Domain XML format

This section describes the XML format used to represent domains, there are variations on the format based on the kind of domains run and the options used to launch them. For hypervisor specific details consult the driver docs

Element and attribute overview

The root element required for all virtual machines is named domain. It has two attributes, the type specifies the hypervisor used for running the domain. The allowed values are driver specific, but include "xen", "kvm", "qemu", "lxc" and "kqemu". The second attribute is id which is a unique integer identifier for the running guest machine. Inactive machines have no id value.

General metadata

<domain type='xen' id='3'>
  <name>fv0</name>
  <uuid>4dea22b31d52d8f32516782e98ab3fa0</uuid>
  <description>Some human readable description</description>
  ...
name
The content of the name element provides a short name for the virtual machine. This name should consist only of alpha-numeric characters and is required to be unique within the scope of a single host. It is often used to form the filename for storing the persistent configuration file. Since 0.0.1
uuid
The content of the uuid element provides a globally unique identifier for the virtual machine. The format must be RFC 4122 compliant, eg 3e3fce45-4f53-4fa7-bb32-11f34168b82b. If omitted when defining/creating a new machine, a random UUID is generated. Since 0.0.1
description
The content of the description element provides a human readable description of the virtual machine. This data is not used by libvirt in any way, it can contain any information the user wants. Since 0.7.2

Operating system booting

There are a number of different ways to boot virtual machines each with their own pros and cons.

BIOS bootloader

Booting via the BIOS is available for hypervisors supporting full virtualization. In this case the BIOS has a boot order priority (floppy, harddisk, cdrom, network) determining where to obtain/find the boot image.

  ...
  <os>
    <type>hvm</type>
    <loader>/usr/lib/xen/boot/hvmloader</loader>
    <boot dev='hd'/>
  </os>
  ...
type
The content of the type element specifies the type of operating system to be booted in the virtual machine. hvm indicates that the OS is one designed to run on bare metal, so requires full virtualization. linux (badly named!) refers to an OS that supports the Xen 3 hypervisor guest ABI. There are also two optional attributes, arch specifying the CPU architecture to virtualization, and machine referring to the machine type. The Capabilities XML provides details on allowed values for these. Since 0.0.1
loader
The optional loader tag refers to a firmware blob used to assist the domain creation process. At this time, it is only needed by Xen fully virtualized domains. Since 0.1.0
boot
The dev attribute takes one of the values "fd", "hd", "cdrom" or "network" and is used to specify the next boot device to consider. The boot element can be repeated multiple times to setup a priority list of boot devices to try in turn. Since 0.1.3

Host bootloader

Hypervisors employing paravirtualization do not usually emulate a BIOS, and instead the host is responsible to kicking off the operating system boot. This may use a pseudo-bootloader in the host to provide an interface to choose a kernel for the guest. An example is pygrub with Xen.

  ...
  <bootloader>/usr/bin/pygrub</bootloader>
  <bootloader_args>--append single</bootloader_args>
  ...
bootloader
The content of the bootloader element provides a fully qualified path to the bootloader executable in the host OS. This bootloader will be run to choose which kernel to boot. The required output of the bootloader is dependent on the hypervisor in use. Since 0.1.0
bootloader_args
The optional bootloader_args element allows command line arguments to be passed to the bootloader. Since 0.2.3

Direct kernel boot

When installing a new guest OS it is often useful to boot directly from a kernel and initrd stored in the host OS, allowing command line arguments to be passed directly to the installer. This capability is usually available for both para and full virtualized guests.

