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@settitle QEMU Emulator User Documentation

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@direntry

* QEMU: (qemu-doc).    The QEMU Emulator User Documentation.

@end direntry

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@iftex

@titlepage

@sp 7

@center @titlefont{QEMU Emulator}

@sp 1

@center @titlefont{User Documentation}

@sp 3

@end titlepage

@end iftex

@ifnottex

@node Top

@top

@menu

* Introduction::

* Installation::

* QEMU PC System emulator::

* QEMU System emulator for non PC targets::

* QEMU User space emulator::

* compilation:: Compilation from the sources

* License::

* Index::

@end menu

@end ifnottex

@contents

@node Introduction

@chapter Introduction

@menu

* intro_features:: Features

@end menu

@node intro_features

@section Features

QEMU is a FAST! processor emulator using dynamic translation to

achieve good emulation speed.

QEMU has two operating modes:

@itemize

@cindex operating modes

@item

@cindex system emulation

Full system emulation. In this mode, QEMU emulates a full system (for

example a PC), including one or several processors and various

peripherals. It can be used to launch different Operating Systems

without rebooting the PC or to debug system code.

@item

@cindex user mode emulation

User mode emulation. In this mode, QEMU can launch

processes compiled for one CPU on another CPU. It can be used to

launch the Wine Windows API emulator (@url{http://www.winehq.org}) or

to ease cross-compilation and cross-debugging.

@end itemize

QEMU can run without an host kernel driver and yet gives acceptable

performance.

For system emulation, the following hardware targets are supported:

@itemize

@cindex emulated target systems

@cindex supported target systems

@item PC (x86 or x86_64 processor)

@item ISA PC (old style PC without PCI bus)

@item PREP (PowerPC processor)

@item G3 Beige PowerMac (PowerPC processor)

@item Mac99 PowerMac (PowerPC processor, in progress)

@item Sun4m/Sun4c/Sun4d (32-bit Sparc processor)

@item Sun4u/Sun4v (64-bit Sparc processor, in progress)

@item Malta board (32-bit and 64-bit MIPS processors)

@item MIPS Magnum (64-bit MIPS processor)

@item ARM Integrator/CP (ARM)

@item ARM Versatile baseboard (ARM)

@item ARM RealView Emulation/Platform baseboard (ARM)

@item Spitz, Akita, Borzoi, Terrier and Tosa PDAs (PXA270 processor)

@item Luminary Micro LM3S811EVB (ARM Cortex-M3)

@item Luminary Micro LM3S6965EVB (ARM Cortex-M3)

@item Freescale MCF5208EVB (ColdFire V2).

@item Arnewsh MCF5206 evaluation board (ColdFire V2).

@item Palm Tungsten|E PDA (OMAP310 processor)

@item N800 and N810 tablets (OMAP2420 processor)

@item MusicPal (MV88W8618 ARM processor)

@item Gumstix "Connex" and "Verdex" motherboards (PXA255/270).

@item Siemens SX1 smartphone (OMAP310 processor)

@item AXIS-Devboard88 (CRISv32 ETRAX-FS).

@item Petalogix Spartan 3aDSP1800 MMU ref design (MicroBlaze).

@item Avnet LX60/LX110/LX200 boards (Xtensa)

@end itemize

@cindex supported user mode targets

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.

@node Installation

@chapter Installation

If you want to compile QEMU yourself, see @ref{compilation}.

@menu

* install_linux::   Linux

* install_windows:: Windows

* install_mac::     Macintosh

@end menu

@node install_linux

@section Linux

@cindex installation (Linux)

If a precompiled package is available for your distribution - you just

have to install it. Otherwise, see @ref{compilation}.

@node install_windows

@section Windows

@cindex installation (Windows)

Download the experimental binary installer at

@url{http://www.free.oszoo.org/@/download.html}.

TODO (no longer available)

@node install_mac

@section Mac OS X

Download the experimental binary installer at

@url{http://www.free.oszoo.org/@/download.html}.

