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
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.
<domain type='xen' id='3'> <name>fv0</name> <uuid>4dea22b31d52d8f32516782e98ab3fa0</uuid> <description>Some human readable description</description> ...
namename 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 0.0.1uuiduuid 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 0.8.7descriptiondescription 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 0.7.2There are a number of different ways to boot virtual machines each with their own pros and cons.
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>
...
typetype 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 0.0.1loaderloader 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 0.1.0bootdev 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
bootmenuenable attribute can be either "yes" or "no".
If not specified, the hypervisor default is used.
Since 0.8.3
smbiosmode 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
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> ...
bootloaderbootloader 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 0.1.0bootloader_argsbootloader_args element allows
command line arguments to be passed to the bootloader.
Since 0.2.3
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>
...
typeloaderkernelinitrdcmdline
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:
smbiossmbios 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:
biossystemuuid
element, the two values must match.
...
<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>
<cputune>
<vcpupin vcpu="0" cpuset="1-4,^2"/>
<vcpupin vcpu="1" cpuset="0,1"/>
<vcpupin vcpu="2" cpuset="2,3"/>
<vcpupin vcpu="3" cpuset="0,4"/>
<shares>2048</shares>
</cputune>
<numatune>
<memory mode="strict" nodeset="1-4,^3"/>
</numatune>
...
memorycurrentMemorymemory elementmemoryBackingmemoryBacking 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.blkiotuneblkiotune element provides the ability
to tune Blkio cgroup tunable parameters for the domain. If this is
omitted, it defaults to the OS provided defaults.weightweight element is the I/O weight of the
guest. The value should be in range [100, 1000].memtunememtune element provides details
regarding the memory tunable parameters for the domain. If this is
omitted, it defaults to the OS provided defaults. For QEMU/KVM, the
parameters are applied to the QEMU process as a whole. Thus, when
counting them, one needs to add up guest RAM, guest video RAM, and
some memory overhead of QEMU itself. The last piece is hard to
determine so one needs guess and try.hard_limithard_limit element is the maximum memory
the guest can use. The units for this value are kilobytes (i.e. blocks
of 1024 bytes)soft_limitsoft_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_limitswap_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 providedmin_guaranteemin_guarantee element is the guaranteed
minimum memory allocation for the guest. The units for this value are
kilobytes (i.e. blocks of 1024 bytes)vcpucpuset 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.
cputunecputune element provides details
regarding the cpu tunable parameters for the domain.
Since 0.9.0
vcpupinvcpupin element specifies which of host
physical CPUS the domain VCPU will be pinned to. If this is ommited,
each VCPU pinned to all the physical CPUS by default. It contains two
required attributes, the attribute vcpu specifies vcpu id,
and the attribute cpuset is same as attribute cpuset
of element vcpu. (NB: Only qemu driver support)
Since 0.9.0
sharesshares element specifies the proportional
weighted share for the domain. If this is ommited, it defaults to
the OS provided defaults. NB, There is no unit for the value, it's a relative
measure based on the setting of other VM, e.g. A VM configured with value
2048 will get twice as much CPU time as a VM configured with value 1024.
Since 0.9.0
numatunenumatune element provides details of
how to tune the performance of a NUMA host via controlling NUMA policy
for domain process. NB, only supported by QEMU driver.
Since 0.9.3
memorymemory element specify how to allocate memory
for the domain process on a NUMA host. It contains two attributes,
attribute mode is either 'interleave', 'strict', or 'preferred',
attribute nodeset specifies the NUMA nodes, it leads same
syntax with attribute cpuset of element vcpu.
Since 0.9.3
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>
...
cpucpu 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:
minimumexactstrictmatch
attribute can be omitted and will default to exact.
modelmodel 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.vendorvendor 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.topologytopology 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.featurecpu 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:
forcerequireoptionaldisableforbidpolicy
attribute can be omitted and will default to require.
