Domain XML format
-
Element and attribute overview
- General metadata
- Operating system booting
- SMBIOS System Information
- CPU Allocation
- CPU Tuning
- Memory Allocation
- Memory Backing
- Memory Tuning
- NUMA Node Tuning
- Block I/O Tuning
- CPU model and topology
- Lifecycle control
- Hypervisor features
- Time keeping
-
Devices
- Hard drives, floppy disks, CDROMs
- Filesystems
- Controllers
- Device leases
- USB and PCI devices
- Redirected devices
- Smartcard devices
-
Network interfaces
- Virtual network
- Bridge to LAN
- Userspace SLIRP stack
- Generic ethernet connection
- Direct attachment to physical interface
- Multicast tunnel
- TCP tunnel
- Setting the NIC model
- Setting NIC driver-specific options
- Overriding the target element
- Specifying boot order
- Quality of service
- Modyfing virtual link state
- Input devices
- Hub devices
- Graphical framebuffers
- Video devices
- Consoles, serial, parallel & channel devices
- Sound devices
- Watchdog device
- Memory balloon device
- Security label
- Example configs
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, eg3e3fce45-4f53-4fa7-bb32-11f34168b82b
. If omitted when defining/creating a new machine, a random UUID is generated. It is also possible to provide the UUID via asysinfo
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'/> <bios useserial='yes'/> </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, andmachine
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. Theboot
element can be repeated multiple times to setup a priority list of boot devices to try in turn. Theboot
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; thevirConnectGetSysinfo
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 bios
- This element has attribute
useserial
with possible valuesyes
orno
. It enables or disables Serial Graphics Adapter which allows users to see BIOS messages on a serial port. Therefore, one needs to have serial port defined. Since 0.9.4
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 theos
element. Each sub-element ofsysinfo
names a SMBIOS block, and within those elements can be a list ofentry
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.
CPU Allocation
<domain> ... <vcpu cpuset="1-4,^3,6" current="1">2</vcpu> ... </domain>
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 attributecurrent
can be used to specify whether fewer than the maximum number of virtual CPUs should be enabled.
CPU Tuning
<domain> ... <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> <period>1000000</period> <quota>-1</quota> </cputune> ... </domain>
cputune
-
The optional
cputune
element provides details regarding the cpu tunable parameters for the domain. Since 0.9.0 vcpupin
-
The optional
vcpupin
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 attributevcpu
specifies vcpu id, and the attributecpuset
is same as attributecpuset
of elementvcpu
. (NB: Only qemu driver support) Since 0.9.0 shares
-
The optional
shares
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 period
-
The optional
period
element specifies the enforcement interval(unit: microseconds). Withinperiod
, each vcpu of the domain will not be allowed to consume more thanquota
worth of runtime. The value should be in range [1000, 1000000]. A period with value 0 means no value. (NB: Only qemu driver support) Since 0.9.4 quota
-
The optional
quota
element specifies the maximum allowed bandwidth(unit: microseconds). A domain withquota
as any negative value indicates that the domain has infinite bandwidth, which means that it is not bandwidth controlled. The value should be in range [1000, 18446744073709551] or less than 0. A quota with value 0 means no value. You can use this feature to ensure that all vcpus run at the same speed. (NB: Only qemu driver support) Since 0.9.4
Memory Allocation
<domain> ... <memory>524288</memory> <currentMemory>524288</currentMemory> ... </domain>
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
Memory Backing
<domain> ... <memoryBacking> <hugepages/> </memoryBacking> ... </domain>
memoryBacking
- The optional
memoryBacking
element, may have anhugepages
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.
Memory Tuning
<domain> ... <memtune> <hard_limit>1048576</hard_limit> <soft_limit>131072</soft_limit> <swap_hard_limit>2097152</swap_hard_limit> <min_guarantee>65536</min_guarantee> </memtune> ... </domain>
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. 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_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)
NUMA Node Tuning
<domain> ... <numatune> <memory mode="strict" nodeset="1-4,^3"/> </numatune> ... </domain>
numatune
-
The optional
numatune
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 memory
-
The optional
memory
element specify how to allocate memory for the domain process on a NUMA host. It contains two attributes, attributemode
is either 'interleave', 'strict', or 'preferred', attributenodeset
specifies the NUMA nodes, it leads same syntax with attributecpuset
of elementvcpu
. Since 0.9.3
Block I/O Tuning
<domain> ... <blkiotune> <weight>800</weight> </blkiotune> ... </domain>
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].
