qemu-img Invocation
qemu-nbd Invocation
qemu-ga Invocation
QEMU is a FAST! processor emulator using dynamic translation to achieve good emulation speed.
QEMU has the following features:
QEMU user mode emulation has the following features:
QEMU full system emulation has the following features:
The QEMU PC System emulator simulates the following peripherals:
SMP is supported with up to 255 CPUs.
QEMU uses the PC BIOS from the Seabios 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.
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.
qemu-system-i386 dos.img -soundhw gus -parallel none
Alternatively:
qemu-system-i386 dos.img -device gus,irq=5
Or some other unclaimed IRQ.
CS4231A is the chip used in Windows Sound System and GUSMAX products
Download and uncompress the linux image (linux.img) and type:
qemu-system-i386 linux.img
Linux should boot and give you a prompt.
qemu-system-i386 [options] [disk_image]
disk_image is a raw hard disk image for IDE hard disk 0. Some targets do not need a disk image.
-machine help to list
available machines. Supported machine properties are:
-cpu help for list and additional feature selection)
firstcpu and lastcpu are CPU indexes. Each ‘cpus’ option represent a contiguous range of CPU indexes (or a single VCPU if lastcpu is omitted). A non-contiguous set of VCPUs can be represented by providing multiple ‘cpus’ options. If ‘cpus’ is omitted on all nodes, VCPUs are automatically split between them.
For example, the following option assigns VCPUs 0, 1, 2 and 5 to a NUMA node:
-numa node,cpus=0-2,cpus=5
‘mem’ assigns a given RAM amount to a node. ‘memdev’ assigns RAM from a given memory backend device to a node. If ‘mem’ and ‘memdev’ are omitted in all nodes, RAM is split equally between them.
‘mem’ and ‘memdev’ are mutually exclusive. Furthermore, if one node uses ‘memdev’, all of them have to use it.
Note that the -numa option doesn't allocate any of the
specified resources, it just assigns existing resources to NUMA
nodes. This means that one still has to use the -m,
-smp options to allocate RAM and VCPUs respectively.
You can open an image using pre-opened file descriptors from an fd set:
qemu-system-i386
-add-fd fd=3,set=2,opaque="rdwr:/path/to/file"
-add-fd fd=4,set=2,opaque="rdonly:/path/to/file"
-drive file=/dev/fdset/2,index=0,media=disk
qemu-system-i386 -global ide-drive.physical_block_size=4096 -drive file=file,if=ide,index=0,media=disk
In particular, you can use this to set driver properties for devices which are created automatically by the machine model. To create a device which is not created automatically and set properties on it, use -device.
-global driver.prop=value is shorthand for -global
driver=driver,property=prop,value=value. The
longhand syntax works even when driver contains a dot.
Interactive boot menus/prompts can be enabled via menu=on as far as firmware/BIOS supports them. The default is non-interactive boot.
A splash picture could be passed to bios, enabling user to show it as logo, when option splash=sp_name is given and menu=on, If firmware/BIOS supports them. Currently Seabios for X86 system support it. limitation: The splash file could be a jpeg file or a BMP file in 24 BPP format(true color). The resolution should be supported by the SVGA mode, so the recommended is 320x240, 640x480, 800x640.
A timeout could be passed to bios, guest will pause for rb_timeout ms when boot failed, then reboot. If rb_timeout is '-1', guest will not reboot, qemu passes '-1' to bios by default. Currently Seabios for X86 system support it.
Do strict boot via strict=on as far as firmware/BIOS supports it. This only effects when boot priority is changed by bootindex options. The default is non-strict boot.
# try to boot from network first, then from hard disk
qemu-system-i386 -boot order=nc
# boot from CD-ROM first, switch back to default order after reboot
qemu-system-i386 -boot once=d
# boot with a splash picture for 5 seconds.
qemu-system-i386 -boot menu=on,splash=/root/boot.bmp,splash-time=5000
Note: The legacy format '-boot drives' is still supported but its
use is discouraged as it may be removed from future versions.
For example, the following command-line sets the guest startup RAM size to 1GB, creates 3 slots to hotplug additional memory and sets the maximum memory the guest can reach to 4GB:
qemu-system-x86_64 -m 1G,slots=3,maxmem=4G
If slots and maxmem are not specified, memory hotplug won't
be enabled and the guest startup RAM will never increase.
fr for
French). This option is only needed where it is not easy to get raw PC
keycodes (e.g. on Macs, with some X11 servers or with a VNC or curses
display). You don't normally need to use it on PC/Linux or PC/Windows
hosts.
The available layouts are:
ar de-ch es fo fr-ca hu ja mk no pt-br sv
da en-gb et fr fr-ch is lt nl pl ru th
de en-us fi fr-be hr it lv nl-be pt sl tr
The default is en-us.
qemu-system-i386 -soundhw sb16,adlib disk.img
qemu-system-i386 -soundhw es1370 disk.img
qemu-system-i386 -soundhw ac97 disk.img
qemu-system-i386 -soundhw hda disk.img
qemu-system-i386 -soundhw all disk.img
qemu-system-i386 -soundhw help
Note that Linux's i810_audio OSS kernel (for AC97) module might require manually specifying clocking.
modprobe i810_audio clocking=48000
-device help and
-device driver,help.
Some drivers are:
The IPMI slave address to use for the BMC. The default is 0x20.
This address is the BMC's address on the I2C network of management
controllers. If you don't know what this means, it is safe to ignore
it.
A connection is made to an external BMC simulator. If you do this, it is strongly recommended that you use the "reconnect=" chardev option to reconnect to the simulator if the connection is lost. Note that if this is not used carefully, it can be a security issue, as the interface has the ability to send resets, NMIs, and power off the VM. It's best if QEMU makes a connection to an external simulator running on a secure port on localhost, so neither the simulator nor QEMU is exposed to any outside network.
See the "lanserv/README.vm" file in the OpenIPMI library for more
details on the external interface.
Special files such as iSCSI devices can be specified using protocol
specific URLs. See the section for "Device URL Syntax" for more information.
By default, the cache=writeback mode is used. It will report data writes as completed as soon as the data is present in the host page cache. This is safe as long as your guest OS makes sure to correctly flush disk caches where needed. If your guest OS does not handle volatile disk write caches correctly and your host crashes or loses power, then the guest may experience data corruption.
For such guests, you should consider using cache=writethrough. This means that the host page cache will be used to read and write data, but write notification will be sent to the guest only after QEMU has made sure to flush each write to the disk. Be aware that this has a major impact on performance.
The host page cache can be avoided entirely with cache=none. This will attempt to do disk IO directly to the guest's memory. QEMU may still perform an internal copy of the data. Note that this is considered a writeback mode and the guest OS must handle the disk write cache correctly in order to avoid data corruption on host crashes.
The host page cache can be avoided while only sending write notifications to the guest when the data has been flushed to the disk using cache=directsync.
In case you don't care about data integrity over host failures, use cache=unsafe. This option tells QEMU that it never needs to write any data to the disk but can instead keep things in cache. If anything goes wrong, like your host losing power, the disk storage getting disconnected accidentally, etc. your image will most probably be rendered unusable. When using the -snapshot option, unsafe caching is always used.
Copy-on-read avoids accessing the same backing file sectors repeatedly and is useful when the backing file is over a slow network. By default copy-on-read is off.
Instead of -cdrom you can use:
qemu-system-i386 -drive file=file,index=2,media=cdrom
Instead of -hda, -hdb, -hdc, -hdd, you can use:
qemu-system-i386 -drive file=file,index=0,media=disk
qemu-system-i386 -drive file=file,index=1,media=disk
qemu-system-i386 -drive file=file,index=2,media=disk
qemu-system-i386 -drive file=file,index=3,media=disk
You can open an image using pre-opened file descriptors from an fd set:
qemu-system-i386
-add-fd fd=3,set=2,opaque="rdwr:/path/to/file"
-add-fd fd=4,set=2,opaque="rdonly:/path/to/file"
-drive file=/dev/fdset/2,index=0,media=disk
You can connect a CDROM to the slave of ide0:
qemu-system-i386 -drive file=file,if=ide,index=1,media=cdrom
If you don't specify the "file=" argument, you define an empty drive:
qemu-system-i386 -drive if=ide,index=1,media=cdrom
Instead of -fda, -fdb, you can use:
qemu-system-i386 -drive file=file,index=0,if=floppy
qemu-system-i386 -drive file=file,index=1,if=floppy
By default, interface is "ide" and index is automatically incremented:
qemu-system-i386 -drive file=a -drive file=b"
is interpreted like:
qemu-system-i386 -hda a -hdb b
-fsdev option is used along with -device driver "virtio-9p-pci".
format=raw to avoid interpreting an untrusted format header.
-serial for the
available devices.
change command
can be used to later start the VNC server.
Following the display value there may be one or more option flags separated by commas. Valid options are
reverse), the d argument
is a TCP port number, not a display number.
websocket=port.
If host is specified connections will only be allowed from this host.
It is possible to control the websocket listen address independently, using
the syntax websocket=host:port.
If no TLS credentials are provided, the websocket connection runs in
unencrypted mode. If TLS credentials are provided, the websocket connection
requires encrypted client connections.
The password must be set separately using the set_password command in
the pcsys_monitor. The syntax to change your password is:
set_password <protocol> <password> where <protocol> could be either
"vnc" or "spice".
If you would like to change <protocol> password expiration, you should use
expire_password <protocol> <expiration-time> where expiration time could
be one of the following options: now, never, +seconds or UNIX time of
expiration, e.g. +60 to make password expire in 60 seconds, or 1335196800
to make password expire on "Mon Apr 23 12:00:00 EDT 2012" (UNIX time for this
date and time).
You can also use keywords "now" or "never" for the expiration time to
allow <protocol> password to expire immediately or never expire.
The tls-creds parameter obsoletes the tls,
x509, and x509verify options, and as such
it is not permitted to set both new and old type options at
the same time.
This option is now deprecated in favor of using the tls-creds
argument.
This option is now deprecated in favour of using the tls-creds
argument.
This option is now deprecated in favour of using the tls-creds
argument.
C=GB,O=ACME,L=Boston,CN=bob. For SASL party, the ACL check is
made against the username, which depending on the SASL plugin, may
include a realm component, eg bob or bob@EXAMPLE.COM.
When the acl flag is set, the initial access list will be
empty, with a deny policy. Thus no one will be allowed to
use the VNC server until the ACLs have been loaded. This can be
achieved using the acl monitor command.
virtio, i82551, i82557b, i82559er,
ne2k_pci, ne2k_isa, pcnet, rtl8139,
e1000, smc91c111, lance and mcf_fec.
Not all devices are supported on all targets. Use -net nic,model=help
for a list of available devices for your target.
ipv4 and ipv6 specify that either IPv4 or IPv6 must
be enabled. If neither is specified both protocols are enabled.
Example:
qemu -net user,dnssearch=mgmt.example.org,dnssearch=example.org [...]
bin of the Unix TFTP client).
Example (using pxelinux):
qemu-system-i386 -hda linux.img -boot n -net user,tftp=/path/to/tftp/files,bootfile=/pxelinux.0
In the guest Windows OS, the line:
10.0.2.4 smbserver
must be added in the file C:\WINDOWS\LMHOSTS (for windows 9x/Me) or C:\WINNT\SYSTEM32\DRIVERS\ETC\LMHOSTS (Windows NT/2000).
Then dir can be accessed in \\smbserver\qemu.
Note that a SAMBA server must be installed on the host OS.
QEMU was tested successfully with smbd versions from Red Hat 9,
Fedora Core 3 and OpenSUSE 11.x.
For example, to redirect host X11 connection from screen 1 to guest screen 0, use the following:
# on the host
qemu-system-i386 -net user,hostfwd=tcp:127.0.0.1:6001-:6000 [...]