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_poweroffon_rebooton_crashEach of these states allow for the same four possible actions.
destroyrestartpreserverename-restarton_crash supports these additional actions since 0.8.4.
coredump-destroycoredump-restartHypervisors 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:
paeacpihapThe 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>
...
clockThe 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.
utclocaltimetimezonetimezone attribute.
Since 0.7.7
variableadjustment 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.
namename attribute selects which timer is
being modified, and can be one of "platform", "pit",
"rtc", "hpet", or "tsc".
tracktrack attribute specifies what the timer
tracks, and can be "boot", "guest", or "wall".
Only valid for name="rtc"
or name="platform".
tickpolicytickpolicy 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.
catchupcatchup element has three optional
attributes, each a positive integer. The attributes
are threshold, slew,
and limit.
frequencyfrequency attribute is an unsigned
integer specifying the frequency at
which name="tsc" runs.
modemode attribute controls how
the name="tsc" timer is managed, and can be
"auto", "native", "emulate", "paravirt", or "smpsafe".
Other timers are always emulated.
presentpresent attribute can be "yes" or "no" to
specify whether a particular timer is available to the guest.
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>
...
emulatoremulator 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.
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" ioeventfd="on"/>
<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>
...
diskdisk 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 0.8.7sourcetype 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. 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 0.0.3targettarget 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 0.4.4drivername attribute selects the primary
backend driver name, while the optional type
attribute provides the sub-type. For example, xen
supports a name of "tap", "tap2", "phy", or "file", with a
type of "aio", while qemu only supports a name of "qemu",
but multiple types including "raw", "bochs", "qcow2", and
"qed".
cache attribute controls the
cache mechanism, possible values are "default", "none",
"writethrough" and "writeback".
Since 0.6.0
error_policy attribute controls
how the hypervisor will behave on an error, possible
values are "stop", "ignore", and "enospace".
Since 0.8.0
io attribute controls specific
policies on I/O; qemu guests support "threads" and
"native". Since 0.8.8
ioeventfd attribute allows users to
set
domain I/O asynchronous handling for disk device.
The default is left to the discretion of the hypervisor.
Accepted values are "on" and "off". Enabling this allows
qemu to execute VM while a separate thread handles I/O.
Typically guests experiencing high system CPU utilization
during I/O will benefit from this. On the other hand,
on overloaded host it could increase guest I/O latency.
Since 0.9.3 (QEMU and KVM only)
In general you should leave this option alone, unless you
are very certain you know what you are doing.
bootorder
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
encryptionshareableserial<serial>WD-WMAP9A966149</serial>.
Since 0.7.1
hosthost 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 |
addressaddress 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.
A directory on the host that can be accessed directly from the guest. since 0.3.3, since 0.8.5 for QEMU/KVM
...
<devices>
<filesystem type='template'>
<source name='my-vm-template'/>
<target dir='/'/>
</filesystem>
<filesystem type='mount' accessmode='passthrough'>
<source dir='/export/to/guest'/>
<target dir='/import/from/host'/>
<readonly/>
</filesystem>
...
</devices>
...
filesystemtype specifies the type of the
source. The possible values are:
type='mount'type if one is not specified.
type='template'type='file'type='block'accessmode
which specifies the security mode for accessing the source
(since 0.8.5). Currently this only works
with type='mount' for the QEMU/KVM driver. The possible
values are:
accessmode='passthrough'source is accessed with the permissions of the
user inside the guest. This is the default accessmode if
one is not specified.
More info
accessmode='mapped'source is accessed with the permissions of the
hypervisor (QEMU process).
More info
accessmode='squash'sourcename attribute must be used with
type='template', and the dir attribute must
be used with type='mount'
targetsource can be accessed in the guest. For
most drivers this is an automatic mount point, but for QEMU/KVM
this is merely an arbitrary string tag that is exported to the
guest as a hint for where to mount.
readonlyreadonly attribute is available but currently
unused.
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.
