QEMU Emulator User Documentation

Table of Contents

1 Introduction

1.1 Features

QEMU is a FAST! processor emulator using dynamic translation to achieve good emulation speed.

QEMU has two operating modes:

QEMU can run without a host kernel driver and yet gives acceptable performance.

For system emulation, the following hardware targets are supported:

For user emulation, x86 (32 and 64 bit), PowerPC (32 and 64 bit), ARM, MIPS (32 bit only), Sparc (32 and 64 bit), Alpha, ColdFire(m68k), CRISv32 and MicroBlaze CPUs are supported.

2 Installation

If you want to compile QEMU yourself, see compilation.

2.1 Linux

If a precompiled package is available for your distribution - you just have to install it. Otherwise, see compilation.

2.2 Windows

Download the experimental binary installer at http://www.free.oszoo.org/download.html. TODO (no longer available)

2.3 Mac OS X

Download the experimental binary installer at http://www.free.oszoo.org/download.html. TODO (no longer available)

3 QEMU PC System emulator

3.1 Introduction

The QEMU PC System emulator simulates the following peripherals:

SMP is supported with up to 255 CPUs.

QEMU uses the PC BIOS from the Seabios project and the Plex86/Bochs LGPL VGA BIOS.

QEMU uses YM3812 emulation by Tatsuyuki Satoh.

QEMU uses GUS emulation (GUSEMU32 http://www.deinmeister.de/gusemu/) by Tibor "TS" Schütz.

Note that, by default, GUS shares IRQ(7) with parallel ports and so QEMU must be told to not have parallel ports to have working GUS.

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

Alternatively:

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

Or some other unclaimed IRQ.

CS4231A is the chip used in Windows Sound System and GUSMAX products

3.2 Quick Start

Download and uncompress the linux image (linux.img) and type:

qemu-system-i386 linux.img

Linux should boot and give you a prompt.

3.3 Invocation


usage: qemu-system-i386 [options] [disk_image]

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

Standard options:

-h
Display help and exit
-version
Display version information and exit
-machine [type=]name[,prop=value[,...]]
Select the emulated machine by name. Use -machine help to list available machines. Supported machine properties are:
accel=accels1[:accels2[:...]]
This is used to enable an accelerator. Depending on the target architecture, kvm, xen, 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
Enables in-kernel irqchip support for the chosen accelerator when available.
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).
iommu=on|off
Enables or disables emulated Intel IOMMU (VT-d) support. The default is off.

-cpu model
Select CPU model (-cpu help for list and additional feature selection)
-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=cpu[-cpu]][,nodeid=node]
-numa node[,memdev=id][,cpus=cpu[-cpu]][,nodeid=node]
Simulate a multi node NUMA system. If ‘mem’, ‘memdev’ and ‘cpus’ are omitted, resources are split equally. Also, note that the -numa option doesn't allocate any of the specified resources. That is, 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, and possibly -object to specify the memory backend for the ‘memdev’ suboption.

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

-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
Set default value of driver's property prop to value, e.g.:
     qemu-system-i386 -global ide-drive.physical_block_size=4096 -drive file=file,if=ide,index=0,media=disk

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.

-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 achitecture. 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.

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
Set virtual 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 hotluggable memory slots and possible maximum amount of memory.
-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 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.
-name name
Sets the name of the guest. This name will be displayed in the SDL window caption. The name will also be used for the VNC server. Also optionally set the top visible process name in Linux. Naming of individual threads can also be enabled on Linux to aid debugging.
-uuid uuid
Set system UUID.

Block device options:

-fda file
-fdb file
Use file as floppy disk 0/1 image (see disk_images). You can use the host floppy by using /dev/fd0 as filename (see host_drives).
-hda file
-hdb file
-hdc file
-hdd file
Use file as hard disk 0, 1, 2 or 3 image (see disk_images).
-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 (see host_drives).
-drive option[,option[,option[,...]]]
Define a new drive. Valid options are:
file=file
This option defines which disk image (see disk_images) 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.
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.
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.
aio=aio
aio is "threads", or "native" and selects between pthread based disk I/O and native Linux AIO.
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.
format=format
Specify which disk format will be used rather than detecting the format. Can be used to specifiy format=raw to avoid interpreting an untrusted format header.
serial=serial
This option specifies the serial number to assign to the device.
addr=addr
Specify the controller's PCI address (if=virtio only).
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.
readonly
Open drive file as read-only. Guest write attempts will fail.
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.
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.

By default, the cache=writeback 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=writethrough. 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.

The host page cache can be avoided entirely with cache=none. This will attempt to do disk IO directly to the guest's memory. QEMU may still perform an internal copy of the data. Note that this is considered a writeback mode and the guest OS must handle the disk write cache correctly in order to avoid data corruption on host crashes.

The host page cache can be avoided while only sending write notifications to the guest when the data has been flushed to the disk using cache=directsync.

In case you don't care about data integrity over host failures, use cache=unsafe. 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. 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

You can connect a SCSI disk with unit ID 6 on the bus #0:

     qemu-system-i386 -drive file=file,if=scsi,bus=0,unit=6

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> (see disk_images).
-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 useful for old MS-DOS disk images.
-fsdev fsdriver,id=id,path=path,[security_model=security_model][,writeout=writeout][,readonly][,socket=socket|sock_fd=sock_fd]
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

-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]
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

-virtfs_synth
Create synthetic file system image

USB options:

-usb
Enable the USB driver (will be the default soon)
-usbdevice devname
Add the USB device devname. See usb_devices.
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 specifiy 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, QEMU uses SDL to display the VGA output. 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, QEMU uses SDL to display the VGA output. 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
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 filter.
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.

-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 one is the default)
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.
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.
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, QEMU uses SDL to display the VGA output. 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 -usbdevice 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
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. By definition the Websocket port is 5700+display. If host is specified connections will only be allowed from this host. As an alternative the Websocket port could be specified by using websocket=port. TLS encryption for the Websocket connection is supported if the required certificates are specified with the VNC option x509.
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
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.
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.
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.
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.

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.
-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

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.
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.
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.
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][,helper=helper]
-net tap[,vlan=n][,name=name][,fd=h][,ifname=name][,script=file][,downscript=dfile][,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. The default network helper executable is /path/to/qemu-bridge-helper.

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 http://user-mode-linux.sf.net.
  3. Use fd=h to specify an already opened UDP multicast socket.

Example:

     # launch one QEMU instance
     qemu-system-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]
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.

Example:

     qemu -m 512 -object memory-backend-file,id=mem,size=512M,mem-path=/hugetlbfs,share=on \
     -numa node,memdev=mem \
     -chardev socket,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.
-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.

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. The key sequence of <Control-a> and <c> will rotate the input focus between attached front-ends. Specify mux=on to enable this mode.

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]
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.

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.

stdio is not available on Windows hosts.

-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 URL Syntax:

In addition to using normal file images for the emulated storage devices, QEMU can also use networked resources such as iSCSI devices. These are specified using a special URL syntax.

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

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

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

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 http://http://www.osrg.net/sheepdog/.

GlusterFS
GlusterFS is an 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

     gluster[+transport]://[server[:port]]/volname/image[?socket=...]

Example

     qemu-system-x86_64 --drive file=gluster://192.0.2.1/testvol/a.img

See also http://www.gluster.org.

HTTP/HTTPS/FTP/FTPS/TFTP
QEMU supports read-only access to files accessed over http(s), ftp(s) and tftp.

Syntax using a single filename:

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

where:

protocol
'http', 'https', 'ftp', 'ftps', or 'tftp'.
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=http://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=http://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":"https://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":"https://user:password@vsphere.example.com/folder/test/test-flat.vmdk?dcPath=Datacenter&dsName=datastore1",, "file.sslverify":"off",, "file.readahead":"64k",, "file.timeout":10}' /tmp/test.qcow2
     
     qemu-system-x86_64 -drive file=/tmp/test.qcow2
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.

TPM device options:

The general form of a TPM 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:

-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
COMn
[Windows only] Use host serial port n
udp:[remote_host]:remote_port[@[src_ip]:src_port]
This implements UDP Net Console. When remote_host or src_ip are not specified they default to 0.0.0.0. When not using a specified src_port a random port is automatically chosen.

If you just want a simple readonly console you can use netcat or nc, by starting QEMU with: -serial udp::4555 and nc as: nc -u -l -p 4555. Any time QEMU writes something to that port it will appear in the netconsole session.

If you plan to send characters back via netconsole or you want to stop and start QEMU a lot of times, you should have QEMU use the same source port each time by using something like -serial udp::4555@:4556 to QEMU. Another approach is to use a patched version of netcat which can listen to a TCP port and send and receive characters via udp. If you have a patched version of netcat which activates telnet remote echo and single char transfer, then you can use the following options to step 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]
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. 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]
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.
-mon [chardev=]name[,mode=readline|control][,default]
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 (see gdb_usage). 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 (see gdb_usage).
-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
-L path
Set the directory for the BIOS, VGA BIOS and keymaps.
-bios file
Set the filename for the BIOS.
-enable-kvm
Enable KVM full virtualization support. This option is only available if KVM support is enabled when compiling.
-xen-domid id
Specify xen guest domain id (XEN only).
-xen-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).
-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.
-clock method
Force the use of the given methods for timer alarm. To see what timers are available use -clock help.
-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]
Enable virtual instruction counter. The virtual cpu will execute one instruction every 2^N ns of virtual time. If auto is specified then the virtual cpu speed will be automatically adjusted to keep virtual time within a few seconds of real time.

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

align=on will activate the delay algorithm which will try to 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 messsage 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).

-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.

The model is the model of hardware watchdog to emulate. Choices for model are: ib700 (iBASE 700) which is a very simple ISA watchdog with a single timer, or i6300esb (Intel 6300ESB I/O controller hub) which is a much more featureful PCI-based dual-timer watchdog. Choose a model for which your guest has drivers.

Use -watchdog help to list available hardware models. Only one watchdog can be enabled for a guest.

