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QEMU Emulator User Documentation

Table of Contents

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1. Introduction

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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 an host kernel driver and yet gives acceptable performance.

For system emulation, the following hardware targets are supported:

For user emulation, x86, PowerPC, ARM, MIPS, Sparc32/64 and ColdFire(m68k) CPUs are supported.

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2. Installation

If you want to compile QEMU yourself, see Compilation from the sources.

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2.1 Linux

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

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2.2 Windows

Download the experimental binary installer at http://www.free.oszoo.org/download.html.

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2.3 Mac OS X

Download the experimental binary installer at http://www.free.oszoo.org/download.html.

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3. QEMU PC System emulator

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3.1 Introduction

The QEMU PC System emulator simulates the following peripherals:

SMP is supported with up to 255 CPUs.

Note that adlib is only available when QEMU was configured with -enable-adlib

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

QEMU uses YM3812 emulation by Tatsuyuki Satoh.

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3.2 Quick Start

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

qemu linux.img

Linux should boot and give you a prompt.

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3.3 Invocation

usage: qemu [options] [disk_image]

disk_image is a raw hard disk image for IDE hard disk 0.

General options:

`-M machine'

Select the emulated machine (-M ? for list)

`-fda file'
`-fdb file'

Use file as floppy disk 0/1 image (see section Disk Images). You can use the host floppy by using `/dev/fd0' as filename (see section Using host drives).

`-hda file'
`-hdb file'
`-hdc file'
`-hdd file'

Use file as hard disk 0, 1, 2 or 3 image (see section Disk Images).

`-cdrom file'

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

`-boot [a|c|d|n]'

Boot on floppy (a), hard disk (c), CD-ROM (d), or Etherboot (n). Hard disk boot is the default.


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 section Disk Images).


Disable boot signature checking for floppy disks in Bochs BIOS. It may be needed to boot from old floppy disks.

`-m megs'

Set virtual RAM size to megs megabytes. Default is 128 MB.

`-smp n'

Simulate an SMP system with n CPUs. On the PC target, up to 255 CPUs are supported.


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. Therefore, you can still use QEMU to debug a Linux kernel with a serial console.

`-vnc display'

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' option to set the keyboard layout if you are not using en-us.

display may be in the form interface:d, in which case connections will only be allowed from interface on display d. Optionally, interface can be omitted. display can also be in the form unix:path where path is the location of a unix socket to listen for connections on.

`-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.


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

`-soundhw card1,card2,... or -soundhw all'

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

qemu -soundhw sb16,adlib hda
qemu -soundhw es1370 hda
qemu -soundhw all hda
qemu -soundhw ?

Set the real time clock to local time (the default is to UTC time). This option is needed to have correct date in MS-DOS or Windows.


Start in full screen.

`-pidfile file'

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


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.


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).

`-option-rom file'

Load the contents of file as an option ROM. This option is useful to load things like EtherBoot.

USB options:


Enable the USB driver (will be the default soon)

`-usbdevice devname'

Add the USB device devname. See section Connecting USB devices.

Network options:

`-net nic[,vlan=n][,macaddr=addr][,model=type]'

Create a new Network Interface Card and connect it to VLAN n (n = 0 is the default). The NIC is currently an NE2000 on the PC target. Optionally, the MAC address can be changed. 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 ne2k_pci, ne2k_isa, rtl8139, smc91c111 and lance. Not all devices are supported on all targets.

`-net user[,vlan=n][,hostname=name]'

Use the user mode network stack which requires no administrator priviledge to run. `hostname=name' can be used to specify the client hostname reported by the builtin DHCP server.

`-net tap[,vlan=n][,fd=h][,ifname=name][,script=file]'

Connect the host TAP network interface name to VLAN n and use the network script file to configure it. The default network script is `/etc/qemu-ifup'. Use `script=no' to disable script execution. If name is not provided, the OS automatically provides one. `fd=h' can be used to specify the handle of an already opened host TAP interface. Example:

qemu linux.img -net nic -net tap

More complicated example (two NICs, each one connected to a TAP device)

qemu linux.img -net nic,vlan=0 -net tap,vlan=0,ifname=tap0 \
               -net nic,vlan=1 -net tap,vlan=1,ifname=tap1
`-net socket[,vlan=n][,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.