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. Itsmatch
attribute specified how strictly has the virtual CPU provided to the guest match these requirements. Since 0.7.6 thematch
attribute can be omitted iftopology
is the only element withincpu
. Possible values for thematch
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.
match
attribute can be omitted and will default toexact
. 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 incpu_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 incpu_map.xml
. topology
- The
topology
element specifies requested topology of virtual CPU provided to the guest. Three non-zero values have to be given forsockets
,cores
, andthreads
: 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 moreelements
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 eachfeature
element depends on itspolicy
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.
policy
attribute can be omitted and will default torequire
.
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 moretimer
sub-elements. Since 0.8.0 timer
-
Each timer element requires a
name
attribute, and has other optional attributes that depend on thename
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 forname="rtc"
orname="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 thecatchup
sub-element.catchup
-
The
catchup
element has three optional attributes, each a positive integer. The attributes arethreshold
,slew
, andlimit
.
frequency
-
The
frequency
attribute is an unsigned integer specifying the frequency at whichname="tsc"
runs. mode
-
The
mode
attribute controls how thename="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' snapshot='external'> <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" event_idx="off"/> <source protocol="sheepdog" name="image_name"> <host name="hostname" port="7000"/> </source> <target dev="hdb" bus="ide"/> <boot order='1'/> <transient/> <address type='drive' controller='0' bus='1' unit='0'/> </disk> <disk type='block' device='cdrom'> <driver name='qemu' type='raw'/> <target def='hdc' bus='ide'/> <readonly/> </disk> </devices> ...
disk
- The
disk
element is the main container for describing disks. Thetype
attribute is either "file", "block", "dir", or "network" and refers to the underlying source for the disk. The optionaldevice
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". The optionalsnapshot
attribute indicates the default behavior of the disk during disk snapshots: "internal" requires a file format such as qcow2 that can store both the snapshot and the data changes since the snapshot; "external" will separate the snapshot from the live data; and "no" means the disk will not participate in snapshots. Read-only disks default to "no", while the default for other disks depends on the hypervisor's capabilities. Some hypervisors allow a per-snapshot choice as well, during domain snapshot creation. Not all snapshot modes are supported; for example,snapshot='yes'
with a transient disk generally does not make sense. Since 0.0.3; "device" attribute since 0.1.4; "network" attribute since 0.8.7; "snapshot" since 0.9.5 source
- If the disk
type
is "file", then thefile
attribute specifies the fully-qualified path to the file holding the disk. If the disktype
is "block", then thedev
attribute specifies the path to the host device to serve as the disk. If the disktype
is "network", then theprotocol
attribute specifies the protocol to access to the requested image; possible values are "nbd", "rbd", and "sheepdog". If theprotocol
attribute is "rbd" or "sheepdog", an additional attributename
is mandatory to specify which image to be used. When the disktype
is "network", thesource
may have zero or morehost
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. Thedev
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 optionalbus
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
-
If the hypervisor supports multiple backend drivers, then
the
name
attribute selects the primary backend driver name, while the optionaltype
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". -
The optional
cache
attribute controls the cache mechanism, possible values are "default", "none", "writethrough", "writeback", and "directsync". "directsync" is like "writethrough", but it bypasses the host page cache. Since 0.6.0 -
The optional
error_policy
attribute controls how the hypervisor will behave on an error, possible values are "stop", "ignore", and "enospace". Since 0.8.0 -
The optional
io
attribute controls specific policies on I/O; qemu guests support "threads" and "native". Since 0.8.8 -
The optional
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. -
The optional
event_idx
attribute controls some aspects of device event processing. The value can be either 'on' or 'off' - if it is on, it will reduce the number of interupts and exits for the guest. The default is determined by QEMU; usually if the feature is supported, default is on. In case there is a situation where this behavior is suboptimal, this attribute provides a way to force the feature off. Since 0.9.5 (QEMU and KVM only) In general you should leave this option alone, unless you are very certain you know what you are doing.
-
If the hypervisor supports multiple backend drivers, then
the
boot
- Specifies that the disk is bootable. The
order
attribute determines the order in which devices will be tried during boot sequence. The per-deviceboot
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.
readonly
- If present, this indicates the device cannot be modified by
the guest. For now, this is the default for disks with
attribute
type='cdrom'
. 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.
transient
- If present, this indicates that changes to the device contents should be reverted automatically when the guest exits. With some hypervisors, marking a disk transient prevents the domain from participating in migration or snapshots. Since 0.9.5
serial
- If present, this specify serial number of virtual hard drive.