  ...
  <os>
    <type>hvm</type>
    <loader>/usr/lib/xen/boot/hvmloader</loader>
    <kernel>/root/f8-i386-vmlinuz</kernel>
    <initrd>/root/f8-i386-initrd</initrd>
    <cmdline>console=ttyS0 ks=http://example.com/f8-i386/os/</cmdline>
  </os>
  ...
type
This element has the same semantics as described earlier in the BIOS boot section
loader
This element has the same semantics as described earlier in the BIOS boot section
kernel
The contents of this element specify the fully-qualified path to the kernel image in the host OS.
initrd
The contents of this element specify the fully-qualified path to the (optional) ramdisk image in the host OS.
cmdline
The contents of this element specify arguments to be passed to the kernel (or installer) at boottime. This is often used to specify an alternate primary console (eg serial port), or the installation media source / kickstart file

Basic resources

  ...
  <memory>524288</memory>
  <currentMemory>524288</currentMemory>
  <memoryBacking>
    <hugepages/>
  </memoryBacking>
  <vcpu>1</vcpu>
  ...
memory
The maximum allocation of memory for the guest at boot time. The units for this value are kilobytes (i.e. blocks of 1024 bytes)
currentMemory
The actual allocation of memory for the guest. This value be less than the maximum allocation, to allow for ballooning up the guests memory on the fly. If this is omitted, it defaults to the same value as the memory element
memoryBacking
The optional memoryBacking element, may have an hugepages element set within it. This tells the hypervisor that the guest should have its memory allocated using hugepages instead of the normal native page size.
vcpu
The content of this element defines the number of virtual CPUs allocated for the guest OS.

CPU model and topology

Requirements for CPU model, its features and topology can be specified using the following collection of elements. Since 0.7.5

  ...
  <cpu match='exact'>
    <model>core2duo</model>
    <topology sockets='1' cores='2' threads='1'/>
    <feature policy='disable' name='lahf_lm'/>
  </cpu>
  ...

In case no restrictions need to be put on CPU model and its features, a simpler cpu element can be used. Since 0.7.6

  ...
  <cpu>
    <topology sockets='1' cores='2' threads='1'/>
  </cpu>
  ...
cpu
The cpu element is the main container for describing guest CPU requirements. Its match attribute specified how strictly has the virtual CPU provided to the guest match these requirements. Since 0.7.6 the match attribute can be omitted if topology is the only element within cpu. Possible values for the match attribute are:
minimum
The specified CPU model and features describes the minimum requested CPU.
exact
The virtual CPU provided to the guest will exactly match the specification
strict
The guest will not be created unless the host CPU does exactly match the specification.
model
The content of the model element specifies CPU model requested by the guest. The list of available CPU models and their definition can be found in cpu_map.xml file installed in libvirt's data directory.
topology
The topology element specifies requested topology of virtual CPU provided to the guest. Three non-zero values have to be given for sockets, cores, and threads: total number of CPU sockets, number of cores per socket, and number of threads per core, respectively.
feature
The cpu element can contain zero or more elements used to fine-tune features provided by the selected CPU model. The list of known feature names can be found in the same file as CPU models. The meaning of each feature element depends on its policy attribute, which has to be set to one of the following values:
force
The virtual CPU will claim the feature is supported regardless of it being supported by host CPU.
require
Guest creation will fail unless the feature is supported by host CPU.
optional
The feature will be supported by virtual CPU if and only if it is supported by host CPU.
disable
The feature will not be supported by virtual CPU.
forbid
Guest creation will fail if the feature is supported by host CPU.

Lifecycle control

It is sometimes necessary to override the default actions taken when a guest OS triggers a lifecycle operation. The following collections of elements allow the actions to be specified. A common use case is to force a reboot to be treated as a poweroff when doing the initial OS installation. This allows the VM to be re-configured for the first post-install bootup.

  ...
  <on_poweroff>destroy</on_poweroff>
  <on_reboot>restart</on_reboot>
  <on_crash>restart</on_crash>
  ...
on_poweroff
The content of this element specifies the action to take when the guest requests a poweroff.
on_reboot
The content of this element specifies the action to take when the guest requests a reboot.
on_crash
The content of this element specifies the action to take when the guest crashes.

Each of these states allow for the same four possible actions.

destroy
The domain will be terminated completely and all resources released
restart
The domain will be terminated, and then restarted with the same configuration
preserve
The domain will be terminated, and its resource preserved to allow analysis.
rename-restart
The domain will be terminated, and then restarted with a new name

Hypervisor features

Hypervisors may allow certain CPU / machine features to be toggled on/off.