TODO (no longer available)

@node QEMU PC System emulator

@chapter QEMU PC System emulator

@cindex system emulation (PC)

@menu

* pcsys_introduction:: Introduction

* pcsys_quickstart::   Quick Start

* sec_invocation::     Invocation

* pcsys_keys::         Keys

* pcsys_monitor::      QEMU Monitor

* disk_images::        Disk Images

* pcsys_network::      Network emulation

* pcsys_other_devs::   Other Devices

* direct_linux_boot::  Direct Linux Boot

* pcsys_usb::          USB emulation

* vnc_security::       VNC security

* gdb_usage::          GDB usage

* pcsys_os_specific::  Target OS specific information

@end menu

@node pcsys_introduction

@section Introduction

@c man begin DESCRIPTION

The QEMU PC System emulator simulates the

following peripherals:

@itemize @minus

@item

i440FX host PCI bridge and PIIX3 PCI to ISA bridge

@item

Cirrus CLGD 5446 PCI VGA card or dummy VGA card with Bochs VESA

extensions (hardware level, including all non standard modes).

@item

PS/2 mouse and keyboard

@item

2 PCI IDE interfaces with hard disk and CD-ROM support

@item

Floppy disk

@item

PCI and ISA network adapters

@item

Serial ports

@item

Creative SoundBlaster 16 sound card

@item

ENSONIQ AudioPCI ES1370 sound card

@item

Intel 82801AA AC97 Audio compatible sound card

@item

Intel HD Audio Controller and HDA codec

@item

Adlib (OPL2) - Yamaha YM3812 compatible chip

@item

Gravis Ultrasound GF1 sound card

@item

CS4231A compatible sound card

@item

PCI UHCI USB controller and a virtual USB hub.

@end itemize

SMP is supported with up to 255 CPUs.

Note that adlib, gus and cs4231a are only available when QEMU was

configured with --audio-card-list option containing the name(s) of

required card(s).

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

VGA BIOS.

QEMU uses YM3812 emulation by Tatsuyuki Satoh.

QEMU uses GUS emulation (GUSEMU32 @url{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

@example

qemu dos.img -soundhw gus -parallel none

@end example

Alternatively:

@example

qemu dos.img -device gus,irq=5

@end example

Or some other unclaimed IRQ.

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

@c man end

@node pcsys_quickstart

@section Quick Start

@cindex quick start

Download and uncompress the linux image (@file{linux.img}) and type:

@example

qemu linux.img

@end example

Linux should boot and give you a prompt.

@node sec_invocation

@section Invocation

@example

@c man begin SYNOPSIS

usage: qemu [options] [@var{disk_image}]

@c man end

@end example

@c man begin OPTIONS

@var{disk_image} is a raw hard disk image for IDE hard disk 0. Some

targets do not need a disk image.

@include qemu-options.texi

@c man end

@node pcsys_keys

@section Keys

@c man begin OPTIONS

During the graphical emulation, you can use special key combinations to change

modes. The default key mappings are shown below, but if you use @code{-alt-grab}

then the modifier is Ctrl-Alt-Shift (instead of Ctrl-Alt) and if you use

@code{-ctrl-grab} then the modifier is the right Ctrl key (instead of Ctrl-Alt):

@table @key

@item Ctrl-Alt-f

@kindex Ctrl-Alt-f

Toggle full screen

@item Ctrl-Alt-+

@kindex Ctrl-Alt-+

Enlarge the screen

@item Ctrl-Alt--

@kindex Ctrl-Alt--

Shrink the screen

@item Ctrl-Alt-u

@kindex Ctrl-Alt-u

Restore the screen's un-scaled dimensions

@item Ctrl-Alt-n

@kindex Ctrl-Alt-n

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

@table @emph

@item 1

Target system display

@item 2

Monitor

@item 3

Serial port

@end table

@item Ctrl-Alt

@kindex Ctrl-Alt

Toggle mouse and keyboard grab.

