QEMU Emulator User Documentation


Table of Contents


1. Introduction

1.1 Features

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

QEMU has two operating modes:

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

For system emulation, the following hardware targets are supported:

For user emulation, x86, PowerPC, ARM, 32-bit MIPS, Sparc32/64, ColdFire(m68k), CRISv32 and MicroBlaze 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.free.oszoo.org/@/download.html.

2.3 Mac OS X

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

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, 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 http://www.deinmeister.de/gusemu/) by Tibor "TS" Schütz.

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

3.2 Quick Start

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

qemu 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. Some targets do not need a disk image.

3.4 Keys

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

Ctrl-Alt-f
Toggle full screen
Ctrl-Alt-n
Switch to virtual console 'n'. Standard console mappings are:
1
Target system display
2
Monitor
3
Serial port
Ctrl-Alt
Toggle mouse and keyboard grab.

In the virtual consoles, you can use Ctrl-Up, Ctrl-Down, Ctrl-PageUp and Ctrl-PageDown to move in the back log.

During emulation, if you are using the `-nographic' option, use Ctrl-a h to get terminal commands:

Ctrl-a h
Ctrl-a ?
Print this help
Ctrl-a x
Exit emulator
Ctrl-a s
Save disk data back to file (if -snapshot)
Ctrl-a t
Toggle console timestamps
Ctrl-a b
Send break (magic sysrq in Linux)
Ctrl-a c
Switch between console and monitor
Ctrl-a Ctrl-a
Send Ctrl-a

3.5 QEMU Monitor

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

3.5.1 Commands

The following commands are available:

3.5.2 Integer expressions

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

3.6 Disk Images

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

3.6.1 Quick start for disk image creation

You can create a disk image with the command:

qemu-img create myimage.img mysize

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

See section 3.6.4 qemu-img Invocation for more information.

3.6.2 Snapshot mode

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

3.6.3 VM snapshots

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

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

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

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

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

When using the (unrelated) -snapshot option (section 3.6.2 Snapshot mode), you can always make VM snapshots, but they are deleted as soon as you exit QEMU.

VM snapshots currently have the following known limitations:

3.6.4 qemu-img Invocation

usage: qemu-img command [command options]

The following commands are supported:

Command parameters:

filename
is a disk image filename
base_image
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
output_base_image
forces the output image to be created as a copy on write image of the specified base image; output_base_image should have the same content as the input's base image, however the path, image format, etc may differ
base_fmt
is the disk image format of base_image. for more information look at fmt
fmt
is the disk image format. It is guessed automatically in most cases. The following formats are supported:
raw
Raw disk image format (default). This format has the advantage of being simple and easily exportable to all other emulators. If your file system supports holes (for example in ext2 or ext3 on Linux or NTFS on Windows), then only the written sectors will reserve space. Use qemu-img info to know the real size used by the image or ls -ls on Unix/Linux.
qcow2
QEMU image format, the most versatile format. Use it to have smaller images (useful if your filesystem does not supports holes, for example on Windows), optional AES encryption, zlib based compression and support of multiple VM snapshots.
qcow
Old QEMU image format. Left for compatibility.
cow
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.
vmdk
VMware 3 and 4 compatible image format.
cloop
Linux Compressed Loop image, useful only to reuse directly compressed CD-ROM images present for example in the Knoppix CD-ROMs.
size
is the disk image size in bytes. Optional suffixes k or K (kilobyte, 1024) M (megabyte, 1024k) and G (gigabyte, 1024M) and T (terabyte, 1024G) are supported. b is ignored.
output_filename
is the destination disk image filename
output_fmt
is the destination format
options
is a comma separated list of format specific options in a name=value format. Use -o ? for an overview of the options supported by the used format
-c
indicates that target image must be compressed (qcow format only)
-h
with or without a command shows help and lists the supported formats

Parameters to snapshot subcommand:

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

Command description:

`create [-F base_fmt] [-b base_image] [-f fmt] [-o options] 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. The size can also be specified using the size option with -o, it doesn't need to be specified separately in this case.
`commit [-f fmt] filename'
Commit the changes recorded in filename in its base image.
`convert [-c] [-f fmt] [-O output_fmt] [-o options] [-B output_base_image] filename [filename2 [...]] output_filename'
Convert the disk image filename to disk image output_filename using format output_fmt. It can be optionally compressed (-c option) or use any format specific options like encryption (-o option). Only the formats qcow and qcow2 support encryption or compression. The compression is read-only. It means that if a compressed sector is rewritten, then it is rewritten as uncompressed data. Encryption uses the AES format which is very secure (128 bit keys). Use a long password (16 characters) to get maximum protection. Image conversion is also useful to get smaller image when using a growable format such as qcow or cow: the empty sectors are detected and suppressed from the destination image.
`info [-f fmt] filename'
Give information about the disk image filename. Use it in particular to know the size reserved on disk which can be different from the displayed size. If VM snapshots are stored in the disk image, they are displayed too.
`snapshot [-l | -a snapshot | -c snapshot | -d snapshot ] filename'
List, apply, create or delete snapshots in image filename.