# launch a first QEMU instance
qemu 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 linux.img -net nic,macaddr=52:54:00:12:34:57 \
               -net socket,connect=
`-net socket[,vlan=n][,fd=h][,mcast=maddr:port]'

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.


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

Example (User Mode Linux compat.):

# launch QEMU instance (note mcast address selected
# is UML's default)
qemu linux.img -net nic,macaddr=52:54:00:12:34:56 \
               -net socket,mcast=
# launch UML
/path/to/linux ubd0=/path/to/root_fs eth0=mcast
`-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.

`-tftp prefix'

When using the user mode network stack, activate a built-in TFTP server. All filenames beginning with prefix can be downloaded from the host to the guest using a TFTP client. The TFTP client on the guest must be configured in binary mode (use the command bin of the Unix TFTP client). The host IP address on the guest is as usual

`-smb dir'

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.

In the guest Windows OS, the line: 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 in `/usr/sbin/smbd'. QEMU was tested successfully with smbd version 2.2.7a from the Red Hat 9 and version 3.0.10-1.fc3 from Fedora Core 3.

`-redir [tcp|udp]:host-port:[guest-host]:guest-port'

When using the user mode network stack, redirect incoming TCP or UDP connections to the host port host-port to the guest guest-host on guest port guest-port. If guest-host is not specified, its value is (default address given by the built-in DHCP server).

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

# on the host
qemu -redir tcp: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 -redir tcp:5555::23 [...]
telnet localhost 5555

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

Linux boot specific: When using these options, you can use a given Linux 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.

`-append cmdline'

Use cmdline as kernel command line

`-initrd file'

Use file as initial ram disk.

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 serials ports.

Use -serial none to disable all serial ports.

Available character devices are:


Virtual console


[Linux only] Pseudo TTY (a new PTY is automatically allocated)


No device is allocated.


void device


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


[Linux only, parallel port only] Use host parallel port N. Currently only SPP parallel port features can be used.


Write output to filename. No character can be read.


[Unix only] standard input/output


name pipe filename


[Windows only] Use host serial port n


This implements UDP Net Console. When remote_host or src_ip are not specified they default to When not using a specifed 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 -t -p 5555 -I -T

telnet options:

localhost 5555


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 algoritm. If host is omitted, 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 port 4444

-serial tcp:

Example to listen and wait on port 4444 for connection

-serial tcp::4444,server

Example to not wait and listen on ip port 4444

-serial tcp:,server,nowait


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.


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.

`-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.


Wait gdb connection to port 1234 (see section GDB usage).

`-p port'

Change gdb connection port. port can be either a decimal number to specify a TCP port, or a host device (same devices as the serial port).


Do not start CPU at startup (you must type 'c' in the monitor).


Output log in /tmp/qemu.log

`-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 thoses parameters. This option is useful for old MS-DOS disk images.

`-L path'

Set the directory for the BIOS, VGA BIOS and keymaps.


Simulate a standard VGA card with Bochs VBE extensions (default is Cirrus Logic GD5446 PCI VGA). 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.


Disable ACPI (Advanced Configuration and Power Interface) support. Use it if your guest OS complains about ACPI problems (PC target machine only).


Exit instead of rebooting.

`-loadvm file'

Start right away with a saved state (loadvm in monitor)


Enable "Angel" semihosting interface (ARM target machines only). Note that this allows guest direct access to the host filesystem, so should only be used with trusted guest OS.

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3.4 Keys

During the graphical emulation, you can use the following keys:


Toggle full screen


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


Target system display




Serial port


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

Print this help

Ctrl-a x

Exit emulator

Ctrl-a s

Save disk data back to file (if -snapshot)

Ctrl-a b

Send break (magic sysrq in Linux)

Ctrl-a c

Switch between console and monitor

Ctrl-a Ctrl-a

Send Ctrl-a

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3.5 QEMU Monitor

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

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3.5.1 Commands

The following commands are available:

`help or ? [cmd]'

Show the help for all commands or just for command cmd.


Commit changes to the disk images (if -snapshot is used)

`info subcommand'

show various information about the system state

`info network'

show the various VLANs and the associated devices

`info block'

show the block devices

`info registers'

show the cpu registers

`info history'

show the command line history

`info pci'

show emulated PCI device

`info usb'

show USB devices plugged on the virtual USB hub

`info usbhost'

show all USB host devices

`info capture'

show information about active capturing

`info snapshots'

show list of VM snapshots

`info mice'

show which guest mouse is receiving events

`q or quit'

Quit the emulator.