@end table

@kindex Ctrl-Up

@kindex Ctrl-Down

@kindex Ctrl-PageUp

@kindex Ctrl-PageDown

In the virtual consoles, you can use @key{Ctrl-Up}, @key{Ctrl-Down},

@key{Ctrl-PageUp} and @key{Ctrl-PageDown} to move in the back log.

@kindex Ctrl-a h

During emulation, if you are using the @option{-nographic} option, use

@key{Ctrl-a h} to get terminal commands:

@table @key

@item Ctrl-a h

@kindex Ctrl-a h

@item Ctrl-a ?

@kindex Ctrl-a ?

Print this help

@item Ctrl-a x

@kindex Ctrl-a x

Exit emulator

@item Ctrl-a s

@kindex Ctrl-a s

Save disk data back to file (if -snapshot)

@item Ctrl-a t

@kindex Ctrl-a t

Toggle console timestamps

@item Ctrl-a b

@kindex Ctrl-a b

Send break (magic sysrq in Linux)

@item Ctrl-a c

@kindex Ctrl-a c

Switch between console and monitor

@item Ctrl-a Ctrl-a

@kindex Ctrl-a a

Send Ctrl-a

@end table

@c man end

@ignore

@c man begin SEEALSO

The HTML documentation of QEMU for more precise information and Linux

user mode emulator invocation.

@c man end

@c man begin AUTHOR

Fabrice Bellard

@c man end

@end ignore

@node pcsys_monitor

@section QEMU Monitor

@cindex QEMU monitor

The QEMU monitor is used to give complex commands to the QEMU

emulator. You can use it to:

@itemize @minus

@item

Remove or insert removable media images

(such as CD-ROM or floppies).

@item

Freeze/unfreeze the Virtual Machine (VM) and save or restore its state

from a disk file.

@item Inspect the VM state without an external debugger.

@end itemize

@subsection Commands

The following commands are available:

@include qemu-monitor.texi

@subsection 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 @emph{$}.

@node disk_images

@section 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.

@menu

* disk_images_quickstart::    Quick start for disk image creation

* disk_images_snapshot_mode:: Snapshot mode

* vm_snapshots::              VM snapshots

* qemu_img_invocation::       qemu-img Invocation

* qemu_nbd_invocation::       qemu-nbd Invocation

* host_drives::               Using host drives

* disk_images_fat_images::    Virtual FAT disk images

* disk_images_nbd::           NBD access

* disk_images_sheepdog::      Sheepdog disk images

* disk_images_iscsi::         iSCSI LUNs

@end menu

@node disk_images_quickstart

@subsection Quick start for disk image creation

You can create a disk image with the command:

@example

qemu-img create myimage.img mysize

@end example

where @var{myimage.img} is the disk image filename and @var{mysize} is its

size in kilobytes. You can add an @code{M} suffix to give the size in

megabytes and a @code{G} suffix for gigabytes.

See @ref{qemu_img_invocation} for more information.

@node disk_images_snapshot_mode

@subsection Snapshot mode

If you use the option @option{-snapshot}, all disk images are

considered as read only. When sectors in written, they are written in

a temporary file created in @file{/tmp}. You can however force the

write back to the raw disk images by using the @code{commit} monitor

command (or @key{C-a s} in the serial console).

@node vm_snapshots

@subsection 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 @code{qcow2} disk image

format. Normally this device is the first virtual hard drive.

Use the monitor command @code{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 @code{loadvm} to restore a VM snapshot and @code{delvm} to remove

a VM snapshot. @code{info snapshots} lists the available snapshots

with their associated information:

@example

(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

@end example

A VM snapshot is made of a VM state info (its size is shown in

@code{info snapshots}) and a snapshot of every writable disk image.

The VM state info is stored in the first @code{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 @code{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) @code{-snapshot} option

(@ref{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:

@itemize

@item

They cannot cope with removable devices if they are removed or

inserted after a snapshot is done.

@item

A few device drivers still have incomplete snapshot support so their

state is not saved or restored properly (in particular USB).