# this host xterm should open in the guest X11 server
xterm -display :1
To redirect telnet connections from host port 5555 to telnet port on the guest, use the following:
# on the host
qemu-system-i386 -net user,hostfwd=tcp::5555-:23 [...]
telnet localhost 5555
Then when you use on the host telnet localhost 5555, you
connect to the guest telnet server.
You can either use a chardev directly and have that one used throughout QEMU's lifetime, like in the following example:
# open 10.10.1.1:4321 on bootup, connect 10.0.2.100:1234 to it whenever
# the guest accesses it
qemu -net user,guestfwd=tcp:10.0.2.100:1234-tcp:10.10.1.1:4321 [...]
Or you can execute a command on every TCP connection established by the guest, so that QEMU behaves similar to an inetd process for that virtual server:
# call "netcat 10.10.1.1 4321" on every TCP connection to 10.0.2.100:1234
# and connect the TCP stream to its stdin/stdout
qemu -net 'user,guestfwd=tcp:10.0.2.100:1234-cmd:netcat 10.10.1.1 4321'
Note: Legacy stand-alone options -tftp, -bootp, -smb and -redir are still
processed and applied to -net user. Mixing them with the new configuration
syntax gives undefined results. Their use for new applications is discouraged
as they will be removed from future versions.
Use the network script file to configure it and the network script dfile to deconfigure it. If name is not provided, the OS automatically provides one. The default network configure script is /etc/qemu-ifup and the default network deconfigure script is /etc/qemu-ifdown. Use script=no or downscript=no to disable script execution.
If running QEMU as an unprivileged user, use the network helper helper to configure the TAP interface and attach it to the bridge. The default network helper executable is /path/to/qemu-bridge-helper and the default bridge device is br0.
fd=h can be used to specify the handle of an already opened host TAP interface.
Examples:
#launch a QEMU instance with the default network script
qemu-system-i386 linux.img -net nic -net tap
#launch a QEMU instance with two NICs, each one connected
#to a TAP device
qemu-system-i386 linux.img \
-net nic,vlan=0 -net tap,vlan=0,ifname=tap0 \
-net nic,vlan=1 -net tap,vlan=1,ifname=tap1
#launch a QEMU instance with the default network helper to
#connect a TAP device to bridge br0
qemu-system-i386 linux.img \
-net nic -net tap,"helper=/path/to/qemu-bridge-helper"
Use the network helper helper to configure the TAP interface and attach it to the bridge. The default network helper executable is /path/to/qemu-bridge-helper and the default bridge device is br0.
Examples:
#launch a QEMU instance with the default network helper to
#connect a TAP device to bridge br0
qemu-system-i386 linux.img -net bridge -net nic,model=virtio
#launch a QEMU instance with the default network helper to
#connect a TAP device to bridge qemubr0
qemu-system-i386 linux.img -net bridge,br=qemubr0 -net nic,model=virtio
Example:
# launch a first QEMU instance
qemu-system-i386 linux.img \
-net nic,macaddr=52:54:00:12:34:56 \
-net socket,listen=:1234
# connect the VLAN 0 of this instance to the VLAN 0
# of the first instance
qemu-system-i386 linux.img \
-net nic,macaddr=52:54:00:12:34:57 \
-net socket,connect=127.0.0.1:1234
Example:
# launch one QEMU instance
qemu-system-i386 linux.img \
-net nic,macaddr=52:54:00:12:34:56 \
-net socket,mcast=230.0.0.1:1234
# launch another QEMU instance on same "bus"
qemu-system-i386 linux.img \
-net nic,macaddr=52:54:00:12:34:57 \
-net socket,mcast=230.0.0.1:1234
# launch yet another QEMU instance on same "bus"
qemu-system-i386 linux.img \
-net nic,macaddr=52:54:00:12:34:58 \
-net socket,mcast=230.0.0.1:1234
Example (User Mode Linux compat.):
# launch QEMU instance (note mcast address selected
# is UML's default)
qemu-system-i386 linux.img \
-net nic,macaddr=52:54:00:12:34:56 \
-net socket,mcast=239.192.168.1:1102
# launch UML
/path/to/linux ubd0=/path/to/root_fs eth0=mcast
Example (send packets from host's 1.2.3.4):
qemu-system-i386 linux.img \
-net nic,macaddr=52:54:00:12:34:56 \
-net socket,mcast=239.192.168.1:1102,localaddr=1.2.3.4
This transport allows a VM to communicate to another VM, router or firewall directly.
For example, to attach a VM running on host 4.3.2.1 via L2TPv3 to the bridge br-lan on the remote Linux host 1.2.3.4:
# Setup tunnel on linux host using raw ip as encapsulation
# on 1.2.3.4
ip l2tp add tunnel remote 4.3.2.1 local 1.2.3.4 tunnel_id 1 peer_tunnel_id 1 \
encap udp udp_sport 16384 udp_dport 16384
ip l2tp add session tunnel_id 1 name vmtunnel0 session_id \
0xFFFFFFFF peer_session_id 0xFFFFFFFF
ifconfig vmtunnel0 mtu 1500
ifconfig vmtunnel0 up
brctl addif br-lan vmtunnel0
# on 4.3.2.1
# launch QEMU instance - if your network has reorder or is very lossy add ,pincounter
qemu-system-i386 linux.img -net nic -net l2tpv3,src=4.2.3.1,dst=1.2.3.4,udp,srcport=16384,dstport=16384,rxsession=0xffffffff,txsession=0xffffffff,counter
Example:
# launch vde switch
vde_switch -F -sock /tmp/myswitch
# launch QEMU instance
qemu-system-i386 linux.img -net nic -net vde,sock=/tmp/myswitch
The hubport netdev lets you connect a NIC to a QEMU "vlan" instead of a single
netdev. -net and -device with parameter vlan create the
required hub automatically.
Example:
qemu -m 512 -object memory-backend-file,id=mem,size=512M,mem-path=/hugetlbfs,share=on \
-numa node,memdev=mem \
-chardev socket,id=chr0,path=/path/to/socket \
-netdev type=vhost-user,id=net0,chardev=chr0 \
-device virtio-net-pci,netdev=net0
The general form of a character device option is:
Use "-chardev help" to print all available chardev backend types.
All devices must have an id, which can be any string up to 127 characters long. It is used to uniquely identify this device in other command line directives.
A character device may be used in multiplexing mode by multiple front-ends. Specify mux=on to enable this mode. A multiplexer is a "1:N" device, and here the "1" end is your specified chardev backend, and the "N" end is the various parts of QEMU that can talk to a chardev. If you create a chardev with id=myid and mux=on, QEMU will create a multiplexer with your specified ID, and you can then configure multiple front ends to use that chardev ID for their input/output. Up to four different front ends can be connected to a single multiplexed chardev. (Without multiplexing enabled, a chardev can only be used by a single front end.) For instance you could use this to allow a single stdio chardev to be used by two serial ports and the QEMU monitor:
-chardev stdio,mux=on,id=char0 \
-mon chardev=char0,mode=readline \
-serial chardev:char0 \
-serial chardev:char0
You can have more than one multiplexer in a system configuration; for instance you could have a TCP port multiplexed between UART 0 and UART 1, and stdio multiplexed between the QEMU monitor and a parallel port:
-chardev stdio,mux=on,id=char0 \
-mon chardev=char0,mode=readline \
-parallel chardev:char0 \
-chardev tcp,...,mux=on,id=char1 \
-serial chardev:char1 \
-serial chardev:char1
When you're using a multiplexed character device, some escape sequences are interpreted in the input. See Keys in the character backend multiplexer.
Note that some other command line options may implicitly create multiplexed character backends; for instance -serial mon:stdio creates a multiplexed stdio backend connected to the serial port and the QEMU monitor, and -nographic also multiplexes the console and the monitor to stdio.
There is currently no support for multiplexing in the other direction (where a single QEMU front end takes input and output from multiple chardevs).
Every backend supports the logfile option, which supplies the path to a file to record all data transmitted via the backend. The logappend option controls whether the log file will be truncated or appended to when opened.
Further options to each backend are described below.
server specifies that the socket shall be a listening socket.
nowait specifies that QEMU should not block waiting for a client to connect to a listening socket.
telnet specifies that traffic on the socket should interpret telnet escape sequences.
reconnect sets the timeout for reconnecting on non-server sockets when the remote end goes away. qemu will delay this many seconds and then attempt to reconnect. Zero disables reconnecting, and is the default.
tls-creds requests enablement of the TLS protocol for encryption, and specifies the id of the TLS credentials to use for the handshake. The credentials must be previously created with the -object tls-creds argument.
TCP and unix socket options are given below:
0.0.0.0.
port for a listening socket specifies the local port to be bound. For a connecting socket specifies the port on the remote host to connect to. port can be given as either a port number or a service name. port is required.
to is only relevant to listening sockets. If it is specified, and port cannot be bound, QEMU will attempt to bind to subsequent ports up to and including to until it succeeds. to must be specified as a port number.
ipv4 and ipv6 specify that either IPv4 or IPv6 must be used. If neither is specified the socket may use either protocol.
nodelay disables the Nagle algorithm.
host specifies the remote host to connect to. If not specified it
defaults to localhost.
port specifies the port on the remote host to connect to. port is required.
localaddr specifies the local address to bind to. If not specified it
defaults to 0.0.0.0.
localport specifies the local port to bind to. If not specified any available local port will be used.
ipv4 and ipv6 specify that either IPv4 or IPv6 must be used.
If neither is specified the device may use either protocol.
width and height specify the width and height respectively of the console, in pixels.
cols and rows specify that the console be sized to fit a text
console with the given dimensions.
64K.
path specifies the path of the file to be opened. This file will be
created if it does not already exist, and overwritten if it does. path
is required.
On Windows, a single duplex pipe will be created at \\.pipe\path.
On other hosts, 2 pipes will be created called path.in and path.out. Data written to path.in will be received by the guest. Data written by the guest can be read from path.out. QEMU will not create these fifos, and requires them to be present.
path forms part of the pipe path as described above. path is
required.
console is only available on Windows hosts.
On Unix hosts serial will actually accept any tty device, not only serial lines.
path specifies the name of the serial device to open.
pty is not available on Windows hosts.
signal controls if signals are enabled on the terminal, that includes
exiting QEMU with the key sequence <Control-c>. This option is enabled by
default, use signal=off to disable it.
path specifies the path to the tty. path is required.
Connect to a local parallel port.
path specifies the path to the parallel port device. path is
required.
debug debug level for spicevmc
name name of spice channel to connect to
Connect to a spice virtual machine channel, such as vdiport.
debug debug level for spicevmc
name name of spice port to connect to
Connect to a spice port, allowing a Spice client to handle the traffic identified by a name (preferably a fqdn).
In addition to using normal file images for the emulated storage devices, QEMU can also use networked resources such as iSCSI devices. These are specified using a special URL syntax.
Syntax for specifying iSCSI LUNs is “iscsi://<target-ip>[:<port>]/<target-iqn>/<lun>”
By default qemu will use the iSCSI initiator-name 'iqn.2008-11.org.linux-kvm[:<name>]' but this can also be set from the command line or a configuration file.
Since version Qemu 2.4 it is possible to specify a iSCSI request timeout to detect stalled requests and force a reestablishment of the session. The timeout is specified in seconds. The default is 0 which means no timeout. Libiscsi 1.15.0 or greater is required for this feature.