-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 port
Prepare for incoming migration, listen on port.
-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. This option is not supported for Windows hosts.
-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
Semihosting mode (ARM, M68K, Xtensa only).
-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-unassigned
Trace unassigned memory or i/o accesses to stderr.
-trace [events=file][,file=file]
Specify tracing options.
events=file
Immediately enable events listed in file. The file must contain one event name (as listed in the trace-events file) per line. This option is only available if QEMU has been compiled with either simple or stderr 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.
-object typename[,prop1=value1,...]
Create an 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.
-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

3.4 Keys

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 the -nographic option, use <Ctrl-a h> to get terminal commands:

<Ctrl-a h>

<Ctrl-a ?>
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>
Switch between console and monitor
<Ctrl-a Ctrl-a>
Send Ctrl-a

3.5 QEMU Monitor

The QEMU monitor is used to give complex commands to the QEMU emulator. You can use it to:

3.5.1 Commands

The following commands are available:

help or ? [cmd]
Show the help for all commands or just for command cmd.
commit
Commit changes to the disk images (if -snapshot is used) or backing files. If the backing file is smaller than the snapshot, then the backing file will be resized to be the same size as the snapshot. If the snapshot is smaller than the backing file, the backing file will not be truncated. If you want the backing file to match the size of the smaller snapshot, you can safely truncate it yourself once the commit operation successfully completes.
q or quit
Quit the emulator.
block_resize
Resize a block image while a guest is running. Usually requires guest action to see the updated size. Resize to a lower size is supported, but should be used with extreme caution. Note that this command only resizes image files, it can not resize block devices like LVM volumes.
block_stream
Copy data from a backing file into a block device.
block_job_set_speed
Set maximum speed for a background block operation.
block_job_cancel
Stop an active background block operation (streaming, mirroring).
block_job_complete
Manually trigger completion of an active background block operation. For mirroring, this will switch the device to the destination path.
block_job_pause
Pause an active block streaming operation.
block_job_resume
Resume a paused block streaming operation.
eject [-f] device
Eject a removable medium (use -f to force it).
drive_del device
Remove host block device. The result is that guest generated IO is no longer submitted against the host device underlying the disk. Once a drive has been deleted, the QEMU Block layer returns -EIO which results in IO errors in the guest for applications that are reading/writing to the device. These errors are always reported to the guest, regardless of the drive's error actions (drive options rerror, werror).
change device setting
Change the configuration of a device.
change diskdevice filename [format]
Change the medium for a removable disk device to point to filename. eg
          (qemu) change ide1-cd0 /path/to/some.iso

format is optional.

change vnc display,options
Change the configuration of the VNC server. The valid syntax for display and options are described at sec_invocation. eg
          (qemu) change vnc localhost:1

change vnc password [password]
Change the password associated with the VNC server. If the new password is not supplied, the monitor will prompt for it to be entered. VNC passwords are only significant up to 8 letters. eg
          (qemu) change vnc password
          Password: ********

screendump filename
Save screen into PPM image filename.
logfile filename
Output logs to filename.
trace-event
changes status of a trace event
trace-file on|off|flush
Open, close, or flush the trace file. If no argument is given, the status of the trace file is displayed.
log item1[,...]
Activate logging of the specified items.
savevm [tag|id]
Create a snapshot of the whole virtual machine. If tag is provided, it is used as human readable identifier. If there is already a snapshot with the same tag or ID, it is replaced. More info at vm_snapshots.
loadvm tag|id
Set the whole virtual machine to the snapshot identified by the tag tag or the unique snapshot ID id.
delvm tag|id
Delete the snapshot identified by tag or id.
singlestep [off]
Run the emulation in single step mode. If called with option off, the emulation returns to normal mode.
stop
Stop emulation.
c or cont
Resume emulation.
system_wakeup
Wakeup guest from suspend.
gdbserver [port]
Start gdbserver session (default port=1234)
x/fmt addr
Virtual memory dump starting at addr.
xp /fmt addr
Physical memory dump starting at addr.

fmt is a format which tells the command how to format the data. Its syntax is: /{count}{format}{size}

count
is the number of items to be dumped.
format
can be x (hex), d (signed decimal), u (unsigned decimal), o (octal), c (char) or i (asm instruction).
size
can be b (8 bits), h (16 bits), w (32 bits) or g (64 bits). On x86, h or w can be specified with the i format to respectively select 16 or 32 bit code instruction size.

Examples:


p or print/fmt expr
Print expression value. Only the format part of fmt is used. Read I/O port. Write to I/O port.
sendkey keys
Send keys to the guest. keys could be the name of the key or the raw value in hexadecimal format. Use - to press several keys simultaneously. Example:
     sendkey ctrl-alt-f1

This command is useful to send keys that your graphical user interface intercepts at low level, such as ctrl-alt-f1 in X Window.

system_reset
Reset the system.
system_powerdown
Power down the system (if supported).
sum addr size
Compute the checksum of a memory region.
usb_add devname
Add the USB device devname. For details of available devices see usb_devices
usb_del devname
Remove the USB device devname from the QEMU virtual USB hub. devname has the syntax bus.addr. Use the monitor command info usb to see the devices you can remove.
device_add config
Add device.
device_del id
Remove device id.
cpu index
Set the default CPU.
mouse_move dx dy [dz]
Move the active mouse to the specified coordinates dx dy with optional scroll axis dz.
mouse_button val
Change the active mouse button state val (1=L, 2=M, 4=R).
mouse_set index
Set which mouse device receives events at given index, index can be obtained with
     info mice

wavcapture filename [frequency [bits [channels]]]
Capture audio into filename. Using sample rate frequency bits per sample bits and number of channels channels.

Defaults:


stopcapture index
Stop capture with a given index, index can be obtained with
     info capture

memsave addr size file
save to disk virtual memory dump starting at addr of size size.
pmemsave addr size file
save to disk physical memory dump starting at addr of size size.
boot_set bootdevicelist
Define new values for the boot device list. Those values will override the values specified on the command line through the -boot option.

The values that can be specified here depend on the machine type, but are the same that can be specified in the -boot command line option.

nmi cpu
Inject an NMI on the default CPU (x86/s390) or all CPUs (ppc64).
ringbuf_write device data
Write data to ring buffer character device device. data must be a UTF-8 string.
ringbuf_read device
Read and print up to size bytes from ring buffer character device device. Certain non-printable characters are printed \uXXXX, where XXXX is the character code in hexadecimal. Character \ is printed \. Bug: can screw up when the buffer contains invalid UTF-8 sequences, NUL characters, after the ring buffer lost data, and when reading stops because the size limit is reached.
migrate [-d] [-b] [-i] uri
Migrate to uri (using -d to not wait for completion). -b for migration with full copy of disk -i for migration with incremental copy of disk (base image is shared)
migrate_cancel
Cancel the current VM migration.
migrate_set_cache_size value
Set cache size to value (in bytes) for xbzrle migrations.
migrate_set_speed value
Set maximum speed to value (in bytes) for migrations.
migrate_set_downtime second
Set maximum tolerated downtime (in seconds) for migration.
migrate_set_capability capability state
Enable/Disable the usage of a capability capability for migration.
client_migrate_info protocol hostname port tls-port cert-subject
Set the spice/vnc connection info for the migration target. The spice/vnc server will ask the spice/vnc client to automatically reconnect using the new parameters (if specified) once the vm migration finished successfully.
dump-guest-memory [-p] filename begin length
dump-guest-memory [-z|-l|-s] filename
Dump guest memory to protocol. The file can be processed with crash or gdb. Without -z|-l|-s, the dump format is ELF. -p: do paging to get guest's memory mapping. -z: dump in kdump-compressed format, with zlib compression. -l: dump in kdump-compressed format, with lzo compression. -s: dump in kdump-compressed format, with snappy compression. filename: dump file name. begin: the starting physical address. It's optional, and should be specified together with length. length: the memory size, in bytes. It's optional, and should be specified together with begin.
snapshot_blkdev
Snapshot device, using snapshot file as target if provided
snapshot_blkdev_internal
Take an internal snapshot on device if it support
snapshot_delete_blkdev_internal
Delete an internal snapshot on device if it support
drive_mirror
Start mirroring a block device's writes to a new destination, using the specified target.
drive_backup
Start a point-in-time copy of a block device to a specificed target.
drive_add
Add drive to PCI storage controller.
pci_add
Hot-add PCI device.
pci_del
Hot remove PCI device.
pcie_aer_inject_error
Inject PCIe AER error
host_net_add
Add host VLAN client.
host_net_remove
Remove host VLAN client.
netdev_add
Add host network device.
netdev_del
Remove host network device.
object_add
Create QOM object.
object_del
Destroy QOM object.
hostfwd_add
Redirect TCP or UDP connections from host to guest (requires -net user).
hostfwd_remove
Remove host-to-guest TCP or UDP redirection.
balloon value
Request VM to change its memory allocation to value (in MB).
set_link name [on|off]
Switch link name on (i.e. up) or off (i.e. down).
watchdog_action
Change watchdog action.
acl_show aclname
List all the matching rules in the access control list, and the default policy. There are currently two named access control lists, vnc.x509dname and vnc.username matching on the x509 client certificate distinguished name, and SASL username respectively.
acl_policy aclname allow|deny
Set the default access control list policy, used in the event that none of the explicit rules match. The default policy at startup is always deny.
acl_add aclname match allow|deny [index]
Add a match rule to the access control list, allowing or denying access. The match will normally be an exact username or x509 distinguished name, but can optionally include wildcard globs. eg *@EXAMPLE.COM to allow all users in the EXAMPLE.COM kerberos realm. The match will normally be appended to the end of the ACL, but can be inserted earlier in the list if the optional index parameter is supplied.
acl_remove aclname match
Remove the specified match rule from the access control list.
acl_reset aclname
Remove all matches from the access control list, and set the default policy back to deny.
nbd_server_start host:port
Start an NBD server on the given host and/or port. If the -a option is included, all of the virtual machine's block devices that have an inserted media on them are automatically exported; in this case, the -w option makes the devices writable too.
nbd_server_add device
Export a block device through QEMU's NBD server, which must be started beforehand with nbd_server_start. The -w option makes the exported device writable too.
nbd_server_stop
Stop the QEMU embedded NBD server.
mce cpu bank status mcgstatus addr misc
Inject an MCE on the given CPU (x86 only).
getfd fdname
If a file descriptor is passed alongside this command using the SCM_RIGHTS mechanism on unix sockets, it is stored using the name fdname for later use by other monitor commands.
closefd fdname
Close the file descriptor previously assigned to fdname using the getfd command. This is only needed if the file descriptor was never used by another monitor command.
block_set_io_throttle device bps bps_rd bps_wr iops iops_rd iops_wr
Change I/O throttle limits for a block drive to bps bps_rd bps_wr iops iops_rd iops_wr
block_passwd device password
Set the encrypted device device password to password
set_password [ vnc | spice ] password [ action-if-connected ]
Change spice/vnc password. Use zero to make the password stay valid forever. action-if-connected specifies what should happen in case a connection is established: fail makes the password change fail. disconnect changes the password and disconnects the client. keep changes the password and keeps the connection up. keep is the default.
expire_password [ vnc | spice ] expire-time
Specify when a password for spice/vnc becomes invalid. expire-time accepts:
now
Invalidate password instantly.
never
Password stays valid forever.
+nsec
Password stays valid for nsec seconds starting now.
nsec
Password is invalidated at the given time. nsec are the seconds passed since 1970, i.e. unix epoch.

chardev_add args
chardev_add accepts the same parameters as the -chardev command line switch.
chardev_remove id
Removes the chardev id.
qemu-io device command
Executes a qemu-io command on the given block device.
cpu-add id
Add CPU with id id
info subcommand
Show various information about the system state.
info version
show the version of QEMU
info network
show the various VLANs and the associated devices
info chardev
show the character devices
info block
show the block devices
info blockstats
show block device statistics
info registers
show the cpu registers
info cpus
show infos for each CPU
info history
show the command line history
info irq
show the interrupts statistics (if available)
info pic
show i8259 (PIC) state
info pci
show emulated PCI device info
info tlb
show virtual to physical memory mappings (i386, SH4, SPARC, PPC, and Xtensa only)
info mem
show the active virtual memory mappings (i386 only)
info jit
show dynamic compiler info
info numa
show NUMA information
info kvm
show KVM information
info usb
show USB devices plugged on the virtual USB hub
info usbhost
show all USB host devices
info profile
show profiling information
info capture
show information about active capturing
info snapshots
show list of VM snapshots
info status
show the current VM status (running|paused)
info pcmcia
show guest PCMCIA status
info mice
show which guest mouse is receiving events
info vnc
show the vnc server status
info name
show the current VM name
info uuid
show the current VM UUID
info cpustats
show CPU statistics
info usernet
show user network stack connection states
info migrate
show migration status
info migrate_capabilities
show current migration capabilities
info migrate_cache_size
show current migration XBZRLE cache size
info balloon
show balloon information
info qtree
show device tree
info qdm
show qdev device model list
info roms
show roms
info tpm
show the TPM device
info memory-devices
show the memory devices

info trace-events
show available trace events and their state

3.5.2 Integer expressions

The monitor understands integers expressions for every integer argument. You can use register names to get the value of specifics CPU registers by prefixing them with $.

