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. It is also possible to provide the UUID via a sysinfo specification. Since 0.0.1, sysinfo since 0.8.7
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'/>
    <boot dev='cdrom'/>
    <bootmenu enable='yes'/>
    <smbios mode='sysinfo'/>
  </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. The boot element cannot be used if per-device boot elements are used (see disks, network interfaces, and USB and PCI devices sections below). Since 0.1.3, per-device boot since 0.8.8
bootmenu
Whether or not to enable an interactive boot menu prompt on guest startup. The enable attribute can be either "yes" or "no". If not specified, the hypervisor default is used. Since 0.8.3
smbios
How to populate SMBIOS information visible in the guest. The mode attribute must be specified, and is either "emulate" (let the hypervisor generate all values), "host" (copy all of Block 0 and Block 1, except for the UUID, from the host's SMBIOS values; the virConnectGetSysinfo call can be used to see what values are copied), or "sysinfo" (use the values in the sysinfo element). If not specified, the hypervisor default is used. Since 0.8.7

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

SMBIOS System Information

Some hypervisors allow control over what system information is presented to the guest (for example, SMBIOS fields can be populated by a hypervisor and inspected via the dmidecode command in the guest). The optional sysinfo element covers all such categories of information. Since 0.8.7

  ...
  <os>
    <smbios mode='sysinfo'/>
    ...
  </os>
  <sysinfo type='smbios'>
    <bios>
      <entry name='vendor'>LENOVO</entry>
    </bios>
    <system>
      <entry name='manufacturer'>Fedora</entry>
      <entry name='vendor'>Virt-Manager</entry>
    </system>
  </sysinfo>
  ...

The sysinfo element has a mandatory attribute type that determine the layout of sub-elements, with supported values of:

smbios
Sub-elements call out specific SMBIOS values, which will affect the guest if used in conjunction with the smbios sub-element of the os element. Each sub-element of sysinfo names a SMBIOS block, and within those elements can be a list of entry elements that describe a field within the block. The following blocks and entries are recognized:
bios
This is block 0 of SMBIOS, with entry names drawn from "vendor", "version", "date", and "release".
system
This is block 1 of SMBIOS, with entry names drawn from "manufacturer", "product", "version", "serial", "uuid", "sku", and "family". If a "uuid" entry is provided alongside a top-level uuid element, the two values must match.

Basic resources

  ...
  <memory>524288</memory>
  <currentMemory>524288</currentMemory>
  <memoryBacking>
    <hugepages/>
  </memoryBacking>
  <blkiotune>
    <weight>800</weight>
  </blkiotune>
  <memtune>
    <hard_limit>1048576</hard_limit>
    <soft_limit>131072</soft_limit>
    <swap_hard_limit>2097152</swap_hard_limit>
    <min_guarantee>65536</min_guarantee>
  </memtune>
  <vcpu cpuset="1-4,^3,6" current="1">2</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 can 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.
blkiotune
The optional blkiotune element provides the ability to tune Blkio cgroup tunable parameters for the domain. If this is omitted, it defaults to the OS provided defaults.
weight
The optional weight element is the I/O weight of the guest. The value should be in range [100, 1000].
memtune
The optional memtune element provides details regarding the memory tunable parameters for the domain. If this is omitted, it defaults to the OS provided defaults.
hard_limit
The optional hard_limit element is the maximum memory the guest can use. The units for this value are kilobytes (i.e. blocks of 1024 bytes)
soft_limit
The optional soft_limit element is the memory limit to enforce during memory contention. The units for this value are kilobytes (i.e. blocks of 1024 bytes)
swap_hard_limit
The optional swap_hard_limit element is the maximum memory plus swap the guest can use. The units for this value are kilobytes (i.e. blocks of 1024 bytes). This has to be more than hard_limit value provided
min_guarantee
The optional min_guarantee element is the guaranteed minimum memory allocation for the guest. The units for this value are kilobytes (i.e. blocks of 1024 bytes)
vcpu
The content of this element defines the maximum number of virtual CPUs allocated for the guest OS, which must be between 1 and the maximum supported by the hypervisor. Since 0.4.4, this element can contain an optional cpuset attribute, which is a comma-separated list of physical CPU numbers that virtual CPUs can be pinned to. Each element in that list is either a single CPU number, a range of CPU numbers, or a caret followed by a CPU number to be excluded from a previous range. Since 0.8.5, the optional attribute current can be used to specify whether fewer than the maximum number of virtual CPUs should be enabled.

