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@settitle QEMU Emulator User Documentation

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@iftex

@titlepage

@sp 7

@center @titlefont{QEMU Emulator}

@sp 1

@center @titlefont{User Documentation}

@sp 3

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@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

* 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 @minus

@item

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

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

@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 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)

@end itemize

For user emulation, x86, PowerPC, ARM, 32-bit MIPS, Sparc32/64 and ColdFire(m68k) 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

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

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

@node install_windows

@section Windows

Download the experimental binary installer at

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

@node install_mac

@section Mac OS X

Download the experimental binary installer at

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

@node QEMU PC System emulator

@chapter QEMU PC System emulator

@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

* 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/ISA PCI 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

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" Sch?tz.

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

@c man end

@node pcsys_quickstart

@section 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 the following keys:

@table @key

@item Ctrl-Alt-f

Toggle full screen

@item 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

Toggle mouse and keyboard grab.

@end table

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.

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

@item Ctrl-a ?

Print this help

@item Ctrl-a x

Exit emulator

@item Ctrl-a s

Save disk data back to file (if -snapshot)

@item Ctrl-a t

Toggle console timestamps

@item Ctrl-a b

Send break (magic sysrq in Linux)

@item Ctrl-a c

Switch between console and monitor

@item Ctrl-a Ctrl-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

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:

@table @option

@item help or ? [@var{cmd}]

Show the help for all commands or just for command @var{cmd}.

@item commit

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

@item info @var{subcommand}

Show various information about the system state.

@table @option

@item info version

show the version of QEMU

@item info network

show the various VLANs and the associated devices

@item info chardev

show the character devices

@item info block

show the block devices

@item info block

show block device statistics

@item info registers

show the cpu registers

@item info cpus

show infos for each CPU

@item info history

show the command line history

@item info irq

show the interrupts statistics (if available)

@item info pic

show i8259 (PIC) state

@item info pci

show emulated PCI device info

@item info tlb

show virtual to physical memory mappings (i386 only)

@item info mem

show the active virtual memory mappings (i386 only)

@item info hpet

show state of HPET (i386 only)

@item info kqemu

show KQEMU information

@item info kvm

show KVM information

@item info usb

show USB devices plugged on the virtual USB hub

@item info usbhost

show all USB host devices

@item info profile

show profiling information

@item info capture

show information about active capturing

@item info snapshots

show list of VM snapshots

@item info status

show the current VM status (running|paused)

@item info pcmcia

show guest PCMCIA status

@item info mice

show which guest mouse is receiving events

@item info vnc

show the vnc server status

@item info name

show the current VM name

@item info uuid

show the current VM UUID

@item info cpustats

show CPU statistics

@item info slirp

show SLIRP statistics (if available)

@item info migrate

show migration status

@item info balloon

show balloon information

@end table

@item q or quit

Quit the emulator.

@item eject [-f] @var{device}

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

@item change @var{device} @var{setting}

Change the configuration of a device.

@table @option

@item change @var{diskdevice} @var{filename} [@var{format}]

Change the medium for a removable disk device to point to @var{filename}. eg

@example

(qemu) change ide1-cd0 /path/to/some.iso

@end example

@var{format} is optional.

@item change vnc @var{display},@var{options}

Change the configuration of the VNC server. The valid syntax for @var{display}

and @var{options} are described at @ref{sec_invocation}. eg

@example

(qemu) change vnc localhost:1

@end example

@item change vnc password [@var{password}]

Change the password associated with the VNC server. If the new password is not

supplied, the monitor will prompt for it to be entered. VNC passwords are only

significant up to 8 letters. eg

@example

(qemu) change vnc password

Password: ********

@end example

@end table

@item acl @var{subcommand} @var{aclname} @var{match} @var{index}

Manage access control lists for network services. There are currently

two named access control lists, @var{vnc.x509dname} and @var{vnc.username}

matching on the x509 client certificate distinguished name, and SASL

username respectively.