`eject [-f] device'

Eject a removable media (use -f to force it).

`change device filename'

Change a removable media.

`screendump filename'

Save screen into PPM image filename.

`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.


`stopcapture index'

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

info capture
`log item1[,...]'

Activate logging of the specified items to `/tmp/qemu.log'.

`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.


Stop emulation.

`c or cont'

Resume emulation.

`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}'


is the number of items to be dumped.


can be x (hexa), d (signed decimal), u (unsigned decimal), o (octal), c (char) or i (asm instruction).


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.


`p or print/fmt expr'

Print expression value. Only the format part of fmt is used.

`sendkey keys'

Send keys to the emulator. 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.


Reset the system.

`usb_add devname'

Add the USB device devname. For details of available devices see Connecting 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.

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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 $.

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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.

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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.

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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).

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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 (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:

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3.6.4 qemu-img Invocation

usage: qemu-img command [command options]

The following commands are supported:

`create [-e] [-b base_image] [-f fmt] filename [size]'
`commit [-f fmt] filename'
`convert [-c] [-e] [-f fmt] filename [-O output_fmt] output_filename'
`info [-f fmt] filename'

Command parameters:


is a disk image filename


is the read-only disk image which is used as base for a copy on write image; the copy on write image only stores the modified data


is the disk image format. It is guessed automatically in most cases. The following formats are supported:


Raw disk image format (default). 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.


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.


Old QEMU image format. Left for compatibility.


User Mode Linux Copy On Write image format. Used to be the only growable image format in QEMU. It is supported only for compatibility with previous versions. It does not work on win32.


VMware 3 and 4 compatible image format.


Linux Compressed Loop image, useful only to reuse directly compressed CD-ROM images present for example in the Knoppix CD-ROMs.


is the disk image size in kilobytes. Optional suffixes M (megabyte) and G (gigabyte) are supported


is the destination disk image filename


is the destination format


indicates that target image must be compressed (qcow format only)


indicates that the target image must be encrypted (qcow format only)

Command description:

`create [-e] [-b base_image] [-f fmt] filename [size]'

Create the new disk image filename of size size and format fmt.

If base_image is specified, then the image will record only the differences from base_image. No size needs to be specified in this case. base_image will never be modified unless you use the commit monitor command.

`commit [-f fmt] filename'

Commit the changes recorded in filename in its base image.

`convert [-c] [-e] [-f fmt] filename [-O output_fmt] output_filename'

Convert the disk image filename to disk image output_filename using format output_fmt. It can be optionnaly encrypted (-e option) or compressed (-c option).

Only the format qcow supports encryption or compression. The compression is read-only. It means that if a compressed sector is rewritten, then it is rewritten as uncompressed data.

Encryption uses the AES format which is very secure (128 bit keys). Use a long password (16 characters) to get maximum protection.

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

`info [-f fmt] 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.

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3.6.5 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.

[ < ] [ > ]   [Contents] [Index] [ ? ] Linux

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


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.


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).

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The prefered 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 medias, 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).

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).

[ < ] [ > ]   [Contents] [Index] [ ? ] Mac OS X

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

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

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3.6.6 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 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 linux.img -fda fat:floppy:/my_directory

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

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

What you should never do:

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3.7 Network emulation

QEMU can simulate several networks cards (NE2000 boards 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 priviledged user mode network stack can replace the TAP device to have a basic network connection.

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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).

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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.

[ < ] [ > ]   [Contents] [Index] [ ? ] 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 Invocation to have examples of command lines using the TAP network interfaces.

[ < ] [ > ]   [Contents] [Index] [ ? ] 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/.

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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 priviledge to use the virtual network). The virtual network configuration is the following:

         QEMU VLAN      <------>  Firewall/DHCP server <-----> Internet
                           |          (
                           ---->  DNS server (
                           ---->  SMB server (

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

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

Note that ping is not supported reliably to the internet as it would require root priviledges. It means you can only ping the local router (

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.

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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 Invocation to have a basic example.

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3.8 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 -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 -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 section Keys).

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3.9 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.

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3.9.1 Connecting USB devices

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


Virtual Mouse. This will override the PS/2 mouse emulation when activated.


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.


Mass storage device based on file (see section Disk Images)


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


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

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3.9.2 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).

