QEMU CPU Emulator User Documentation
redistributed by Mep Produções for Kemula

Table of Contents

QEMU CPU Emulator User Documentation

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 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, and Sparc32/64 CPUs are supported.

2. Installation

If you want to compile QEMU yourself, see section 6. Compilation from the sources.

2.1 Linux

If a precompiled package is available for your distribution - you just have to install it. Otherwise, see section 6. Compilation from the sources.

2.2 Windows

Download the experimental binary installer at http://www.freeoszoo.org/download.php.

2.3 Mac OS X

Download the experimental binary installer at http://www.freeoszoo.org/download.php.

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.

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.

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.

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 3.6 Disk Images). You can use the host floppy by using `/dev/fd0' as filename.
`-hda file'
`-hdb file'
`-hdc file'
`-hdd file'
Use file as hard disk 0, 1, 2 or 3 image (See section 3.6 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.
`-boot [a|c|d]'
Boot on floppy (a), hard disk (c) or CD-ROM (d). 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 3.6 Disk Images).
`-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.
`-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 or with some X11 servers). You don't 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.
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).

USB options:

Enable the USB driver (will be the default soon)
`-usbdevice devname'
Add the USB device devname. See the monitor command usb_add to have more information.

Network options:

`-net nic[,vlan=n][,macaddr=addr]'
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.
`-net user[,vlan=n]'
Use the user mode network stack which requires no administrator priviledge to run. This is the default if no `-net' option is specified.
`-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'. 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. Example:
# 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 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 succesfully 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 device dev. Available devices are:
Virtual console
[Linux only] Pseudo TTY (a new PTY is automatically 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
[Unix only] name pipe filename
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.
`-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.
`-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 3.10 GDB usage).
`-p port'
Change gdb connection 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.
Simulate a standard VGA card with Bochs VBE extensions (default is Cirrus Logic GD5446 PCI VGA)
`-loadvm file'
Start right away with a saved state (loadvm in monitor)

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 emulatior
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

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 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
`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.
`log item1[,...]'
Activate logging of the specified items to `/tmp/qemu.log'.
`savevm filename'
Save the whole virtual machine state to filename.
`loadvm filename'
Restore the whole virtual machine state from filename.
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'
Plug the USB device devname to the QEMU virtual USB hub. devname is either a virtual device name (for example mouse) or a host USB device identifier. Host USB device identifiers have the following syntax: host:bus.addr or host:vendor_id:product_id.
`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.

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.

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 section 3.6.3 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 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), 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 and zlib based compression.
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.

3.6.4 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:

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.

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.

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 section 3.8 Direct Linux Boot to have an example of network use with a Linux distribution and section 3.3 Invocation to have examples of command lines using the TAP network interfaces.

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.

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 section 3.3 Invocation to have a basic example.

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 QEMU network configuration is also explained.