  ...
  <features>
    <pae/>
    <acpi/>
    <apic/>
  </features>
  ...

All features are listed within the features element, omitting a togglable feature tag turns it off. The available features can be found by asking for the capabilities XML, but a common set for fully virtualized domains are:

pae
Physical address extension mode allows 32-bit guests to address more than 4 GB of memory.
acpi
ACPI is useful for power management, for example, with KVM guests it is required for graceful shutdown to work.

Time keeping

The guest clock is typically initialized from the host clock. Most operating systems expect the hardware clock to be kept in UTC, and this is the default. Windows, however, expects it to be in so called 'localtime'.

  ...
  <clock offset="localtime"/>
  ...
clock

The offset attribute takes three possible values, allowing fine grained control over how the guest clock is synchronized to the host. NB, not all hypervisors support all modes.

utc
The guest clock will always be synchronized to UTC when booted
localtime
The guest clock will be synchronized to the host's configured timezone when booted, if any.
timezone
The guest clock will be synchronized to the requested timezone using the timezone attribute.
variable
The guest clock will have an arbitrary offset applied relative to UTC. The delta relative to UTC is specified in seconds, using the adjustment attribute. The guest is free to adjust the RTC over time an expect that it will be honoured at next reboot. This is in contrast to 'utc' mode, where the RTC adjustments are lost at each reboot.

NB, at time of writing, only QEMU supports the variable clock mode, or custom timezones.

Devices

The final set of XML elements are all used to describe devices provided to the guest domain. All devices occur as children of the main devices element. Since 0.1.3

  ...
  <devices>
    <emulator>/usr/lib/xen/bin/qemu-dm</emulator>
  </devices>
  ...
emulator
The contents of the emulator element specify the fully qualified path to the device model emulator binary. The capabilities XML specifies the recommended default emulator to use for each particular domain type / architecture combination.

Hard drives, floppy disks, CDROMs

Any device that looks like a disk, be it a floppy, harddisk, cdrom, or paravirtualized driver is specified via the disk element.

  ...
  <devices>
    <disk type='file'>
      <driver name="tap" type="aio" cache="default">
      <source file='/var/lib/xen/images/fv0'/>
      <target dev='hda' bus='ide'/>
      <encryption type='...'>
        ...
      </encryption>
      <shareable/>
    </disk>
  </devices>
  ...
disk
The disk element is the main container for describing disks. The type attribute is either "file" or "block" and refers to the underlying source for the disk. The optional device attribute indicates how the disk is to be exposed to the guest OS. Possible values for this attribute are "floppy", "disk" and "cdrom", defaulting to "disk". Since 0.0.3; "device" attribute since 0.1.4
source
If the disk type is "file", then the file attribute specifies the fully-qualified path to the file holding the disk. If the disk type is "block", then the dev attribute specifies the path to the host device to serve as the disk. Since 0.0.3
target
The target element controls the bus / device under which the disk is exposed to the guest OS. The dev attribute indicates the "logical" device name. The actual device name specified is not guaranteed to map to the device name in the guest OS. Treat it as a device ordering hint. The optional bus attribute specifies the type of disk device to emulate; possible values are driver specific, with typical values being "ide", "scsi", "virtio", "xen" or "usb". If omitted, the bus type is inferred from the style of the device name. eg, a device named 'sda' will typically be exported using a SCSI bus. Since 0.0.3; bus attribute since 0.4.3; "usb" attribute value since after 0.4.4
driver
If the hypervisor supports multiple backend drivers, then the optional driver element allows them to be selected. The name attribute is the primary backend driver name, while the optional type attribute provides the sub-type. The optional cache attribute controls the cache mechanism, possible values are "default", "none", "writethrough" and "writeback". Since 0.1.8
encryption
If present, specifies how the volume is encrypted. See the Storage Encryption page for more information.
shareable
If present, this indicates the device is expected to be shared between domains (assuming the hypervisor and OS support this), which means that caching should be deactivated for that device.