Example (without authentication):
qemu-system-i386 -iscsi initiator-name=iqn.2001-04.com.example:my-initiator \
-cdrom iscsi://192.0.2.1/iqn.2001-04.com.example/2 \
-drive file=iscsi://192.0.2.1/iqn.2001-04.com.example/1
Example (CHAP username/password via URL):
qemu-system-i386 -drive file=iscsi://user%password@192.0.2.1/iqn.2001-04.com.example/1
Example (CHAP username/password via environment variables):
LIBISCSI_CHAP_USERNAME="user" \
LIBISCSI_CHAP_PASSWORD="password" \
qemu-system-i386 -drive file=iscsi://192.0.2.1/iqn.2001-04.com.example/1
iSCSI support is an optional feature of QEMU and only available when compiled and linked against libiscsi.
iSCSI parameters such as username and password can also be specified via
a configuration file. See qemu-doc for more information and examples.
Syntax for specifying a NBD device using TCP “nbd:<server-ip>:<port>[:exportname=<export>]”
Syntax for specifying a NBD device using Unix Domain Sockets “nbd:unix:<domain-socket>[:exportname=<export>]”
Example for TCP
qemu-system-i386 --drive file=nbd:192.0.2.1:30000
Example for Unix Domain Sockets
qemu-system-i386 --drive file=nbd:unix:/tmp/nbd-socket
Examples:
qemu-system-i386 -drive file=ssh://user@host/path/to/disk.img
qemu-system-i386 -drive file.driver=ssh,file.user=user,file.host=host,file.port=22,file.path=/path/to/disk.img
Currently authentication must be done using ssh-agent. Other
authentication methods may be supported in future.
Syntax for specifying a sheepdog device
sheepdog[+tcp|+unix]://[host:port]/vdiname[?socket=path][#snapid|#tag]
Example
qemu-system-i386 --drive file=sheepdog://192.0.2.1:30000/MyVirtualMachine
See also https://sheepdog.github.io/sheepdog/.
Syntax for specifying a VM disk image on GlusterFS volume is
URI:
gluster[+type]://[host[:port]]/volume/path[?socket=...][,debug=N][,logfile=...]
JSON:
'json:{"driver":"qcow2","file":{"driver":"gluster","volume":"testvol","path":"a.img","debug":N,"logfile":"...",
"server":[{"type":"tcp","host":"...","port":"..."},
{"type":"unix","socket":"..."}]}}'
Example
URI:
qemu-system-x86_64 --drive file=gluster://192.0.2.1/testvol/a.img,
file.debug=9,file.logfile=/var/log/qemu-gluster.log
JSON:
qemu-system-x86_64 'json:{"driver":"qcow2",
"file":{"driver":"gluster",
"volume":"testvol","path":"a.img",
"debug":9,"logfile":"/var/log/qemu-gluster.log",
"server":[{"type":"tcp","host":"1.2.3.4","port":24007},
{"type":"unix","socket":"/var/run/glusterd.socket"}]}}'
qemu-system-x86_64 -drive driver=qcow2,file.driver=gluster,file.volume=testvol,file.path=/path/a.img,
file.debug=9,file.logfile=/var/log/qemu-gluster.log,
file.server.0.type=tcp,file.server.0.host=1.2.3.4,file.server.0.port=24007,
file.server.1.type=unix,file.server.1.socket=/var/run/glusterd.socket
See also http://www.gluster.org.
Syntax using a single filename:
<protocol>://[<username>[:<password>]@]<host>/<path>
where:
The following options are also supported:
Note that when passing options to qemu explicitly, driver is the value of <protocol>.
Example: boot from a remote Fedora 20 live ISO image
qemu-system-x86_64 --drive media=cdrom,file=http://dl.fedoraproject.org/pub/fedora/linux/releases/20/Live/x86_64/Fedora-Live-Desktop-x86_64-20-1.iso,readonly
qemu-system-x86_64 --drive media=cdrom,file.driver=http,file.url=http://dl.fedoraproject.org/pub/fedora/linux/releases/20/Live/x86_64/Fedora-Live-Desktop-x86_64-20-1.iso,readonly
Example: boot from a remote Fedora 20 cloud image using a local overlay for writes, copy-on-read, and a readahead of 64k
qemu-img create -f qcow2 -o backing_file='json:{"file.driver":"http",, "file.url":"https://dl.fedoraproject.org/pub/fedora/linux/releases/20/Images/x86_64/Fedora-x86_64-20-20131211.1-sda.qcow2",, "file.readahead":"64k"}' /tmp/Fedora-x86_64-20-20131211.1-sda.qcow2
qemu-system-x86_64 -drive file=/tmp/Fedora-x86_64-20-20131211.1-sda.qcow2,copy-on-read=on
Example: boot from an image stored on a VMware vSphere server with a self-signed certificate using a local overlay for writes, a readahead of 64k and a timeout of 10 seconds.
qemu-img create -f qcow2 -o backing_file='json:{"file.driver":"https",, "file.url":"https://user:password@vsphere.example.com/folder/test/test-flat.vmdk?dcPath=Datacenter&dsName=datastore1",, "file.sslverify":"off",, "file.readahead":"64k",, "file.timeout":10}' /tmp/test.qcow2
qemu-system-x86_64 -drive file=/tmp/test.qcow2
-bt hci[...] option is valid and defines the HCI's
logic. The Transport Layer is decided by the machine type. Currently
the machines n800 and n810 have one HCI and all other
machines have none.
The following three types are recognized:
bluez only) The corresponding HCI passes commands / events
to / from the physical HCI identified by the name id (default:
hci0) on the computer running QEMU. Only available on bluez
capable systems like Linux.
0). Similarly to -net
VLANs, devices inside a bluetooth network n can only communicate
with other devices in the same network (scatternet).
vhci driver installed. Can
be used as following:
qemu-system-i386 [...OPTIONS...] -bt hci,vlan=5 -bt vhci,vlan=5
0). QEMU can only emulate one type of bluetooth devices
currently:
The general form of a TPM device option is:
The specific backend type will determine the applicable options.
The -tpmdev option creates the TPM backend and requires a
-device option that specifies the TPM frontend interface model.
Options to each backend are described below.
Use 'help' to print all available TPM backend types.
qemu -tpmdev help
path specifies the path to the host's TPM device, i.e., on
a Linux host this would be /dev/tpm0.
path is optional and by default /dev/tpm0 is used.
cancel-path specifies the path to the host TPM device's sysfs entry allowing for cancellation of an ongoing TPM command. cancel-path is optional and by default QEMU will search for the sysfs entry to use.
Some notes about using the host's TPM with the passthrough driver:
The TPM device accessed by the passthrough driver must not be used by any other application on the host.
Since the host's firmware (BIOS/UEFI) has already initialized the TPM, the VM's firmware (BIOS/UEFI) will not be able to initialize the TPM again and may therefore not show a TPM-specific menu that would otherwise allow the user to configure the TPM, e.g., allow the user to enable/disable or activate/deactivate the TPM. Further, if TPM ownership is released from within a VM then the host's TPM will get disabled and deactivated. To enable and activate the TPM again afterwards, the host has to be rebooted and the user is required to enter the firmware's menu to enable and activate the TPM. If the TPM is left disabled and/or deactivated most TPM commands will fail.
To create a passthrough TPM use the following two options:
-tpmdev passthrough,id=tpm0 -device tpm-tis,tpmdev=tpm0
Note that the -tpmdev id is tpm0 and is referenced by
tpmdev=tpm0 in the device option.
When using these options, you can use a given Linux or Multiboot kernel without installing it in the disk image. It can be useful for easier testing of various kernels.
Use file1 and file2 as modules and pass arg=foo as parameter to the
first module.
The terminating NUL character of the contents of str will not be included as part of the fw_cfg item data. To insert contents with embedded NUL characters, you have to use the file parameter.
The fw_cfg entries are passed by QEMU through to the guest.
Example:
-fw_cfg name=opt/com.mycompany/blob,file=./my_blob.bin
creates an fw_cfg entry named opt/com.mycompany/blob with contents
from ./my_blob.bin.
vc in graphical mode and
stdio in non graphical mode.
This option can be used several times to simulate up to 4 serial ports.
Use -serial none to disable all serial ports.
Available character devices are:
vc:800x600
It is also possible to specify width or height in characters:
vc:80Cx24C
-chardev option.
0.0.0.0.
When not using a specified src_port a random port is automatically chosen.
If you just want a simple readonly console you can use netcat or
nc, by starting QEMU with: -serial udp::4555 and nc as:
nc -u -l -p 4555. Any time QEMU writes something to that port it
will appear in the netconsole session.
If you plan to send characters back via netconsole or you want to stop
and start QEMU a lot of times, you should have QEMU use the same
source port each time by using something like -serial
udp::4555@:4556 to QEMU. Another approach is to use a patched
version of netcat which can listen to a TCP port and send and receive
characters via udp. If you have a patched version of netcat which
activates telnet remote echo and single char transfer, then you can
use the following options to set up a netcat redirector to allow
telnet on port 5555 to access the QEMU port.
QEMU Options:netcat options:telnet options:nowait
option was specified. The nodelay option disables the Nagle buffering
algorithm. The reconnect option only applies if noserver is
set, if the connection goes down it will attempt to reconnect at the
given interval. If host is omitted, 0.0.0.0 is assumed. Only
one TCP connection at a time is accepted. You can use telnet to
connect to the corresponding character device.
Example to send tcp console to 192.168.0.2 port 4444Example to listen and wait on port 4444 for connectionExample to not wait and listen on ip 192.168.0.100 port 4444-serial tcp. The
difference is that the port acts like a telnet server or client using
telnet option negotiation. This will also allow you to send the
MAGIC_SYSRQ sequence if you use a telnet that supports sending the break
sequence. Typically in unix telnet you do it with Control-] and then
type "send break" followed by pressing the enter key.
-serial tcp except the unix domain socket
path is used for connections.
-serial mon:telnet::4444,server,nowaitThis option can be used several times to simulate up to 3 parallel ports.
Use -parallel none to disable all parallel ports.
vc in graphical mode and stdio in
non graphical mode.
Use -monitor none to disable the default monitor.
vc in graphical mode and stdio in
non graphical mode.
(gdb) target remote | exec qemu-system-i386 -gdb stdio ...
-dfilter 0x8000..0x8fff,0xffffffc000080000+0x200,0xffffffc000060000-0x1000
Will dump output for any code in the 0x1000 sized block starting at 0x8000 and
the 0x200 sized block starting at 0xffffffc000080000 and another 0x1000 sized
block starting at 0xffffffc00005f000.
To list all the data directories, use -L help.
loadvm in monitor)
utc or localtime to let the RTC start at the current
UTC or local time, respectively. localtime is required for correct date in
MS-DOS or Windows. To start at a specific point in time, provide date in the
format 2006-06-17T16:01:21 or 2006-06-17. The default base is UTC.
By default the RTC is driven by the host system time. This allows using of the
RTC as accurate reference clock inside the guest, specifically if the host
time is smoothly following an accurate external reference clock, e.g. via NTP.
If you want to isolate the guest time from the host, you can set clock
to rt instead. To even prevent it from progressing during suspension,
you can set it to vm.
Enable driftfix (i386 targets only) if you experience time drift problems,
specifically with Windows' ACPI HAL. This option will try to figure out how
many timer interrupts were not processed by the Windows guest and will
re-inject them.
auto is specified
then the virtual cpu speed will be automatically adjusted to keep virtual
time within a few seconds of real time.
When the virtual cpu is sleeping, the virtual time will advance at default speed unless sleep=on|off is specified. With sleep=on|off, the virtual time will jump to the next timer deadline instantly whenever the virtual cpu goes to sleep mode and will not advance if no timer is enabled. This behavior give deterministic execution times from the guest point of view.
Note that while this option can give deterministic behavior, it does not provide cycle accurate emulation. Modern CPUs contain superscalar out of order cores with complex cache hierarchies. The number of instructions executed often has little or no correlation with actual performance.
align=on will activate the delay algorithm which will try
to synchronise the host clock and the virtual clock. The goal is to
have a guest running at the real frequency imposed by the shift option.