3.6 Disk Images

Since version 0.6.1, QEMU supports many disk image formats, including growable disk images (their size increase as non empty sectors are written), compressed and encrypted disk images. Version 0.8.3 added the new qcow2 disk image format which is essential to support VM snapshots.

3.6.1 Quick start for disk image creation

You can create a disk image with the command:

qemu-img create myimage.img mysize

where myimage.img is the disk image filename and mysize is its size in kilobytes. You can add an M suffix to give the size in megabytes and a G suffix for gigabytes.

See qemu_img_invocation for more information.

3.6.2 Snapshot mode

If you use the option -snapshot, all disk images are considered as read only. When sectors in written, they are written in a temporary file created in /tmp. You can however force the write back to the raw disk images by using the commit monitor command (or <C-a s> in the serial console).

3.6.3 VM snapshots

VM snapshots are snapshots of the complete virtual machine including CPU state, RAM, device state and the content of all the writable disks. In order to use VM snapshots, you must have at least one non removable and writable block device using the qcow2 disk image format. Normally this device is the first virtual hard drive.

Use the monitor command savevm to create a new VM snapshot or replace an existing one. A human readable name can be assigned to each snapshot in addition to its numerical ID.

Use loadvm to restore a VM snapshot and delvm to remove a VM snapshot. info snapshots lists the available snapshots with their associated information:

(qemu) info snapshots
Snapshot devices: hda
Snapshot list (from hda):
ID        TAG                 VM SIZE                DATE       VM CLOCK
1         start                   41M 2006-08-06 12:38:02   00:00:14.954
2                                 40M 2006-08-06 12:43:29   00:00:18.633
3         msys                    40M 2006-08-06 12:44:04   00:00:23.514

A VM snapshot is made of a VM state info (its size is shown in info snapshots) and a snapshot of every writable disk image. The VM state info is stored in the first qcow2 non removable and writable block device. The disk image snapshots are stored in every disk image. The size of a snapshot in a disk image is difficult to evaluate and is not shown by info snapshots because the associated disk sectors are shared among all the snapshots to save disk space (otherwise each snapshot would need a full copy of all the disk images).

When using the (unrelated) -snapshot option (disk_images_snapshot_mode), you can always make VM snapshots, but they are deleted as soon as you exit QEMU.

VM snapshots currently have the following known limitations:

3.6.4 qemu-img Invocation


usage: qemu-img command [command options]

qemu-img allows you to create, convert and modify images offline. It can handle all image formats supported by QEMU.

Warning: Never use qemu-img to modify images in use by a running virtual machine or any other process; this may destroy the image. Also, be aware that querying an image that is being modified by another process may encounter inconsistent state.

The following commands are supported:

check [-q] [-f fmt] [--output=ofmt] [-r [leaks | all]] [-T src_cache] filename
create [-q] [-f fmt] [-o options] filename [size]
commit [-q] [-f fmt] [-t cache] filename
compare [-f fmt] [-F fmt] [-T src_cache] [-p] [-q] [-s] filename1 filename2
convert [-c] [-p] [-q] [-n] [-f fmt] [-t cache] [-T src_cache] [-O output_fmt] [-o options] [-s snapshot_id_or_name] [-l snapshot_param] [-S sparse_size] filename [filename2 [...]] output_filename
info [-f fmt] [--output=ofmt] [--backing-chain] filename
map [-f fmt] [--output=ofmt] filename
snapshot [-q] [-l | -a snapshot | -c snapshot | -d snapshot] filename
rebase [-q] [-f fmt] [-t cache] [-T src_cache] [-p] [-u] -b backing_file [-F backing_fmt] filename
resize [-q] filename [+ | -]size
update [-f fmt] filename [attr1=val1 attr2=val2 ...]")
amend [-q] [-f fmt] [-t cache] -o options filename

Command parameters:

filename
is a disk image filename
fmt
is the disk image format. It is guessed automatically in most cases. See below for a description of the supported disk formats.
–backing-chain
will enumerate information about backing files in a disk image chain. Refer below for further description.
size
is the disk image size in bytes. Optional suffixes k or K (kilobyte, 1024) M (megabyte, 1024k) and G (gigabyte, 1024M) and T (terabyte, 1024G) are supported. b is ignored.
output_filename
is the destination disk image filename
output_fmt
is the destination format
options
is a comma separated list of format specific options in a name=value format. Use -o ? for an overview of the options supported by the used format or see the format descriptions below for details.
snapshot_param
is param used for internal snapshot, format is 'snapshot.id=[ID],snapshot.name=[NAME]' or '[ID_OR_NAME]'
snapshot_id_or_name
is deprecated, use snapshot_param instead
-c
indicates that target image must be compressed (qcow format only)
-h
with or without a command shows help and lists the supported formats
-p
display progress bar (compare, convert and rebase commands only). If the -p option is not used for a command that supports it, the progress is reported when the process receives a SIGUSR1 signal.
-q
Quiet mode - do not print any output (except errors). There's no progress bar in case both -q and -p options are used.
-S size
indicates the consecutive number of bytes that must contain only zeros for qemu-img to create a sparse image during conversion. This value is rounded down to the nearest 512 bytes. You may use the common size suffixes like k for kilobytes.
-t cache
specifies the cache mode that should be used with the (destination) file. See the documentation of the emulator's -drive cache=... option for allowed values.
-T src_cache
specifies the cache mode that should be used with the source file(s). See the documentation of the emulator's -drive cache=... option for allowed values.

Parameters to snapshot subcommand:

snapshot
is the name of the snapshot to create, apply or delete
-a
applies a snapshot (revert disk to saved state)
-c
creates a snapshot
-d
deletes a snapshot
-l
lists all snapshots in the given image

Parameters to compare subcommand:

-f
First image format
-F
Second image format
-s
Strict mode - fail on on different image size or sector allocation

Parameters to convert subcommand:

-n
Skip the creation of the target volume

Command description:

check [-f fmt] [--output=ofmt] [-r [leaks | all]] [-T src_cache] filename
Perform a consistency check on the disk image filename. The command can output in the format ofmt which is either human or json.

If -r is specified, qemu-img tries to repair any inconsistencies found during the check. -r leaks repairs only cluster leaks, whereas -r all fixes all kinds of errors, with a higher risk of choosing the wrong fix or hiding corruption that has already occurred.

Only the formats qcow2, qed and vdi support consistency checks.

In case the image does not have any inconsistencies, check exits with 0. Other exit codes indicate the kind of inconsistency found or if another error occurred. The following table summarizes all exit codes of the check subcommand:

0
Check completed, the image is (now) consistent
1
Check not completed because of internal errors
2
Check completed, image is corrupted
3
Check completed, image has leaked clusters, but is not corrupted
63
Checks are not supported by the image format

If -r is specified, exit codes representing the image state refer to the state after (the attempt at) repairing it. That is, a successful -r all will yield the exit code 0, independently of the image state before.

create [-f fmt] [-o options] filename [size]
Create the new disk image filename of size size and format fmt. Depending on the file format, you can add one or more options that enable additional features of this format.

If the option backing_file is specified, then the image will record only the differences from backing_file. No size needs to be specified in this case. backing_file will never be modified unless you use the commit monitor command (or qemu-img commit).

The size can also be specified using the size option with -o, it doesn't need to be specified separately in this case.

commit [-f fmt] [-t cache] filename
Commit the changes recorded in filename in its base image or backing file. If the backing file is smaller than the snapshot, then the backing file will be resized to be the same size as the snapshot. If the snapshot is smaller than the backing file, the backing file will not be truncated. If you want the backing file to match the size of the smaller snapshot, you can safely truncate it yourself once the commit operation successfully completes.
compare [-f fmt] [-F fmt] [-T src_cache] [-p] [-s] [-q] filename1 filename2
Check if two images have the same content. You can compare images with different format or settings.

The format is probed unless you specify it by -f (used for filename1) and/or -F (used for filename2) option.

By default, images with different size are considered identical if the larger image contains only unallocated and/or zeroed sectors in the area after the end of the other image. In addition, if any sector is not allocated in one image and contains only zero bytes in the second one, it is evaluated as equal. You can use Strict mode by specifying the -s option. When compare runs in Strict mode, it fails in case image size differs or a sector is allocated in one image and is not allocated in the second one.

By default, compare prints out a result message. This message displays information that both images are same or the position of the first different byte. In addition, result message can report different image size in case Strict mode is used.

Compare exits with 0 in case the images are equal and with 1 in case the images differ. Other exit codes mean an error occurred during execution and standard error output should contain an error message. The following table sumarizes all exit codes of the compare subcommand:

0
Images are identical
1
Images differ
2
Error on opening an image
3
Error on checking a sector allocation
4
Error on reading data

convert [-c] [-p] [-n] [-f fmt] [-t cache] [-T src_cache] [-O output_fmt] [-o options] [-s snapshot_id_or_name] [-l snapshot_param] [-S sparse_size] filename [filename2 [...]] output_filename
Convert the disk image filename or a snapshot snapshot_param(snapshot_id_or_name is deprecated) to disk image output_filename using format output_fmt. It can be optionally compressed (-c option) or use any format specific options like encryption (-o option).

Only the formats qcow and qcow2 support compression. The compression is read-only. It means that if a compressed sector is rewritten, then it is rewritten as uncompressed data.

Image conversion is also useful to get smaller image when using a growable format such as qcow: the empty sectors are detected and suppressed from the destination image.

sparse_size indicates the consecutive number of bytes (defaults to 4k) that must contain only zeros for qemu-img to create a sparse image during conversion. If sparse_size is 0, the source will not be scanned for unallocated or zero sectors, and the destination image will always be fully allocated.

You can use the backing_file option to force the output image to be created as a copy on write image of the specified base image; the backing_file should have the same content as the input's base image, however the path, image format, etc may differ.

If the -n option is specified, the target volume creation will be skipped. This is useful for formats such as rbd if the target volume has already been created with site specific options that cannot be supplied through qemu-img.

info [-f fmt] [--output=ofmt] [--backing-chain] filename
Give information about the disk image filename. Use it in particular to know the size reserved on disk which can be different from the displayed size. If VM snapshots are stored in the disk image, they are displayed too. The command can output in the format ofmt which is either human or json.

If a disk image has a backing file chain, information about each disk image in the chain can be recursively enumerated by using the option --backing-chain.

For instance, if you have an image chain like:

     base.qcow2 <- snap1.qcow2 <- snap2.qcow2

To enumerate information about each disk image in the above chain, starting from top to base, do:

     qemu-img info --backing-chain snap2.qcow2

map [-f fmt] [--output=ofmt] filename
Dump the metadata of image filename and its backing file chain. In particular, this commands dumps the allocation state of every sector of filename, together with the topmost file that allocates it in the backing file chain.

