Section: Xen (1)
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xm - Xen management user interface
xm <subcommand> [args]
The xm program is the main interface for managing Xen guest
domains. The program can be used to create, pause, and shutdown
domains. It can also be used to list current domains, enable or pin
VCPUs, and attach or detach virtual block devices.
The basic structure of every xm command is almost always:
xm <subcommand> <domain-id> [OPTIONS]
Where subcommand is one of the sub commands listed below, domain-id
is the numeric domain id, or the domain name (which will be internally
translated to domain id), and OPTIONS are sub command specific
options. There are a few exceptions to this rule in the cases where
the sub command in question acts on all domains, the entire machine,
or directly on the xen hypervisor. Those exceptions will be clear for
each of those sub commands.
All xm operations rely upon the Xen control daemon, aka xend.
For any xm commands to run xend must also be running. For this reason
you should start xend as a service when your system first boots using
Most xm commands require root privileges to run due to the
communications channels used to talk to the hypervisor. Running as
non root will return an error.
Most xm commands act asynchronously, so just because the xm
command returned, doesn't mean the action is complete. This is
important, as many operations on domains, like create and shutdown,
can take considerable time (30 seconds or more) to bring the machine
into a fully compliant state. If you want to know when one of these
actions has finished you must poll through xm list periodically.
The following sub commands manipulate domains directly, as stated
previously most commands take domain-id as the first parameter.
- console domain-id
Attach to domain domain-id's console. If you've set up your Domains to
have a traditional log in console this will look much like a normal
text log in screen.
This uses the back end xenconsole service which currently only
works for para-virtual domains.
The attached console will perform much like a standard serial console,
so running curses based interfaces over the console is not
advised. Vi tends to get very odd when using it over this interface.
- create [-c] configfile [name=value]..
The create sub command requires a configfile and can optional take a
series of name value pairs that add to or override variables defined
in the config file. See xmdomain.cfg for full details of that file
format, and possible options used in either the configfile or
Configfile can either be an absolute path to a file, or a relative
path to a file located in /etc/xen.
Create will return as soon as the domain is started. This does
not mean the guest OS in the domain has actually booted, or is
available for input.
Attache console to the domain as soon as it has started. This is
useful for determining issues with crashing domains.
- with config file
xm create Fedora4
This creates a domain with the file /etc/xen/Fedora4, and returns as
soon as it is run.
- without config file
xm create /dev/null ramdisk=initrd.img \
name=ramdisk nics=0 vcpus=1 \
This creates the domain without using a config file (more specifically
using /dev/null as an empty config file), kernel and ramdisk as
specified, setting the name of the domain to ``ramdisk'', also disabling
virtual networking. (This example comes from the xm-test test suite.)
- destroy domain-id
Immediately terminate the domain domain-id. This doesn't give the domain
OS any chance to react, and it the equivalent of ripping the power
cord out on a physical machine. In most cases you will want to use
the shutdown command instead.
- domid domain-name
Converts a domain name to a domain id using xend's internal mapping.
- domname domain-id
Converts a domain id to a domain name using xend's internal mapping.
- help [--long]
Displays the short help message (i.e. common commands).
The --long option prints out the complete set of xm subcommands,
grouped by function.
- list [--long | --label] [domain-id, ...]
Prints information about one or more domains. If no domains are
specified it prints out information about all domains.
An example format for the list is as follows:
Name ID Mem(MiB) VCPUs State Time(s)
Domain-0 0 98 1 r----- 5068.6
Fedora3 164 128 1 r----- 7.6
Fedora4 165 128 1 ------ 0.6
Mandrake2006 166 128 1 -b---- 3.6
Mandrake10.2 167 128 1 ------ 2.5
Suse9.2 168 100 1 ------ 1.8
Name is the name of the domain. ID the domain numeric id. Mem is the
size of the memory allocated to the domain. VCPUS is the number of
VCPUS allocated to domain. State is the run state (see below). Time
is the total run time of the domain as accounted for by Xen.