For example, it may look
like
<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). Thetype
attribute is mandatory, and is typically "pci" or "drive". For a "pci" controller, additional attributes forbus
,slot
, andfunction
must be present, as well as optionaldomain
andmultifunction
. Multifunction defaults to 'off'; any other value requires QEMU 0.1.3 and libvirt 0.9.7. For a "drive" controller, additional attributescontroller
,bus
, andunit
are available, each defaulting to 0.
Filesystems
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> ...
filesystem
-
The filesystem attribute
type
specifies the type of thesource
. The possible values are:type='mount'
-
A host directory to mount in the guest. Used by LXC,
OpenVZ (since 0.6.2)
and QEMU/KVM (since 0.8.5).
This is the default
type
if one is not specified. type='template'
- OpenVZ filesystem template. Only used by OpenVZ driver.
type='file'
- Currently unused.
type='block'
- Currently unused.
accessmode
which specifies the security mode for accessing the source (since 0.8.5). Currently this only works withtype='mount'
for the QEMU/KVM driver. The possible values are:accessmode='passthrough'
-
The
source
is accessed with the permissions of the user inside the guest. This is the defaultaccessmode
if one is not specified. More info accessmode='mapped'
-
The
source
is accessed with the permissions of the hypervisor (QEMU process). More info accessmode='squash'
- Similar to 'passthrough', the exception is that failure of privileged operations like 'chown' are ignored. This makes a passthrough-like mode usable for people who run the hypervisor as non-root. More info
source
-
The resource on the host that is being accessed in the guest. The
name
attribute must be used withtype='template'
, and thedir
attribute must be used withtype='mount'
target
-
Where the
source
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. readonly
-
An optional
readonly
attribute is available but currently unused.
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", "usb",
"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".
A "usb" controller has an optional attribute model
,
which is one of "piix3-uhci", "piix4-uhci", "ehci",
"ich9-ehci1", "ich9-uhci1", "ich9-uhci2", "ich9-uhci3",
"vt82c686b-uhci" or "pci-ohci".
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 companion controllers have an optional
sub-element <master>
to specify the exact
relationship of the companion to its master controller.
A companion controller is on the same bus as its master, so
the companion index
value should be equal.
... <devices> <controller type='usb' index='0' model='ich9-ehci1'> <address type='pci' domain='0' bus='0' slot='4' function='7'/> </controller> <controller type='usb' index='0' model='ich9-uhci1'> <master startport='0'/> <address type='pci' domain='0' bus='0' slot='4' function='0' multifunction='on'/> </controller> ... </devices> ...
Device leases
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> ...
- lockspace
- This is an arbitrary string, identifying the lockspace within which the key is held. Lock managers may impose extra restrictions on the format, or length of the lockspace name.
- key
- This is an arbitrary string, uniquely identifying the lease to be acquired. Lock managers may impose extra restrictions on the format, or length of the key.
- target
- This is the fully qualified path of the file associated with the lockspace. The offset specifies where the lease is stored within the file. If the lock manager does not require a offset, just pass 0.
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 passthroughmode
is always "subsystem" andtype
is "usb" for a USB device and "pci" for a PCI device. Whenmanaged
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
andproduct
elements or by the device's address on the hosts using theaddress
element. PCI devices on the other hand can only be described by theiraddress
vendor
,product
- The
vendor
andproduct
elements each have anid
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-deviceboot
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 abus
anddevice
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 thelspci
or withvirsh nodedev-list
. Thebus
attribute allows the hexadecimal values 0 to ff, theslot
attribute allows the hexadecimal values 0 to 1f, and thefunction
attribute allows the hexadecimal values 0 to 7. Themultifunction
attribute controls turning on the multifunction bit for a particular slot/function in the PCI control registersince 0.9.7, requires QEMU 0.13.multifunction
defaults to 'off', but should be set to 'on' for function 0 of a slot that will have multiple functions used. There is also an optionaldomain
attribute for the PCI domain, with hexadecimal values 0 to ffff, but it is currently not used by qemu.