Two option formats are possible. The default format (human) only dumps known-nonzero areas of the file. Known-zero parts of the file are omitted altogether, and likewise for parts that are not allocated throughout the chain. qemu-img output will identify a file from where the data can be read, and the offset in the file. Each line will include four fields, the first three of which are hexadecimal numbers. For example the first line of:

     Offset          Length          Mapped to       File
     0               0x20000         0x50000         /tmp/overlay.qcow2
     0x100000        0x10000         0x95380000      /tmp/backing.qcow2

means that 0x20000 (131072) bytes starting at offset 0 in the image are available in /tmp/overlay.qcow2 (opened in raw format) starting at offset 0x50000 (327680). Data that is compressed, encrypted, or otherwise not available in raw format will cause an error if human format is in use. Note that file names can include newlines, thus it is not safe to parse this output format in scripts.

The alternative format json will return an array of dictionaries in JSON format. It will include similar information in the start, length, offset fields; it will also include other more specific information:

In JSON format, the offset field is optional; it is absent in cases where human format would omit the entry or exit with an error. If data is false and the offset field is present, the corresponding sectors in the file are not yet in use, but they are preallocated.

For more information, consult include/block/block.h in QEMU's source code.

snapshot [-l | -a snapshot | -c snapshot | -d snapshot ] filename
List, apply, create or delete snapshots in image filename.
rebase [-f fmt] [-t cache] [-T src_cache] [-p] [-u] -b backing_file [-F backing_fmt] filename
Changes the backing file of an image. Only the formats qcow2 and qed support changing the backing file.

The backing file is changed to backing_file and (if the image format of filename supports this) the backing file format is changed to backing_fmt. If backing_file is specified as “” (the empty string), then the image is rebased onto no backing file (i.e. it will exist independently of any backing file).

cache specifies the cache mode to be used for filename, whereas src_cache specifies the cache mode for reading backing files.

There are two different modes in which rebase can operate:

Safe mode
This is the default mode and performs a real rebase operation. The new backing file may differ from the old one and qemu-img rebase will take care of keeping the guest-visible content of filename unchanged.

In order to achieve this, any clusters that differ between backing_file and the old backing file of filename are merged into filename before actually changing the backing file.

Note that the safe mode is an expensive operation, comparable to converting an image. It only works if the old backing file still exists.

Unsafe mode
qemu-img uses the unsafe mode if -u is specified. In this mode, only the backing file name and format of filename is changed without any checks on the file contents. The user must take care of specifying the correct new backing file, or the guest-visible content of the image will be corrupted.

This mode is useful for renaming or moving the backing file to somewhere else. It can be used without an accessible old backing file, i.e. you can use it to fix an image whose backing file has already been moved/renamed.

You can use rebase to perform a “diff” operation on two disk images. This can be useful when you have copied or cloned a guest, and you want to get back to a thin image on top of a template or base image.

Say that base.img has been cloned as modified.img by copying it, and that the modified.img guest has run so there are now some changes compared to base.img. To construct a thin image called diff.qcow2 that contains just the differences, do:

     qemu-img create -f qcow2 -b modified.img diff.qcow2
     qemu-img rebase -b base.img diff.qcow2

At this point, modified.img can be discarded, since base.img + diff.qcow2 contains the same information.

resize filename [+ | -]size
Change the disk image as if it had been created with size.

Before using this command to shrink a disk image, you MUST use file system and partitioning tools inside the VM to reduce allocated file systems and partition sizes accordingly. Failure to do so will result in data loss!

After using this command to grow a disk image, you must use file system and partitioning tools inside the VM to actually begin using the new space on the device.

amend [-f fmt] [-t cache] -o options filename
Amends the image format specific options for the image file filename. Not all file formats support this operation.

3.6.5 qemu-nbd Invocation


usage: qemu-nbd [OPTION]...  filename

Export QEMU disk image using NBD protocol.

filename
is a disk image filename
-p, --port=port
port to listen on (default ‘10809’)
-o, --offset=offset
offset into the image
-b, --bind=iface
interface to bind to (default ‘0.0.0.0’)
-k, --socket=path
Use a unix socket with path path
-f, --format=format
Set image format as format
-r, --read-only
export read-only
-P, --partition=num
only expose partition num
-s, --snapshot
use filename as an external snapshot, create a temporary file with backing_file=filename, redirect the write to the temporary one
-l, --load-snapshot=snapshot_param
load an internal snapshot inside filename and export it as an read-only device, snapshot_param format is 'snapshot.id=[ID],snapshot.name=[NAME]' or '[ID_OR_NAME]'
-n, --nocache
--cache=cache
set cache mode to be used with the file. See the documentation of the emulator's -drive cache=... option for allowed values.
--aio=aio
choose asynchronous I/O mode between ‘threads’ (the default) and ‘native’ (Linux only).
--discard=discard
toggles whether discard (also known as trim or unmap) requests are ignored or passed to the filesystem. The default is no (‘--discard=ignore’).
-c, --connect=dev
connect filename to NBD device dev
-d, --disconnect
disconnect the specified device
-e, --shared=num
device can be shared by num clients (default ‘1’)
-f, --format=fmt
force block driver for format fmt instead of auto-detecting
-t, --persistent
don't exit on the last connection
-v, --verbose
display extra debugging information
-h, --help
display this help and exit
-V, --version
output version information and exit

3.6.6 Disk image file formats

QEMU supports many image file formats that can be used with VMs as well as with any of the tools (like qemu-img). This includes the preferred formats raw and qcow2 as well as formats that are supported for compatibility with older QEMU versions or other hypervisors.

Depending on the image format, different options can be passed to qemu-img create and qemu-img convert using the -o option. This section describes each format and the options that are supported for it.

raw
Raw disk image format. This format has the advantage of being simple and easily exportable to all other emulators. If your file system supports holes (for example in ext2 or ext3 on Linux or NTFS on Windows), then only the written sectors will reserve space. Use qemu-img info to know the real size used by the image or ls -ls on Unix/Linux.

Supported options:

preallocation
Preallocation mode (allowed values: off, falloc, full). falloc mode preallocates space for image by calling posix_fallocate(). full mode preallocates space for image by writing zeros to underlying storage.

qcow2
QEMU image format, the most versatile format. Use it to have smaller images (useful if your filesystem does not supports holes, for example on Windows), optional AES encryption, zlib based compression and support of multiple VM snapshots.

Supported options:

compat
Determines the qcow2 version to use. compat=0.10 uses the traditional image format that can be read by any QEMU since 0.10. compat=1.1 enables image format extensions that only QEMU 1.1 and newer understand (this is the default). Amongst others, this includes zero clusters, which allow efficient copy-on-read for sparse images.
backing_file
File name of a base image (see create subcommand)
backing_fmt
Image format of the base image
encryption
If this option is set to on, the image is encrypted with 128-bit AES-CBC.

The use of encryption in qcow and qcow2 images is considered to be flawed by modern cryptography standards, suffering from a number of design problems:

  • The AES-CBC cipher is used with predictable initialization vectors based on the sector number. This makes it vulnerable to chosen plaintext attacks which can reveal the existence of encrypted data.
  • The user passphrase is directly used as the encryption key. A poorly chosen or short passphrase will compromise the security of the encryption.
  • In the event of the passphrase being compromised there is no way to change the passphrase to protect data in any qcow images. The files must be cloned, using a different encryption passphrase in the new file. The original file must then be securely erased using a program like shred, though even this is ineffective with many modern storage technologies.

Use of qcow / qcow2 encryption is thus strongly discouraged. Users are recommended to use an alternative encryption technology such as the Linux dm-crypt / LUKS system.

cluster_size
Changes the qcow2 cluster size (must be between 512 and 2M). Smaller cluster sizes can improve the image file size whereas larger cluster sizes generally provide better performance.
preallocation
Preallocation mode (allowed values: off, metadata, falloc, full). An image with preallocated metadata is initially larger but can improve performance when the image needs to grow. falloc and full preallocations are like the same options of raw format, but sets up metadata also.
lazy_refcounts
If this option is set to on, reference count updates are postponed with the goal of avoiding metadata I/O and improving performance. This is particularly interesting with cache=writethrough which doesn't batch metadata updates. The tradeoff is that after a host crash, the reference count tables must be rebuilt, i.e. on the next open an (automatic) qemu-img check -r all is required, which may take some time.

This option can only be enabled if compat=1.1 is specified.

nocow
If this option is set to on, it will turn off COW of the file. It's only valid on btrfs, no effect on other file systems.

Btrfs has low performance when hosting a VM image file, even more when the guest on the VM also using btrfs as file system. Turning off COW is a way to mitigate this bad performance. Generally there are two ways to turn off COW on btrfs: a) Disable it by mounting with nodatacow, then all newly created files will be NOCOW. b) For an empty file, add the NOCOW file attribute. That's what this option does.

Note: this option is only valid to new or empty files. If there is an existing file which is COW and has data blocks already, it couldn't be changed to NOCOW by setting nocow=on. One can issue lsattr filename to check if the NOCOW flag is set or not (Capital 'C' is NOCOW flag).


qed
Old QEMU image format with support for backing files and compact image files (when your filesystem or transport medium does not support holes).

When converting QED images to qcow2, you might want to consider using the lazy_refcounts=on option to get a more QED-like behaviour.

Supported options:

backing_file
File name of a base image (see create subcommand).
backing_fmt
Image file format of backing file (optional). Useful if the format cannot be autodetected because it has no header, like some vhd/vpc files.
cluster_size
Changes the cluster size (must be power-of-2 between 4K and 64K). Smaller cluster sizes can improve the image file size whereas larger cluster sizes generally provide better performance.
table_size
Changes the number of clusters per L1/L2 table (must be power-of-2 between 1 and 16). There is normally no need to change this value but this option can be used for performance benchmarking.

qcow
Old QEMU image format with support for backing files, compact image files, encryption and compression.

Supported options:

backing_file
File name of a base image (see create subcommand)
encryption
If this option is set to on, the image is encrypted.

vdi
VirtualBox 1.1 compatible image format. Supported options:
static
If this option is set to on, the image is created with metadata preallocation.

vmdk
VMware 3 and 4 compatible image format.

Supported options:

backing_file
File name of a base image (see create subcommand).
compat6
Create a VMDK version 6 image (instead of version 4)
subformat
Specifies which VMDK subformat to use. Valid options are monolithicSparse (default), monolithicFlat, twoGbMaxExtentSparse, twoGbMaxExtentFlat and streamOptimized.

vpc
VirtualPC compatible image format (VHD). Supported options:
subformat
Specifies which VHD subformat to use. Valid options are dynamic (default) and fixed.

VHDX
Hyper-V compatible image format (VHDX). Supported options:
subformat
Specifies which VHDX subformat to use. Valid options are dynamic (default) and fixed.
block_state_zero
Force use of payload blocks of type 'ZERO'.
block_size
Block size; min 1 MB, max 256 MB. 0 means auto-calculate based on image size.
log_size
Log size; min 1 MB.
3.6.6.1 Read-only formats

More disk image file formats are supported in a read-only mode.

bochs
Bochs images of growing type.
cloop
Linux Compressed Loop image, useful only to reuse directly compressed CD-ROM images present for example in the Knoppix CD-ROMs.
dmg
Apple disk image.
parallels
Parallels disk image format.

