Local VGs may exist on shared storage where they are visible to
multiple hosts. These VGs are intended to be used by only a single
machine, even though they are visible to many. A system_id
identifying a single host can be assigned to a VG to indicate the VGs
owner. The VG owner can use the VG as usual, and all other hosts
will ignore it. This protects the VG from accidental use by other
The system_id is not a dynamic property, and can only be changed in
very limited circumstances (see vgexport and vgimport). Even limited
changes to the VG system_id are not perfectly reflected across hosts.
A more coherent view of shared storage requires using an inter-host
locking system to coordinate access and update caches.
The system_id is a string uniquely identifying a host. It can be
manually set to a custom value or it can be assigned automatically by
lvm using a unique identifier already available on the host, e.g.
machine-id or uname.
In vgcreate, the local system_id is saved in the new VG metadata.
The local host owns the new VG, and other hosts cannot use it.
A VG without a system_id can be used by any host, and a VG with a
system_id can only be used by a host with a matching system_id. A
foreign VG is a VG with a system_id as viewed by a host with a
system_id that does not match the VGs system_id. (Or from a host
without a system_id.)
Valid system_id characters are the same as valid VG name characters.
If a system_id contains invalid characters, those characters are
omitted and remaining characters are used. If a system_id is longer
than the maximum name length, the characters up to the maximum length
are used. The maximum length of a system_id is 128 characters.
Limitations and warnings
To benefit fully from system_id, all hosts must have system_id set,
and VGs must have system_id set. A VG on shared storage can be
damaged or destroyed in some cases which the user must be careful to
· A VG without a system_id can be used without restriction from any
host, even from hosts that have a system_id. Many VGs will not
have a system_id and are unprotected. Verify that a VG has a
system_id by running the command 'vgs -o+systemid'
A VG will not have a system_id if it was created before this
feature was added to lvm, or if it was created by a host that did
not have a system_id defined. A system_id can be assigned to these
VGs by using vgchange --systemid (see below).
· Two hosts should not be assigned the same system_id. Doing so
defeats the purpose of the system_id which is to distinguish
· Orphan PVs (or unused devices) on shared storage are completely
unprotected by the system_id feature. Commands that use these PVs,
such as vgcreate or vgextend, are not prevented from performing
conflicting operations and corrupting the PVs. See the orphans
section for more information.
· A host using an old version of lvm without the system_id feature
will not recognize a new system_id in VGs from other hosts. Even
though the old version of lvm is not blocked from reading a VG with
a system_id, it is blocked from writing to the VG (or its LVs).
The new system_id changes the write mode of a VG, making it appear
read-only to previous lvm versions.
This also means that if a host downgrades its version of lvm, it
would lose access to any VGs it had created with a system_id. To
avoid this, the system_id should be removed from VGs before
downgrading to an lvm version without the system_id feature.
Types of VG access
A local VG is meant to be used by a single host.
A shared or clustered VG is meant to be used by multiple hosts.
These can be further distinguished as:
Unrestricted: A local VG that has no system_id. This VG type is
unprotected and accessible to any host.
Owned: A local VG that has a system_id set, as viewed from the one
host with a matching system_id (the owner). This VG type is by
Foreign: A local VG that has a system_id set, as viewed from any host
with an unmatching system_id (or no system_id). It is owned by
another host. This VG type is by definition not accessible.
Exported: A local VG that has been exported with vgexport and has no
system_id. This VG type can only be accessed by vgimport which will
change it to owned.
Shared: A shared or "lockd" VG has lock_type set and no system_id. A
shared VG is meant to be used on shared storage from multiple hosts,
and is only accessible to hosts using lvmlockd. Applicable only if
LVM is compiled with lockd support.
Clustered: A clustered or "clvm" VG has the clustered flag set and no
system_id. A clustered VG is meant to be used on shared storage from
multiple hosts, and is only accessible to hosts using clvmd.
A host's own system_id can be defined in a number of ways. lvm.conf
global/system_id_source defines the method lvm will use to find the
lvm will not use a system_id. lvm is allowed to access VGs
without a system_id, and will create new VGs without a
system_id. An undefined system_id_source is equivalent to
system_id_source = "none"
The content of /etc/machine-id is used as the system_id if
available. See machine-id(5) and systemd-machine-id-setup(1)
to check if machine-id is available on the host.
system_id_source = "machineid"
The string utsname.nodename from uname(2) is used as the
system_id. A uname beginning with "localhost" is ignored and
equivalent to none.
system_id_source = "uname"
The system_id is defined in lvmlocal.conf local/system_id.
system_id_source = "lvmlocal"
system_id = "example_name"
The system_id is defined in a file specified by lvm.conf
system_id_source = "file"
system_id_file = "/path/to/file"
Changing system_id_source will often cause the system_id to change,
which may prevent the host from using VGs that it previously used
(see extra_system_ids below to handle this.)