USB and PCI devices

USB and PCI devices attached to the host can be passed through to the guest using the hostdev element. since after 0.4.4 for USB and 0.6.0 for PCI (KVM only):

  ...
  <devices>
    <hostdev mode='subsystem' type='usb'>
      <source>
        <vendor id='0x1234'/>
        <product id='0xbeef'/>
      </source>
    </hostdev>
  </devices>
  ...

or:

  ...
  <devices>
    <hostdev mode='subsystem' type='pci'>
      <source>
        <address bus='0x06' slot='0x02' function='0x0'/>
      </source>
    </hostdev>
  </devices>
  ...
hostdev
The hostdev element is the main container for describing host devices. For usb device passthrough mode is always "subsystem" and type is "usb" for an USB device and "pci" for a PCI device..
source
The source element describes the device as seen from the host. The USB device can either be addressed by vendor / product id using the vendor and product elements or by the device's address on the hosts using the address element. PCI devices on the other hand can only be described by their address
vendor, product
The vendor and product elements each have an id attribute that specifies the USB vendor and product id. The ids can be given in decimal, hexadecimal (starting with 0x) or octal (starting with 0) form.
address
The address element for USB devices has a bus and device attribute to specify the USB bus and device number the device appears at on the host. The values of these attributes can be given in decimal, hexadecimal (starting with 0x) or octal (starting with 0) form. For PCI devices the element carries 3 attributes allowing to designate the device as can be found with the lspci or with virsh nodedev-list. The bus attribute allows the hexadecimal values 0 to ff, the slot attribute allows the hexadecimal values 0 to 1f, and the function attribute allows the hexadecimal values 0 to 7. There is also an optional domain attribute for the PCI domain, with hexadecimal values 0 to ffff, but it is currently not used by qemu.

Network interfaces

  ...
  <devices>
    <interface type='bridge'>
      <source bridge='xenbr0'/>
      <mac address='00:16:3e:5d:c7:9e'/>
      <script path='vif-bridge'/>
    </interface>
  </devices>
  ...
Virtual network

This is the recommended config for general guest connectivity on hosts with dynamic / wireless networking configs

Provides a virtual network using a bridge device in the host. Depending on the virtual network configuration, the network may be totally isolated, NAT'ing to an explicit network device, or NAT'ing to the default route. DHCP and DNS are provided on the virtual network in all cases and the IP range can be determined by examining the virtual network config with 'virsh net-dumpxml [networkname]'. There is one virtual network called 'default' setup out of the box which does NAT'ing to the default route and has an IP range of 192.168.22.0/255.255.255.0. Each guest will have an associated tun device created with a name of vnetN, which can also be overridden with the <target> element (see overriding the target element).

  ...
  <devices>
    <interface type='network'>
      <source network='default'/>
    </interface>
    ...
    <interface type='network'>
      <source network='default'/>
      <target dev='vnet7'/>
      <mac address="11:22:33:44:55:66"/>
    </interface>
  </devices>
  ...
Bridge to LAN

This is the recommended config for general guest connectivity on hosts with static wired networking configs

Provides a bridge from the VM directly onto the LAN. This assumes there is a bridge device on the host which has one or more of the hosts physical NICs enslaved. The guest VM will have an associated tun device created with a name of vnetN, which can also be overridden with the <target> element (see overriding the target element). The tun device will be enslaved to the bridge. The IP range / network configuration is whatever is used on the LAN. This provides the guest VM full incoming & outgoing net access just like a physical machine.

  ...
  <devices>
    <interface type='bridge'>
      <source bridge='br0'/>
    </interface>
    ...
    <interface type='bridge'>
      <source bridge='br0'/>
      <target dev='vnet7'/>
      <mac address="11:22:33:44:55:66"/>
    </interface>
  </devices>
  ...
Userspace SLIRP stack

Provides a virtual LAN with NAT to the outside world. The virtual network has DHCP & DNS services and will give the guest VM addresses starting from 10.0.2.15. The default router will be 10.0.2.2 and the DNS server will be 10.0.2.3. This networking is the only option for unprivileged users who need their VMs to have outgoing access.