Whenever the guest clock is behind the host clock and if
align=on is specified then we print a message to the user
to inform about the delay.
Currently this option does not work when shift is auto.
Note: The sync algorithm will work for those shift values for which
the guest clock runs ahead of the host clock. Typically this happens
when the shift value is high (how high depends on the host machine).
When rr option is specified deterministic record/replay is enabled. Replay log is written into filename file in record mode and read from this file in replay mode.
Option rrsnapshot is used to create new vm snapshot named snapshot
at the start of execution recording. In replay mode this option is used
to load the initial VM state.
The model is the model of hardware watchdog to emulate. Use
-watchdog help to list available hardware models. Only one
watchdog can be enabled for a guest.
The following models may be available:
reset (forcefully reset the guest).
Other possible actions are:
shutdown (attempt to gracefully shutdown the guest),
poweroff (forcefully poweroff the guest),
pause (pause the guest),
debug (print a debug message and continue), or
none (do nothing).
Note that the shutdown action requires that the guest responds
to ACPI signals, which it may not be able to do in the sort of
situations where the watchdog would have expired, and thus
-watchdog-action shutdown is not recommended for production use.
Examples:
-watchdog i6300esb -watchdog-action pause-watchdog ib7000x01 when using the
-nographic option. 0x01 is equal to pressing
Control-a. You can select a different character from the ascii
control keys where 1 through 26 map to Control-a through Control-z. For
instance you could use the either of the following to change the escape
character to Control-t.
-echr 0x14-echr 20This option is maintained for backward compatibility.
Please use -device virtconsole for the new way of invocation.
-nodefaults option will disable all those
default devices.
native|gdb|autonative)
or to GDB (gdb). The default is auto, which means gdb
during debug sessions and native otherwise.
-kernel/-append method of passing a
command line is still supported for backward compatibility. If both the
--semihosting-config arg and the -kernel/-append are
specified, the former is passed to semihosting as it always takes precedence.
-) character to print the
output to stdout. This can be later used as input file for -readconfig option.
-nodefconfig option will prevent QEMU from loading any of those config files.
-no-user-config option makes QEMU not load any of the user-provided
config files on sysconfdir, but won't make it skip the QEMU-provided config
files from datadir.
Use -trace help to print a list of names of trace points.
The dir parameter tells QEMU where to find the credential
files. For server endpoints, this directory may contain a file
dh-params.pem providing diffie-hellman parameters to use
for the TLS server. If the file is missing, QEMU will generate
a set of DH parameters at startup. This is a computationally
expensive operation that consumes random pool entropy, so it is
recommended that a persistent set of parameters be generated
upfront and saved.
The dir parameter tells QEMU where to find the credential files. For server endpoints, this directory may contain a file dh-params.pem providing diffie-hellman parameters to use for the TLS server. If the file is missing, QEMU will generate a set of DH parameters at startup. This is a computationally expensive operation that consumes random pool entropy, so it is recommended that a persistent set of parameters be generated upfront and saved.
For x509 certificate credentials the directory will contain further files providing the x509 certificates. The certificates must be stored in PEM format, in filenames ca-cert.pem, ca-crl.pem (optional), server-cert.pem (only servers), server-key.pem (only servers), client-cert.pem (only clients), and client-key.pem (only clients).
For the server-key.pem and client-key.pem files which
contain sensitive private keys, it is possible to use an encrypted
version by providing the passwordid parameter. This provides
the ID of a previously created secret object containing the
password for decryption.
queue all|rx|tx is an option that can be applied to any netfilter.
all: the filter is attached both to the receive and the transmit queue of the netdev (default).
rx: the filter is attached to the receive queue of the netdev, where it will receive packets sent to the netdev.
tx: the filter is attached to the transmit queue of the netdev,
where it will receive packets sent by the netdev.
filter-redirector on netdev netdevid,redirect filter's net packet to chardev
chardevid,and redirect indev's packet to filter.
Create a filter-redirector we need to differ outdev id from indev id, id can not
be the same. we can just use indev or outdev, but at least one of indev or outdev
need to be specified.
usage:
colo secondary:
-object filter-redirector,id=f1,netdev=hn0,queue=tx,indev=red0
-object filter-redirector,id=f2,netdev=hn0,queue=rx,outdev=red1
-object filter-rewriter,id=rew0,netdev=hn0,queue=all
Colo-compare gets packet from primary_inchardevid and secondary_inchardevid, than compare primary packet with secondary packet. If the packets are same, we will output primary packet to outdevchardevid, else we will notify colo-frame do checkpoint and send primary packet to outdevchardevid.
we must use it with the help of filter-mirror and filter-redirector.
primary:
-netdev tap,id=hn0,vhost=off,script=/etc/qemu-ifup,downscript=/etc/qemu-ifdown
-device e1000,id=e0,netdev=hn0,mac=52:a4:00:12:78:66
-chardev socket,id=mirror0,host=3.3.3.3,port=9003,server,nowait
-chardev socket,id=compare1,host=3.3.3.3,port=9004,server,nowait
-chardev socket,id=compare0,host=3.3.3.3,port=9001,server,nowait
-chardev socket,id=compare0-0,host=3.3.3.3,port=9001
-chardev socket,id=compare_out,host=3.3.3.3,port=9005,server,nowait
-chardev socket,id=compare_out0,host=3.3.3.3,port=9005
-object filter-mirror,id=m0,netdev=hn0,queue=tx,outdev=mirror0
-object filter-redirector,netdev=hn0,id=redire0,queue=rx,indev=compare_out
-object filter-redirector,netdev=hn0,id=redire1,queue=rx,outdev=compare0
-object colo-compare,id=comp0,primary_in=compare0-0,secondary_in=compare1,outdev=compare_out0
secondary:
-netdev tap,id=hn0,vhost=off,script=/etc/qemu-ifup,down script=/etc/qemu-ifdown
-device e1000,netdev=hn0,mac=52:a4:00:12:78:66
-chardev socket,id=red0,host=3.3.3.3,port=9003
-chardev socket,id=red1,host=3.3.3.3,port=9004
-object filter-redirector,id=f1,netdev=hn0,queue=tx,indev=red0
-object filter-redirector,id=f2,netdev=hn0,queue=rx,outdev=red1
If you want to know the detail of above command line, you can read
the colo-compare git log.
# qemu-system-x86_64 \
[...] \
-object cryptodev-backend-builtin,id=cryptodev0 \
-device virtio-crypto-pci,id=crypto0,cryptodev=cryptodev0 \
[...]
The sensitive data can be provided in raw format (the default), or base64. When encoded as JSON, the raw format only supports valid UTF-8 characters, so base64 is recommended for sending binary data. QEMU will convert from which ever format is provided to the format it needs internally. eg, an RBD password can be provided in raw format, even though it will be base64 encoded when passed onto the RBD sever.
For added protection, it is possible to encrypt the data associated with a secret using the AES-256-CBC cipher. Use of encryption is indicated by providing the keyid and iv parameters. The keyid parameter provides the ID of a previously defined secret that contains the AES-256 decryption key. This key should be 32-bytes long and be base64 encoded. The iv parameter provides the random initialization vector used for encryption of this particular secret and should be a base64 encrypted string of the 16-byte IV.
The simplest (insecure) usage is to provide the secret inline
# $QEMU -object secret,id=sec0,data=letmein,format=raw
The simplest secure usage is to provide the secret via a file
# echo -n "letmein" > mypasswd.txt # $QEMU -object secret,id=sec0,file=mypasswd.txt,format=raw
For greater security, AES-256-CBC should be used. To illustrate usage, consider the openssl command line tool which can encrypt the data. Note that when encrypting, the plaintext must be padded to the cipher block size (32 bytes) using the standard PKCS#5/6 compatible padding algorithm.
First a master key needs to be created in base64 encoding:
# openssl rand -base64 32 > key.b64
# KEY=$(base64 -d key.b64 | hexdump -v -e '/1 "%02X"')
Each secret to be encrypted needs to have a random initialization vector generated. These do not need to be kept secret
# openssl rand -base64 16 > iv.b64
# IV=$(base64 -d iv.b64 | hexdump -v -e '/1 "%02X"')
The secret to be defined can now be encrypted, in this case we're telling openssl to base64 encode the result, but it could be left as raw bytes if desired.
# SECRET=$(echo -n "letmein" |
openssl enc -aes-256-cbc -a -K $KEY -iv $IV)
When launching QEMU, create a master secret pointing to key.b64
and specify that to be used to decrypt the user password. Pass the
contents of iv.b64 to the second secret
# $QEMU \
-object secret,id=secmaster0,format=base64,file=key.b64 \
-object secret,id=sec0,keyid=secmaster0,format=base64,\
data=$SECRET,iv=$(<iv.b64)
During the graphical emulation, you can use special key combinations to change
modes. The default key mappings are shown below, but if you use -alt-grab
then the modifier is Ctrl-Alt-Shift (instead of Ctrl-Alt) and if you use
-ctrl-grab then the modifier is the right Ctrl key (instead of Ctrl-Alt):
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 a character backend multiplexer (which is the default if you are using -nographic) then several commands are available via an escape sequence. These key sequences all start with an escape character, which is <Ctrl-a> by default, but can be changed with -echr. The list below assumes you're using the default.
The QEMU monitor is used to give complex commands to the QEMU emulator. You can use it to:
The following commands are available:
(qemu) change ide1-cd0 /path/to/some.iso
format is optional.
read-only-mode may be used to change the read-only status of the device. It accepts the following values:
(qemu) change vnc localhost:1
(qemu) change vnc password
Password: ********
fmt is a format which tells the command how to format the data. Its syntax is: /{count}{format}{size}
h or w can be specified with the i format to
respectively select 16 or 32 bit code instruction size.
Examples:
(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
(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
- to press
several keys simultaneously. Example:
sendkey ctrl-alt-f1
This command is useful to send keys that your graphical user interface
intercepts at low level, such as ctrl-alt-f1 in X Window.
bus.addr. Use the monitor
command info usb to see the devices you can remove.
info mice
Defaults:
info capture
-boot option.
The values that can be specified here depend on the machine type, but are
the same that can be specified in the -boot command line option.
allow|denydeny.
allow|deny [index]*@EXAMPLE.COM to
allow all users in the 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 index parameter is supplied.
deny.
getfd command. This is only needed if the file descriptor was never
used by another monitor command.
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 $.
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.
You can create a disk image with the command:
qemu-img create myimage.img mysize
where myimage.img is the disk image filename and mysize is its
size in kilobytes. You can add an M suffix to give the size in
megabytes and a G suffix for gigabytes.
See qemu_img_invocation for more information.
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).
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
(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:
qemu-img Invocation
qemu-img [standard options] command [command options]
qemu-img allows you to create, convert and modify images offline. It can handle all image formats supported by QEMU.
Warning: Never use qemu-img to modify images in use by a running virtual machine or any other process; this may destroy the image. Also, be aware that querying an image that is being modified by another process may encounter inconsistent state.
Standard options:
Use -trace help to print a list of names of trace points.
The following commands are supported:
Command parameters:
qemu(1) manual
page for a description of the object properties. The most common object
type is a secret, which is used to supply passwords and/or encryption
keys.
k or K
(kilobyte, 1024) M (megabyte, 1024k) and G (gigabyte, 1024M)
and T (terabyte, 1024G) are supported. b is ignored.
-o ? for an overview of the options supported
by the used format or see the format descriptions below for details.
SIGUSR1 signal.
k for kilobytes.
-drive cache=... option for allowed
values.
-drive cache=... option for allowed
values.
Parameters to snapshot subcommand:
Parameters to compare subcommand:
Parameters to convert subcommand:
Parameters to dd subcommand:
Command description:
-w is
specified, a write test is performed, otherwise a read test is performed.