  1. Download the archive `linux-test-xxx.tar.gz' containing a Linux kernel and a disk image.
  2. Optional: If you want network support (for example to launch X11 examples), you must 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 TUN/TAP network interfaces: the device `/dev/net/tun' must be present. When network is enabled, there is a virtual network connection between the host kernel and the emulated kernel. The emulated kernel is seen from the host kernel at IP address and the host kernel is seen from the emulated kernel at IP address
  3. Launch qemu.sh. You should have the following output:
    > ./qemu.sh 
    Connected to host network interface: tun0
    Linux version 2.4.21 (bellard@voyager.localdomain) (gcc version 3.2.2 20030222 (Red Hat Linux 3.2.2-5)) #5 Tue Nov 11 18:18:53 CET 2003
    BIOS-provided physical RAM map:
     BIOS-e801: 0000000000000000 - 000000000009f000 (usable)
     BIOS-e801: 0000000000100000 - 0000000002000000 (usable)
    32MB LOWMEM available.
    On node 0 totalpages: 8192
    zone(0): 4096 pages.
    zone(1): 4096 pages.
    zone(2): 0 pages.
    Kernel command line: root=/dev/hda sb=0x220,5,1,5 ide2=noprobe ide3=noprobe ide4=noprobe ide5=noprobe console=ttyS0
    ide_setup: ide2=noprobe
    ide_setup: ide3=noprobe
    ide_setup: ide4=noprobe
    ide_setup: ide5=noprobe
    Initializing CPU#0
    Detected 2399.621 MHz processor.
    Console: colour EGA 80x25
    Calibrating delay loop... 4744.80 BogoMIPS
    Memory: 28872k/32768k available (1210k kernel code, 3508k reserved, 266k data, 64k init, 0k highmem)
    Dentry cache hash table entries: 4096 (order: 3, 32768 bytes)
    Inode cache hash table entries: 2048 (order: 2, 16384 bytes)
    Mount cache hash table entries: 512 (order: 0, 4096 bytes)
    Buffer-cache hash table entries: 1024 (order: 0, 4096 bytes)
    Page-cache hash table entries: 8192 (order: 3, 32768 bytes)
    CPU: Intel Pentium Pro stepping 03
    Checking 'hlt' instruction... OK.
    POSIX conformance testing by UNIFIX
    Linux NET4.0 for Linux 2.4
    Based upon Swansea University Computer Society NET3.039
    Initializing RT netlink socket
    apm: BIOS not found.
    Starting kswapd
    Journalled Block Device driver loaded
    Detected PS/2 Mouse Port.
    pty: 256 Unix98 ptys configured
    Serial driver version 5.05c (2001-07-08) with no serial options enabled
    ttyS00 at 0x03f8 (irq = 4) is a 16450
    ne.c:v1.10 9/23/94 Donald Becker (becker@scyld.com)
    Last modified Nov 1, 2000 by Paul Gortmaker
    NE*000 ethercard probe at 0x300: 52 54 00 12 34 56
    eth0: NE2000 found at 0x300, using IRQ 9.
    RAMDISK driver initialized: 16 RAM disks of 4096K size 1024 blocksize
    Uniform Multi-Platform E-IDE driver Revision: 7.00beta4-2.4
    ide: Assuming 50MHz system bus speed for PIO modes; override with idebus=xx
    hda: QEMU HARDDISK, ATA DISK drive
    ide0 at 0x1f0-0x1f7,0x3f6 on irq 14
    hda: attached ide-disk driver.
    hda: 20480 sectors (10 MB) w/256KiB Cache, CHS=20/16/63
    Partition check:
    Soundblaster audio driver Copyright (C) by Hannu Savolainen 1993-1996
    NET4: Linux TCP/IP 1.0 for NET4.0
    IP Protocols: ICMP, UDP, TCP, IGMP
    IP: routing cache hash table of 512 buckets, 4Kbytes
    TCP: Hash tables configured (established 2048 bind 4096)
    NET4: Unix domain sockets 1.0/SMP for Linux NET4.0.
    EXT2-fs warning: mounting unchecked fs, running e2fsck is recommended
    VFS: Mounted root (ext2 filesystem).
    Freeing unused kernel memory: 64k freed
    Linux version 2.4.21 (bellard@voyager.localdomain) (gcc version 3.2.2 20030222 (Red Hat Linux 3.2.2-5)) #5 Tue Nov 11 18:18:53 CET 2003
    QEMU Linux test distribution (based on Redhat 9)
    Type 'exit' to halt the system
  4. Then you can play with the kernel inside the virtual serial console. You can launch ls for example. Type Ctrl-a h to have an help about the keys you can type inside the virtual serial console. In particular, use Ctrl-a x to exit QEMU and use Ctrl-a b as the Magic SysRq key.
  5. If the network is enabled, launch the script `/etc/linuxrc' in the emulator (don't forget the leading dot):
    . /etc/linuxrc
    Then enable X11 connections on your PC from the emulated Linux:
    xhost +
    You can now launch `xterm' or `xlogo' and verify that you have a real Virtual Linux system !