  ...
  <devices>
    <interface type='user'/>
    ...
    <interface type='user'>
      <mac address="11:22:33:44:55:66"/>
    </interface>
  </devices>
  ...
Generic ethernet connection

Provides a means for the administrator to execute an arbitrary script to connect the guest's network to the LAN. The guest will have a tun device created with a name of vnetN, which can also be overridden with the <target> element. After creating the tun device a shell script will be run which is expected to do whatever host network integration is required. By default this script is called /etc/qemu-ifup but can be overridden.

  ...
  <devices>
    <interface type='ethernet'/>
    ...
    <interface type='ethernet'>
      <target dev='vnet7'/>
      <script path='/etc/qemu-ifup-mynet'/>
    </interface>
  </devices>
  ...
Direct attachment to physical interface

Provides direct attachment of the virtual machine's NIC to the given physial interface of the host. Since 0.7.7 (QEMU and KVM only)
This setup requires the Linux macvtap driver to be available. (Since Linux 2.6.34.) One of the modes 'vepa' ( 'Virtual Ethernet Port Aggregator'), 'bridge' or 'private' can be chosen for the operation mode of the macvtap device, 'vepa' being the default mode. The individual modes cause the delivery of packets to behave as follows:

vepa
All VMs' packets are sent to the external bridge. Packets whose destination is a VM on the same host as where the packet originates from are sent back to the host by the VEPA capable bridge (today's bridges are typically not VEPA capable).
bridge
Packets whose destination is on the same host as where they originate from are directly delivered to the target macvtap device. Both origin and destination devices need to be in bridge mode for direct delivery. If either one of them is in vepa mode, a VEPA capable bridge is required.
private
All packets are sent to the external bridge and will only be delivered to a target VM on the same host if they are sent through an external router or gateway and that device sends them back to the host. This procedure is followed if either the source or destination device is in private mode.
  ...
  <devices>
    <interface type='direct'/>
    ...
    <interface type='direct'>
      <source dev='eth0' mode='vepa'/>
    </interface>
  </devices>
  ...
Multicast tunnel

A multicast group is setup to represent a virtual network. Any VMs whose network devices are in the same multicast group can talk to each other even across hosts. This mode is also available to unprivileged users. There is no default DNS or DHCP support and no outgoing network access. To provide outgoing network access, one of the VMs should have a 2nd NIC which is connected to one of the first 4 network types and do the appropriate routing. The multicast protocol is compatible with that used by user mode linux guests too. The source address used must be from the multicast address block.

  ...
  <devices>
    <interface type='mcast'>
      <source address='230.0.0.1' port='5558'/>
    </interface>
  </devices>
  ...
TCP tunnel

A TCP client/server architecture provides a virtual network. One VM provides the server end of the network, all other VMS are configured as clients. All network traffic is routed between the VMs via the server. This mode is also available to unprivileged users. There is no default DNS or DHCP support and no outgoing network access. To provide outgoing network access, one of the VMs should have a 2nd NIC which is connected to one of the first 4 network types and do the appropriate routing.

  ...
  <devices>
    <interface type='server'>
      <source address='192.168.0.1' port='5558'/>
    </interface>
    ...
    <interface type='client'>
    <source address='192.168.0.1' port='5558'/>
    </interface>
  </devices>
  ...
Setting the NIC model
  ...
  <devices>
    <interface type='network'>
      <source network='default'/>
      <target dev='vnet1'/>
      <model type='ne2k_pci'/>
    </interface>
  </devices>
  ...

For hypervisors which support this, you can set the model of emulated network interface card.