The State field lists 6 states for a Xen Domain, and which ones the
current Domain is in.
- r - running
The domain is currently running on a CPU
- b - blocked
The domain is blocked, and not running or runnable. This can be caused
because the domain is waiting on IO (a traditional wait state) or has
gone to sleep because there was nothing else for it to do.
- p - paused
The domain has been paused, usually occurring through the administrator
running xm pause. When in a paused state the domain will still
consume allocated resources like memory, but will not be eligible for
scheduling by the Xen hypervisor.
- s - shutdown
The guest has requested to be shutdown, rebooted or suspended, and the
domain is in the process of being destroyed in response.
- c - crashed
The domain has crashed, which is always a violent ending. Usually
this state can only occur if the domain has been configured not to
restart on crash. See xmdomain.cfg for more info.
- d - dying
The domain is in process of dying, but hasn't completely shutdown or
If --long is specified, the output for xm list is not the table
view shown above, but instead is an S-Expression representing all
information known about all domains asked for. This is mostly only
useful for external programs to parse the data.
Note: there is no stable guarantees on the format of this data.
Use at your own risk.
If --label is specified, the security labels are added to the
output of xm list and the lines are sorted by the labels (ignoring
case). The --long option prints the labels by default and cannot be
combined with --label. See the ACCESS CONTROL SUBCOMMAND section of
this man page for more information about labels.
The Time column is deceptive. Virtual IO (network and block devices)
used by Domains requires coordination by Domain0, which means that
Domain0 is actually charged for much of the time that a DomainU is
doing IO. Use of this time value to determine relative utilizations
by domains is thus very suspect, as a high IO workload may show as
less utilized than a high CPU workload. Consider yourself warned.
- mem-max domain-id mem
Specify the maximum amount of memory the Domain is able to use. Mem
is specified in megabytes.
The mem-max value may not correspond to the actual memory used in the
Domain, as it may balloon down it's memory to give more back to the OS.
- mem-set domain-id mem
Set the domain's used memory using the balloon driver. Because this
operation requires cooperation from the domain operating system, there
is no guarantee that it will succeed.
Warning: there is no good way to know in advance how small of a
mem-set will make a domain unstable and cause it to crash. Be very
careful when using this command on running domains.
- migrate domain-id host [options]
Migrate a domain to another Host machine. Xend must be running on
other host machine, it must be running the same version of xen, it
must have the migration TCP port open and accepting connections from
the source host, and there must be sufficient resources for the domain
to run (memory, disk, etc).
Migration is pretty complicated, and has many security implications,
please read the Xen Users Guide to ensure you understand the
ramifications and limitations on migration before attempting it in
- -l, --live
Use live migration. This will migrate the domain between hosts
without shutting down the domain. See the Xen Users Guide for more
- -r, --resource Mbs
Set maximum Mbs allowed for migrating the domain. This ensures that
the network link is not saturated with migration traffic while
attempting to do other useful work.
- pause domain-id
Pause a domain. When in a paused state the domain will still consume
allocated resources such as memory, but will not be eligible for
scheduling by the Xen hypervisor.
- reboot [options] domain-id
Reboot a domain. This acts just as if the domain had the reboot
command run from the console. The command returns as soon as it has
executed the reboot action, which may be significantly before the
domain actually reboots.
The behavior of what happens to a domain when it reboots is set by the
on_reboot parameter of the xmdomain.cfg file when the domain was
- -a, --all
Reboot all domains
- -w, --wait
Wait for reboot to complete before returning. This may take a while,
as all services in the domain will have to be shut down cleanly.
- restore state-file
Build a domain from an xm save state file. See save for more info.
- save domain-id state-file
Saves a running domain to a state file so that it can be restored
later. Once saved, the domain will no longer be running on the
system, thus the memory allocated for the domain will be free for
other domains to use. xm restore restores from this state file.
This is roughly equivalent to doing a hibernate on a running computer,
with all the same limitations. Open network connections may be
severed upon restore, as TCP timeouts may have expired.