  1. A 2.5.74 kernel is also included in the archive. Just replace the bzImage in qemu.sh to try it.
  2. In order to exit cleanly from qemu, you can do a shutdown inside qemu. qemu will automatically exit when the Linux shutdown is done.
  3. You can boot slightly faster by disabling the probe of non present IDE interfaces. To do so, add the following options on the kernel command line:
    ide1=noprobe ide2=noprobe ide3=noprobe ide4=noprobe ide5=noprobe
  4. The example disk image is a modified version of the one made by Kevin Lawton for the plex86 Project (www.plex86.org).

3.9 USB emulation

QEMU emulates a PCI UHCI USB controller and a 8 port USB hub connected to it. You can virtually plug to the hub virtual USB devices or real host USB devices (experimental, works only on Linux hosts).

3.9.1 Using virtual USB devices

A virtual USB mouse device is available for testing in QEMU.

You can try it with the following monitor commands:

# add the mouse device
(qemu) usb_add mouse 

# show the virtual USB devices plugged on the QEMU Virtual USB hub
(qemu) info usb
  Device 0.3, speed 12 Mb/s

# after some time you can try to remove the mouse
(qemu) usb_del 0.3

The option `-usbdevice' is similar to the monitor command usb_add.

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).

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.

3.11 Target OS specific information

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.

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. 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. 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. 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). 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. Share a directory between Unix and Windows

See section 3.3 Invocation about the help of the option `-smb'. Windows XP security problems

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 only known workaround is to boot in Safe mode without networking support.

Future QEMU releases are likely to correct this bug.

3.11.3 MS-DOS and FreeDOS 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 mentionned in the following sections.

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/.

4.2 Sparc32 System emulator invocation

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

QEMU emulates the following sun4m peripherals:

The number of peripherals is fixed in the architecture.

QEMU uses the Proll, a PROM replacement available at http://people.redhat.com/zaitcev/linux/. The required QEMU-specific patches are included with the sources.

A sample Linux 2.6 series kernel and ram disk image are available on the QEMU web site. Please note that currently neither Linux 2.4 series, NetBSD, nor OpenBSD kernels work.

The following options are specific to the Sparc emulation:

`-g WxH'
Set the initial TCX graphic mode. The default is 1024x768.

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:

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.

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:

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

5. QEMU Linux User space emulator

5.1 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 Wine launch

5.3 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

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):


Then type as root user:

make install

to install QEMU in `/usr/local'.

6.1.2 Tested tool versions

In order to compile QEMU succesfully, it is very important that you have the right tools. The most important one is gcc. I cannot guaranty that QEMU works if you do not use a tested gcc version. Look at 'configure' and 'Makefile' if you want to make a different gcc version work.

host      gcc      binutils      glibc    linux       distribution
x86       3.2      2.13.2        2.1.3    2.4.18
          2.96   2.2.5    2.4.18      Red Hat 7.3
          3.2.2  2.3.2    2.4.20      Red Hat 9

PowerPC   3.3 [4]  2.3.1    2.4.20briq

Alpha     3.3 [1]   2.2.5    2.2.20 [2]  Debian 3.0

Sparc32   2.95.4   2.2.5    2.4.18      Debian 3.0

ARM       2.95.4   2.2.5    2.4.9 [3]   Debian 3.0

[1] On Alpha, QEMU needs the gcc 'visibility' attribute only available
    for gcc version >= 3.3.
[2] Linux >= 2.4.20 is necessary for precise exception support
[3] 2.4.9-ac10-rmk2-np1-cerf2

[4] gcc 2.95.x generates invalid code when using too many register
variables. You must use gcc 3.x on PowerPC.

6.2 Windows

6.3 Cross compilation for Windows with Linux

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

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.

This document was generated on 19 December 2005 using texi2html 1.56k.