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3.10 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 -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.

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3.11 Target OS specific information

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3.11.1 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 incorporte this patch by default. Newer kernels don't have it.

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3.11.2 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.

[ < ] [ > ]   [Contents] [Index] [ ? ] 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').

[ < ] [ > ]   [Contents] [Index] [ ? ] 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.

[ < ] [ > ]   [Contents] [Index] [ ? ] 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).

[ < ] [ > ]   [Contents] [Index] [ ? ] 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.

[ < ] [ > ]   [Contents] [Index] [ ? ] Share a directory between Unix and Windows

See Invocation about the help of the option `-smb'.

[ < ] [ > ]   [Contents] [Index] [ ? ] 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").

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3.11.3 MS-DOS and FreeDOS

[ < ] [ > ]   [Contents] [Index] [ ? ] 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.

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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 mentionned in the following sections.

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4.1 QEMU 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 available at http://perso.magic.fr/l_indien/OpenHackWare/index.htm.

The following options are specific to the PowerPC emulation:

`-g WxH[xDEPTH]'

Set the initial VGA graphic mode. The default is 800x600x15.

More information is available at http://perso.magic.fr/l_indien/qemu-ppc/.

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4.2 Sparc32 System emulator invocation

Use the executable `qemu-system-sparc' to simulate a SparcStation 5 (sun4m architecture). The emulation is somewhat complete.

QEMU emulates the following sun4m peripherals:

The number of peripherals is fixed in the architecture.

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. Please note that currently NetBSD, OpenBSD or Solaris kernels don't work.

The following options are specific to the Sparc emulation:

`-g WxH'

Set the initial TCX graphic mode. The default is 1024x768.

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4.3 Sparc64 System emulator invocation

Use the executable `qemu-system-sparc64' to simulate a Sun4u machine. The emulator is not usable for anything yet.

QEMU emulates the following sun4u peripherals:

[ < ] [ > ]   [Contents] [Index] [ ? ]

4.4 MIPS System emulator invocation

Use the executable `qemu-system-mips' to simulate a MIPS machine. The emulator is able to boot a Linux kernel and to run a Linux Debian installation from NFS. The following devices are emulated:

More information is available in the QEMU mailing-list archive.

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4.5 ARM System emulator invocation

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:

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

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5. QEMU User space emulator

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5.1 Supported Operating Systems

The following OS are supported in user space emulation:

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5.2 Linux User space emulator

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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.

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5.2.2 Wine launch

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5.2.3 Command line options

usage: qemu-i386 [-h] [-d] [-L path] [-s size] program [arguments...]

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)

Debug options:


Activate log (logfile=/tmp/qemu.log)

`-p pagesize'

Act as if the host page size was 'pagesize' bytes

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5.2.4 Other binaries

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.

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5.3 Mac OS X/Darwin User space emulator

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5.3.1 Mac OS X/Darwin Status

[1] If you're host commpage can be executed by qemu.

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5.3.2 Quick Start

In order to launch a Mac OS X/Darwin process, QEMU needs the process executable itself and all the target dynamic libraries used by it. If you don't have the FAT libraries (you're running Mac OS X/ppc) you'll need to obtain it from a Mac OS X CD or compile them by hand.

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5.3.3 Command line options

usage: qemu-darwin-i386 [-h] [-d] [-L path] [-s size] program [arguments...]

Print the help

`-L path'

Set the library root path (default=/)

`-s size'

Set the stack size in bytes (default=524288)

Debug options:


Activate log (logfile=/tmp/qemu.log)

`-p pagesize'

Act as if the host page size was 'pagesize' bytes

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6. Compilation from the sources

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6.1 Linux/Unix

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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):


Then type as root user:

make install

to install QEMU in `/usr/local'.

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6.1.2 GCC version

In order to compile QEMU successfully, it is very important that you have the right tools. The most important one is gcc. On most hosts and in particular on x86 ones, gcc 4.x is not supported. If your Linux distribution includes a gcc 4.x compiler, you can usually install an older version (it is invoked by gcc32 or gcc34). The QEMU configure script automatically probes for these older versions so that usally you don't have to do anything.

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6.2 Windows

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6.3 Cross compilation for Windows with Linux

Note: Currently, Wine does not seem able to launch QEMU for Win32.

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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.

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7. Index

Table of Contents

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