- shutdown [options] domain-id
Gracefully shuts down a domain. This coordinates with the domain OS
to perform graceful shutdown, so there is no guarantee that it will
succeed, and may take a variable length of time depending on what
services must be shutdown in the domain. The command returns
immediately after signally the domain unless that -w flag is used.
The behavior of what happens to a domain when it reboots is set by the
on_shutdown parameter of the xmdomain.cfg file when the domain was
Shutdown all domains. Often used when doing a complete shutdown of
a Xen system.
Wait for the domain to complete shutdown before returning.
- sysrq domain-id letter
Send a Magic System Request signal to the domain. For more
information on available magic sys req operations, see sysrq.txt in
your Linux Kernel sources.
- unpause domain-id
Moves a domain out of the paused state. This will allow a previously
paused domain to now be eligible for scheduling by the Xen hypervisor.
- vcpu-set domain-id vcpu-count
Enables the vcpu-count virtual CPUs for the domain in question.
Like mem-set, this command can only allocate up to the maximum virtual
CPU count configured at boot for the domain.
If the vcpu-count is smaller than the current number of active
VCPUs, the highest number VCPUs will be hotplug removed. This may be
important for pinning purposes.
Attempting to set the VCPUs to a number larger than the initially
configured VCPU count is an error. Trying to set VCPUs to < 1 will be
- vcpu-list [domain-id]
Lists VCPU information for a specific domain. If no domain is
specified, VCPU information for all domains will be provided.
- vcpu-pin domain-id vcpu cpus
Pins the the VCPU to only run on the specific CPUs. The keyword
all can be used to apply the cpus list to all VCPUs in the
Normally VCPUs can float between available CPUs whenever Xen deems a
different run state is appropriate. Pinning can be used to restrict
this, by ensuring certain VCPUs can only run on certain physical
XEN HOST SUBCOMMANDS
- dmesg [-c]
Reads the Xen message buffer, similar to dmesg on a Linux system. The
buffer contains informational, warning, and error messages created
during Xen's boot process. If you are having problems with Xen, this
is one of the first places to look as part of problem determination.
- -c, --clear
Clears Xen's message buffer.
Print information about the Xen host in name : value format. When
reporting a Xen bug, please provide this information as part of the
Sample xen domain info looks as follows (lines wrapped manually to
make the man page more readable):
host : talon
release : 188.8.131.52-xen0
version : #1 Mon Nov 14 14:26:26 EST 2005
machine : i686
nr_cpus : 2
nr_nodes : 1
sockets_per_node : 2
cores_per_socket : 1
threads_per_core : 1
cpu_mhz : 696
hw_caps : 0383fbff:00000000:00000000:00000040
total_memory : 767
free_memory : 37
xen_major : 3
xen_minor : 0
xen_extra : -devel
xen_caps : xen-3.0-x86_32
xen_pagesize : 4096
platform_params : virt_start=0xfc000000
xen_changeset : Mon Nov 14 18:13:38 2005 +0100
cc_compiler : gcc version 3.4.3 (Mandrakelinux
cc_compile_by : sdague
cc_compile_domain : (none)
cc_compile_date : Mon Nov 14 14:16:48 EST 2005
xend_config_format : 2
Not all fields will be explained here, but some of the less obvious
ones deserve explanation:
A vector showing what hardware capabilities are supported by your
processor. This is equivalent to, though more cryptic, the flags
field in /proc/cpuinfo on a normal Linux machine.
Available memory (in MB) not allocated to Xen, or any other Domains.
The xen version, architecture. Architecture values can be one of:
x86_32, x86_32p (i.e. PAE enabled), x86_64, ia64.
The xen mercurial changeset id. Very useful for determining exactly
what version of code your Xen system was built from.