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>
    <vendor>Intel</vendor>
    <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.
Since 0.8.5 the match attribute can be omitted and will default to exact.
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.
vendor
Since 0.8.3 the content of the vendor element specifies CPU vendor requested by the guest. If this element is missing, the guest can be run on a CPU matching given features regardless on its vendor. The list of supported vendors can be found in cpu_map.xml.
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.
Since 0.8.5 the policy attribute can be omitted and will default to require.

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

on_crash supports these additional actions since 0.8.4.

coredump-destroy
The crashed domain's core will be dumped, and then the domain will be terminated completely and all resources released
coredump-restart
The crashed domain's core will be dumped, and then the domain will be restarted with the same configuration

Hypervisor features

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

  ...
  <features>
    <pae/>
    <acpi/>
    <apic/>
    <hap/>
  </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.
hap
Enable use of Hardware Assisted Paging if available in the hardware.

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">
    <timer name="rtc" tickpolicy="catchup" track="guest">
      <catchup threshold=123 slew=120 limit=10000/>
    </timer>
    <timer name="pit" tickpolicy="none"/>
  </clock>
  ...
clock

The offset attribute takes four 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. Since 0.7.7
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. Since 0.7.7

A clock may have zero or more timersub-elements. Since 0.8.0

timer

Each timer element requires a name attribute, and has other optional attributes that depend on the name specified. Various hypervisors support different combinations of attributes.

name
The name attribute selects which timer is being modified, and can be one of "platform", "pit", "rtc", "hpet", or "tsc".
track
The track attribute specifies what the timer tracks, and can be "boot", "guest", or "wall". Only valid for name="rtc" or name="platform".
tickpolicy
The tickpolicy attribute determines how missed ticks in the guest are handled, and can be "delay", "catchup", "merge", or "discard". If the policy is "catchup", there can be further details in the catchup sub-element.
catchup
The catchup element has three optional attributes, each a positive integer. The attributes are threshold, slew, and limit.
frequency
The frequency attribute is an unsigned integer specifying the frequency at which name="tsc" runs.
mode
The mode attribute controls how the name="tsc" timer is managed, and can be "auto", "native", "emulate", "paravirt", or "smpsafe". Other timers are always emulated.
present
The present attribute can be "yes" or "no" to specify whether a particular timer is available to the guest.

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'/>
      <boot order='2'/>
      <encryption type='...'>
        ...
      </encryption>
      <shareable/>
      <serial>
        ...
      </serial>
    </disk>
      ...
    <disk type='network'>
      <driver name="qemu" type="raw" io="threads"/>
      <source protocol="sheepdog" name="image_name">
        <host name="hostname" port="7000"/>
      </source>
      <target dev="hdb" bus="ide"/>
      <boot order='1'/>
      <address type='drive' controller='0' bus='1' unit='0'/>
    </disk>
  </devices>
  ...
disk
The disk element is the main container for describing disks. The type attribute is either "file", "block", "dir", or "network" 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; "network" attribute since 0.8.7
source
If the disk type is "file", then the 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. If the disk type is "network", then the protocol attribute specifies the protocol to access to the requested image; possible values are "nbd", "rbd", and "sheepdog". If the protocol attribute is "rbd" or "sheepdog", an additional attribute name is mandatory to specify which image to be used. When the disk type is "network", the source may have zero or more host sub-elements used to specify the hosts to connect. 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
The optional driver element allows specifying further details related to the hypervisor driver used to provide the disk. Since 0.1.8
boot
Specifies that the disk is bootable. The order attribute determines the order in which devices will be tried during boot sequence. The per-device boot elements cannot be used together with general boot elements in BIOS bootloader section. Since 0.8.8
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.
serial
If present, this specify serial number of virtual hard drive. For example, it may look as <serial>WD-WMAP9A966149</serial>. Since 0.7.1
host
The host element has two attributes "name" and "port", which specify the hostname and the port number. The meaning of this element and the number of the elements depend on the protocol attribute.
Protocol Meaning Number of hosts
nbd a server running nbd-server only one
rbd monitor servers of RBD one or more
sheepdog one of the sheepdog servers (default is localhost:7000) zero or one
address
If present, the address element ties the disk to a given slot of a controller (the actual <controller> device can often be inferred by libvirt, although it can be explicitly specified). The type attribute is mandatory, and is typically "pci" or "drive". For a "pci" controller, additional attributes for bus, slot, and function must be present, as well as an optional domain. For a "drive" controller, additional attributes controller, bus, and unit are available, each defaulting to 0.