@end itemize

@node qemu_img_invocation

@subsection @code{qemu-img} Invocation

@include qemu-img.texi

@node qemu_nbd_invocation

@subsection @code{qemu-nbd} Invocation

@include qemu-nbd.texi

@node host_drives

@subsection 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.

@subsubsection 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 @file{/dev/cdrom} to access to the CDROM or

@file{/dev/fd0} for the floppy.

@table @code

@item 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.

@item 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).

@item Hard disks

Hard disks can be used. Normally you must specify the whole disk

(@file{/dev/hdb} instead of @file{/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 @option{-snapshot} command

line option or modify the device permissions accordingly).

@end table

@subsubsection Windows

@table @code

@item CD

The preferred syntax is the drive letter (e.g. @file{d:}). The

alternate syntax @file{\\.\d:} is supported. @file{/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 @code{change} or @code{eject} monitor commands to

change or eject media.

@item Hard disks

Hard disks can be used with the syntax: @file{\\.\PhysicalDrive@var{N}}

where @var{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 @option{-snapshot} command line so that the

modifications are written in a temporary file).

@end table

@subsubsection Mac OS X

@file{/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 @code{change} or @code{eject} monitor commands to

change or eject media.

@node disk_images_fat_images

@subsection Virtual FAT disk images

QEMU can automatically create a virtual FAT disk image from a

directory tree. In order to use it, just type:

@example

qemu linux.img -hdb fat:/my_directory

@end example

Then you access access to all the files in the @file{/my_directory}

directory without having to copy them in a disk image or to export

them via SAMBA or NFS. The default access is @emph{read-only}.

Floppies can be emulated with the @code{:floppy:} option:

@example

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

@end example

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

@code{:rw:} option:

@example

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

@end example

What you should @emph{never} do:

@itemize

@item use non-ASCII filenames ;

@item use "-snapshot" together with ":rw:" ;

@item expect it to work when loadvm'ing ;

@item write to the FAT directory on the host system while accessing it with the guest system.

@end itemize

@node disk_images_nbd

@subsection NBD access

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

protocol.

@example

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

@end example

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

of an inet socket:

@example

qemu linux.img -hdb nbd:unix:/tmp/my_socket

@end example

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

@example

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

@end example

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

@example

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

@end example

and then you can use it with two guests:

@example

qemu linux1.img -hdb nbd:unix:/tmp/my_socket

qemu linux2.img -hdb nbd:unix:/tmp/my_socket

@end example

If the nbd-server uses named exports (since NBD 2.9.18), you must use the

"exportname" option:

@example

qemu -cdrom nbd:localhost:exportname=debian-500-ppc-netinst

qemu -cdrom nbd:localhost:exportname=openSUSE-11.1-ppc-netinst

@end example

@node disk_images_sheepdog

@subsection 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:

@example

qemu-img create sheepdog:@var{image} @var{size}

@end example

where @var{image} is the Sheepdog image name and @var{size} is its

size.

To import the existing @var{filename} to Sheepdog, you can use a

convert command.

@example

qemu-img convert @var{filename} sheepdog:@var{image}

@end example

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

@example

qemu sheepdog:@var{image}

@end example

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

@example

qemu-img snapshot -c @var{tag} sheepdog:@var{image}

@end example

where @var{tag} is a tag name of the newly created snapshot.

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

snapshot.

@example

qemu sheepdog:@var{image}:@var{tag}

@end example

You can create a cloned image from the existing snapshot.

@example

qemu-img create -b sheepdog:@var{base}:@var{tag} sheepdog:@var{image}

@end example

where @var{base} is a image name of the source snapshot and @var{tag}

is its tag name.

If the Sheepdog daemon doesn't run on the local host, you need to

specify one of the Sheepdog servers to connect to.