@table @option

@item acl show <aclname>

list all the match rules in the access control list, and the default

policy

@item acl policy <aclname> @code{allow|deny}

set the default access control list policy, used in the event that

none of the explicit rules match. The default policy at startup is

always @code{deny}

@item acl allow <aclname> <match> [<index>]

add a match to the access control list, allowing access. The match will

normally be an exact username or x509 distinguished name, but can

optionally include wildcard globs. eg @code{*@@EXAMPLE.COM} to allow

all users in the @code{EXAMPLE.COM} kerberos realm. The match will

normally be appended to the end of the ACL, but can be inserted

earlier in the list if the optional @code{index} parameter is supplied.

@item acl deny <aclname> <match> [<index>]

add a match to the access control list, denying access. The match will

normally be an exact username or x509 distinguished name, but can

optionally include wildcard globs. eg @code{*@@EXAMPLE.COM} to allow

all users in the @code{EXAMPLE.COM} kerberos realm. The match will

normally be appended to the end of the ACL, but can be inserted

earlier in the list if the optional @code{index} parameter is supplied.

@item acl remove <aclname> <match>

remove the specified match rule from the access control list.

@item acl reset <aclname>

remove all matches from the access control list, and set the default

policy back to @code{deny}.

@end table

@item screendump @var{filename}

Save screen into PPM image @var{filename}.

@item logfile @var{filename}

Output logs to @var{filename}.

@item log @var{item1}[,...]

Activate logging of the specified items to @file{/tmp/qemu.log}.

@item savevm [@var{tag}|@var{id}]

Create a snapshot of the whole virtual machine. If @var{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

@ref{vm_snapshots}.

@item loadvm @var{tag}|@var{id}

Set the whole virtual machine to the snapshot identified by the tag

@var{tag} or the unique snapshot ID @var{id}.

@item delvm @var{tag}|@var{id}

Delete the snapshot identified by @var{tag} or @var{id}.

@item singlestep [off]

Run the emulation in single step mode.

If called with option off, the emulation returns to normal mode.

@item stop

Stop emulation.

@item c or cont

Resume emulation.

@item gdbserver [@var{port}]

Start gdbserver session (default @var{port}=1234)

@item x/fmt @var{addr}

Virtual memory dump starting at @var{addr}.

@item xp /@var{fmt} @var{addr}

Physical memory dump starting at @var{addr}.

@var{fmt} is a format which tells the command how to format the

data. Its syntax is: @option{/@{count@}@{format@}@{size@}}

@table @var

@item count

is the number of items to be dumped.

@item format

can be x (hex), d (signed decimal), u (unsigned decimal), o (octal),

c (char) or i (asm instruction).

@item size

can be b (8 bits), h (16 bits), w (32 bits) or g (64 bits). On x86,

@code{h} or @code{w} can be specified with the @code{i} format to

respectively select 16 or 32 bit code instruction size.

@end table

Examples:

@itemize

@item

Dump 10 instructions at the current instruction pointer:

@example

(qemu) x/10i $eip

0x90107063:  ret

0x90107064:  sti

0x90107065:  lea    0x0(%esi,1),%esi

0x90107069:  lea    0x0(%edi,1),%edi

0x90107070:  ret

0x90107071:  jmp    0x90107080

0x90107073:  nop

0x90107074:  nop

0x90107075:  nop

0x90107076:  nop

@end example

@item

Dump 80 16 bit values at the start of the video memory.