Controllers

Many devices that have an <address> sub-element are designed to work with a controller to manage related devices. Normally, libvirt can automatically infer such controllers without requiring explicit XML markup, but sometimes it is necessary to provide an explicit controller element.

  ...
  <devices>
    <controller type='ide' index='0'/>
    <controller type='virtio-serial' index='0' ports='16' vectors='4'/>
    <controller type='virtio-serial' index='1'>
      <address type='pci' domain='0x0000' bus='0x00' slot='0x0a' function='0x0'/>
    </controller>
    ...
  </devices>
  ...

Each controller has a mandatory attribute type, which must be one of "ide", "fdc", "scsi", "sata", "ccid", or "virtio-serial", and a mandatory attribute index which is the decimal integer describing in which order the bus controller is encountered (for use in controller attributes of <address> elements). The "virtio-serial" controller has two additional optional attributes ports and vectors, which control how many devices can be connected through the controller. A "scsi" controller has an optional attribute model, which is one of "auto", "buslogic", "lsilogic", "lsias1068", or "vmpvscsi".

For controllers that are themselves devices on a PCI or USB bus, an optional sub-element <address> can specify the exact relationship of the controller to its master bus, with semantics like any other device's address sub-element.

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>
      <boot order='2'/>
    </hostdev>
  </devices>
  ...

or:

  ...
  <devices>
    <hostdev mode='subsystem' type='pci' managed='yes'>
      <source>
        <address bus='0x06' slot='0x02' function='0x0'/>
      </source>
      <boot order='1'/>
    </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 a USB device and "pci" for a PCI device. When managed is "yes" for a PCI device, it is detached from the host before being passed on to the guest.
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.
boot
Specifies that the device is bootable. The order attribute determines the order in which devices will be tried during boot sequence. The per-device boot elements cannot be used together with general boot elements in BIOS bootloader section. Since 0.8.8
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.

Smartcard devices

A virtual smartcard device can be supplied to the guest via the smartcard element. A USB smartcard reader device on the host cannot be used on a guest with simple device passthrough, since it will then not be available on the host, possibly locking the host computer when it is "removed". Therefore, some hypervisors provide a specialized virtual device that can present a smartcard interface to the guest, with several modes for describing how credentials are obtained from the host or even a from a channel created to a third-party smartcard provider. Since 0.8.8

  ...
  <devices>
    <smartcard mode='host'/>
    <smartcard mode='host-certificates'>
      <certificate>cert1</certificate>
      <certificate>cert2</certificate>
      <certificate>cert3</certificate>
      <database>/etc/pki/nssdb/</database>
    </smartcard>
    <smartcard mode='passthrough' type='tcp'>
      <source mode='bind' host='127.0.0.1' service='2001'/>
      <protocol type='raw'/>
      <address type='ccid' controller='0' slot='0'/>
    </smartcard>
    <smartcard mode='passthrough' type='spicevmc'/>
  </devices>
  ...

The <smartcard> element has a mandatory attribute mode. The following modes are supported; in each mode, the guest sees a device on its USB bus that behaves like a physical USB CCID (Chip/Smart Card Interface Device) card.

mode='host'
The simplest operation, where the hypervisor relays all requests from the guest into direct access to the host's smartcard via NSS. No other attributes or sub-elements are required. See below about the use of an optional <address> sub-element.
mode='host-certificates'
Rather than requiring a smartcard to be plugged into the host, it is possible to provide three NSS certificate names residing in a database on the host. These certificates can be generated via the command certutil -d /etc/pki/nssdb -x -t CT,CT,CT -S -s CN=cert1 -n cert1, and the resulting three certificate names must be supplied as the content of each of three <certificate> sub-elements. An additional sub-element <database> can specify the absolute path to an alternate directory (matching the -d option of the certutil command when creating the certificates); if not present, it defaults to /etc/pki/nssdb.
mode='passthrough'
Rather than having the hypervisor directly communicate with the host, it is possible to tunnel all requests through a secondary character device to a third-party provider (which may in turn be talking to a smartcard or using three certificate files). In this mode of operation, an additional attribute type is required, matching one of the supported serial device types, to describe the host side of the tunnel; type='tcp' or type='spicevmc' (which uses the smartcard channel of a SPICE graphics device) are typical. Further sub-elements, such as <source>, may be required according to the given type, although a <target> sub-element is not required (since the consumer of the character device is the hypervisor itself, rather than a device visible in the guest).