A total number of count I/O requests is performed, each buffer_size bytes in size, and with depth requests in parallel. The first request starts at the position given by offset, each following request increases the current position by step_size. If step_size is not given, buffer_size is used for its value.
If flush_interval is specified for a write test, the request queue is
drained and a flush is issued before new writes are made whenever the number of
remaining requests is a multiple of flush_interval. If additionally
--no-drain is specified, a flush is issued without draining the request
queue first.
If -n is specified, the native AIO backend is used if possible. On
Linux, this option only works if -t none or -t directsync is
specified as well.
For write tests, by default a buffer filled with zeros is written. This can be
overridden with a pattern byte specified by pattern.
human or json.
If -r is specified, qemu-img tries to repair any inconsistencies found
during the check. -r leaks repairs only cluster leaks, whereas
-r all fixes all kinds of errors, with a higher risk of choosing the
wrong fix or hiding corruption that has already occurred.
Only the formats qcow2, qed and vdi support
consistency checks.
In case the image does not have any inconsistencies, check exits with 0.
Other exit codes indicate the kind of inconsistency found or if another error
occurred. The following table summarizes all exit codes of the check subcommand:
If -r is specified, exit codes representing the image state refer to the
state after (the attempt at) repairing it. That is, a successful -r all
will yield the exit code 0, independently of the image state before.
If the option backing_file is specified, then the image will record
only the differences from backing_file. No size needs to be specified in
this case. backing_file will never be modified unless you use the
commit monitor command (or qemu-img commit).
The size can also be specified using the size option with -o,
it doesn't need to be specified separately in this case.
The image filename is emptied after the operation has succeeded. If you do
not need filename afterwards and intend to drop it, you may skip emptying
filename by specifying the -d flag.
If the backing chain of the given image file filename has more than one
layer, the backing file into which the changes will be committed may be
specified as base (which has to be part of filename's backing
chain). If base is not specified, the immediate backing file of the top
image (which is filename) will be used. For reasons of consistency,
explicitly specifying base will always imply -d (since emptying an
image after committing to an indirect backing file would lead to different data
being read from the image due to content in the intermediate backing chain
overruling the commit target).
The format is probed unless you specify it by -f (used for filename1) and/or -F (used for filename2) option.
By default, images with different size are considered identical if the larger image contains only unallocated and/or zeroed sectors in the area after the end of the other image. In addition, if any sector is not allocated in one image and contains only zero bytes in the second one, it is evaluated as equal. You can use Strict mode by specifying the -s option. When compare runs in Strict mode, it fails in case image size differs or a sector is allocated in one image and is not allocated in the second one.
By default, compare prints out a result message. This message displays information that both images are same or the position of the first different byte. In addition, result message can report different image size in case Strict mode is used.
Compare exits with 0 in case the images are equal and with 1
in case the images differ. Other exit codes mean an error occurred during
execution and standard error output should contain an error message.
The following table sumarizes all exit codes of the compare subcommand:
-c
option) or use any format specific options like encryption (-o option).
Only the formats qcow and qcow2 support compression. The
compression is read-only. It means that if a compressed sector is
rewritten, then it is rewritten as uncompressed data.
Image conversion is also useful to get smaller image when using a
growable format such as qcow: the empty sectors are detected and
suppressed from the destination image.
sparse_size indicates the consecutive number of bytes (defaults to 4k) that must contain only zeros for qemu-img to create a sparse image during conversion. If sparse_size is 0, the source will not be scanned for unallocated or zero sectors, and the destination image will always be fully allocated.
You can use the backing_file option to force the output image to be created as a copy on write image of the specified base image; the backing_file should have the same content as the input's base image, however the path, image format, etc may differ.
If the -n option is specified, the target volume creation will be
skipped. This is useful for formats such as rbd if the target
volume has already been created with site specific options that cannot
be supplied through qemu-img.
Out of order writes can be enabled with -W to improve performance.
This is only recommended for preallocated devices like host devices or other
raw block devices. Out of order write does not work in combination with
creating compressed images.
num_coroutines specifies how many coroutines work in parallel during
the convert process (defaults to 8).
The data is by default read and written using blocks of 512 bytes but can be modified by specifying block_size. If count=blocks is specified dd will stop reading input after reading blocks input blocks.
The size syntax is similar to dd(1)'s size syntax.
human or json.
If a disk image has a backing file chain, information about each disk image in
the chain can be recursively enumerated by using the option --backing-chain.
For instance, if you have an image chain like:
base.qcow2 <- snap1.qcow2 <- snap2.qcow2
To enumerate information about each disk image in the above chain, starting from top to base, do:
qemu-img info --backing-chain snap2.qcow2
Two option formats are possible. The default format (human)
only dumps known-nonzero areas of the file. Known-zero parts of the
file are omitted altogether, and likewise for parts that are not allocated
throughout the chain. qemu-img output will identify a file
from where the data can be read, and the offset in the file. Each line
will include four fields, the first three of which are hexadecimal
numbers. For example the first line of:
Offset Length Mapped to File
0 0x20000 0x50000 /tmp/overlay.qcow2
0x100000 0x10000 0x95380000 /tmp/backing.qcow2
means that 0x20000 (131072) bytes starting at offset 0 in the image are
available in /tmp/overlay.qcow2 (opened in raw format) starting
at offset 0x50000 (327680). Data that is compressed, encrypted, or
otherwise not available in raw format will cause an error if human
format is in use. Note that file names can include newlines, thus it is
not safe to parse this output format in scripts.
The alternative format json will return an array of dictionaries
in JSON format. It will include similar information in
the start, length, offset fields;
it will also include other more specific information:
data;
if false, the sectors are either unallocated or stored as optimized
all-zero clusters);
zero);
depth; for example, a depth of 2 refers to the backing file
of the backing file of filename.
In JSON format, the offset field is optional; it is absent in
cases where human format would omit the entry or exit with an error.
If data is false and the offset field is present, the
corresponding sectors in the file are not yet in use, but they are
preallocated.
For more information, consult include/block/block.h in QEMU's
source code.
qcow2 and
qed support changing the backing file.
The backing file is changed to backing_file and (if the image format of filename supports this) the backing file format is changed to backing_fmt. If backing_file is specified as “” (the empty string), then the image is rebased onto no backing file (i.e. it will exist independently of any backing file).
cache specifies the cache mode to be used for filename, whereas src_cache specifies the cache mode for reading backing files.
There are two different modes in which rebase can operate:
In order to achieve this, any clusters that differ between backing_file and the old backing file of filename are merged into filename before actually changing the backing file.
Note that the safe mode is an expensive operation, comparable to converting
an image. It only works if the old backing file still exists.
-u is specified. In this mode, only the
backing file name and format of filename is changed without any checks
on the file contents. The user must take care of specifying the correct new
backing file, or the guest-visible content of the image will be corrupted.
This mode is useful for renaming or moving the backing file to somewhere else. It can be used without an accessible old backing file, i.e. you can use it to fix an image whose backing file has already been moved/renamed.
You can use rebase to perform a “diff” operation on two
disk images. This can be useful when you have copied or cloned
a guest, and you want to get back to a thin image on top of a
template or base image.
Say that base.img has been cloned as modified.img by
copying it, and that the modified.img guest has run so there
are now some changes compared to base.img. To construct a thin
image called diff.qcow2 that contains just the differences, do:
qemu-img create -f qcow2 -b modified.img diff.qcow2
qemu-img rebase -b base.img diff.qcow2
At this point, modified.img can be discarded, since
base.img + diff.qcow2 contains the same information.
Before using this command to shrink a disk image, you MUST use file system and partitioning tools inside the VM to reduce allocated file systems and partition sizes accordingly. Failure to do so will result in data loss!
After using this command to grow a disk image, you must use file system and
partitioning tools inside the VM to actually begin using the new space on the
device.
qemu-nbd Invocationqemu-nbd [OPTION]... filename qemu-nbd -d dev
Export a QEMU disk image using the NBD protocol.
filename is a disk image filename, or a set of block driver options if –image-opts is specified.
dev is an NBD device.
qemu(1) manual page for full details of the properties
supported. The common object types that it makes sense to define are the
secret object, which is used to supply passwords and/or encryption
keys, and the tls-creds object, which is used to supply TLS
credentials for the qemu-nbd server.
format=' option should be set.
-drive cache=... option for allowed values.
Use -trace help to print a list of names of trace points.
qemu-ga Invocation
qemu-ga [OPTIONS]
The QEMU Guest Agent is a daemon intended to be run within virtual machines. It allows the hypervisor host to perform various operations in the guest, such as:
qemu-ga will read a system configuration file on startup (located at /etc/qemu/qemu-ga.conf by default), then parse remaining configuration options on the command line. For the same key, the last option wins, but the lists accumulate (see below for configuration file format).
The syntax of the qemu-ga.conf configuration file follows the Desktop Entry Specification, here is a quick summary: it consists of groups of key-value pairs, interspersed with comments.
# qemu-ga configuration sample [general] daemonize = 0 pidfile = /var/run/qemu-ga.pid verbose = 0 method = virtio-serial path = /dev/virtio-ports/org.qemu.guest_agent.0 statedir = /var/run
The list of keys follows the command line options:
QEMU supports many image file formats that can be used with VMs as well as with
any of the tools (like qemu-img). This includes the preferred formats
raw and qcow2 as well as formats that are supported for compatibility with
older QEMU versions or other hypervisors.
Depending on the image format, different options can be passed to
qemu-img create and qemu-img convert using the -o option.
This section describes each format and the options that are supported for it.
qemu-img info to know the real size used by the
image or ls -ls on Unix/Linux.
Supported options:
preallocationoff, falloc, full).
falloc mode preallocates space for image by calling posix_fallocate().
full mode preallocates space for image by writing zeros to underlying
storage.
Supported options:
compatcompat=0.10 uses the
traditional image format that can be read by any QEMU since 0.10.
compat=1.1 enables image format extensions that only QEMU 1.1 and
newer understand (this is the default). Amongst others, this includes
zero clusters, which allow efficient copy-on-read for sparse images.
backing_filebacking_fmtencryptionon, the image is encrypted with 128-bit AES-CBC.
The use of encryption in qcow and qcow2 images is considered to be flawed by modern cryptography standards, suffering from a number of design problems:
Use of qcow / qcow2 encryption with QEMU is deprecated, and support for
it will go away in a future release. Users are recommended to use an
alternative encryption technology such as the Linux dm-crypt / LUKS
system.
cluster_sizepreallocationoff, metadata, falloc,
full). An image with preallocated metadata is initially larger but can
improve performance when the image needs to grow. falloc and full
preallocations are like the same options of raw format, but sets up
metadata also.
lazy_refcountson, reference count updates are postponed with
the goal of avoiding metadata I/O and improving performance. This is
particularly interesting with cache=writethrough which doesn't batch
metadata updates. The tradeoff is that after a host crash, the reference count
tables must be rebuilt, i.e. on the next open an (automatic) qemu-img
check -r all is required, which may take some time.
This option can only be enabled if compat=1.1 is specified.
nocowon, it will turn off COW of the file. It's only
valid on btrfs, no effect on other file systems.
Btrfs has low performance when hosting a VM image file, even more when the guest on the VM also using btrfs as file system. Turning off COW is a way to mitigate this bad performance. Generally there are two ways to turn off COW on btrfs: a) Disable it by mounting with nodatacow, then all newly created files will be NOCOW. b) For an empty file, add the NOCOW file attribute. That's what this option does.
Note: this option is only valid to new or empty files. If there is an existing
file which is COW and has data blocks already, it couldn't be changed to NOCOW
by setting nocow=on. One can issue lsattr filename to check if
the NOCOW flag is set or not (Capital 'C' is NOCOW flag).
When converting QED images to qcow2, you might want to consider using the
lazy_refcounts=on option to get a more QED-like behaviour.