The values for type aren't defined specifically by libvirt, but by what the underlying hypervisor supports (if any). For QEMU and KVM you can get a list of supported models with these commands:

qemu -net nic,model=? /dev/null
qemu-kvm -net nic,model=? /dev/null

Typical values for QEMU and KVM include: ne2k_isa i82551 i82557b i82559er ne2k_pci pcnet rtl8139 e1000 virtio

Overriding the target element
  ...
  <devices>
    <interface type='network'>
      <source network='default'/>
      <target dev='vnet1'/>
    </interface>
  </devices>
  ...

If no target is specified, certain hypervisors will automatically generate a name for the created tun device. This name can be manually specifed, however the name must not start with either 'vnet' or 'vif', which are prefixes reserved by libvirt and certain hypervisors. Manually specified targets using these prefixes will be ignored.

Input devices

Input devices allow interaction with the graphical framebuffer in the guest virtual machine. When enabling the framebuffer, an input device is automatically provided. It may be possible to add additional devices explicitly, for example, to provide a graphics tablet for absolute cursor movement.

  ...
  <devices>
    <input type='mouse' bus='usb'/>
  </devices>
  ...
input
The input element has one mandatory attribute, the type whose value can be either 'mouse' or 'tablet'. The latter provides absolute cursor movement, while the former uses relative movement. The optional bus attribute can be used to refine the exact device type. It takes values "xen" (paravirtualized), "ps2" and "usb".

Graphical framebuffers

A graphics device allows for graphical interaction with the guest OS. A guest will typically have either a framebuffer or a text console configured to allow interaction with the admin.

  ...
  <devices>
    <graphics type='sdl' display=':0.0'/>
    <graphics type='vnc' port='5904'/>
    <graphics type='rdp' autoport='yes' multiUser='yes' />
    <graphics type='desktop' fullscreen='yes'/>
  </devices>
  ...
graphics
The graphics element has a mandatory type attribute which takes the value "sdl", "vnc", "rdp" or "desktop":
"sdl"
This displays a window on the host desktop, it can take 3 optional arguments: a display attribute for the display to use, an xauth attribute for the authentication identifier, and an optional fullscreen attribute accepting values 'yes' or 'no'.
"vnc"
Starts a VNC server. The port attribute specifies the TCP port number (with -1 as legacy syntax indicating that it should be auto-allocated). The autoport attribute is the new preferred syntax for indicating autoallocation of the TCP port to use. The listen attribute is an IP address for the server to listen on. The passwd attribute provides a VNC password in clear text. The keymap attribute specifies the keymap to use.
"rdp"
Starts a RDP server. The port attribute specifies the TCP port number (with -1 as legacy syntax indicating that it should be auto-allocated). The autoport attribute is the new preferred syntax for indicating autoallocation of the TCP port to use. The replaceUser attribute is a boolean deciding whether multiple simultaneous connections to the VM are permitted. The multiUser whether the existing connection must be dropped and a new connection must be established by the VRDP server, when a new client connects in single connection mode.
"desktop"
This value is reserved for VirtualBox domains for the moment. It displays a window on the host desktop, similarly to "sdl", but using the VirtualBox viewer. Just like "sdl", it accepts the optional attributes display and fullscreen.

Video devices

A video device.

  ...
  <devices>
    <video>
      <model type='vga' vram='8192' heads='1'>
        <acceleration accel3d='yes' accel3d='yes'/>
      </model>
    </video>
  </devices>
  ...
video
The video element is the a container for describing video devices.
model
The model element has a mandatory type attribute which takes the value "vga", "cirrus", "vmvga", "xen" or "vbox". You can also provide the amount of video memory in kilobytes using vram and the number of screen with heads.
acceleration
If acceleration should be enabled (if supported) using the accel3d and accel2d attributes in the acceleration element.

Consoles, serial, parallel & channel devices

A character device provides a way to interact with the virtual machine. Paravirtualized consoles, serial ports, parallel ports and channels are all classed as character devices and so represented using the same syntax.