Print out the xend log. This log file can be found in
Executes the xentop command, which provides real time monitoring of
domains. Xentop is a curses interface, and reasonably self
VIRTUAL DEVICE COMMANDS
Most virtual devices can be added and removed while guests are
running. The effect to the guest OS is much the same as any hotplug
- block-attach domain-id be-dev fe-dev mode [bedomain-id]
Create a new virtual block device. This will trigger a hotplug event
for the guest.
The domain id of the guest domain that the device will be attached to.
The device in the backend domain (usually domain 0) to be exported.
This can be specified as a physical partition (phy:sda7) or as a file
mounted as loopback (file://path/to/loop.iso).
How the device should be presented to the guest domain. It can be
specified as either a symbolic name, such as /dev/hdc, for common
devices, or by device id, such as 0x1400 (/dev/hdc device id in hex).
The access mode for the device from the guest domain. Supported modes
are w (read/write) or r (read-only).
The back end domain hosting the device. This defaults to domain 0.
- Mount an ISO as a Disk
xm block-attach guestdomain file://path/to/dsl-2.0RC2.iso /dev/hdc ro
This will mount the dsl iso as /dev/hdc in the guestdomain as a read
only device. This will probably not be detected as a cdrom by the
guest, but mounting /dev/hdc manually will work.
- block-detach domain-id devid
Destroy a domain's virtual block device. devid must be the device
id given to the device by domain 0. You will need to run xm
block-list to determine that number.
- block-list [-l|--long] domain-id
List virtual block devices for a domain. The returned output is
formatted as a list or as an S-Expression if the '--long' option was given.
- network-attach domain-id [script=scriptname] [ip=ipaddr] [mac=macaddr] [bridge=bridge-name] [backend=bedomain-id]
Creates a new network device in the domain specified by domain-id. It
takes the following optional options:
Use the specified script name to bring up the network. Defaults to
the default setting in xend-config.sxp for vif-script.
Passes the specified IP Address to the adapter on creation.
The MAC address that the domain will see on its Ethernet device. If
the device is not specified it will be randomly generated with the
00:16:3e vendor id prefix.
The name of the bridge to attach the vif to, in case you have more
than one. This defaults to
The backend domain id. By default this is domain 0.
- network-detach domain-id devid
Removes the network device from the domain specified by domain-id.
devid is the virtual interface device number within the domain
(i.e. the 3 in vif22.3).
- network-list [-l|--long] domain-id
List virtual network interfaces for a domain. The returned output is
formatted as a list or as an S-Expression if the '--long' option was given.
VIRTUAL TPM DEVICES
- vtpm-list [-l|--long] domain-id
Show the virtual TPM device for a domain. The returned output is
formatted as a list or as an S-Expression if the '--long' option was given.
ACCESS CONTROL SUBCOMMANDS
Access Control in Xen consists of two components: (i) The Access
Control Policy (ACP) defines security labels and access rules based on
these labels. (ii) The Access Control Module (ACM) makes access control
decisions by interpreting the policy when domains require to
communicate or to access resources. The Xen access control has
sufficient mechanisms in place to enforce the access decisions even
against maliciously acting user domains (mandatory access control).
Access rights for domains in Xen are determined by the domain security
label only and not based on the domain Name or ID. The ACP specifies
security labels that can then be assigned to domains and
resources. Every domain must be assigned exactly one security label,
otherwise access control decisions could become indeterministic. ACPs
are distinguished by their name, which is a parameter to most of the
subcommands described below. Currently, the ACP specifies two ways to
(1) Simple Type Enforcement: Labels are interpreted to decide access
of domains to comunication means and virtual or physical
resources. Communication between domains as well as access to
resources are forbidden by default and can only take place if they are
explicitly allowed by the security policy. The proper assignment of
labels to domains controls the sharing of information (directly
through communication or indirectly through shared resources) between
domains. This interpretation allows to control the overt (intended)
communication channels in Xen.