Each mode supports an optional sub-element <address>, which fine-tunes the correlation between the smartcard and a ccid bus controller. If present, the element must have an attribute of type='ccid' as well as a bus attribute listing the index of the bus that the smartcard utilizes. An optional slot attribute lists which slot within the bus. For now, qemu only supports at most one smartcard, with an address of bus=0 slot=0.

Network interfaces

  ...
  <devices>
    <interface type='bridge'>
      <source bridge='xenbr0'/>
      <mac address='00:16:3e:5d:c7:9e'/>
      <script path='vif-bridge'/>
      <boot order='1'/>
    </interface>
  </devices>
  ...

There are several possibilities for specifying a network interface visible to the guest. Each subsection below provides more details about common setup options. Additionally, each <interface> element has an optional <address> sub-element that can tie the interface to a particular pci slot, with attribute type='pci' and additional attributes domain, bus, slot, and function as appropriate.

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 192.168.122.0/255.255.255.0. 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="00:11:22:33:44:55"/>
    </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="00:11:22:33:44:55"/>
    </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="00:11:22:33:44:55"/>
    </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>
  ...

The network access of direct attached virtual machines can be managed by the hardware switch to which the physical interface of the host machine is connected to.

The interface can have additional parameters as shown below, if the switch is conforming to the IEEE 802.1Qbg standard. The parameters of the virtualport element are documented in more detail in the IEEE 802.1Qbg standard. The values are network specific and should be provided by the network administrator. In 802.1Qbg terms, the Virtual Station Interface (VSI) represents the virtual interface of a virtual machine.

managerid
The VSI Manager ID identifies the database containing the VSI type and instance definitions. This is an integer value and the value 0 is reserved.
typeid
The VSI Type ID identifies a VSI type characterizing the network access. VSI types are typically managed by network administrator. This is an integer value.
typeidversion
The VSI Type Version allows multiple versions of a VSI Type. This is an integer value.
instanceid
The VSI Instance ID Identifier is generated when a VSI instance (i.e. a virtual interface of a virtual machine) is created. This is a globally unique identifier.
  ...
  <devices>
    <interface type='direct'/>
    ...
    <interface type='direct'>
      <source dev='eth0' mode='vepa'/>
      <virtualport type="802.1Qbg">
        <parameters managerid="11" typeid="1193047" typeidversion="2" instanceid="09b11c53-8b5c-4eeb-8f00-d84eaa0aaa4f"/>
      </virtualport>
    </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

Setting NIC driver-specific options
  ...
  <devices>
    <interface type='network'>
      <source network='default'/>
      <target dev='vnet1'/>
      <model type='virtio'/>
      <driver name='vhost' txmode='iothread'/>
    </interface>
  </devices>
  ...

Some NICs may have tunable driver-specific options. These are set as attributes of the driver sub-element of the interface definition. Currently the following attributes are available for the "virtio" NIC driver:

name
The optional name attribute forces which type of backend driver to use. The value can be either 'qemu' (a user-space backend) or 'vhost' (a kernel backend, which requires the vhost module to be provided by the kernel); an attempt to require the vhost driver without kernel support will be rejected. If this attribute is not present, then the domain defaults to 'vhost' if present, but silently falls back to 'qemu' without error. Since 0.8.8 (QEMU and KVM only)
txmode
The txmode attribute specifies how to handle transmission of packets when the transmit buffer is full. The value can be either 'iothread' or 'timer'. Since 0.8.8 (QEMU and KVM only)

If set to 'iothread', packet tx is all done in an iothread in the bottom half of the driver (this option translates into adding "tx=bh" to the qemu commandline -device virtio-net-pci option).

If set to 'timer', tx work is done in qemu, and if there is more tx data than can be sent at the present time, a timer is set before qemu moves on to do other things; when the timer fires, another attempt is made to send more data.

The resulting difference, according to the qemu developer who added the option is: "bh makes tx more asynchronous and reduces latency, but potentially causes more processor bandwidth contention since the cpu doing the tx isn't necessarily the cpu where the guest generated the packets."

In general you should leave this option alone, unless you are very certain you know what you are doing.
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.

Specifying boot order
  ...
  <devices>
    <interface type='network'>
      <source network='default'/>
      <target dev='vnet1'/>
      <boot order='1'/>
    </interface>
  </devices>
  ...

For hypervisors which support this, you can set exact NIC which should be used for network boot. The order attribute determines the order in which devices will be tried during boot sequence. The per-device boot elements cannot be used together with general boot elements in BIOS bootloader section. Since 0.8.8

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".