3.6.7 Using host drives

In addition to disk image files, QEMU can directly access host devices. We describe here the usage for QEMU version >= 0.8.3.

3.6.7.1 Linux

On Linux, you can directly use the host device filename instead of a disk image filename provided you have enough privileges to access it. For example, use /dev/cdrom to access to the CDROM or /dev/fd0 for the floppy.

CD
You can specify a CDROM device even if no CDROM is loaded. QEMU has specific code to detect CDROM insertion or removal. CDROM ejection by the guest OS is supported. Currently only data CDs are supported.
Floppy
You can specify a floppy device even if no floppy is loaded. Floppy removal is currently not detected accurately (if you change floppy without doing floppy access while the floppy is not loaded, the guest OS will think that the same floppy is loaded).
Hard disks
Hard disks can be used. Normally you must specify the whole disk (/dev/hdb instead of /dev/hdb1) so that the guest OS can see it as a partitioned disk. WARNING: unless you know what you do, it is better to only make READ-ONLY accesses to the hard disk otherwise you may corrupt your host data (use the -snapshot command line option or modify the device permissions accordingly).
3.6.7.2 Windows
CD
The preferred syntax is the drive letter (e.g. d:). The alternate syntax \\.\d: is supported. /dev/cdrom is supported as an alias to the first CDROM drive.

Currently there is no specific code to handle removable media, so it is better to use the change or eject monitor commands to change or eject media.

Hard disks
Hard disks can be used with the syntax: \\.\PhysicalDriveN where N is the drive number (0 is the first hard disk). /dev/hda is supported as an alias to the first hard disk drive \\.\PhysicalDrive0.

WARNING: unless you know what you do, it is better to only make READ-ONLY accesses to the hard disk otherwise you may corrupt your host data (use the -snapshot command line so that the modifications are written in a temporary file).

3.6.7.3 Mac OS X

/dev/cdrom is an alias to the first CDROM.

Currently there is no specific code to handle removable media, so it is better to use the change or eject monitor commands to change or eject media.

3.6.8 Virtual FAT disk images

QEMU can automatically create a virtual FAT disk image from a directory tree. In order to use it, just type:

qemu-system-i386 linux.img -hdb fat:/my_directory

Then you access access to all the files in the /my_directory directory without having to copy them in a disk image or to export them via SAMBA or NFS. The default access is read-only.

Floppies can be emulated with the :floppy: option:

qemu-system-i386 linux.img -fda fat:floppy:/my_directory

A read/write support is available for testing (beta stage) with the :rw: option:

qemu-system-i386 linux.img -fda fat:floppy:rw:/my_directory

What you should never do:

3.6.9 NBD access

QEMU can access directly to block device exported using the Network Block Device protocol.

qemu-system-i386 linux.img -hdb nbd://my_nbd_server.mydomain.org:1024/

If the NBD server is located on the same host, you can use an unix socket instead of an inet socket:

qemu-system-i386 linux.img -hdb nbd+unix://?socket=/tmp/my_socket

In this case, the block device must be exported using qemu-nbd:

qemu-nbd --socket=/tmp/my_socket my_disk.qcow2

The use of qemu-nbd allows sharing of a disk between several guests:

qemu-nbd --socket=/tmp/my_socket --share=2 my_disk.qcow2

and then you can use it with two guests:

qemu-system-i386 linux1.img -hdb nbd+unix://?socket=/tmp/my_socket
qemu-system-i386 linux2.img -hdb nbd+unix://?socket=/tmp/my_socket

If the nbd-server uses named exports (supported since NBD 2.9.18, or with QEMU's own embedded NBD server), you must specify an export name in the URI:

qemu-system-i386 -cdrom nbd://localhost/debian-500-ppc-netinst
qemu-system-i386 -cdrom nbd://localhost/openSUSE-11.1-ppc-netinst

The URI syntax for NBD is supported since QEMU 1.3. An alternative syntax is also available. Here are some example of the older syntax:

qemu-system-i386 linux.img -hdb nbd:my_nbd_server.mydomain.org:1024
qemu-system-i386 linux2.img -hdb nbd:unix:/tmp/my_socket
qemu-system-i386 -cdrom nbd:localhost:10809:exportname=debian-500-ppc-netinst

3.6.10 Sheepdog disk images

Sheepdog is a distributed storage system for QEMU. It provides highly available block level storage volumes that can be attached to QEMU-based virtual machines.

You can create a Sheepdog disk image with the command:

qemu-img create sheepdog:///image size

where image is the Sheepdog image name and size is its size.

To import the existing filename to Sheepdog, you can use a convert command.

qemu-img convert filename sheepdog:///image

You can boot from the Sheepdog disk image with the command:

qemu-system-i386 sheepdog:///image

You can also create a snapshot of the Sheepdog image like qcow2.

qemu-img snapshot -c tag sheepdog:///image

where tag is a tag name of the newly created snapshot.

To boot from the Sheepdog snapshot, specify the tag name of the snapshot.

qemu-system-i386 sheepdog:///image#tag

You can create a cloned image from the existing snapshot.

qemu-img create -b sheepdog:///base#tag sheepdog:///image

where base is a image name of the source snapshot and tag is its tag name.

You can use an unix socket instead of an inet socket:

qemu-system-i386 sheepdog+unix:///image?socket=path

If the Sheepdog daemon doesn't run on the local host, you need to specify one of the Sheepdog servers to connect to.

qemu-img create sheepdog://hostname:port/image size
qemu-system-i386 sheepdog://hostname:port/image

3.6.11 iSCSI LUNs

iSCSI is a popular protocol used to access SCSI devices across a computer network.

There are two different ways iSCSI devices can be used by QEMU.

The first method is to mount the iSCSI LUN on the host, and make it appear as any other ordinary SCSI device on the host and then to access this device as a /dev/sd device from QEMU. How to do this differs between host OSes.

The second method involves using the iSCSI initiator that is built into QEMU. This provides a mechanism that works the same way regardless of which host OS you are running QEMU on. This section will describe this second method of using iSCSI together with QEMU.

In QEMU, iSCSI devices are described using special iSCSI URLs

URL syntax:
iscsi://[<username>[%<password>]@]<host>[:<port>]/<target-iqn-name>/<lun>

Username and password are optional and only used if your target is set up using CHAP authentication for access control. Alternatively the username and password can also be set via environment variables to have these not show up in the process list

export LIBISCSI_CHAP_USERNAME=<username>
export LIBISCSI_CHAP_PASSWORD=<password>
iscsi://<host>/<target-iqn-name>/<lun>

Various session related parameters can be set via special options, either in a configuration file provided via '-readconfig' or directly on the command line.

If the initiator-name is not specified qemu will use a default name of 'iqn.2008-11.org.linux-kvm[:<name>'] where <name> is the name of the virtual machine.

Setting a specific initiator name to use when logging in to the target
-iscsi initiator-name=iqn.qemu.test:my-initiator
Controlling which type of header digest to negotiate with the target
-iscsi header-digest=CRC32C|CRC32C-NONE|NONE-CRC32C|NONE

These can also be set via a configuration file

[iscsi]
  user = "CHAP username"
  password = "CHAP password"
  initiator-name = "iqn.qemu.test:my-initiator"
  # header digest is one of CRC32C|CRC32C-NONE|NONE-CRC32C|NONE
  header-digest = "CRC32C"

Setting the target name allows different options for different targets

[iscsi "iqn.target.name"]
  user = "CHAP username"
  password = "CHAP password"
  initiator-name = "iqn.qemu.test:my-initiator"
  # header digest is one of CRC32C|CRC32C-NONE|NONE-CRC32C|NONE
  header-digest = "CRC32C"

Howto use a configuration file to set iSCSI configuration options:

cat >iscsi.conf <<EOF
[iscsi]
  user = "me"
  password = "my password"
  initiator-name = "iqn.qemu.test:my-initiator"
  header-digest = "CRC32C"
EOF

qemu-system-i386 -drive file=iscsi://127.0.0.1/iqn.qemu.test/1 \
    -readconfig iscsi.conf

Howto set up a simple iSCSI target on loopback and accessing it via QEMU:

This example shows how to set up an iSCSI target with one CDROM and one DISK
using the Linux STGT software target. This target is available on Red Hat based
systems as the package 'scsi-target-utils'.

tgtd --iscsi portal=127.0.0.1:3260
tgtadm --lld iscsi --op new --mode target --tid 1 -T iqn.qemu.test
tgtadm --lld iscsi --mode logicalunit --op new --tid 1 --lun 1 \
    -b /IMAGES/disk.img --device-type=disk
tgtadm --lld iscsi --mode logicalunit --op new --tid 1 --lun 2 \
    -b /IMAGES/cd.iso --device-type=cd
tgtadm --lld iscsi --op bind --mode target --tid 1 -I ALL

qemu-system-i386 -iscsi initiator-name=iqn.qemu.test:my-initiator \
    -boot d -drive file=iscsi://127.0.0.1/iqn.qemu.test/1 \
    -cdrom iscsi://127.0.0.1/iqn.qemu.test/2

3.6.12 GlusterFS disk images

GlusterFS is an user space distributed file system.

You can boot from the GlusterFS disk image with the command:

qemu-system-x86_64 -drive file=gluster[+transport]://[server[:port]]/volname/image[?socket=...]

gluster is the protocol.

transport specifies the transport type used to connect to gluster management daemon (glusterd). Valid transport types are tcp, unix and rdma. If a transport type isn't specified, then tcp type is assumed.

server specifies the server where the volume file specification for the given volume resides. This can be either hostname, ipv4 address or ipv6 address. ipv6 address needs to be within square brackets [ ]. If transport type is unix, then server field should not be specifed. Instead socket field needs to be populated with the path to unix domain socket.

port is the port number on which glusterd is listening. This is optional and if not specified, QEMU will send 0 which will make gluster to use the default port. If the transport type is unix, then port should not be specified.

volname is the name of the gluster volume which contains the disk image.

image is the path to the actual disk image that resides on gluster volume.

You can create a GlusterFS disk image with the command:

qemu-img create gluster://server/volname/image size

Examples

qemu-system-x86_64 -drive file=gluster://1.2.3.4/testvol/a.img
qemu-system-x86_64 -drive file=gluster+tcp://1.2.3.4/testvol/a.img
qemu-system-x86_64 -drive file=gluster+tcp://1.2.3.4:24007/testvol/dir/a.img
qemu-system-x86_64 -drive file=gluster+tcp://[1:2:3:4:5:6:7:8]/testvol/dir/a.img
qemu-system-x86_64 -drive file=gluster+tcp://[1:2:3:4:5:6:7:8]:24007/testvol/dir/a.img
qemu-system-x86_64 -drive file=gluster+tcp://server.domain.com:24007/testvol/dir/a.img
qemu-system-x86_64 -drive file=gluster+unix:///testvol/dir/a.img?socket=/tmp/glusterd.socket
qemu-system-x86_64 -drive file=gluster+rdma://1.2.3.4:24007/testvol/a.img

3.6.13 Secure Shell (ssh) disk images

You can access disk images located on a remote ssh server by using the ssh protocol:

qemu-system-x86_64 -drive file=ssh://[user@]server[:port]/path[?host_key_check=host_key_check]

Alternative syntax using properties:

qemu-system-x86_64 -drive file.driver=ssh[,file.user=user],file.host=server[,file.port=port],file.path=path[,file.host_key_check=host_key_check]

ssh is the protocol.

user is the remote user. If not specified, then the local username is tried.

server specifies the remote ssh server. Any ssh server can be used, but it must implement the sftp-server protocol. Most Unix/Linux systems should work without requiring any extra configuration.

port is the port number on which sshd is listening. By default the standard ssh port (22) is used.

path is the path to the disk image.