(2) Chinese Wall: Labels are interpreted to decide which domains can
co-exist (be run simultaneously) on the same system. This
interpretation allows to prevent direct covert (unintended) channels
and mitigates risks caused by imperfect core domain isolation
(trade-off between security and other system requirements). For a
short introduction to covert channels, please refer to
The following subcommands help you to manage security policies in Xen
and to assign security labels to domains. To enable access control
security in Xen, you must compile Xen with ACM support enabled as
described under ``Configuring Security'' below. There, you will find
also examples of each subcommand described here.
- makepolicy policy
Compiles the XML source representation of the security policy. It
creates a mapping (.map) as well as a binary (.bin) version of the
policy. The compiled policy can be loaded into Xen with the
loadpolicy subcommand or can be configured to be loaded at boot
time with the cfgbootpolicy subcommand.
policy is a dot-separated list of names. The last part is the file
name pre-fix for the policy xml file. The preceding name parts are
translated into the local path pointing to the policy xml file
relative to the global policy root directory
(/etc/xen/acm-security/policies). For example,
example.chwall_ste.client_v1 denotes the policy file
example/chwall_ste/client_v1-security_policy.xml relative to the
global policy root directory.
- loadpolicy policy
Loads the binary representation of the policy into Xen. The binary
representation can be created with the makepolicy subcommand.
- cfgbootpolicy policy [kernelversion]
Configures policy as the boot policy for Xen. It copies the binary
policy representation into the /boot directory and adds a module line
specifying the binary policy to the /boot/grub/menu.lst file. If your
boot configuration includes multiple Xen boot titles, then use the
kernelversion parameter to select the proper title.
Prints the current security policy state information of Xen.
- labels [policy] [type=dom|res|any]
Lists all labels of a type (domain, resource, or both) that are
defined in the policy. Unless specified, the default policy is
the currently enforced access control policy. The default for type
is 'dom'. The labels are arranged in alphabetical order.
- addlabel label dom configfile [policy]
- addlabel label res resource [policy]
Adds the security label with name label to a domain
configfile (dom) or to the global resource label file for the
given resource (res). Unless specified, the default policy is the
currently enforced access control policy. This subcommand also
verifies that the policy definition supports the specified label
- rmlabel dom configfile
- rmlabel res resource
Works the same as the addlabel command (above), except that this
command will remove the label from the domain configfile (dom) or
the global resource label file (res).
- getlabel dom configfile
- getlabel res resource
Shows the label for the given configfile or resource
Lists all resources in the global resource label file. Each resource
is listed with its associated label and policy name.
- dry-run configfile
Determines if the specified configfile describes a domain with a valid
security configuration for type enforcement. The test shows the policy
decision made for each resource label against the domain label as well as
the overall decision.
In xen_source_dir/Config.mk set the following parameters:
ACM_SECURITY ?= y
ACM_DEFAULT_SECURITY_POLICY ?= \
Then recompile and install xen and the security tools and then reboot:
cd xen_source_dir/xen; make clean; make; cp xen.gz /boot;
cd xen_source_dir/tools/security; make install;
reboot into xen
COMPILING A SECURITY POLICY
This step creates client_v1.map and client_v1.bin files in
xm makepolicy example.chwall_ste.client_v1
LOADING A SECURITY POLICY
This step activates client_v1.bin as new security policy in Xen. You
can use the dumppolicy subcommand before and afterwards to see the
change in the Xen policy state.
xm loadpolicy example.chwall_ste.client_v1
CONFIGURING A BOOT SECURITY POLICY
This configures the boot loader to load client_v1.bin at boot
time. During system start, the ACM configures Xen with this policy and
Xen enforces this policy from then on.
xm cfgbootpolicy example.chwall_ste.client_v1
LISTING SECURITY LABELS
This subcommand shows all labels that are defined and which can be
attached to domains.
xm labels example.chwall_ste.client_v1 type=dom
will print for our example policy:
ATTACHING A SECURITY LABEL TO A DOMAIN
The addlabel subcommand can attach a security label to a domain
configuration file, here a HomeBanking label. The example policy
ensures that this domain does not share information with other
non-hombanking user domains (i.e., domains labeled as dom_Fun or
dom_Boinc) and that it will not run simultaneously with domains
labeled as dom_Fun.