Redirected devices
USB device redirection through a character device is supported since after 0.9.5 (KVM only):
... <devices> <redirdev bus='usb' type='tcp'> <source mode='connect' host='localhost' service='4000'/> </redirdev> </devices> ...
redirdev
- The
redirdev
element is the main container for describing redirected devices.bus
must be "usb" for a USB device. An additional attributetype
is required, matching one of the supported serial device types, to describe the host side of the tunnel;type='tcp'
ortype='spicevmc'
(which uses the usbredir channel of a SPICE graphics device) are typical.
The redirdev element has an optional sub-element
<address>
which can tie the device to a
particular controller.
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).
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 thecertutil
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'
ortype='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
,
function
, and multifunction
since 0.9.7, requires QEMU 0.13 as appropriate.
Virtual network
This is the recommended config for general guest connectivity on
hosts with dynamic / wireless networking configs (or multi-host
environments where the host hardware details are described
separately in a <network>
definition Since 0.9.4).
Provides a connection whose details are described by the named
network definition. Depending on the virtual network's "forward
mode" configuration, the network may be totally isolated
(no <forward>
element given), NAT'ing to an
explicit network device or to the default route
(<forward mode='nat'>
), routed with no NAT
(<forward mode='route'/>
), or connected
directly to one of the host's network interfaces (via macvtap)
or bridge devices ((<forward
mode='bridge|private|vepa|passthrough'/>
Since
0.9.4)
For networks with a forward mode of bridge, private, vepa, and
passthrough, it is assumed that the host has any necessary DNS
and DHCP services already setup outside the scope of libvirt. In
the case of isolated, nat, and routed networks, DHCP and DNS are
provided on the virtual network by libvirt, 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).
When the source of an interface is a network,
a portgroup
can be specified along with the name of
the network; one network may have multiple portgroups defined,
with each portgroup containing slightly different configuration
information for different classes of network
connections. Since 0.9.4). Also,
similar to direct
network connections (described
below), a connection of type network
may specify
a virtportprofile
element, with configuration data
to be forwarded to a vepa or 802.1Qbh compliant switch.
... <devices> <interface type='network'> <source network='default'/> </interface> ... <interface type='network'> <source network='default' portgroup='engineering'/> <target dev='vnet7'/> <mac address="00:11:22:33:44:55"/> <virtualport type='802.1Qbg'> <parameters managerid='11' typeid='1193047' typeidversion='2' instanceid='09b11c53-8b5c-4eeb-8f00-d84eaa0aaa4f'/> </virtualport> </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. passthrough
- This feature attaches a virtual function of a SRIOV capable NIC directly to a VM without losing the migration capability. All packets are sent to the VF/IF of the configured network device. Depending on the capabilities of the device additional prerequisites or limitations may apply; for example, on Linux this requires kernel 2.6.38 or newer. Since 0.9.2
... <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. Since 0.8.2
Please note that IEEE 802.1Qbg requires a non-zero value for the VLAN ID.
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='eth0.2' mode='vepa'/> <virtualport type="802.1Qbg"> <parameters managerid="11" typeid="1193047" typeidversion="2" instanceid="09b11c53-8b5c-4eeb-8f00-d84eaa0aaa4f"/> </virtualport> </interface> </devices> ...
The interface can have additional parameters as shown below if the switch is conforming to the IEEE 802.1Qbh standard. The values are network specific and should be provided by the network administrator. Since 0.8.2
profileid
- The profile ID contains the name of the port profile that is to be applied onto this interface. This name is resolved by the port profile database into the network parameters from the port profile, and those network parameters will be applied to this interface.
... <devices> <interface type='direct'/> ... <interface type='direct'> <source dev='eth0' mode='private'/> <virtualport type='802.1Qbh'> <parameters profileid='finance'/> </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' ioeventfd='on' event_idx='off'/> </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. ioeventfd
-
This optional attribute allows users to set
domain I/O asynchronous handling for interface 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. event_idx
-
The
event_idx
attribute controls some aspects of device event processing. The value can be either 'on' or 'off' - if it is on, it will reduce the number of interupts and exits for the guest. The default is determined by QEMU; usually if the feature is supported, default is on. In case there is a situation where this behavior is suboptimal, this attribute provides a way to force the feature off. Since 0.9.5 (QEMU and KVM only)
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
Quality of service
... <devices> <interface type='network'> <source network='default'/> <target dev='vnet0'/> <bandwidth> <inbound average='1000' peak='5000' burst='1024'/> <outbound average='128' peak='256' burst='256'/> </bandwidth> </interface> <devices> ...