When using a lock manager, it may be desirable to record device leases against a VM. The lock manager will ensure the VM won't start unless the leases can be acquired.
...
<devices>
...
<lease>
<lockspace>somearea</lockspace>
<key>somekey</key>
<target path='/some/lease/path' offset='1024'/>
</lease>
...
</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>
...
hostdevhostdev 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.sourcevendor 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
addressvendor, productvendor 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.bootorder
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 0.8.8addressaddress 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.
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'<address> sub-element.mode='host-certificates'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'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.
...
<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.
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>
...
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>
...
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>
...
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>
...
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:
vepabridgevepa mode,
a VEPA capable bridge is required.privateprivate mode.passthrough
...
<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.
Please note that IEEE 802.1Qbg requires a non-zero value for the VLAN ID.
manageridtypeidtypeidversioninstanceid
...
<devices>
<interface type='direct'/>
...
<interface type='direct'>
<source dev='eth0.2' mode='vepa'/>
<virtualport type="802.1Qbg">
<parameters managerid="11" typeid="1193047" typeidversion="2" instanceid="09b11c53-8b5c-4eeb-8f00-d84eaa0aaa4f"/>
</virtualport>
</interface>
</devices>
...
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>
...
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>
...
...
<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
...
<devices>
<interface type='network'>
<source network='default'/>
<target dev='vnet1'/>
<model type='virtio'/>
<driver name='vhost' txmode='iothread' ioeventfd='on'/>
</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:
namename 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)
txmodetxmode 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)ioeventfd
...
<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.
...
<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 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>
...
inputinput 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.
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>
...
graphicsgraphics element has a mandatory type
attribute which takes the value "sdl", "vnc", "rdp" or "desktop":
"sdl"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"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.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'/>
<image compression='auto_glz'/>
<streaming mode='filter'/>
<clipboard copypaste='no'/>
</graphics>
Spice supports variable compression settings for audio,
images and streaming, since
0.9.1. These settings are accessible via
the compression attribute in all following
elements: image to set image compression
(accepts auto_glz, auto_lz,
quic, glz, lz,
off), jpeg for JPEG
compression for images over wan
(accepts auto, never,
always), zlib for configuring
wan image compression (accepts auto,
never, always)
and playback for enabling audio stream
compression (accepts on or off).
Streaming mode is set by the streaming
element, settings it's mode attribute to one
of filter, all
or off, since 0.9.2.
Copy & Paste functionality (via Spice agent) is set
by the clipboard element. It is enabled by
default, and can be disabled by setting
the copypaste property
to no, since
0.9.3.
"rdp"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"display
and fullscreen.
A video device.
...
<devices>
<video>
<model type='vga' vram='8192' heads='1'>
<acceleration accel3d='yes' accel3d='yes'/>
</model>
</video>
</devices>
...
videovideo element is the a container for describing
video devices. For backwards compatability, if no video
is set but there is a graphics in domain xml, then libvirt
will add a default video according to the guest type.
For a guest of type "kvm", the default video for it is:
type with value "cirrus", vram with value
"9216", and heads with value "1".
modelmodel 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.
accelerationaccel3d and accel2d attributes in the
acceleration element.
addressaddress sub-element can be used to
tie the video device to a particular PCI slot.
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.
A character device presents itself to the guest as one of the following types.
...
<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 0. There are
usually 0, 1 or 2 parallel ports.
...
<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 0. There are
usually 0, 1 or 2 serial ports.
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.
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.
guestfwdtarget
element must have address and port attributes.
Since 0.7.3virtioname 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 0.7.7spicevmcmain 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 0.8.8A character device presents itself to the host as one of the following types.
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>
...
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>
...
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>
...
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>
...
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.
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>
...
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>
...
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>
...
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>
...
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>
...
A virtual sound card can be attached to the host via the
sound element. Since 0.4.3
...
<devices>
<sound model='es1370'/>
</devices>
...
soundsound 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.
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.
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 configurations for each driver are provide on the driver specific pages listed below