@example

qemu-img create sheepdog:@var{hostname}:@var{port}:@var{image} @var{size}

qemu sheepdog:@var{hostname}:@var{port}:@var{image}

@end example

@node disk_images_iscsi

@subsection 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

@example

URL syntax:

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

@end example

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

@example

export LIBISCSI_CHAP_USERNAME=<username>

export LIBISCSI_CHAP_PASSWORD=<password>

iscsi://<host>/<target-iqn-name>/<lun>

@end example

Various session related parameters can be set via special options, either

in a configuration file provided via '-readconfig' or directly on the

command line.

@example

Setting a specific initiator name to use when logging in to the target

-iscsi initiator-name=iqn.qemu.test:my-initiator

@end example

@example

Controlling which type of header digest to negotiate with the target

-iscsi header-digest=CRC32C|CRC32C-NONE|NONE-CRC32C|NONE

@end example

These can also be set via a configuration file

@example

[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"

@end example

Setting the target name allows different options for different targets

@example

[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"

@end example

Howto use a configuration file to set iSCSI configuration options:

@example

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

@end example

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

@example

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

@end example

@node pcsys_network

@section 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.

@subsection 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).

@subsection 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 @code{tapN}), and you

can then configure it as if it was a real ethernet card.

@subsubsection Linux host

As an example, you can download the @file{linux-test-xxx.tar.gz}

archive and copy the script @file{qemu-ifup} in @file{/etc} and

configure properly @code{sudo} so that the command @code{ifconfig}

contained in @file{qemu-ifup} can be executed as root. You must verify

that your host kernel supports the TAP network interfaces: the

device @file{/dev/net/tun} must be present.

See @ref{sec_invocation} to have examples of command lines using the

TAP network interfaces.

@subsubsection 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 : @url{http://openvpn.net/}.

@subsection Using the user mode network stack

By using the option @option{-net user} (default configuration if no

@option{-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:

@example

         QEMU VLAN      <------>  Firewall/DHCP server <-----> Internet

                           |          (10.0.2.2)

                           |

                           ---->  DNS server (10.0.2.3)

                           |

                           ---->  SMB server (10.0.2.4)

@end example

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 @code{ping} is not supported reliably to the internet as it

would require root privileges. It means you can only ping the local

router (10.0.2.2).

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

server.

When using the @option{-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.

@subsection Connecting VLANs between QEMU instances

Using the @option{-net socket} option, it is possible to make VLANs

that span several QEMU instances. See @ref{sec_invocation} to have a

basic example.

@node pcsys_other_devs

@section Other Devices

@subsection 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:

@example

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

@end example

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:

@example

qemu -device ivshmem,size=<size in format accepted by -m>[,chardev=<id>]

                        [,msi=on][,ioeventfd=on][,vectors=n][,role=peer|master]

qemu -chardev socket,path=<path>,id=<id>

@end example

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 @option{role} argument can be set to either master or peer and will affect

how the shared memory is migrated.  With @option{role=master}, the guest will

copy the shared memory on migration to the destination host.  With

@option{role=peer}, the guest will not be able to migrate with the device attached.

With the @option{peer} case, the device should be detached and then reattached

after migration using the PCI hotplug support.

@node direct_linux_boot

@section 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:

@example

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

@end example

Use @option{-kernel} to provide the Linux kernel image and

@option{-append} to give the kernel command line arguments. The

@option{-initrd} option can be used to provide an INITRD image.

When using the direct Linux boot, a disk image for the first hard disk

@file{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

@option{-nographic} option. The typical command line is:

@example

qemu -kernel arch/i386/boot/bzImage -hda root-2.4.20.img \

     -append "root=/dev/hda console=ttyS0" -nographic

@end example

Use @key{Ctrl-a c} to switch between the serial console and the

monitor (@pxref{pcsys_keys}).

@node pcsys_usb

@section 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.

@menu

* usb_devices::

* host_usb_devices::

@end menu

@node usb_devices

@subsection Connecting USB devices

USB devices can be connected with the @option{-usbdevice} commandline option

or the @code{usb_add} monitor command.  Available devices are:

@table @code

@item mouse

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

@item 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.

@item disk:@var{file}