Supported options:
backing_filebacking_fmtcluster_sizetable_sizeSupported options:
backing_fileencryptionon, the image is encrypted.
staticon, the image is created with metadata
preallocation.
Supported options:
backing_filecompat6hwversionsubformatmonolithicSparse (default),
monolithicFlat,
twoGbMaxExtentSparse,
twoGbMaxExtentFlat and
streamOptimized.
subformatdynamic (default) and fixed.
subformatdynamic (default) and fixed.
block_state_zeroon (default)
or off. When set to off, new blocks will be created as
PAYLOAD_BLOCK_NOT_PRESENT, which means parsers are free to return
arbitrary data for those blocks. Do not set to off when using
qemu-img convert with subformat=dynamic.
block_sizelog_sizeMore disk image file formats are supported in a read-only mode.
growing type.
In addition to disk image files, QEMU can directly access host devices. We describe here the usage for QEMU version >= 0.8.3.
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.
CDFloppyHard disksCDCurrently 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 disksWARNING: 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).
/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.
QEMU can automatically create a virtual FAT disk image from a directory tree. In order to use it, just type:
qemu-system-i386 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-system-i386 linux.img -fda fat:floppy:/my_directory
A read/write support is available for testing (beta stage) with the
:rw: option:
qemu-system-i386 linux.img -fda fat:floppy:rw:/my_directory
What you should never do:
QEMU can access directly to block device exported using the Network Block Device protocol.
qemu-system-i386 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-system-i386 linux.img -hdb nbd+unix://?socket=/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 sharing of 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-system-i386 linux1.img -hdb nbd+unix://?socket=/tmp/my_socket qemu-system-i386 linux2.img -hdb nbd+unix://?socket=/tmp/my_socket
If the nbd-server uses named exports (supported since NBD 2.9.18, or with QEMU's own embedded NBD server), you must specify an export name in the URI:
qemu-system-i386 -cdrom nbd://localhost/debian-500-ppc-netinst qemu-system-i386 -cdrom nbd://localhost/openSUSE-11.1-ppc-netinst
The URI syntax for NBD is supported since QEMU 1.3. An alternative syntax is also available. Here are some example of the older syntax:
qemu-system-i386 linux.img -hdb nbd:my_nbd_server.mydomain.org:1024 qemu-system-i386 linux2.img -hdb nbd:unix:/tmp/my_socket qemu-system-i386 -cdrom nbd:localhost:10809:exportname=debian-500-ppc-netinst
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:
qemu-img create sheepdog:///image size
where image is the Sheepdog image name and size is its size.
To import the existing filename to Sheepdog, you can use a convert command.
qemu-img convert filename sheepdog:///image
You can boot from the Sheepdog disk image with the command:
qemu-system-i386 sheepdog:///image
You can also create a snapshot of the Sheepdog image like qcow2.
qemu-img snapshot -c tag sheepdog:///image
where tag is a tag name of the newly created snapshot.
To boot from the Sheepdog snapshot, specify the tag name of the snapshot.
qemu-system-i386 sheepdog:///image#tag
You can create a cloned image from the existing snapshot.
qemu-img create -b sheepdog:///base#tag sheepdog:///image
where base is a image name of the source snapshot and tag is its tag name.
You can use an unix socket instead of an inet socket:
qemu-system-i386 sheepdog+unix:///image?socket=path
If the Sheepdog daemon doesn't run on the local host, you need to specify one of the Sheepdog servers to connect to.
qemu-img create sheepdog://hostname:port/image size qemu-system-i386 sheepdog://hostname:port/image
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
URL syntax: iscsi://[<username>[%<password>]@]<host>[:<port>]/<target-iqn-name>/<lun>
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
export LIBISCSI_CHAP_USERNAME=<username> export LIBISCSI_CHAP_PASSWORD=<password> iscsi://<host>/<target-iqn-name>/<lun>
Various session related parameters can be set via special options, either in a configuration file provided via '-readconfig' or directly on the command line.
If the initiator-name is not specified qemu will use a default name of 'iqn.2008-11.org.linux-kvm[:<name>'] where <name> is the name of the virtual machine.
Setting a specific initiator name to use when logging in to the target -iscsi initiator-name=iqn.qemu.test:my-initiator
Controlling which type of header digest to negotiate with the target -iscsi header-digest=CRC32C|CRC32C-NONE|NONE-CRC32C|NONE
These can also be set via a configuration file
[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"
Setting the target name allows different options for different targets
[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"
Howto use a configuration file to set iSCSI configuration options:
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
Howto set up a simple iSCSI target on loopback and accessing it via QEMU:
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
GlusterFS is a user space distributed file system.
You can boot from the GlusterFS disk image with the command:
URI:
qemu-system-x86_64 -drive file=gluster[+type]://[host[:port]]/volume/path
[?socket=...][,file.debug=9][,file.logfile=...]
JSON:
qemu-system-x86_64 'json:{"driver":"qcow2",
"file":{"driver":"gluster",
"volume":"testvol","path":"a.img","debug":9,"logfile":"...",
"server":[{"type":"tcp","host":"...","port":"..."},
{"type":"unix","socket":"..."}]}}'
gluster is the protocol.
type specifies the transport type used to connect to gluster management daemon (glusterd). Valid transport types are tcp and unix. In the URI form, if a transport type isn't specified, then tcp type is assumed.
host specifies the server where the volume file specification for the given volume resides. This can be either a hostname or an ipv4 address. If transport type is unix, then host field should not be specified. Instead socket field needs to be populated with the path to unix domain socket.
port is the port number on which glusterd is listening. This is optional and if not specified, it defaults to port 24007. If the transport type is unix, then port should not be specified.
volume is the name of the gluster volume which contains the disk image.
path is the path to the actual disk image that resides on gluster volume.
debug is the logging level of the gluster protocol driver. Debug levels are 0-9, with 9 being the most verbose, and 0 representing no debugging output. The default level is 4. The current logging levels defined in the gluster source are 0 - None, 1 - Emergency, 2 - Alert, 3 - Critical, 4 - Error, 5 - Warning, 6 - Notice, 7 - Info, 8 - Debug, 9 - Trace
logfile is a commandline option to mention log file path which helps in logging to the specified file and also help in persisting the gfapi logs. The default is stderr.
You can create a GlusterFS disk image with the command:
qemu-img create gluster://host/volume/path size
Examples
qemu-system-x86_64 -drive file=gluster://1.2.3.4/testvol/a.img
qemu-system-x86_64 -drive file=gluster+tcp://1.2.3.4/testvol/a.img
qemu-system-x86_64 -drive file=gluster+tcp://1.2.3.4:24007/testvol/dir/a.img
qemu-system-x86_64 -drive file=gluster+tcp://[1:2:3:4:5:6:7:8]/testvol/dir/a.img
qemu-system-x86_64 -drive file=gluster+tcp://[1:2:3:4:5:6:7:8]:24007/testvol/dir/a.img
qemu-system-x86_64 -drive file=gluster+tcp://server.domain.com:24007/testvol/dir/a.img
qemu-system-x86_64 -drive file=gluster+unix:///testvol/dir/a.img?socket=/tmp/glusterd.socket
qemu-system-x86_64 -drive file=gluster+rdma://1.2.3.4:24007/testvol/a.img
qemu-system-x86_64 -drive file=gluster://1.2.3.4/testvol/a.img,file.debug=9,file.logfile=/var/log/qemu-gluster.log
qemu-system-x86_64 'json:{"driver":"qcow2",
"file":{"driver":"gluster",
"volume":"testvol","path":"a.img",
"debug":9,"logfile":"/var/log/qemu-gluster.log",
"server":[{"type":"tcp","host":"1.2.3.4","port":24007},
{"type":"unix","socket":"/var/run/glusterd.socket"}]}}'
qemu-system-x86_64 -drive driver=qcow2,file.driver=gluster,file.volume=testvol,file.path=/path/a.img,
file.debug=9,file.logfile=/var/log/qemu-gluster.log,
file.server.0.type=tcp,file.server.0.host=1.2.3.4,file.server.0.port=24007,
file.server.1.type=unix,file.server.1.socket=/var/run/glusterd.socket
You can access disk images located on a remote ssh server by using the ssh protocol:
qemu-system-x86_64 -drive file=ssh://[user@]server[:port]/path[?host_key_check=host_key_check]
Alternative syntax using properties:
qemu-system-x86_64 -drive file.driver=ssh[,file.user=user],file.host=server[,file.port=port],file.path=path[,file.host_key_check=host_key_check]
ssh is the protocol.
user is the remote user. If not specified, then the local username is tried.
server specifies the remote ssh server. Any ssh server can be used, but it must implement the sftp-server protocol. Most Unix/Linux systems should work without requiring any extra configuration.
port is the port number on which sshd is listening. By default the standard ssh port (22) is used.
path is the path to the disk image.
The optional host_key_check parameter controls how the remote
host's key is checked. The default is yes which means to use
the local .ssh/known_hosts file. Setting this to no
turns off known-hosts checking. Or you can check that the host key
matches a specific fingerprint:
host_key_check=md5:78:45:8e:14:57:4f:d5:45:83:0a:0e:f3:49:82:c9:c8
(sha1: can also be used as a prefix, but note that OpenSSH
tools only use MD5 to print fingerprints).
Currently authentication must be done using ssh-agent. Other authentication methods may be supported in future.
Note: Many ssh servers do not support an fsync-style operation.
The ssh driver cannot guarantee that disk flush requests are
obeyed, and this causes a risk of disk corruption if the remote
server or network goes down during writes. The driver will
print a warning when fsync is not supported:
warning: ssh server ssh.example.com:22 does not support fsync
With sufficiently new versions of libssh2 and OpenSSH, fsync is
supported.
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.
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).
This is the standard way to connect QEMU to a real network. QEMU adds
a virtual network device on your host (called tapN), and you
can then configure it as if it was a real ethernet card.
As an example, you can download the linux-test-xxx.tar.gz
archive and copy the script qemu-ifup in /etc and
configure properly sudo so that the command ifconfig
contained in qemu-ifup can be executed as root. You must verify
that your host kernel supports the TAP network interfaces: the
device /dev/net/tun must be present.
See sec_invocation to have examples of command lines using the TAP network interfaces.
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/.
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 ICMP traffic in general does not work with user mode networking.
ping, aka. ICMP echo, to the local router (10.0.2.2) shall work,
however. If you're using QEMU on Linux >= 3.0, it can use unprivileged ICMP
ping sockets to allow ping to the Internet. The host admin has to set
the ping_group_range in order to grant access to those sockets. To allow ping
for GID 100 (usually users group):
echo 100 100 > /proc/sys/net/ipv4/ping_group_range
When using the built-in TFTP server, the router is also the TFTP server.
When using the '-netdev user,hostfwd=...' 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.
Using the -net socket option, it is possible to make VLANs that span several QEMU instances. See sec_invocation to have a basic example.
On Linux hosts, a shared memory device is available. The basic syntax is:
qemu-system-x86_64 -device ivshmem-plain,memdev=hostmem
where hostmem names a host memory backend. For a POSIX shared memory backend, use something like
-object memory-backend-file,size=1M,share,mem-path=/dev/shm/ivshmem,id=hostmem
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:
# First start the ivshmem server once and for all
ivshmem-server -p pidfile -S path -m shm-name -l shm-size -n vectors
# Then start your qemu instances with matching arguments
qemu-system-x86_64 -device ivshmem-doorbell,vectors=vectors,chardev=id
-chardev socket,path=path,id=id
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 ivshmem-spec.txt).
With device property master=on, the guest will copy the shared memory on migration to the destination host. With master=off, the guest will not be able to migrate with the device attached. In the latter case, the device should be detached and then reattached after migration using the PCI hotplug support.
At most one of the devices sharing the same memory can be master. The master must complete migration before you plug back the other devices.