This part of interface XML provides setting quality of service. Incoming
and outgoing traffic can be shaped independently. The
bandwidth
element can have at most one inbound
and at most one outbound
child elements. Leaving any of these
children element out result in no QoS applied on that traffic direction.
So, when you want to shape only domain's incoming traffic, use
inbound
only, and vice versa. Each of these elements have one
mandatory attribute average
. It specifies average bit rate on
interface being shaped. Then there are two optional attributes:
peak
, which specifies maximum rate at which interface can send
data, and burst
, amount of bytes that can be burst at
peak
speed. Accepted values for attributes are integer
numbers. The units for average
and peak
attributes
are kilobytes per second, and for the burst
just kilobytes.
Since 0.9.4
Modyfing virtual link state
... <devices> <interface type='network'> <source network='default'/> <target dev='vnet0'/> <link state='down'/> </interface> <devices> ...
This element provides means of setting state of the virtual network link.
Possible values for attribute state
are up
and
down
. If down
is specified as the value, the interface
behaves as if it had the network cable disconnected. Default behavior if this
element is unspecified is to have the link state up
.
Since 0.9.5
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, thetype
whose value can be either 'mouse' or 'tablet'. The latter provides absolute cursor movement, while the former uses relative movement. The optionalbus
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.
Hub devices
A hub is a device that expands a single port into several so that there are more ports available to connect devices to a host system.
... <devices> <hub type='usb'/> </devices> ...
hub
- The
hub
element has one mandatory attribute, thetype
whose value can only be 'usb'.
The hub
element has an optional
sub-element <address>
which can tie the
device to a particular controller.
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'> <listen type='address' address='1.2.3.4'/> </graphics> <graphics type='rdp' autoport='yes' multiUser='yes' /> <graphics type='desktop' fullscreen='yes'/> <graphics type='spice'> <listen type='network' network='rednet'/> </graphics> </devices> ...
graphics
- The
graphics
element has a mandatorytype
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, anxauth
attribute for the authentication identifier, and an optionalfullscreen
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). Theautoport
attribute is the new preferred syntax for indicating autoallocation of the TCP port to use. Thelisten
attribute is an IP address for the server to listen on. Thepasswd
attribute provides a VNC password in clear text. Thekeymap
attribute specifies the keymap to use. It is possible to set a limit on the validity of the password be giving an timestamppasswdValidTo='2010-04-09T15:51:00'
assumed to be in UTC. Theconnected
attribute allows control of connected client during password changes. VNC acceptskeep
value only. since 0.9.3 NB, this may not be supported by all hypervisors.
Rather than using listen/port, QEMU supports asocket
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), whiletlsPort
gives an alternative secure port number. Theautoport
attribute is the new preferred syntax for indicating autoallocation of both port numbers. Thelisten
attribute is an IP address for the server to listen on. Thepasswd
attribute provides a SPICE password in clear text. Thekeymap
attribute specifies the keymap to use. It is possible to set a limit on the validity of the password be giving an timestamppasswdValidTo='2010-04-09T15:51:00'
assumed to be in UTC. Theconnected
attribute allows control of connected client during password changes. SPICE acceptskeep
to keep client connected,disconnect
to disconnect client andfail
to fail changing password. Since 0.9.3 NB, this may not be supported by all hypervisors. "spice" since 0.8.6. ThedefaultMode
attribute sets the default channel security policy, valid values aresecure
,insecure
and the defaultany
(which is secure if possible, but falls back to insecure rather than erroring out if no secure path is available). "defaultMode" since 0.9.12.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
(all since 0.8.6);smartcard
(since 0.8.8); andusbredir
(since 0.9.12).<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 (acceptsauto_glz
,auto_lz
,quic
,glz
,lz
,off
),jpeg
for JPEG compression for images over wan (acceptsauto
,never
,always
),zlib
for configuring wan image compression (acceptsauto
,never
,always
) andplayback
for enabling audio stream compression (acceptson
oroff
).Streaming mode is set by the
streaming
element, settings it'smode
attribute to one offilter
,all
oroff
, 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 thecopypaste
property tono
, since 0.9.3. "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). Theautoport
attribute is the new preferred syntax for indicating autoallocation of the TCP port to use. ThereplaceUser
attribute is a boolean deciding whether multiple simultaneous connections to the VM are permitted. ThemultiUser
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
andfullscreen
.