If a system_id_source other than none fails to resolve a system_id,
the host will be allowed to access VGs with no system_id, but will
not be allowed to access VGs with a defined system_id.
In some cases, it may be useful for a host to access VGs with
different system_id's, e.g. if a host's system_id changes, and it
wants to use VGs that it created with its old system_id. To allow a
host to access VGs with other system_id's, those other system_id's
can be listed in lvmlocal.conf local/extra_system_ids.
extra_system_ids = [ "my_other_name" ]
In vgcreate, the host running the command assigns its own system_id
to the new VG. To override this and set another system_id:
vgcreate --systemid SystemID VG Devices
Overriding the system_id makes it possible for a host to create a VG
that it may not be able to use. Another host with a system_id
matching the one specified may not recognize the new VG without
manually rescanning devices.
If the --systemid argument is an empty string (""), the VG is created
with no system_id, making it accessible to other hosts (see warnings
The system_id of a VG is displayed with the "systemid" reporting
Report/display commands ignore foreign VGs by default. To report
foreign VGs, the --foreign option can be used. This causes the VGs
to be read from disk. Because lvmetad caching is not used, this
option can cause poor performance.
vgs --foreign -o+systemid
When a host with no system_id sees foreign VGs, it warns about them
as they are skipped. The host should be assigned a system_id, after
which standard reporting commands will silently ignore foreign VGs.
vgexport clears the system_id.
Other hosts will continue to see a newly exported VG as foreign
because of local caching (when lvmetad is used). Manually updating
the local lvmetad cache with pvscan --cache will allow a host to
recognize the newly exported VG.
vgimport sets the VG system_id to the local system_id as determined
by lvm.conf system_id_source. vgimport automatically scans storage
for newly exported VGs.
After vgimport, the exporting host will continue to see the VG as
exported, and not owned by the new host. Manually updating the local
cache with pvscan --cache will allow a host to recognize the newly
imported VG as foreign.
A host can change the system_id of its own VGs, but the command
requires confirmation because the host may lose access to the VG
vgchange --systemid SystemID VG
The system_id can be removed from a VG by specifying an empty string
("") as the new system_id. This makes the VG accessible to other
hosts (see warnings above.)
A host cannot directly change the system_id of a foreign VG.
To move a VG from one host to another, vgexport and vgimport should
To forcibly gain ownership of a foreign VG, a host can add the
foreign system_id to its extra_system_ids list, change the system_id
of the foreign VG to its own, and remove the foreign system_id from
its extra_system_ids list.
A shared/lockd VG has no system_id set, allowing multiple hosts to
use it via lvmlockd. Changing a VG to a lockd type will clear the
existing system_id. Applicable only if LVM is compiled with lockd
A clustered/clvm VG has no system_id set, allowing multiple hosts to
use it via clvmd. Changing a VG to clustered will clear the existing
system_id. Changing a VG to not clustered will set the system_id to
the host running the vgchange command.
In vgcreate, the VG metadata field creation_host is set by default to
the host's uname. The creation_host cannot be changed, and is not
used to control access. When system_id_source is "uname", the
system_id and creation_host will be the same.
Orphan PVs are unused devices; they are not currently used in any VG.
Because of this, they are not protected by a system_id, and any host
can use them. Coordination of changes to orphan PVs is beyond the
scope of system_id. The same is true of any block device that is not
The effects of this are especially evident when lvm uses lvmetad
caching. For example, if multiple hosts see an orphan PV, and one
host creates a VG using the orphan, the other hosts will continue to
report the PV as an orphan. Nothing would automatically prevent the
other hosts from using the newly allocated PV and corrupting it. If
the other hosts run a command to rescan devices, and update lvmetad,
they would then recognize that the PV has been used by another host.
A command that rescans devices could be pvscan --cache, or vgs
This page is part of the lvm2 (Logical Volume Manager 2) project.
Information about the project can be found at
⟨http://www.sourceware.org/lvm2/⟩. If you have a bug report for this
manual page, send it to firstname.lastname@example.org. This page was obtained
from the project's upstream Git repository
⟨https://git.fedorahosted.org/git/lvm2.git⟩ on 2017-03-13. If you
discover any rendering problems in this HTML version of the page, or
you believe there is a better or more up-to-date source for the page,
or you have corrections or improvements to the information in this
COLOPHON (which is not part of the original manual page), send a mail
Red Hat, Inc LVM TOOLS 2.02.169(2)-git (2016-11-30) LVMSYSTEMID(7)