3.6.5 qemu-nbd Invocation

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

Export Qemu disk image using NBD protocol.

`filename'
is a disk image filename
`-p, --port=port'
port to listen on (default `1024')
`-o, --offset=offset'
offset into the image
`-b, --bind=iface'
interface to bind to (default `0.0.0.0')
`-k, --socket=path'
Use a unix socket with path path
`-r, --read-only'
export read-only
`-P, --partition=num'
only expose partition num
`-s, --snapshot'
use snapshot file
`-n, --nocache'
disable host cache
`-c, --connect'
connect FILE to NBD device DEV
`-d, --disconnect'
disconnect the specified device
`-e, --shared=num'
device can be shared by num clients (default `1')
`-t, --persistent'
don't exit on the last connection
`-v, --verbose'
display extra debugging information
`-h, --help'
display this help and exit
`-V, --version'
output version information and exit

3.6.6 Using host drives

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

3.6.6.1 Linux

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

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

3.6.6.2 Windows

CD
The preferred syntax is the drive letter (e.g. `d:'). The alternate syntax `\\.\d:' is supported. `/dev/cdrom' is supported as an alias to the first CDROM drive. Currently there is no specific code to handle removable media, so it is better to use the change or eject monitor commands to change or eject media.
Hard disks
Hard disks can be used with the syntax: `\\.\PhysicalDriveN' where N is the drive number (0 is the first hard disk). WARNING: unless you know what you do, it is better to only make READ-ONLY accesses to the hard disk otherwise you may corrupt your host data (use the `-snapshot' command line so that the modifications are written in a temporary file).

3.6.6.3 Mac OS X

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

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

3.6.7 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:

3.6.8 NBD access

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

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

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

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

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

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

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

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

and then you can use it with two guests:

qemu linux1.img -hdb nbd:unix:/tmp/my_socket
qemu linux2.img -hdb nbd:unix:/tmp/my_socket

3.7 Network emulation

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

3.7.1 VLANs

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

3.7.2 Using TAP network interfaces

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

3.7.2.1 Linux host

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

See section 3.3 Invocation to have examples of command lines using the TAP network interfaces.

3.7.2.2 Windows host

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

3.7.3 Using the user mode network stack

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


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

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

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

Note that 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 `-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 syntax is:

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

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

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

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

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

Use Ctrl-a c to switch between the serial console and the monitor (see section 3.4 Keys).

3.9 USB emulation

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

3.9.1 Connecting USB devices

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

mouse
Virtual Mouse. This will override the PS/2 mouse emulation when activated.
tablet
Pointer device that uses absolute coordinates (like a touchscreen). This means qemu is able to report the mouse position without having to grab the mouse. Also overrides the PS/2 mouse emulation when activated.
disk:file
Mass storage device based on file (see section 3.6 Disk Images)
host:bus.addr
Pass through the host device identified by bus.addr (Linux only)
host:vendor_id:product_id
Pass through the host device identified by vendor_id:product_id (Linux only)
wacom-tablet
Virtual Wacom PenPartner tablet. This device is similar to the tablet above but it can be used with the tslib library because in addition to touch coordinates it reports touch pressure.
keyboard
Standard USB keyboard. Will override the PS/2 keyboard (if present).
serial:[vendorid=vendor_id][,product_id=product_id]:dev
Serial converter. This emulates an FTDI FT232BM chip connected to host character device dev. The available character devices are the same as for the -serial option. The vendorid and productid options can be used to override the default 0403:6001. For instance,
usb_add serial:productid=FA00:tcp:192.168.0.2:4444
will connect to tcp port 4444 of ip 192.168.0.2, and plug that to the virtual serial converter, faking a Matrix Orbital LCD Display (USB ID 0403:FA00).
braille
Braille device. This will use BrlAPI to display the braille output on a real or fake device.
net:options
Network adapter that supports CDC ethernet and RNDIS protocols. options specifies NIC options as with -net nic,options (see description). For instance, user-mode networking can be used with
qemu [...OPTIONS...] -net user,vlan=0 -usbdevice net:vlan=0
Currently this cannot be used in machines that support PCI NICs.
bt[:hci-type]
Bluetooth dongle whose type is specified in the same format as with the `-bt hci' option, @xref{bt-hcis,,allowed HCI types}. If no type is given, the HCI logic corresponds to -bt hci,vlan=0. This USB device implements the USB Transport Layer of HCI. Example usage:
qemu [...OPTIONS...] -usbdevice bt:hci,vlan=3 -bt device:keyboard,vlan=3