We assume that the specified myconfig.xm configuration file actually
instantiates a domain that runs workloads related to home-banking,
probably just a browser environment for online-banking.
xm addlabel dom_HomeBanking dom myconfig.xm
The very simple configuration file might now look as printed
below. The addlabel subcommand added the access_control entry at
the end of the file, consisting of a label name and the policy that
specifies this label name:
kernel = "/boot/vmlinuz-2.6.16-xen"
memory = 164
name = "homebanking"
vif = [ '' ]
dhcp = "dhcp"
access_control = ['policy=example.chwall_ste.client_v1,
Security labels must be assigned to domain configurations because
these labels are essential for making access control decisions as
early as during the configuration phase of a newly instantiated
domain. Consequently, a security-enabled Xen hypervisor will only
start domains that have a security label configured and whose security
label is consistent with the currently enforced policy. Otherwise,
starting the domain will fail with the error condition ``operation not
ATTACHING A SECURITY LABEL TO A RESOURCE
The addlabel subcommand can also be used to attach a security
label to a resource. Following the home banking example from above,
we can label a disk resource (e.g., a physical partition or a file)
to make it accessible to the home banking domain. The example policy
provides a resource label, res_LogicalDiskPartition1(hda1), that is
compatible with the HomeBanking domain label.
xm addlabel "res_LogicalDiskPartition1(hda1)" res phy:hda6
After labeling this disk resource, it can be attached to the domain
by adding a line to the domain configuration file. The line below
attaches this disk to the domain at boot time.
disk = [ 'phy:hda6,sda2,w' ]
Alternatively, the resource can be attached after booting the domain
by using the block-attach subcommand.
xm block-attach homebanking phy:hda6 sda2 w
Note that labeled resources cannot be used when security is turned
off. Any attempt to use labeled resources with security turned off
will result in a failure with a corresponding error message. The
solution is to enable security or, if security is no longer desired,
to remove the resource label using the rmlabel subcommand.
STARTING AND LISTING LABELED DOMAINS
xm create myconfig.xm
xm list --label
Name ID ... Time(s) Label
homebanking 23 ... 4.4 dom_HomeBanking
Domain-0 0 ... 2658.8 dom_SystemManagement
LISTING LABELED RESOURCES
We distinguish three representations of the Xen access control policy:
the source XML version, its binary counterpart, and a mapping
representation that enables the tools to deterministically translate
back and forth between label names of the XML policy and label
identifiers of the binary policy. All three versions must be kept
consistent to achieve predictable security guarantees.
The XML version is the version that users are supposed to create or
change, either by manually editing the XML file or by using the Xen
policy generation tool (xensec_gen). After changing the XML file,
run the makepolicy subcommand to ensure that these changes are
reflected in the other versions. Use, for example, the subcommand
cfgbootpolicy to activate the changes during the next system
The binary version of the policy is derived from the XML policy by
tokenizing the specified labels and is used inside Xen only. It is
created with the makepolicy subcommand. Essentially, the binary
version is much more compact than the XML version and is easier to
evaluate during access control decisions.
The mapping version of the policy is created during the XML-to-binary
policy translation (makepolicy) and is used by the Xen management
tools to translate between label names used as input to the tools and
their binary identifiers (ssidrefs) used inside Xen.
Sean Dague <sean at dague dot net>
Daniel Stekloff <dsteklof at us dot ibm dot com>
Reiner Sailer <sailer at us dot ibm dot com>
- DOMAIN SUBCOMMANDS
- XEN HOST SUBCOMMANDS
- VIRTUAL DEVICE COMMANDS
- BLOCK DEVICES
- NETWORK DEVICES
- VIRTUAL TPM DEVICES
- ACCESS CONTROL SUBCOMMANDS
- SEE ALSO
linux.jgfs.net manual pages