Instead of specifying the <shm size> using POSIX shm, you may specify a memory backend that has hugepage support:
qemu-system-x86_64 -object memory-backend-file,size=1G,mem-path=/dev/hugepages/my-shmem-file,share,id=mb1
-device ivshmem-plain,memdev=mb1
ivshmem-server also supports hugepages mount points with the -m memory path argument.
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-system-i386 -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-system-i386 -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 pcsys_keys).
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.
USB devices can be connected with the -usbdevice commandline option
or the usb_add monitor command. Available devices are:
mousetabletdisk:filehost:bus.addrhost:vendor_id:product_idwacom-tablettablet
above but it can be used with the tslib library because in addition to touch
coordinates it reports touch pressure.
keyboardserial:[vendorid=vendor_id][,product_id=product_id]:dev-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).
braillenet:options-net nic,options (see description).
For instance, user-mode networking can be used with
qemu-system-i386 [...OPTIONS...] -net user,vlan=0 -usbdevice net:vlan=0
Currently this cannot be used in machines that support PCI NICs.
bt[:hci-type]-bt hci,vlan=0.
This USB device implements the USB Transport Layer of HCI. Example
usage:
qemu-system-i386 [...OPTIONS...] -usbdevice bt:hci,vlan=3 -bt device:keyboard,vlan=3
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.
ls /proc/bus/usb
001 devices drivers
chown -R myuid /proc/bus/usb
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).
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.
When relaunching QEMU, you may have to unplug and plug again the USB device to make it work again (this is a bug).
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.
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-system-i386 [...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.
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 not supported when operating
in FIPS 140-2 compliance mode as it requires the use of the DES cipher. 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-system-i386 [...OPTIONS...] -vnc :1,password -monitor stdio (qemu) change vnc password Password: ******** (qemu)
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-system-i386 [...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.
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-system-i386 [...OPTIONS...] -vnc :1,tls,x509verify=/etc/pki/qemu -monitor stdio
Finally, the previous method can be combined with VNC password authentication to provide two layers of authentication for clients.
qemu-system-i386 [...OPTIONS...] -vnc :1,password,tls,x509verify=/etc/pki/qemu -monitor stdio (qemu) change vnc password Password: ******** (qemu)
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-system-i386 [...OPTIONS...] -vnc :1,sasl -monitor stdio
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-system-i386 [...OPTIONS...] -vnc :1,tls,x509,sasl -monitor stdio
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 necessary 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.
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.
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-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.
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
organization = 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.
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 Kerberos 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.
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-system-i386 -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:
info reg to display all the CPU registers.
x/10i $eip to display the code at the PC position.
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 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 (gdb) maintenance packet qqemu.sstepbits
sending: "qqemu.sstepbits"
received: "ENABLE=1,NOIRQ=2,NOTIMER=4"
maintenance packet qqemu.sstep (gdb) maintenance packet qqemu.sstep
sending: "qqemu.sstep"
received: "0x7"
maintenance packet Qqemu.sstep=HEX_VALUE (gdb) maintenance packet Qqemu.sstep=0x5
sending: "qemu.sstep=0x5"
received: "OK"
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.
If you have a slow host, using Windows 95 is better as it gives the best speed. Windows 2000 is also a good choice.
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).
Windows 9x does not correctly use the CPU HLT instruction. The result is that it takes host CPU cycles even when idle. You can install the utility from http://www.user.cityline.ru/~maxamn/amnhltm.zip to solve this problem. Note that no such tool is needed for NT, 2000 or XP.
Windows 2000 has a bug which gives a disk full problem during its installation. When installing it, use the -win2k-hack QEMU option to enable a specific workaround. After Windows 2000 is installed, you no longer need this option (this option slows down the IDE transfers).
Windows 2000 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.
See sec_invocation about the help of the option '-netdev user,smb=...'.
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").
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.
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.
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:
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/.
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.
QEMU emulates the following sun4m 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 most kernel versions work. Please note that currently older Solaris kernels don't work probably due to interface issues between OpenBIOS and Solaris.
The following options are specific to the Sparc32 emulation:
qemu-system-sparc -prom-env 'auto-boot?=false' \
-prom-env 'boot-device=sd(0,2,0):d' -prom-env 'boot-args=linux single'
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 Sun4u emulator is mostly complete, being able to run Linux, NetBSD and OpenBSD in headless (-nographic) mode. The Sun4v emulator is still a work in progress.
The Niagara T1 emulator makes use of firmware and OS binaries supplied in the S10image/ directory of the OpenSPARC T1 project http://download.oracle.com/technetwork/systems/opensparc/OpenSPARCT1_Arch.1.5.tar.bz2 and is able to boot the disk.s10hw2 Solaris image.
qemu-system-sparc64 -M niagara -L /path-to/S10image/ \
-nographic -m 256 \
-drive if=pflash,readonly=on,file=/S10image/disk.s10hw2
QEMU emulates the following peripherals:
The following options are specific to the Sparc64 emulation:
qemu-system-sparc64 -prom-env 'auto-boot?=false'
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 similar to what the proprietary MIPS emulator uses for running Linux. It supports:
The MIPS Magnum R4000 emulation supports:
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:
Several variants of the ARM RealView baseboard are emulated, including the EB, PB-A8 and PBX-A9. Due to interactions with the bootloader, only certain Linux kernel configurations work out of the box on these boards.
Kernels for the PB-A8 board should have CONFIG_REALVIEW_HIGH_PHYS_OFFSET enabled in the kernel, and expect 512M RAM. Kernels for The PBX-A9 board should have CONFIG_SPARSEMEM enabled, CONFIG_REALVIEW_HIGH_PHYS_OFFSET disabled and expect 1024M RAM.
The following devices are emulated:
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 emulation 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:
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.
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 ColdFire 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.
Two executables cover simulation of both Xtensa endian options, qemu-system-xtensa and qemu-system-xtensaeb. Two different machine types are emulated:
The sim pseudo board emulation provides an environment similar to one provided by the proprietary Tensilica ISS. It supports:
The Avnet LX60/LX110/LX200 emulation supports:
The following options are specific to the Xtensa emulation:
Xtensa semihosting provides basic file IO calls, such as open/read/write/seek/select. Tensilica baremetal libc for ISS and linux platform "sim" use this interface.
Note that this allows guest direct access to the host filesystem, so should only be used with trusted guest OS.
The following OS are supported in user space emulation:
QEMU user space emulation has the following notable features:
SIGALRM), as well as synthesize signals from
virtual CPU exceptions (for example SIGFPE when the program
executes a division by zero).
QEMU relies on the host kernel to emulate most signal system
calls, for example to emulate the signal mask. On Linux, QEMU
supports both normal and real-time signals.
clone syscall and create a real
host thread (with a separate virtual CPU) for each emulated thread.
Note that not all targets currently emulate atomic operations correctly.
x86 and ARM use a global lock in order to preserve their semantics.
QEMU was conceived so that ultimately it can emulate itself. Although it is not very useful, it is an important test to show the power of the emulator.
In order to launch a Linux process, QEMU needs the process executable itself and all the target (x86) dynamic libraries used by it.
qemu-i386 -L / /bin/ls
-L / tells that the x86 dynamic linker must be searched with a
/ prefix.
qemu-i386 -L / qemu-i386 -L / /bin/ls
LD_LIBRARY_PATH is not set:
unset LD_LIBRARY_PATH
Then you can launch the precompiled ls x86 executable:
qemu-i386 tests/i386/ls
You can look at scripts/qemu-binfmt-conf.sh so that
QEMU is automatically launched by the Linux kernel when you try to
launch x86 executables. It requires the binfmt_misc module in the
Linux kernel.
qemu-i386 /usr/local/qemu-i386/bin/qemu-i386 \
/usr/local/qemu-i386/bin/ls-i386
qemu-i386 /usr/local/qemu-i386/bin/ls-i386
${HOME}/.wine directory is saved to ${HOME}/.wine.org.
qemu-i386 /usr/local/qemu-i386/wine/bin/wine \
/usr/local/qemu-i386/wine/c/Program\ Files/putty.exe
qemu-i386 [-h] [-d] [-L path] [-s size] [-cpu model] [-g port] [-B offset] [-R size] program [arguments...]
Debug options:
Environment variables:
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-i386 TODO. qemu-x86_64 TODO.
qemu-mips TODO. qemu-mipsel TODO.
qemu-ppc64abi32 TODO. qemu-ppc64 TODO. qemu-ppc TODO.
qemu-sh4eb TODO. qemu-sh4 TODO.
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).
In order to launch a BSD process, QEMU needs the process executable itself and all the target dynamic libraries used by it.
qemu-sparc64 /bin/ls
qemu-sparc64 [-h] [-d] [-L path] [-s size] [-bsd type] program [arguments...]
Debug options:
QEMU x86 target features:
Current QEMU limitations:
Current QEMU limitations:
Current QEMU limitations:
QEMU is a dynamic translator. When it first encounters a piece of code, it converts it to the host instruction set. Usually dynamic translators are very complicated and highly CPU dependent. QEMU uses some tricks which make it relatively easily portable and simple while achieving good performances.
QEMU's dynamic translation backend is called TCG, for "Tiny Code
Generator". For more information, please take a look at tcg/README.
Some notable features of QEMU's dynamic translator are:
In order to accelerate the most common cases where the new simulated PC is known, QEMU can patch a basic block so that it jumps directly to the next one.
The most portable code uses an indirect jump. An indirect jump makes
it easier to make the jump target modification atomic. On some host
architectures (such as x86 or PowerPC), the JUMP opcode is
directly patched so that the block chaining has no overhead.
User-mode emulation marks a host page as write-protected (if it is not already read-only) every time translated code is generated for a basic block. Then, if a write access is done to the page, Linux raises a SEGV signal. QEMU then invalidates all the translated code in the page and enables write accesses to the page. For system emulation, write protection is achieved through the software MMU.
Correct translated code invalidation is done efficiently by maintaining a linked list of every translated block contained in a given page. Other linked lists are also maintained to undo direct block chaining.
On RISC targets, correctly written software uses memory barriers and
cache flushes, so some of the protection above would not be
necessary. However, QEMU still requires that the generated code always
matches the target instructions in memory in order to handle
exceptions correctly.
The host SIGSEGV and SIGBUS signal handlers are used to get invalid memory accesses. QEMU keeps a map from host program counter to target program counter, and looks up where the exception happened based on the host program counter at the exception point.
On some targets, some bits of the virtual CPU's state are not flushed to the
memory until the end of the translation block. This is done for internal
emulation state that is rarely accessed directly by the program and/or changes
very often throughout the execution of a translation block—this includes
condition codes on x86, delay slots on SPARC, conditional execution on
ARM, and so on. This state is stored for each target instruction, and
looked up on exceptions.
QEMU uses an address translation cache (TLB) to speed up the translation. In order to avoid flushing the translated code each time the MMU mappings change, all caches in QEMU are physically indexed. This means that each basic block is indexed with its physical address.
In order to avoid invalidating the basic block chain when MMU mappings change, chaining is only performed when the destination of the jump shares a page with the basic block that is performing the jump.
The MMU can also distinguish RAM and ROM memory areas from MMIO memory areas. Access is faster for RAM and ROM because the translation cache also hosts the offset between guest address and host memory. Accessing MMIO memory areas instead calls out to C code for device emulation. Finally, the MMU helps tracking dirty pages and pages pointed to by translation blocks.
Like bochs [1], QEMU emulates an x86 CPU. But QEMU is much faster than bochs as it uses dynamic compilation. Bochs is closely tied to x86 PC emulation while QEMU can emulate several processors.