The optional host_key_check parameter controls how the remote host's key is checked. The default is yes which means to use the local .ssh/known_hosts file. Setting this to no turns off known-hosts checking. Or you can check that the host key matches a specific fingerprint: host_key_check=md5:78:45:8e:14:57:4f:d5:45:83:0a:0e:f3:49:82:c9:c8 (sha1: can also be used as a prefix, but note that OpenSSH tools only use MD5 to print fingerprints).

Currently authentication must be done using ssh-agent. Other authentication methods may be supported in future.

Note: Many ssh servers do not support an fsync-style operation. The ssh driver cannot guarantee that disk flush requests are obeyed, and this causes a risk of disk corruption if the remote server or network goes down during writes. The driver will print a warning when fsync is not supported:

warning: ssh server ssh.example.com:22 does not support fsync

With sufficiently new versions of libssh2 and OpenSSH, fsync is supported.

3.7 Network emulation

QEMU can simulate several network cards (PCI or ISA cards on the PC target) and can connect them to an arbitrary number of Virtual Local Area Networks (VLANs). Host TAP devices can be connected to any QEMU VLAN. VLAN can be connected between separate instances of QEMU to simulate large networks. For simpler usage, a non privileged user mode network stack can replace the TAP device to have a basic network connection.

3.7.1 VLANs

QEMU simulates several VLANs. A VLAN can be symbolised as a virtual connection between several network devices. These devices can be for example QEMU virtual Ethernet cards or virtual Host ethernet devices (TAP devices).

3.7.2 Using TAP network interfaces

This is the standard way to connect QEMU to a real network. QEMU adds a virtual network device on your host (called tapN), and you can then configure it as if it was a real ethernet card.

3.7.2.1 Linux host

As an example, you can download the linux-test-xxx.tar.gz archive and copy the script qemu-ifup in /etc and configure properly sudo so that the command ifconfig contained in qemu-ifup can be executed as root. You must verify that your host kernel supports the TAP network interfaces: the device /dev/net/tun must be present.

See sec_invocation to have examples of command lines using the TAP network interfaces.

3.7.2.2 Windows host

There is a virtual ethernet driver for Windows 2000/XP systems, called TAP-Win32. But it is not included in standard QEMU for Windows, so you will need to get it separately. It is part of OpenVPN package, so download OpenVPN from : http://openvpn.net/.

3.7.3 Using the user mode network stack

By using the option -net user (default configuration if no -net option is specified), QEMU uses a completely user mode network stack (you don't need root privilege to use the virtual network). The virtual network configuration is the following:

         QEMU VLAN      <------>  Firewall/DHCP server <-----> Internet
                           |          (10.0.2.2)
                           |
                           ---->  DNS server (10.0.2.3)
                           |
                           ---->  SMB server (10.0.2.4)

The QEMU VM behaves as if it was behind a firewall which blocks all incoming connections. You can use a DHCP client to automatically configure the network in the QEMU VM. The DHCP server assign addresses to the hosts starting from 10.0.2.15.

In order to check that the user mode network is working, you can ping the address 10.0.2.2 and verify that you got an address in the range 10.0.2.x from the QEMU virtual DHCP server.

Note that ICMP traffic in general does not work with user mode networking. ping, aka. ICMP echo, to the local router (10.0.2.2) shall work, however. If you're using QEMU on Linux >= 3.0, it can use unprivileged ICMP ping sockets to allow ping to the Internet. The host admin has to set the ping_group_range in order to grant access to those sockets. To allow ping for GID 100 (usually users group):

echo 100 100 > /proc/sys/net/ipv4/ping_group_range

When using the built-in TFTP server, the router is also the TFTP server.

When using the -redir option, TCP or UDP connections can be redirected from the host to the guest. It allows for example to redirect X11, telnet or SSH connections.

3.7.4 Connecting VLANs between QEMU instances

Using the -net socket option, it is possible to make VLANs that span several QEMU instances. See sec_invocation to have a basic example.

3.8 Other Devices

3.8.1 Inter-VM Shared Memory device

With KVM enabled on a Linux host, a shared memory device is available. Guests map a POSIX shared memory region into the guest as a PCI device that enables zero-copy communication to the application level of the guests. The basic syntax is:

qemu-system-i386 -device ivshmem,size=<size in format accepted by -m>[,shm=<shm name>]

If desired, interrupts can be sent between guest VMs accessing the same shared memory region. Interrupt support requires using a shared memory server and using a chardev socket to connect to it. The code for the shared memory server is qemu.git/contrib/ivshmem-server. An example syntax when using the shared memory server is:

qemu-system-i386 -device ivshmem,size=<size in format accepted by -m>[,chardev=<id>]
                 [,msi=on][,ioeventfd=on][,vectors=n][,role=peer|master]
qemu-system-i386 -chardev socket,path=<path>,id=<id>

When using the server, the guest will be assigned a VM ID (>=0) that allows guests using the same server to communicate via interrupts. Guests can read their VM ID from a device register (see example code). Since receiving the shared memory region from the server is asynchronous, there is a (small) chance the guest may boot before the shared memory is attached. To allow an application to ensure shared memory is attached, the VM ID register will return -1 (an invalid VM ID) until the memory is attached. Once the shared memory is attached, the VM ID will return the guest's valid VM ID. With these semantics, the guest application can check to ensure the shared memory is attached to the guest before proceeding.

The role argument can be set to either master or peer and will affect how the shared memory is migrated. With role=master, the guest will copy the shared memory on migration to the destination host. With role=peer, the guest will not be able to migrate with the device attached. With the peer case, the device should be detached and then reattached after migration using the PCI hotplug support.

3.9 Direct Linux Boot

This section explains how to launch a Linux kernel inside QEMU without having to make a full bootable image. It is very useful for fast Linux kernel testing.

The syntax is:

qemu-system-i386 -kernel arch/i386/boot/bzImage -hda root-2.4.20.img -append "root=/dev/hda"

Use -kernel to provide the Linux kernel image and -append to give the kernel command line arguments. The -initrd option can be used to provide an INITRD image.

When using the direct Linux boot, a disk image for the first hard disk hda is required because its boot sector is used to launch the Linux kernel.

If you do not need graphical output, you can disable it and redirect the virtual serial port and the QEMU monitor to the console with the -nographic option. The typical command line is:

qemu-system-i386 -kernel arch/i386/boot/bzImage -hda root-2.4.20.img \
                 -append "root=/dev/hda console=ttyS0" -nographic

Use <Ctrl-a c> to switch between the serial console and the monitor (see pcsys_keys).

3.10 USB emulation

QEMU emulates a PCI UHCI USB controller. You can virtually plug virtual USB devices or real host USB devices (experimental, works only on Linux hosts). QEMU will automatically create and connect virtual USB hubs as necessary to connect multiple USB devices.

3.10.1 Connecting USB devices

USB devices can be connected with the -usbdevice commandline option or the usb_add monitor command. Available devices are:

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:file
Mass storage device based on file (see disk_images)
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)
wacom-tablet
Virtual Wacom PenPartner tablet. This device is similar to the tablet above but it can be used with the tslib library because in addition to touch coordinates it reports touch pressure.
keyboard
Standard USB keyboard. Will override the PS/2 keyboard (if present).
serial:[vendorid=vendor_id][,product_id=product_id]:dev
Serial converter. This emulates an FTDI FT232BM chip connected to host character device dev. The available character devices are the same as for the -serial option. The vendorid and productid options can be used to override the default 0403:6001. For instance,
     usb_add serial:productid=FA00:tcp:192.168.0.2:4444

will connect to tcp port 4444 of ip 192.168.0.2, and plug that to the virtual serial converter, faking a Matrix Orbital LCD Display (USB ID 0403:FA00).

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. options specifies NIC options as with -net nic,options (see description). For instance, user-mode networking can be used with
     qemu-system-i386 [...OPTIONS...] -net user,vlan=0 -usbdevice net:vlan=0

Currently this cannot be used in machines that support PCI NICs.

bt[:hci-type]
Bluetooth dongle whose type is specified in the same format as with the -bt hci option, see allowed HCI types. If no type is given, the HCI logic corresponds to -bt hci,vlan=0. This USB device implements the USB Transport Layer of HCI. Example usage:
     qemu-system-i386 [...OPTIONS...] -usbdevice bt:hci,vlan=3 -bt device:keyboard,vlan=3

3.10.2 Using host USB devices on a Linux host

WARNING: this is an experimental feature. QEMU will slow down when using it. USB devices requiring real time streaming (i.e. USB Video Cameras) are not supported yet.

  1. If you use an early Linux 2.4 kernel, verify that no Linux driver is actually using the USB device. A simple way to do that is simply to disable the corresponding kernel module by renaming it from mydriver.o to mydriver.o.disabled.
  2. Verify that /proc/bus/usb is working (most Linux distributions should enable it by default). You should see something like that:
         ls /proc/bus/usb
         001  devices  drivers
    
  3. Since only root can access to the USB devices directly, you can either launch QEMU as root or change the permissions of the USB devices you want to use. For testing, the following suffices:
         chown -R myuid /proc/bus/usb
    
  4. Launch QEMU and do in the monitor:
         info usbhost
           Device 1.2, speed 480 Mb/s
             Class 00: USB device 1234:5678, USB DISK
    

    You should see the list of the devices you can use (Never try to use hubs, it won't work).

  5. Add the device in QEMU by using:
         usb_add host:1234:5678
    

    Normally the guest OS should report that a new USB device is plugged. You can use the option -usbdevice to do the same.

  6. Now you can try to use the host USB device in QEMU.

When relaunching QEMU, you may have to unplug and plug again the USB device to make it work again (this is a bug).

3.11 VNC security

The VNC server capability provides access to the graphical console of the guest VM across the network. This has a number of security considerations depending on the deployment scenarios.

3.11.1 Without passwords

The simplest VNC server setup does not include any form of authentication. For this setup it is recommended to restrict it to listen on a UNIX domain socket only. For example

qemu-system-i386 [...OPTIONS...] -vnc unix:/home/joebloggs/.qemu-myvm-vnc

This ensures that only users on local box with read/write access to that path can access the VNC server. To securely access the VNC server from a remote machine, a combination of netcat+ssh can be used to provide a secure tunnel.

3.11.2 With passwords

The VNC protocol has limited support for password based authentication. Since the protocol limits passwords to 8 characters it should not be considered to provide high security. The password can be fairly easily brute-forced by a client making repeat connections. For this reason, a VNC server using password authentication should be restricted to only listen on the loopback interface or UNIX domain sockets. Password authentication is not supported when operating in FIPS 140-2 compliance mode as it requires the use of the DES cipher. Password authentication is requested with the password option, and then once QEMU is running the password is set with the monitor. Until the monitor is used to set the password all clients will be rejected.

qemu-system-i386 [...OPTIONS...] -vnc :1,password -monitor stdio
(qemu) change vnc password
Password: ********
(qemu)

3.11.3 With x509 certificates

The QEMU VNC server also implements the VeNCrypt extension allowing use of TLS for encryption of the session, and x509 certificates for authentication. The use of x509 certificates is strongly recommended, because TLS on its own is susceptible to man-in-the-middle attacks. Basic x509 certificate support provides a secure session, but no authentication. This allows any client to connect, and provides an encrypted session.

qemu-system-i386 [...OPTIONS...] -vnc :1,tls,x509=/etc/pki/qemu -monitor stdio

In the above example /etc/pki/qemu should contain at least three files, ca-cert.pem, server-cert.pem and server-key.pem. Unprivileged users will want to use a private directory, for example $HOME/.pki/qemu. NB the server-key.pem file should be protected with file mode 0600 to only be readable by the user owning it.

