inject them.

-icount [shift=N|auto][,rr=record|replay,rrfile=filename,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.

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

Note that while this option can give deterministic behavior, it does not provide cycle accurate emulation. Modern CPUs contain superscalar out of order cores with complex cache hierarchies. The number of instructions executed often has little or no correlation with actual performance.

align=on will activate the delay algorithm which will try to synchronise the host clock and the virtual clock. The goal is to have a guest running at the real frequency imposed by the shift option. Whenever the guest clock is behind the host clock and if align=on is specified then we print a message to the user to 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).

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

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

VM

state.

-watchdog model

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

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

The following models may be available:

ib700

iBASE 700 is a very simple

ISA

watchdog with a single timer.

i6300esb

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

diag288

A virtual watchdog for s390x backed by the diagnose 288 hypercall (currently

KVM

only).

-watchdog-action action

The action controls what

QEMU

will do when the watchdog timer expires. The default is "reset" (forcefully reset the guest). Other possible actions are: "shutdown" (attempt to gracefully shutdown the guest), "poweroff" (forcefully poweroff the guest), "pause" (pause the guest), "debug" (print a debug message and continue), or "none" (do nothing).

Note that the "shutdown" action requires that the guest responds to

ACPI

signals, which it may not be able to do in the sort of situations where the watchdog would have expired, and thus "-watchdog-action shutdown" is not recommended for production use.

Examples:

-watchdog i6300esb -watchdog-action pause

-watchdog ib700

-echr numeric_ascii_value

Change the escape character used for switching to the monitor when using monitor and serial sharing. The default is 0x01 when using the "-nographic" option. 0x01 is equal to pressing "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

-virtioconsole c

Set virtio console.

This option is maintained for backward compatibility.

Please use "-device virtconsole" for the new way of invocation.

-show-cursor

Show cursor.

-tb-size n

Set

TB

size.

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

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

Prepare for incoming migration, listen on a given tcp port.

-incoming unix:socketpath

Prepare for incoming migration, listen on a given unix socket.

-incoming fd:fd

Accept incoming migration from a given filedescriptor.

-incoming exec:cmdline

Accept incoming migration as an output from specified external command.

-incoming defer

Wait for the

URI

to be specified via migrate_incoming. The 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.

-chroot dir

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

-runas user

Immediately before starting guest execution, drop root privileges, switching to the specified user.

-prom-env variable=value

Set OpenBIOS nvram variable to given value (

PPC, SPARC

only).

-semihosting

Enable semihosting mode (

ARM, M68K,

Xtensa,

MIPS

only).

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

Enable and configure semihosting (

ARM, M68K,

Xtensa,

MIPS

only).

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.

arg=str1,arg=str2,...

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

-old-param

Old param mode (

ARM

only).

-sandbox arg

Enable Seccomp mode 2 system call filter. 'on' will enable syscall filtering and 'off' will disable it. The default is 'off'.

-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.

-writeconfig file

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

-nodefconfig

Normally

QEMU

loads configuration files from sysconfdir and datadir at startup. The "-nodefconfig" option will prevent

QEMU

from loading any of those config files.

-no-user-config

The "-no-user-config" option makes

QEMU

not load any of the user-provided config files on sysconfdir, but won't make it skip the QEMU-provided config files from datadir.

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

Specify tracing options.

[enable=]pattern

Immediately enable events matching pattern. 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. 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.

-enable-fips

Enable

FIPS 140-2

compliance mode.

-msg timestamp[=on|off]

prepend a timestamp to each log message.(default:on)

-dump-vmstate file

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

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

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 when configuring the -numa argument. The size option provides the size of the memory region, and accepts common suffixes, eg 500M. The mem-path provides the path to either a shared memory or huge page filesystem mount. The share boolean option determines whether the memory region is marked as private to

QEMU,

or shared. The latter allows a co-operating external process to access the

QEMU

memory region.

-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/random.

-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-x509,id=id,endpoint=endpoint,dir=/path/to/cred/dir,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.