The input element has an optional sub-element <address> which can tie the device to a particular PCI slot.

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. It is possible to set a limit on the validity of the password be giving an timestamp passwdValidTo='2010-04-09T15:51:00' assumed to be in UTC. NB, this may not be supported by all hypervisors.

Rather than using listen/port, QEMU supports a socket attribute for listening on a unix domain socket path. Since 0.8.8
"spice"

Starts a SPICE server. The port attribute specifies the TCP port number (with -1 as legacy syntax indicating that it should be auto-allocated), while tlsPort gives an alternative secure port number. The autoport attribute is the new preferred syntax for indicating autoallocation of both port numbers. The listen attribute is an IP address for the server to listen on. The passwd attribute provides a SPICE password in clear text. The keymap attribute specifies the keymap to use. It is possible to set a limit on the validity of the password be giving an timestamp passwdValidTo='2010-04-09T15:51:00' assumed to be in UTC. NB, this may not be supported by all hypervisors. "spice" since 0.8.6.

When SPICE has both a normal and TLS secured TCP port configured, it can be desirable to restrict what channels can be run on each port. This is achieved by adding one or more <channel> elements inside the main <graphics> element. Valid channel names include main, display, inputs, cursor, playback, record; and since 0.8.8: smartcard.

  <graphics type='spice' port='-1' tlsPort='-1' autoport='yes'>
    <channel name='main' mode='secure'/>
    <channel name='record' mode='insecure'/>
  </graphics>
"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", "vbox", or "qxl" (since 0.8.6) depending on the hypervisor features available. 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.
address
The optional address sub-element can be used to tie the video device to a particular PCI slot.

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.

Each character device element has an optional sub-element <address> which can tie the device to a particular controller or PCI slot.

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, virtio console for QEMU/KVM, or duplicates the primary serial port for fully virtualized guests without a paravirtualized console.

A virtio console device is exposed in the guest as /dev/hvc[0-7] (for more information, see http://fedoraproject.org/wiki/Features/VirtioSerial) Since 0.8.3

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

    <!-- KVM virtio console -->
    <console type='pty'>
      <source path='/dev/pts/5'/>
      <target type='virtio' 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>

    <!-- KVM virtio channel -->
    <channel type='pty'>
      <target type='virtio' name='arbitrary.virtio.serial.port.name'/>
    </channel>
    <channel type='spicevmc'>
      <target type='virtio' name='com.redhat.spice.0'/>
    </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
virtio
Paravirtualized virtio channel. Channel is exposed in the guest under /dev/vport*, and if the optional element name is specified, /dev/virtio-ports/$name (for more info, please see http://fedoraproject.org/wiki/Features/VirtioSerial). The optional element address can tie the channel to a particular type='virtio-serial' controller. Since 0.7.7
spicevmc
Paravirtualized SPICE channel. The domain must also have a SPICE server as a graphics device, at which point the host piggy-backs messages across the main channel. The target element must be present, with attribute type='virtio'; an optional attribute name controls how the guest will have access to the channel, and defaults to name='com.redhat.spice.0'. The optional address element can tie the channel to a particular type='virtio-serial' controller. Since 0.8.8
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. Since 0.8.5 you can also use telnets (secure telnet) and tls.

  ...
  <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', 'ac97', and 'ich6' ( 'ac97' only since 0.6.0, 'ich6' only since 0.8.8)

Each sound element has an optional sub-element <address> which can tie the device to a particular PCI slot.

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:

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:

Note 1: 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.

Note 2: the directory to save dump files can be configured by auto_dump_path in file /etc/libvirt/qemu.conf.

Memory balloon device

A virtual memory balloon device is added to all Xen and KVM/QEMU guests. It will be seen as memballoon element. It will be automatically added when appropriate, so there is no need to explicitly add this element in the guest XML unless a specific PCI slot needs to be assigned. Since 0.8.3, Xen, QEMU and KVM only Additionally, since 0.8.4, if the memballoon device needs to be explicitly disabled, model='none' may be used.

Example automatically added device with KVM

  ...
  <devices>
    <memballoon model='virtio'/>
  </devices>
  ...

Example manually added device with static PCI slot 2 requested

  ...
  <devices>
    <watchdog model='virtio'/>
    <address type='pci' domain='0x0000' bus='0x00' slot='0x02' function='0x0'/>
  </devices>
</domain>
model

The required model attribute specifies what type of balloon device is provided. Valid values are specific to the virtualization platform

Example configs

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