Rather than putting the address information used to set up the
listening socket for graphics types vnc
and spice
in
the <graphics>
listen
attribute,
a separate subelement of <graphics>
,
called <listen>
can be specified (see the
examples above)since
0.9.4. <listen>
accepts the following
attributes:
type
- Set to either
address
ornetwork
. This tells whether this listen element is specifying the address to be used directly, or by naming a network (which will then be used to determine an appropriate address for listening).
address
- if
type='address'
, theaddress
attribute will contain either an IP address or hostname (which will be resolved to an IP address via a DNS query) to listen on. In the "live" XML of a running domain, this attribute will be set to the IP address used for listening, even iftype='network'
.
network
- if
type='network'
, thenetwork
attribute will contain the name of a network in libvirt's list of configured networks. The named network configuration will be examined to determine an appropriate listen address. For example, if the network has an IPv4 address in its configuration (e.g. if it has a forward type ofroute
,nat
, or no forward type (isolated)), the first IPv4 address listed in the network's configuration will be used. If the network is describing a host bridge, the first IPv4 address associated with that bridge device will be used, and if the network is describing one of the 'direct' (macvtap) modes, the first IPv4 address of the first forward dev will be used.
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. For backwards compatability, if novideo
is set but there is agraphics
in domain xml, then libvirt will add a defaultvideo
according to the guest type. For a guest of type "kvm", the defaultvideo
for it is:type
with value "cirrus",vram
with value "9216", andheads
with value "1". model
-
The
model
element has a mandatorytype
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 usingvram
and the number of screen withheads
. acceleration
-
If acceleration should be enabled (if supported) using the
accel3d
andaccel2d
attributes in theacceleration
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 0. 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 0. 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 haveaddress
andport
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 elementaddress
can tie the channel to a particulartype='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. Thetarget
element must be present, with attributetype='virtio'
; an optional attributename
controls how the guest will have access to the channel, and defaults toname='com.redhat.spice.0'
. The optionaladdress
element can tie the channel to a particulartype='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:
- 'i6300esb' — the recommended device, emulating a PCI Intel 6300ESB
- 'ib700' — emulating an ISA iBase IB700
action
-
The optional
action
attribute describes what action to take when the watchdog expires. Valid values are specific to the underlying hypervisor.QEMU and KVM support:
- 'reset' — default, forcefully reset the guest
- 'shutdown' — gracefully shutdown the guest (not recommended)
- 'poweroff' — forcefully power off the guest
- 'pause' — pause the guest
- 'none' — do nothing
- 'dump' — automatically dump the guest Since 0.8.7
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- 'virtio' — default with QEMU/KVM
- 'xen' — default with Xen
Security label
The seclabel
element allows control over the
operation of the security drivers. There are two basic
modes of operation, dynamic where libvirt automatically
generates a unique security label, or static where the
application/administrator chooses the labels. With dynamic
label generation, libvirt will always automatically
relabel any resources associated with the virtual machine.
With static label assignment, by default, the administrator
or application must ensure labels are set correctly on any
resources, however, automatic relabeling can be enabled
if desired
Valid input XML configurations for the security label are:
<seclabel type='dynamic' model='selinux'/> <seclabel type='dynamic' model='selinux'> <baselabel>system_u:system_r:my_svirt_t:s0</baselabel> </seclabel> <seclabel type='static' model='selinux' relabel='no'> <label>system_u:system_r:svirt_t:s0:c392,c662</label> </seclabel> <seclabel type='static' model='selinux' relabel='yes'> <label>system_u:system_r:svirt_t:s0:c392,c662</label> </seclabel>
When viewing the XML for a running guest with automatic
resource relabeling active, an additional XML element,
imagelabel
, will be included. This is an
output-only element, so will be ignored in user supplied
XML documents
type
- Either
static
ordynamic
to determine whether libvirt automatically generates a unique security label or not. model
- A valid security model name, matching the currently activated security model
relabel
- Either
yes
orno
. This must always beyes
if dynamic label assignment is used. With static label assignment it will default tono
. label
- If static labelling is used, this must specify the full security label to assign to the virtual domain. The format of the content depends on the security driver in use
baselabel
- If dynamic labelling is used, this can optionally be used to specify the base security label. The format of the content depends on the security driver in use
imagelabel
- This is an output only element, which shows the security label used on resources associated with the virtual domain. The format of the content depends on the security driver in use
Example configs
Example configurations for each driver are provide on the driver specific pages listed below