Like Valgrind [2], QEMU does user space emulation and dynamic translation. Valgrind is mainly a memory debugger while QEMU has no support for it (QEMU could be used to detect out of bound memory accesses as Valgrind, but it has no support to track uninitialised data as Valgrind does). The Valgrind dynamic translator generates better code than QEMU (in particular it does register allocation) but it is closely tied to an x86 host and target and has no support for precise exceptions and system emulation.
EM86 [3] is the closest project to user space QEMU (and QEMU still uses some of its code, in particular the ELF file loader). EM86 was limited to an alpha host and used a proprietary and slow interpreter (the interpreter part of the FX!32 Digital Win32 code translator [4]).
TWIN from Willows Software was a Windows API emulator like Wine. It is less accurate than Wine but includes a protected mode x86 interpreter to launch x86 Windows executables. Such an approach has greater potential because most of the Windows API is executed natively but it is far more difficult to develop because all the data structures and function parameters exchanged between the API and the x86 code must be converted.
User mode Linux [5] was the only solution before QEMU to launch a Linux kernel as a process while not needing any host kernel patches. However, user mode Linux requires heavy kernel patches while QEMU accepts unpatched Linux kernels. The price to pay is that QEMU is slower.
The Plex86 [6] PC virtualizer is done in the same spirit as the now obsolete qemu-fast system emulator. It requires a patched Linux kernel to work (you cannot launch the same kernel on your PC), but the patches are really small. As it is a PC virtualizer (no emulation is done except for some privileged instructions), it has the potential of being faster than QEMU. The downside is that a complicated (and potentially unsafe) host kernel patch is needed.
The commercial PC Virtualizers (VMWare [7], VirtualPC [8]) are faster than QEMU (without virtualization), but they all need specific, proprietary and potentially unsafe host drivers. Moreover, they are unable to provide cycle exact simulation as an emulator can.
VirtualBox [9], Xen [10] and KVM [11] are based on QEMU. QEMU-SystemC [12] uses QEMU to simulate a system where some hardware devices are developed in SystemC.
QEMU is a trademark of Fabrice Bellard.
QEMU is released under the GNU General Public License (TODO: add link). Parts of QEMU have specific licenses, see file LICENSE.
TODO (refer to file LICENSE, include it, include the GPL?)
This is the main index. Should we combine all keywords in one index? TODO
This index could be used for command line options and monitor functions.
--trace: qemu_nbd_invocation--trace: qemu_img_invocation-accel: sec_invocation-acpitable: sec_invocation-add-fd: sec_invocation-alt-grab: sec_invocation-append: sec_invocation-audio-help: sec_invocation-balloon: sec_invocation-bios: sec_invocation-boot: sec_invocation-bt: sec_invocation-cdrom: sec_invocation-chardev: sec_invocation-chroot: sec_invocation-cpu: sec_invocation-ctrl-grab: sec_invocation-curses: sec_invocation-D: sec_invocation-d: sec_invocation-daemonize: sec_invocation-debugcon: sec_invocation-device: sec_invocation-dfilter: sec_invocation-display: sec_invocation-drive: sec_invocation-dtb: sec_invocation-dump-vmstate: sec_invocation-echr: sec_invocation-enable-fips: sec_invocation-enable-hax: sec_invocation-enable-kvm: sec_invocation-fda: sec_invocation-fdb: sec_invocation-fsdev: sec_invocation-full-screen: sec_invocation-fw_cfg: sec_invocation-g: sec_invocation-gdb: sec_invocation-global: sec_invocation-h: sec_invocation-hda: sec_invocation-hdachs: sec_invocation-hdb: sec_invocation-hdc: sec_invocation-hdd: sec_invocation-icount: sec_invocation-incoming: sec_invocation-initrd: sec_invocation-k: sec_invocation-kernel: sec_invocation-L: sec_invocation-loadvm: sec_invocation-m: sec_invocation-machine: sec_invocation-mem-path: sec_invocation-mem-prealloc: sec_invocation-mon: sec_invocation-monitor: sec_invocation-msg: sec_invocation-mtdblock: sec_invocation-name: sec_invocation-net: sec_invocation-netdev: sec_invocation-no-acpi: sec_invocation-no-fd-bootchk: sec_invocation-no-frame: sec_invocation-no-hpet: sec_invocation-no-quit: sec_invocation-no-reboot: sec_invocation-no-shutdown: sec_invocation-no-user-config: sec_invocation-nodefaults: sec_invocation-nodefconfig: sec_invocation-nographic: sec_invocation-numa: sec_invocation-object: sec_invocation-old-param (ARM): sec_invocation-only-migratable: sec_invocation-option-rom: sec_invocation-parallel: sec_invocation-pflash: sec_invocation-pidfile: sec_invocation-portrait: sec_invocation-prom-env: sec_invocation-qmp: sec_invocation-qmp-pretty: sec_invocation-readconfig: sec_invocation-realtime: sec_invocation-rotate: sec_invocation-rtc: sec_invocation-runas: sec_invocation-s: sec_invocation-S: sec_invocation-sandbox: sec_invocation-sd: sec_invocation-sdl: sec_invocation-semihosting: sec_invocation-semihosting-config: sec_invocation-serial: sec_invocation-set: sec_invocation-show-cursor: sec_invocation-singlestep: sec_invocation-smbios: sec_invocation-smp: sec_invocation-snapshot: sec_invocation-soundhw: sec_invocation-spice: sec_invocation-tb-size: sec_invocation-tpmdev: sec_invocation-trace: sec_invocation-usb: sec_invocation-usbdevice: sec_invocation-uuid: sec_invocation-version: sec_invocation-vga: sec_invocation-virtfs: sec_invocation-virtfs_synth: sec_invocation-virtioconsole: sec_invocation-vnc: sec_invocation-watchdog: sec_invocation-watchdog-action: sec_invocation-win2k-hack: sec_invocation-writeconfig: sec_invocation-xen-attach: sec_invocation-xen-create: sec_invocation-xen-domid: sec_invocationacl_add: pcsys_monitoracl_policy: pcsys_monitoracl_remove: pcsys_monitoracl_reset: pcsys_monitoracl_show: pcsys_monitorballoon: pcsys_monitorblock: pcsys_monitorblock-jobs: pcsys_monitorblock_job_cancel: pcsys_monitorblock_job_complete: pcsys_monitorblock_job_pause: pcsys_monitorblock_job_resume: pcsys_monitorblock_job_set_speed: pcsys_monitorblock_passwd: pcsys_monitorblock_resize: pcsys_monitorblock_set_io_throttle: pcsys_monitorblock_stream: pcsys_monitorblockstats: pcsys_monitorboot_set: pcsys_monitorcapture: pcsys_monitorchange: pcsys_monitorchardev: pcsys_monitorchardev-add: pcsys_monitorchardev-remove: pcsys_monitorclient_migrate_info: pcsys_monitorclosefd: pcsys_monitorcommit: pcsys_monitorcont: pcsys_monitorcpu: pcsys_monitorcpu-add: pcsys_monitorcpus: pcsys_monitorcpustats: pcsys_monitordelvm: pcsys_monitordevice_add: pcsys_monitordevice_del: pcsys_monitordrive_add: pcsys_monitordrive_backup: pcsys_monitordrive_del: pcsys_monitordrive_mirror: pcsys_monitordump: pcsys_monitordump-guest-memory: pcsys_monitordump-skeys: pcsys_monitoreject: pcsys_monitorexpire_password: pcsys_monitorgdbserver: pcsys_monitorgetfd: pcsys_monitorhelp: pcsys_monitorhistory: pcsys_monitorhost_net_add: pcsys_monitorhost_net_remove: pcsys_monitorhostfwd_add: pcsys_monitorhostfwd_remove: pcsys_monitorhotpluggable-cpus: pcsys_monitori: pcsys_monitorinfo: pcsys_monitorioapic: pcsys_monitoriothreads: pcsys_monitorirq: pcsys_monitorjit: pcsys_monitorkvm: pcsys_monitorlapic: pcsys_monitorloadvm: pcsys_monitorlog: pcsys_monitorlogfile: pcsys_monitormce (x86): pcsys_monitormem: pcsys_monitormemdev: pcsys_monitormemory-devices: pcsys_monitormemsave: pcsys_monitormice: pcsys_monitormigrate: pcsys_monitormigrate_cache_size: pcsys_monitormigrate_cancel: pcsys_monitormigrate_capabilities: pcsys_monitormigrate_incoming: pcsys_monitormigrate_parameters: pcsys_monitormigrate_set_cache_size: pcsys_monitormigrate_set_capability: pcsys_monitormigrate_set_downtime: pcsys_monitormigrate_set_parameter: pcsys_monitormigrate_set_speed: pcsys_monitormigrate_start_postcopy: pcsys_monitormouse_button: pcsys_monitormouse_move: pcsys_monitormouse_set: pcsys_monitormtree: pcsys_monitorname: pcsys_monitornbd_server_add: pcsys_monitornbd_server_start: pcsys_monitornbd_server_stop: pcsys_monitornetdev_add: pcsys_monitornetdev_del: pcsys_monitornetwork: pcsys_monitornmi: pcsys_monitornuma: pcsys_monitoro: pcsys_monitorobject_add: pcsys_monitorobject_del: pcsys_monitorocker-ports: pcsys_monitoropcount: pcsys_monitorpci: pcsys_monitorpcie_aer_inject_error: pcsys_monitorpic: pcsys_monitorpmemsave: pcsys_monitorprint: pcsys_monitorprofile: pcsys_monitorqdm: pcsys_monitorqemu-io: pcsys_monitorqom-tree: pcsys_monitorqtree: pcsys_monitorquit: pcsys_monitorregisters: pcsys_monitorringbuf_read: pcsys_monitorringbuf_write: pcsys_monitorrocker: pcsys_monitorrocker-of-dpa-flows: pcsys_monitorrocker-of-dpa-groups: pcsys_monitorroms: pcsys_monitorsavevm: pcsys_monitorscreendump: pcsys_monitorsendkey: pcsys_monitorset_link: pcsys_monitorset_password: pcsys_monitorsinglestep: pcsys_monitorskeys: pcsys_monitorsnapshot_blkdev: pcsys_monitorsnapshot_blkdev_internal: pcsys_monitorsnapshot_delete_blkdev_internal: pcsys_monitorsnapshots: pcsys_monitorspice: pcsys_monitorstatus: pcsys_monitorstop: pcsys_monitorstopcapture: pcsys_monitorsum: pcsys_monitorsystem_powerdown: pcsys_monitorsystem_reset: pcsys_monitorsystem_wakeup: pcsys_monitortlb: pcsys_monitortpm: pcsys_monitortrace-event: pcsys_monitortrace-events: pcsys_monitortrace-file: pcsys_monitorusb: pcsys_monitorusb_add: pcsys_monitorusb_del: pcsys_monitorusbhost: pcsys_monitorusernet: pcsys_monitoruuid: pcsys_monitorversion: pcsys_monitorvm-generation-id: pcsys_monitorvnc: pcsys_monitorwatchdog_action: pcsys_monitorwavcapture: pcsys_monitorx: pcsys_monitorx_colo_lost_heartbeat: pcsys_monitorxp: pcsys_monitorThis is a list of all keystrokes which have a special function in system emulation.
Ctrl-a b: mux_keysCtrl-a c: mux_keysCtrl-a Ctrl-a: mux_keysCtrl-a h: mux_keysCtrl-a s: mux_keysCtrl-a t: mux_keysCtrl-a x: mux_keysCtrl-Alt: pcsys_keysCtrl-Alt-+: pcsys_keysCtrl-Alt--: pcsys_keysCtrl-Alt-f: pcsys_keysCtrl-Alt-n: pcsys_keysCtrl-Alt-u: pcsys_keysCtrl-Down: pcsys_keysCtrl-PageDown: pcsys_keysCtrl-PageUp: pcsys_keysCtrl-Up: pcsys_keysThis index could be used for qdev device names and options.