-object filter-buffer,id=id,netdev=netdevid,interval=t[,queue=all|rx|tx][,status=on|off]

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.

-object filter-mirror,id=id,netdev=netdevid,outdev=chardevid,queue=all|rx|tx[,vnet_hdr_support]

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]

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]

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]

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

-object colo-compare,id=id,primary_in=chardevid,secondary_in=chardevid,outdev=chardevid[,vnet_hdr_support]

Colo-compare gets packet from primary_inchardevid and secondary_inchardevid, than compare primary packet with secondary packet. If the packets are same, we will output primary packet to outdevchardevid, else we will notify colo-frame do checkpoint and send primary packet to outdevchardevid. if it has the vnet_hdr_support flag, colo compare will send/recv packet with vnet_hdr_len.

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

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

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

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

Creates a cryptodev backend which executes crypto opreation from the

QEMU

cipher

APIS.

The id parameter is a unique

ID

that will be used to reference this cryptodev backend from the virtio-crypto device. The queues 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 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 -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 -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

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

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

Ctrl-Alt-f

Toggle full screen

Ctrl-Alt-+

Enlarge the screen

Ctrl-Alt---

Shrink the screen

Ctrl-Alt-u

Restore the screen's un-scaled dimensions

Ctrl-Alt-n

Switch to virtual console 'n'. Standard console mappings are:

1

Target system display

2

Monitor

3

Serial port

Ctrl-Alt

Toggle mouse and keyboard grab.

In the virtual consoles, you can use Ctrl-Up, Ctrl-Down, Ctrl-PageUp and Ctrl-PageDown to move in the back log.

During emulation, if you are using a character backend multiplexer (which is the default if you are using -nographic) then several commands are available via an escape sequence. These key sequences all start with an escape character, which is Ctrl-a by default, but can be changed with -echr. The list below assumes you're using the default.

Ctrl-a h

Print this help

Ctrl-a x

Exit emulator

Ctrl-a s

Save disk data back to file (if -snapshot)

Ctrl-a t

Toggle console timestamps

Ctrl-a b

Send break (magic sysrq in Linux)

Ctrl-a c

Rotate between the frontends connected to the multiplexer (usually this switches between the monitor and the console)

Ctrl-a Ctrl-a

Send the escape character to the frontend

The following options are specific to the PowerPC emulation:

-g WxH[x

DEPTH

]

Set the initial

VGA

graphic mode. The default is 800x600x32.

-prom-env string

Set OpenBIOS variables in

NVRAM,

for example:

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

These variables are not used by Open Hack'Ware.

The following options are specific to the Sparc32 emulation:

-g WxHx[x

DEPTH

]

Set the initial graphics mode. For

TCX,

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.

-prom-env string

Set OpenBIOS variables in

NVRAM,

for example:

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

-M [SS-4|SS-5|SS-10|SS-20|SS-600MP|LX|Voyager|SPARCClassic] [|SPARCbook]

Set the emulated machine type. Default is

SS-5.

The following options are specific to the Sparc64 emulation:

-prom-env string

Set OpenBIOS variables in

NVRAM,

for example:

        qemu-system-sparc64 -prom-env 'auto-boot?=false'

-M [sun4u|sun4v|niagara]

Set the emulated machine type. The default is sun4u.

The following options are specific to the

emulation:

-semihosting

Enable semihosting syscall emulation.

On

ARM

this implements the ``Angel'' interface.

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

OS.

The following options are specific to the ColdFire emulation:

-semihosting

Enable semihosting syscall emulation.

On M68K this implements the ``ColdFire

GDB''

interface used by libgloss.

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

OS.

The following options are specific to the Xtensa emulation:

-semihosting

Enable semihosting syscall emulation.

Xtensa semihosting provides basic file

IO

calls, such as open/read/write/seek/select. Tensilica baremetal libc for

ISS

and linux platform ``sim'' use this interface.

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

OS.

SEE ALSO

The documentation of for more precise information and Linux user mode emulator invocation.

AUTHOR

Fabrice Bellard