3.11.4 With x509 certificates and client verification

Certificates can also provide a means to authenticate the client connecting. The server will request that the client provide a certificate, which it will then validate against the CA certificate. This is a good choice if deploying in an environment with a private internal certificate authority.

qemu-system-i386 [...OPTIONS...] -vnc :1,tls,x509verify=/etc/pki/qemu -monitor stdio

3.11.5 With x509 certificates, client verification and passwords

Finally, the previous method can be combined with VNC password authentication to provide two layers of authentication for clients.

qemu-system-i386 [...OPTIONS...] -vnc :1,password,tls,x509verify=/etc/pki/qemu -monitor stdio
(qemu) change vnc password
Password: ********
(qemu)

3.11.6 With SASL authentication

The SASL authentication method is a VNC extension, that provides an easily extendable, pluggable authentication method. This allows for integration with a wide range of authentication mechanisms, such as PAM, GSSAPI/Kerberos, LDAP, SQL databases, one-time keys and more. The strength of the authentication depends on the exact mechanism configured. If the chosen mechanism also provides a SSF layer, then it will encrypt the datastream as well.

Refer to the later docs on how to choose the exact SASL mechanism used for authentication, but assuming use of one supporting SSF, then QEMU can be launched with:

qemu-system-i386 [...OPTIONS...] -vnc :1,sasl -monitor stdio

3.11.7 With x509 certificates and SASL authentication

If the desired SASL authentication mechanism does not supported SSF layers, then it is strongly advised to run it in combination with TLS and x509 certificates. This provides securely encrypted data stream, avoiding risk of compromising of the security credentials. This can be enabled, by combining the 'sasl' option with the aforementioned TLS + x509 options:

qemu-system-i386 [...OPTIONS...] -vnc :1,tls,x509,sasl -monitor stdio

3.11.8 Generating certificates for VNC

The GNU TLS packages provides a command called certtool which can be used to generate certificates and keys in PEM format. At a minimum it is necessary to setup a certificate authority, and issue certificates to each server. If using certificates for authentication, then each client will also need to be issued a certificate. The recommendation is for the server to keep its certificates in either /etc/pki/qemu or for unprivileged users in $HOME/.pki/qemu.

3.11.8.1 Setup the Certificate Authority

This step only needs to be performed once per organization / organizational unit. First the CA needs a private key. This key must be kept VERY secret and secure. If this key is compromised the entire trust chain of the certificates issued with it is lost.

# certtool --generate-privkey > ca-key.pem

A CA needs to have a public certificate. For simplicity it can be a self-signed certificate, or one issue by a commercial certificate issuing authority. To generate a self-signed certificate requires one core piece of information, the name of the organization.

# cat > ca.info <<EOF
cn = Name of your organization
ca
cert_signing_key
EOF
# certtool --generate-self-signed \
           --load-privkey ca-key.pem
           --template ca.info \
           --outfile ca-cert.pem

The ca-cert.pem file should be copied to all servers and clients wishing to utilize TLS support in the VNC server. The ca-key.pem must not be disclosed/copied at all.

3.11.8.2 Issuing server certificates

Each server (or host) needs to be issued with a key and certificate. When connecting the certificate is sent to the client which validates it against the CA certificate. The core piece of information for a server certificate is the hostname. This should be the fully qualified hostname that the client will connect with, since the client will typically also verify the hostname in the certificate. On the host holding the secure CA private key:

# cat > server.info <<EOF
organization = Name  of your organization
cn = server.foo.example.com
tls_www_server
encryption_key
signing_key
EOF
# certtool --generate-privkey > server-key.pem
# certtool --generate-certificate \
           --load-ca-certificate ca-cert.pem \
           --load-ca-privkey ca-key.pem \
           --load-privkey server server-key.pem \
           --template server.info \
           --outfile server-cert.pem

The server-key.pem and server-cert.pem files should now be securely copied to the server for which they were generated. The server-key.pem is security sensitive and should be kept protected with file mode 0600 to prevent disclosure.

3.11.8.3 Issuing client certificates

If the QEMU VNC server is to use the x509verify option to validate client certificates as its authentication mechanism, each client also needs to be issued a certificate. The client certificate contains enough metadata to uniquely identify the client, typically organization, state, city, building, etc. On the host holding the secure CA private key:

# cat > client.info <<EOF
country = GB
state = London
locality = London
organiazation = Name of your organization
cn = client.foo.example.com
tls_www_client
encryption_key
signing_key
EOF
# certtool --generate-privkey > client-key.pem
# certtool --generate-certificate \
           --load-ca-certificate ca-cert.pem \
           --load-ca-privkey ca-key.pem \
           --load-privkey client-key.pem \
           --template client.info \
           --outfile client-cert.pem

The client-key.pem and client-cert.pem files should now be securely copied to the client for which they were generated.

3.11.9 Configuring SASL mechanisms

The following documentation assumes use of the Cyrus SASL implementation on a Linux host, but the principals should apply to any other SASL impl. When SASL is enabled, the mechanism configuration will be loaded from system default SASL service config /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.

The default configuration might contain

mech_list: digest-md5
sasldb_path: /etc/qemu/passwd.db

This says to use the 'Digest MD5' mechanism, which is similar to the HTTP Digest-MD5 mechanism. The list of valid usernames & passwords is maintained in the /etc/qemu/passwd.db file, and can be updated using the saslpasswd2 command. While this mechanism is easy to configure and use, it is not considered secure by modern standards, so only suitable for developers / ad-hoc testing.

A more serious deployment might use Kerberos, which is done with the 'gssapi' mechanism

mech_list: gssapi
keytab: /etc/qemu/krb5.tab

For this to work the administrator of your KDC must generate a Kerberos principal for the server, with a name of 'qemu/somehost.example.com@EXAMPLE.COM' replacing 'somehost.example.com' with the fully qualified host name of the machine running QEMU, and 'EXAMPLE.COM' with the Kerberos Realm.

Other configurations will be left as an exercise for the reader. It should be noted that only Digest-MD5 and GSSAPI provides a SSF layer for data encryption. For all other mechanisms, VNC should always be configured to use TLS and x509 certificates to protect security credentials from snooping.

3.12 GDB usage

QEMU has a primitive support to work with gdb, so that you can do 'Ctrl-C' while the virtual machine is running and inspect its state.

In order to use gdb, launch QEMU with the '-s' option. It will wait for a gdb connection:

qemu-system-i386 -s -kernel arch/i386/boot/bzImage -hda root-2.4.20.img \
                    -append "root=/dev/hda"
Connected to host network interface: tun0
Waiting gdb connection on port 1234

Then launch gdb on the 'vmlinux' executable:

> gdb vmlinux

In gdb, connect to QEMU:

(gdb) target remote localhost:1234

Then you can use gdb normally. For example, type 'c' to launch the kernel:

(gdb) c

Here are some useful tips in order to use gdb on system code:

  1. Use info reg to display all the CPU registers.
  2. Use x/10i $eip to display the code at the PC position.
  3. Use set architecture i8086 to dump 16 bit code. Then use x/10i $cs*16+$eip to dump the code at the PC position.

Advanced debugging options:

The default single stepping behavior is step with the IRQs and timer service routines off. It is set this way because when gdb executes a single step it expects to advance beyond the current instruction. With the IRQs and and timer service routines on, a single step might jump into the one of the interrupt or exception vectors instead of executing the current instruction. This means you may hit the same breakpoint a number of times before executing the instruction gdb wants to have executed. Because there are rare circumstances where you want to single step into an interrupt vector the behavior can be controlled from GDB. There are three commands you can query and set the single step behavior:

maintenance packet qqemu.sstepbits
This will display the MASK bits used to control the single stepping IE:
     (gdb) maintenance packet qqemu.sstepbits
     sending: "qqemu.sstepbits"
     received: "ENABLE=1,NOIRQ=2,NOTIMER=4"

maintenance packet qqemu.sstep
This will display the current value of the mask used when single stepping IE:
     (gdb) maintenance packet qqemu.sstep
     sending: "qqemu.sstep"
     received: "0x7"

maintenance packet Qqemu.sstep=HEX_VALUE
This will change the single step mask, so if wanted to enable IRQs on the single step, but not timers, you would use:
     (gdb) maintenance packet Qqemu.sstep=0x5
     sending: "qemu.sstep=0x5"
     received: "OK"

3.13 Target OS specific information

3.13.1 Linux

To have access to SVGA graphic modes under X11, use the vesa or the cirrus X11 driver. For optimal performances, use 16 bit color depth in the guest and the host OS.

When using a 2.6 guest Linux kernel, you should add the option clock=pit on the kernel command line because the 2.6 Linux kernels make very strict real time clock checks by default that QEMU cannot simulate exactly.

When using a 2.6 guest Linux kernel, verify that the 4G/4G patch is not activated because QEMU is slower with this patch. The QEMU Accelerator Module is also much slower in this case. Earlier Fedora Core 3 Linux kernel (< 2.6.9-1.724_FC3) were known to incorporate this patch by default. Newer kernels don't have it.

3.13.2 Windows

If you have a slow host, using Windows 95 is better as it gives the best speed. Windows 2000 is also a good choice.

3.13.2.1 SVGA graphic modes support

QEMU emulates a 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.

If you are using Windows XP as guest OS and if you want to use high resolution modes which the Cirrus Logic BIOS does not support (i.e. >= 1280x1024x16), then you should use the VESA VBE virtual graphic card (option -std-vga).

3.13.2.2 CPU usage reduction

Windows 9x does not correctly use the CPU HLT instruction. The result is that it takes host CPU cycles even when idle. You can install the utility from http://www.user.cityline.ru/~maxamn/amnhltm.zip to solve this problem. Note that no such tool is needed for NT, 2000 or XP.

3.13.2.3 Windows 2000 disk full problem

Windows 2000 has a bug which gives a disk full problem during its installation. When installing it, use the -win2k-hack QEMU option to enable a specific workaround. After Windows 2000 is installed, you no longer need this option (this option slows down the IDE transfers).

3.13.2.4 Windows 2000 shutdown

Windows 2000 cannot automatically shutdown in QEMU although Windows 98 can. It comes from the fact that Windows 2000 does not automatically use the APM driver provided by the BIOS.

In order to correct that, do the following (thanks to Struan Bartlett): go to the Control Panel => Add/Remove Hardware & Next => Add/Troubleshoot a device => Add a new device & Next => No, select the hardware from a list & Next => NT Apm/Legacy Support & Next => Next (again) a few times. Now the driver is installed and Windows 2000 now correctly instructs QEMU to shutdown at the appropriate moment.

3.13.2.5 Share a directory between Unix and Windows

See sec_invocation about the help of the option -smb.