@smallexample

(qemu) xp/80hx 0xb8000

0x000b8000: 0x0b50 0x0b6c 0x0b65 0x0b78 0x0b38 0x0b36 0x0b2f 0x0b42

0x000b8010: 0x0b6f 0x0b63 0x0b68 0x0b73 0x0b20 0x0b56 0x0b47 0x0b41

0x000b8020: 0x0b42 0x0b69 0x0b6f 0x0b73 0x0b20 0x0b63 0x0b75 0x0b72

0x000b8030: 0x0b72 0x0b65 0x0b6e 0x0b74 0x0b2d 0x0b63 0x0b76 0x0b73

0x000b8040: 0x0b20 0x0b30 0x0b35 0x0b20 0x0b4e 0x0b6f 0x0b76 0x0b20

0x000b8050: 0x0b32 0x0b30 0x0b30 0x0b33 0x0720 0x0720 0x0720 0x0720

0x000b8060: 0x0720 0x0720 0x0720 0x0720 0x0720 0x0720 0x0720 0x0720

0x000b8070: 0x0720 0x0720 0x0720 0x0720 0x0720 0x0720 0x0720 0x0720

0x000b8080: 0x0720 0x0720 0x0720 0x0720 0x0720 0x0720 0x0720 0x0720

0x000b8090: 0x0720 0x0720 0x0720 0x0720 0x0720 0x0720 0x0720 0x0720

@end smallexample

@end itemize

@item p or print/@var{fmt} @var{expr}

Print expression value. Only the @var{format} part of @var{fmt} is

used.

@item sendkey @var{keys}

Send @var{keys} to the emulator. @var{keys} could be the name of the

key or @code{#} followed by the raw value in either decimal or hexadecimal

format. Use @code{-} to press several keys simultaneously. Example:

@example

sendkey ctrl-alt-f1

@end example

This command is useful to send keys that your graphical user interface

intercepts at low level, such as @code{ctrl-alt-f1} in X Window.

@item system_reset

Reset the system.

@item system_powerdown

Power down the system (if supported).

@item sum @var{addr} @var{size}

Compute the checksum of a memory region.

@item usb_add @var{devname}

Add the USB device @var{devname}.  For details of available devices see

@ref{usb_devices}

@item usb_del @var{devname}

Remove the USB device @var{devname} from the QEMU virtual USB

hub. @var{devname} has the syntax @code{bus.addr}. Use the monitor

command @code{info usb} to see the devices you can remove.

@item mouse_move @var{dx} @var{dy} [@var{dz}]

Move the active mouse to the specified coordinates @var{dx} @var{dy}

with optional scroll axis @var{dz}.

@item mouse_button @var{val}

Change the active mouse button state @var{val} (1=L, 2=M, 4=R).

@item mouse_set @var{index}

Set which mouse device receives events at given @var{index}, index

can be obtained with

@example

info mice

@end example

@item wavcapture @var{filename} [@var{frequency} [@var{bits} [@var{channels}]]]

Capture audio into @var{filename}. Using sample rate @var{frequency}

bits per sample @var{bits} and number of channels @var{channels}.

Defaults:

@itemize @minus

@item Sample rate = 44100 Hz - CD quality

@item Bits = 16

@item Number of channels = 2 - Stereo

@end itemize

@item stopcapture @var{index}

Stop capture with a given @var{index}, index can be obtained with

@example

info capture

@end example

@item memsave @var{addr} @var{size} @var{file}

save to disk virtual memory dump starting at @var{addr} of size @var{size}.

@item pmemsave @var{addr} @var{size} @var{file}

save to disk physical memory dump starting at @var{addr} of size @var{size}.

@item boot_set @var{bootdevicelist}

Define new values for the boot device list. Those values will override

the values specified on the command line through the @code{-boot} option.

The values that can be specified here depend on the machine type, but are

the same that can be specified in the @code{-boot} command line option.

@item nmi @var{cpu}

Inject an NMI on the given CPU.

@item migrate [-d] @var{uri}

Migrate to @var{uri} (using -d to not wait for completion).

@item migrate_cancel

Cancel the current VM migration.

@item migrate_set_speed @var{value}

Set maximum speed to @var{value} (in bytes) for migrations.

@item balloon @var{value}

Request VM to change its memory allocation to @var{value} (in MB).

@item set_link @var{name} [up|down]

Set link @var{name} up or down.

@end table

@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

@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

@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