  ...
  <devices>
    <parallel type='pty'>
      <source path='/dev/pts/2'/>
      <target port='0'/>
    </parallel>
    <serial type='pty'>
      <source path='/dev/pts/3'/>
      <target port='0'/>
    </serial>
    <console type='pty'>
      <source path='/dev/pts/4'/>
      <target port='0'/>
    </console>
    <channel type='unix'>
      <source mode='bind' path='/tmp/guestfwd'/>
      <target type='guestfwd' address='10.0.2.1' port='4600'/>
    </channel>
  </devices>
  ...

In each of these directives, the top-level element name (parallel, serial, console, channel) describes how the device is presented to the guest. The guest interface is configured by the target element.

The interface presented to the host is given in the type attribute of the top-level element. The host interface is configured by the source element.

Guest interface

A character device presents itself to the guest as one of the following types.

Parallel port
  ...
  <devices>
    <parallel type='pty'>
      <source path='/dev/pts/2'/>
      <target port='0'/>
    </parallel>
  </devices>
  ...

target can have a port attribute, which specifies the port number. Ports are numbered starting from 1. There are usually 0, 1 or 2 parallel ports.

Serial port
  ...
  <devices>
    <serial type='pty'>
      <source path='/dev/pts/3'/>
      <target port='0'/>
    </serial>
  </devices>
  ...

target can have a port attribute, which specifies the port number. Ports are numbered starting from 1. There are usually 0, 1 or 2 serial ports.

Console

This represents the primary console. This can be the paravirtualized console with Xen guests, or duplicates the primary serial port for fully virtualized guests without a paravirtualized console.

  ...
  <devices>
    <console type='pty'>
      <source path='/dev/pts/4'/>
      <target port='0'/>
    </console>
  </devices>
  ...

If the console is presented as a serial port, the target element has the same attributes as for a serial port. There is usually only 1 console.

Channel

This represents a private communication channel between the host and the guest.

  ...
  <devices>
    <channel type='unix'>
      <source mode='bind' path='/tmp/guestfwd'/>
      <target type='guestfwd' address='10.0.2.1' port='4600'/>
    </channel>
  </devices>
  ...

This can be implemented in a variety of ways. The specific type of channel is given in the type attribute of the target element. Different channel types have different target attributes.

guestfwd
TCP traffic sent by the guest to a given IP address and port is forwarded to the channel device on the host. The target element must have address and port attributes. Since 0.7.3
Host interface

A character device presents itself to the host as one of the following types.

Domain logfile

This disables all input on the character device, and sends output into the virtual machine's logfile

  ...
  <devices>
    <console type='stdio'>
      <target port='1'>
    </console>
  </devices>
  ...
Device logfile

A file is opened and all data sent to the character device is written to the file.

  ...
  <devices>
    <serial type="file">
      <source path="/var/log/vm/vm-serial.log"/>
      <target port="1"/>
    </serial>
  </devices>
  ...
Virtual console

Connects the character device to the graphical framebuffer in a virtual console. This is typically accessed via a special hotkey sequence such as "ctrl+alt+3"

  ...
  <devices>
    <serial type='vc'>
      <target port="1"/>
    </serial>
  </devices>
  ...
Null device

Connects the character device to the void. No data is ever provided to the input. All data written is discarded.

  ...
  <devices>
    <serial type='null'>
      <target port="1"/>
    </serial>
  </devices>
  ...
Pseudo TTY

A Pseudo TTY is allocated using /dev/ptmx. A suitable client such as 'virsh console' can connect to interact with the serial port locally.

  ...
  <devices>
    <serial type="pty">
      <source path="/dev/pts/3"/>
      <target port="1"/>
    </serial>
  </devices>
  ...

NB special case if <console type='pty'>, then the TTY path is also duplicated as an attribute tty='/dev/pts/3' on the top level <console> tag. This provides compat with existing syntax for <console> tags.

Host device proxy

The character device is passed through to the underlying physical character device. The device types must match, eg the emulated serial port should only be connected to a host serial port - don't connect a serial port to a parallel port.