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 VNC security

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

3.10.1 Without passwords

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

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

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

3.10.2 With passwords

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

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

3.10.3 With x509 certificates

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

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

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

3.10.4 With x509 certificates and client verification

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

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

3.10.5 With x509 certificates, client verification and passwords

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

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

3.10.6 With SASL authentication

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

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

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

3.10.7 With x509 certificates and SASL authentication

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

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

3.10.8 Generating certificates for VNC

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

3.10.8.1 Setup the Certificate Authority

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

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

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

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

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

3.10.8.2 Issuing server certificates

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

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

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

3.10.8.3 Issuing client certificates

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

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

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

3.10.9 Configuring SASL mechanisms

The following documentation assumes use of the Cyrus SASL implementation on a Linux host, but the principals should apply to any other SASL impl. When SASL is enabled, the mechanism configuration will be loaded from system default SASL service config /etc/sasl2/qemu.conf. If running QEMU as an unprivileged user, an environment variable SASL_CONF_PATH can be used to make it search alternate locations for the service config.

The default configuration might contain

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

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

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

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

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

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

3.11 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.

Advanced debugging options:

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

maintenance packet qqemu.sstepbits
This will display the MASK bits used to control the single stepping IE:
(gdb) maintenance packet qqemu.sstepbits
sending: "qqemu.sstepbits"
received: "ENABLE=1,NOIRQ=2,NOTIMER=4"
maintenance packet qqemu.sstep
This will display the current value of the mask used when single stepping IE:
(gdb) maintenance packet qqemu.sstep
sending: "qqemu.sstep"
received: "0x7"
maintenance packet Qqemu.sstep=HEX_VALUE
This will change the single step mask, so if wanted to enable IRQs on the single step, but not timers, you would use:
(gdb) maintenance packet Qqemu.sstep=0x5
sending: "qemu.sstep=0x5"
received: "OK"

3.12 Target OS specific information

3.12.1 Linux

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

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

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

3.12.2 Windows

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

3.12.2.1 SVGA graphic modes support

QEMU emulates a Cirrus Logic GD5446 Video card. All Windows versions starting from Windows 95 should recognize and use this graphic card. For optimal performances, use 16 bit color depth in the guest and the host OS.

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

3.12.2.2 CPU usage reduction

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

3.12.2.3 Windows 2000 disk full problem

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

3.12.2.4 Windows 2000 shutdown

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

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

3.12.2.5 Share a directory between Unix and Windows

See section 3.3 Invocation about the help of the option `-smb'.

3.12.2.6 Windows XP security problem

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

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

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

3.12.3 MS-DOS and FreeDOS

3.12.3.1 CPU usage reduction

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

4. QEMU System emulator for non PC targets

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

4.1 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.

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

The following options are specific to the PowerPC emulation:

`-g WxH[xDEPTH]'
Set the initial VGA graphic mode. The default is 800x600x15.
`-prom-env string'
Set OpenBIOS variables in NVRAM, for example:
qemu-system-ppc -prom-env 'auto-boot?=false' \
 -prom-env 'boot-device=hd:2,\yaboot' \
 -prom-env 'boot-args=conf=hd:2,\yaboot.conf'
These variables are not used by Open Hack'Ware.

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

4.2 Sparc32 System emulator

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

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

It's also possible to simulate a SPARCstation 2 (sun4c architecture), SPARCserver 1000, or SPARCcenter 2000 (sun4d architecture), but these emulators are not usable yet.

QEMU emulates the following sun4m/sun4c/sun4d peripherals:

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

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

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

The following options are specific to the Sparc32 emulation:

`-g WxHx[xDEPTH]'
Set the initial TCX graphic mode. The default is 1024x768x8, currently the only other possible mode is 1024x768x24.
`-prom-env string'
Set OpenBIOS variables in NVRAM, for example:
qemu-system-sparc -prom-env 'auto-boot?=false' \
 -prom-env 'boot-device=sd(0,2,0):d' -prom-env 'boot-args=linux single'
`-M [SS-4|SS-5|SS-10|SS-20|SS-600MP|LX|Voyager|SPARCClassic|SPARCbook|SS-2|SS-1000|SS-2000]'
Set the emulated machine type. Default is SS-5.