3.13.2.6 Windows XP security problem

Some releases of Windows XP install correctly but give a security error when booting:

A problem is preventing Windows from accurately checking the
license for this computer. Error code: 0x800703e6.

The workaround is to install a service pack for XP after a boot in safe mode. Then reboot, and the problem should go away. Since there is no network while in safe mode, its recommended to download the full installation of SP1 or SP2 and transfer that via an ISO or using the vvfat block device ("-hdb fat:directory_which_holds_the_SP").

3.13.3 MS-DOS and FreeDOS

3.13.3.1 CPU usage reduction

DOS does not correctly use the CPU HLT instruction. The result is that it takes host CPU cycles even when idle. You can install the utility from http://www.vmware.com/software/dosidle210.zip to solve this problem.

4 QEMU System emulator for non PC targets

QEMU is a generic emulator and it emulates many non PC machines. Most of the options are similar to the PC emulator. The differences are mentioned in the following sections.

4.1 PowerPC System emulator

Use the executable qemu-system-ppc to simulate a complete PREP or PowerMac PowerPC system.

QEMU emulates the following PowerMac peripherals:

QEMU emulates the following PREP peripherals:

QEMU uses the Open Hack'Ware Open Firmware Compatible BIOS.

Since version 0.9.1, QEMU uses OpenBIOS http://www.openbios.org/ for the g3beige and mac99 PowerMac machines. OpenBIOS is a free (GPL v2) portable firmware implementation. The goal is to implement a 100% IEEE 1275-1994 (referred to as Open Firmware) compliant firmware.

The following options are specific to the PowerPC emulation:

-g WxH[xDEPTH]
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.

4.2 Sparc32 System emulator

Use the executable qemu-system-sparc to simulate the following Sun4m architecture machines:

The emulation is somewhat complete. SMP up to 16 CPUs is supported, but Linux limits the number of usable CPUs to 4.

QEMU emulates the following sun4m peripherals:

The number of peripherals is fixed in the architecture. Maximum memory size depends on the machine type, for SS-5 it is 256MB and for others 2047MB.

Since version 0.8.2, QEMU uses OpenBIOS http://www.openbios.org/. OpenBIOS is a free (GPL v2) portable firmware implementation. The goal is to implement a 100% IEEE 1275-1994 (referred to as Open Firmware) compliant firmware.

A sample Linux 2.6 series kernel and ram disk image are available on the QEMU web site. There are still issues with NetBSD and OpenBSD, but some kernel versions work. Please note that currently older Solaris kernels don't work probably due to interface issues between OpenBIOS and Solaris.

The following options are specific to the Sparc32 emulation:

-g WxHx[xDEPTH]
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.

4.3 Sparc64 System emulator

Use the executable qemu-system-sparc64 to simulate a Sun4u (UltraSPARC PC-like machine), Sun4v (T1 PC-like machine), or generic Niagara (T1) machine. The emulator is not usable for anything yet, but it can launch some kernels.

QEMU emulates the following peripherals:

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.

4.4 MIPS System emulator

Four executables cover simulation of 32 and 64-bit MIPS systems in both endian options, qemu-system-mips, qemu-system-mipsel qemu-system-mips64 and qemu-system-mips64el. Five different machine types are emulated:

The generic emulation is supported by Debian 'Etch' and is able to install Debian into a virtual disk image. The following devices are emulated:

The Malta emulation supports the following devices:

The ACER Pica emulation supports:

The mipssim pseudo board emulation provides an environment similar to what the proprietary MIPS emulator uses for running Linux. It supports:

The MIPS Magnum R4000 emulation supports:

4.5 ARM System emulator

Use the executable qemu-system-arm to simulate a ARM machine. The ARM Integrator/CP board is emulated with the following devices:

The ARM Versatile baseboard is emulated with the following devices:

Several variants of the ARM RealView baseboard are emulated, including the EB, PB-A8 and PBX-A9. Due to interactions with the bootloader, only certain Linux kernel configurations work out of the box on these boards.

Kernels for the PB-A8 board should have CONFIG_REALVIEW_HIGH_PHYS_OFFSET enabled in the kernel, and expect 512M RAM. Kernels for The PBX-A9 board should have CONFIG_SPARSEMEM enabled, CONFIG_REALVIEW_HIGH_PHYS_OFFSET disabled and expect 1024M RAM.

The following devices are emulated:

The XScale-based clamshell PDA models ("Spitz", "Akita", "Borzoi" and "Terrier") emulation includes the following peripherals:

The Palm Tungsten|E PDA (codename "Cheetah") emulation includes the following elements:

Nokia N800 and N810 internet tablets (known also as RX-34 and RX-44 / 48) emulation supports the following elements:

The Luminary Micro Stellaris LM3S811EVB emulation includes the following devices:

The Luminary Micro Stellaris LM3S6965EVB emulation includes the following devices:

The Freecom MusicPal internet radio emulation includes the following elements:

The Siemens SX1 models v1 and v2 (default) basic emulation. The emulation includes the following elements:

A Linux 2.6 test image is available on the QEMU web site. More information is available in the QEMU mailing-list archive.

The following options are specific to the ARM 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.

4.6 ColdFire System emulator

Use the executable qemu-system-m68k to simulate a ColdFire machine. The emulator is able to boot a uClinux kernel.

The M5208EVB emulation includes the following devices:

The AN5206 emulation includes the following devices:

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.

4.7 Cris System emulator

TODO

4.8 Microblaze System emulator

TODO

4.9 SH4 System emulator

TODO

4.10 Xtensa System emulator

Two executables cover simulation of both Xtensa endian options, qemu-system-xtensa and qemu-system-xtensaeb. Two different machine types are emulated:

The sim pseudo board emulation provides an environment similar to one provided by the proprietary Tensilica ISS. It supports:

The Avnet LX60/LX110/LX200 emulation supports:

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.

5 QEMU User space emulator

5.1 Supported Operating Systems

The following OS are supported in user space emulation:

5.2 Linux User space emulator

5.2.1 Quick Start

In order to launch a Linux process, QEMU needs the process executable itself and all the target (x86) dynamic libraries used by it.

5.2.2 Wine launch

5.2.3 Command line options

usage: qemu-i386 [-h] [-d] [-L path] [-s size] [-cpu model] [-g port] [-B offset] [-R size] program [arguments...]
-h
Print the help
-L path
Set the x86 elf interpreter prefix (default=/usr/local/qemu-i386)
-s size
Set the x86 stack size in bytes (default=524288)
-cpu model
Select CPU model (-cpu help for list and additional feature selection)
-E var=value
Set environment var to value.
-U var
Remove var from the environment.
-B offset
Offset guest address by the specified number of bytes. This is useful when the address region required by guest applications is reserved on the host. This option is currently only supported on some hosts.
-R size
Pre-allocate a guest virtual address space of the given size (in bytes). "G", "M", and "k" suffixes may be used when specifying the size.

Debug options:

-d item1,...
Activate logging of the specified items (use '-d help' for a list of log items)
-p pagesize
Act as if the host page size was 'pagesize' bytes
-g port
Wait gdb connection to port
-singlestep
Run the emulation in single step mode.

Environment variables:

QEMU_STRACE
Print system calls and arguments similar to the 'strace' program (NOTE: the actual 'strace' program will not work because the user space emulator hasn't implemented ptrace). At the moment this is incomplete. All system calls that don't have a specific argument format are printed with information for six arguments. Many flag-style arguments don't have decoders and will show up as numbers.

5.2.4 Other binaries

qemu-alpha TODO.

qemu-armeb TODO.

qemu-arm is also capable of running ARM "Angel" semihosted ELF binaries (as implemented by the arm-elf and arm-eabi Newlib/GDB configurations), and arm-uclinux bFLT format binaries.

qemu-m68k is capable of running semihosted binaries using the BDM (m5xxx-ram-hosted.ld) or m68k-sim (sim.ld) syscall interfaces, and coldfire uClinux bFLT format binaries.

The binary format is detected automatically.

qemu-cris TODO.

qemu-i386 TODO. qemu-x86_64 TODO.

qemu-microblaze TODO.

qemu-mips TODO. qemu-mipsel TODO.

qemu-ppc64abi32 TODO. qemu-ppc64 TODO. qemu-ppc TODO.

qemu-sh4eb TODO. qemu-sh4 TODO.

qemu-sparc can execute Sparc32 binaries (Sparc32 CPU, 32 bit ABI).

qemu-sparc32plus can execute Sparc32 and SPARC32PLUS binaries (Sparc64 CPU, 32 bit ABI).

qemu-sparc64 can execute some Sparc64 (Sparc64 CPU, 64 bit ABI) and SPARC32PLUS binaries (Sparc64 CPU, 32 bit ABI).

5.3 BSD User space emulator

5.3.1 BSD Status

5.3.2 Quick Start

In order to launch a BSD process, QEMU needs the process executable itself and all the target dynamic libraries used by it.

5.3.3 Command line options

usage: qemu-sparc64 [-h] [-d] [-L path] [-s size] [-bsd type] program [arguments...]
-h
Print the help
-L path
Set the library root path (default=/)
-s size
Set the stack size in bytes (default=524288)
-ignore-environment
Start with an empty environment. Without this option, the initial environment is a copy of the caller's environment.
-E var=value
Set environment var to value.
-U var
Remove var from the environment.
-bsd type
Set the type of the emulated BSD Operating system. Valid values are FreeBSD, NetBSD and OpenBSD (default).

Debug options:

-d item1,...
Activate logging of the specified items (use '-d help' for a list of log items)
-p pagesize
Act as if the host page size was 'pagesize' bytes
-singlestep
Run the emulation in single step mode.

6 Compilation from the sources

6.1 Linux/Unix

6.1.1 Compilation

First you must decompress the sources:

cd /tmp
tar zxvf qemu-x.y.z.tar.gz
cd qemu-x.y.z

Then you configure QEMU and build it (usually no options are needed):

./configure
make

Then type as root user:

make install

to install QEMU in /usr/local.

6.2 Windows

6.3 Cross compilation for Windows with Linux

Wine can be used to launch the resulting qemu-system-i386.exe and all other qemu-system-target.exe compiled for Win32.

wine qemu-system-i386

6.4 Mac OS X

The Mac OS X patches are not fully merged in QEMU, so you should look at the QEMU mailing list archive to have all the necessary information. (TODO: is this still true?)

6.5 Make targets

make
make all
Make everything which is typically needed.
install
TODO
install-doc
TODO
make clean
Remove most files which were built during make.
make distclean
Remove everything which was built during make.
make dvi
make html
make info
make pdf
Create documentation in dvi, html, info or pdf format.
make cscope
TODO
make defconfig
(Re-)create some build configuration files. User made changes will be overwritten.
tar
tarbin
TODO

Appendix A License

QEMU is a trademark of Fabrice Bellard.

QEMU is released under the GNU General Public License (TODO: add link). Parts of QEMU have specific licenses, see file LICENSE.

TODO (refer to file LICENSE, include it, include the GPL?)

Appendix B Index

B.1 Concept Index

This is the main index. Should we combine all keywords in one index? TODO

B.2 Function Index

This index could be used for command line options and monitor functions.

B.3 Keystroke Index

This is a list of all keystrokes which have a special function in system emulation.

B.4 Program Index

B.5 Data Type Index

This index could be used for qdev device names and options.

B.6 Variable Index