  ...
  <devices>
    <serial type="dev">
      <source path="/dev/ttyS0"/>
      <target port="1"/>
  </serial>
  </devices>
  ...
Named pipe

The character device writes output to a named pipe. See pipe(7) for more info.

  ...
  <devices>
    <serial type="pipe">
      <source path="/tmp/mypipe"/>
      <target port="1"/>
    </serial>
  </devices>
  ...
TCP client/server

The character device acts as a TCP client connecting to a remote server.

  ...
  <devices>
    <serial type="tcp">
      <source mode="connect" host="0.0.0.0" service="2445"/>
      <protocol type="raw"/>
      <target port="1"/>
    </serial>
  </devices>
   ...

Or as a TCP server waiting for a client connection.

  ...
  <devices>
    <serial type="tcp">
      <source mode="bind" host="127.0.0.1" service="2445"/>
      <protocol type="raw"/>
      <target port="1"/>
    </serial>
  </devices>
  ...

Alternatively you can use telnet instead of raw TCP.

  ...
  <devices>
    <serial type="tcp">
      <source mode="connect" host="0.0.0.0" service="2445"/>
      <protocol type="telnet"/>
      <target port="1"/>
    </serial>
    ...
    <serial type="tcp">
      <source mode="bind" host="127.0.0.1" service="2445"/>
      <protocol type="telnet"/>
      <target port="1"/>
    </serial>
  </devices>
  ...
UDP network console

The character device acts as a UDP netconsole service, sending and receiving packets. This is a lossy service.

  ...
  <devices>
    <serial type="udp">
      <source mode="bind" host="0.0.0.0" service="2445"/>
      <source mode="connect" host="0.0.0.0" service="2445"/>
      <target port="1"/>
    </serial>
  </devices>
  ...
UNIX domain socket client/server

The character device acts as a UNIX domain socket server, accepting connections from local clients.

  ...
  <devices>
    <serial type="unix">
      <source mode="bind" path="/tmp/foo"/>
      <target port="1"/>
    </serial>
  </devices>
  ...

Sound devices

A virtual sound card can be attached to the host via the sound element. Since 0.4.3

  ...
  <devices>
    <sound model='es1370'/>
  </devices>
  ...
sound
The sound element has one mandatory attribute, model, which specifies what real sound device is emulated. Valid values are specific to the underlying hypervisor, though typical choices are 'es1370', 'sb16', and 'ac97' ('ac97' only since 0.6.0)

Watchdog device

A virtual hardware watchdog device can be added to the guest via the watchdog element. Since 0.7.3, QEMU and KVM only

The watchdog device requires an additional driver and management daemon in the guest. Just enabling the watchdog in the libvirt configuration does not do anything useful on its own.

Currently libvirt does not support notification when the watchdog fires. This feature is planned for a future version of libvirt.

  ...
  <devices>
    <watchdog model='i6300esb'/>
  </devices>
  ...
  ...
  <devices>
    <watchdog model='i6300esb' action='poweroff'/>
  </devices>
</domain>
model

The required model attribute specifies what real watchdog device is emulated. Valid values are specific to the underlying hypervisor.

QEMU and KVM support:

  • 'i6300esb' — the recommended device, emulating a PCI Intel 6300ESB
  • 'ib700' — emulating an ISA iBase IB700
action

The optional action attribute describes what action to take when the watchdog expires. Valid values are specific to the underlying hypervisor.

QEMU and KVM support:

  • 'reset' — default, forcefully reset the guest
  • 'shutdown' — gracefully shutdown the guest (not recommended)
  • 'poweroff' — forcefully power off the guest
  • 'pause' — pause the guest
  • 'none' — do nothing

Note that the 'shutdown' action requires that the guest is responsive to ACPI signals. In the sort of situations where the watchdog has expired, guests are usually unable to respond to ACPI signals. Therefore using 'shutdown' is not recommended.

Example configs

Example configurations for each driver are provide on the driver specific pages listed below