4.3 Sparc64 System emulator

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

QEMU emulates the following peripherals:

The following options are specific to the Sparc64 emulation:

`-prom-env string'
Set OpenBIOS variables in NVRAM, for example:
qemu-system-sparc64 -prom-env 'auto-boot?=false'
`-M [sun4u|sun4v|Niagara]'
Set the emulated machine type. The default is sun4u.

4.4 MIPS System emulator

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

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

The Malta emulation supports the following devices:

The ACER Pica emulation supports:

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

The MIPS Magnum R4000 emulation supports:

4.5 ARM System emulator

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

The ARM Versatile baseboard is emulated with the following devices:

The ARM RealView Emulation baseboard is emulated with the following devices:

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

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

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

The Luminary Micro Stellaris LM3S811EVB emulation includes the following devices:

The Luminary Micro Stellaris LM3S6965EVB emulation includes the following devices:

The Freecom MusicPal internet radio emulation includes the following elements:

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

The "Syborg" Symbian Virtual Platform base model includes the following elements:

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

The following options are specific to the ARM emulation:

`-semihosting'
Enable semihosting syscall emulation. On ARM this implements the "Angel" interface. Note that this allows guest direct access to the host filesystem, so should only be used with trusted guest OS.

4.6 ColdFire System emulator

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

The M5208EVB emulation includes the following devices:

The AN5206 emulation includes the following devices:

The following options are specific to the ARM emulation:

`-semihosting'
Enable semihosting syscall emulation. On M68K this implements the "ColdFire GDB" interface used by libgloss. Note that this allows guest direct access to the host filesystem, so should only be used with trusted guest OS.

5. QEMU User space emulator

5.1 Supported Operating Systems

The following OS are supported in user space emulation:

5.2 Linux User space emulator

5.2.1 Quick Start

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

5.2.2 Wine launch

5.2.3 Command line options

usage: qemu-i386 [-h] [-d] [-L path] [-s size] [-cpu model] [-g port] program [arguments...]
`-h'
Print the help
`-L path'
Set the x86 elf interpreter prefix (default=/usr/local/qemu-i386)
`-s size'
Set the x86 stack size in bytes (default=524288)
`-cpu model'
Select CPU model (-cpu ? for list and additional feature selection)

Debug options:

`-d'
Activate log (logfile=/tmp/qemu.log)
`-p pagesize'
Act as if the host page size was 'pagesize' bytes
`-g port'
Wait gdb connection to port
`-singlestep'
Run the emulation in single step mode.

Environment variables:

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

5.2.4 Other binaries

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

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

The binary format is detected automatically.

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

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

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

5.3 Mac OS X/Darwin User space emulator

5.3.1 Mac OS X/Darwin Status

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

5.3.2 Quick Start

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

5.3.3 Command line options

usage: qemu-i386 [-h] [-d] [-L path] [-s size] program [arguments...]
`-h'
Print the help
`-L path'
Set the library root path (default=/)
`-s size'
Set the stack size in bytes (default=524288)

Debug options:

`-d'
Activate log (logfile=/tmp/qemu.log)
`-p pagesize'
Act as if the host page size was 'pagesize' bytes
`-singlestep'
Run the emulation in single step mode.

5.4 BSD User space emulator

5.4.1 BSD Status

5.4.2 Quick Start

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

5.4.3 Command line options

usage: qemu-sparc64 [-h] [-d] [-L path] [-s size] [-bsd type] program [arguments...]
`-h'
Print the help
`-L path'
Set the library root path (default=/)
`-s size'
Set the stack size in bytes (default=524288)
`-bsd type'
Set the type of the emulated BSD Operating system. Valid values are FreeBSD, NetBSD and OpenBSD (default).

Debug options:

`-d'
Activate log (logfile=/tmp/qemu.log)
`-p pagesize'
Act as if the host page size was 'pagesize' bytes
`-singlestep'
Run the emulation in single step mode.

6. Compilation from the sources

6.1 Linux/Unix

6.1.1 Compilation

First you must decompress the sources:

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

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

./configure
make

Then type as root user:

make install

to install QEMU in `/usr/local'.

6.2 Windows

6.3 Cross compilation for Windows with Linux

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.

7. Index

Jump to:


This document was generated on 2 October 2009 using texi2html 1.56k.