The lvmetad daemon caches LVM metadata so that LVM commands can read
metadata from the cache rather than scanning disks. This can be an
advantage because scanning disks is time consuming and may interfere
with the normal work of the system. lvmetad can be a disadvantage
when disk event notifications from the system are unreliable.
lvmetad does not read metadata from disks itself. Instead, it relies
on an LVM command, like pvscan --cache, to read metadata from disks
and send it to lvmetad to be cached.
New LVM disks that appear on the system must be scanned before
lvmetad knows about them. If lvmetad does not know about a disk,
then LVM commands using lvmetad will also not know about it. When
disks are added or removed from the system, lvmetad must be updated.
lvmetad is usually combined with event-based system services that
automatically run pvscan --cache on disks added or removed. This
way, the cache is automatically updated with metadata from new disks
when they appear. LVM udev rules and systemd services implement this
automation. Automatic scanning is usually combined with automatic
activation. For more information, see pvscan(8).
If lvmetad is started or restarted after disks have been added to the
system, or if the global_filter has changed, the cache must be
updated. This can be done by running pvscan --cache, or it will be
done automatically by the next LVM command that's run.
When lvmetad is not used, LVM commands revert to scanning disks for
In some cases, lvmetad will be temporarily disabled while it
continues running. In this state, LVM commands will ignore the
lvmetad cache and revert to scanning disks. A warning will also be
printed which includes the reason why lvmetad is not being used. The
most common reason is the existence of duplicate PVs (lvmetad cannot
cache data for duplicate PVs.) Once duplicates have been resolved,
the lvmetad cache is can be updated with pvscan --cache and commands
will return to using the cache.
Use of lvmetad is enabled/disabled by:
For more information on this setting, see:
lvmconfig --withcomments global/use_lvmetad
To ignore disks from LVM at the system level, e.g. lvmetad, pvscan
For more information on this setting, see
lvmconfig --withcomments devices/global_filter
To run the daemon in a test environment both the pidfile_path and the
socket_path should be changed from the defaults.
-f Don't fork, but run in the foreground.
-h, -? Show help information.
Specify the levels of log messages to generate as a comma
separated list. Messages are logged by syslog. Additionally,
when -f is given they are also sent to standard error.
Possible levels are: all, fatal, error, warn, info, wire,
Path to the pidfile. This overrides both the built-in default
(/run/lvmetad.pid) and the environment variable
LVM_LVMETAD_PIDFILE. This file is used to prevent more than
one instance of the daemon running simultaneously.
Path to the socket file. This overrides both the built-in
default (/run/lvm/lvmetad.socket) and the environment variable
LVM_LVMETAD_SOCKET. To communicate successfully with lvmetad,
all LVM2 processes should use the same socket path.
The daemon may shutdown after being idle for the given time
(in seconds). When the option is omitted or the value given is
zero the daemon never shutdowns on idle.
-V Display the version of lvmetad daemon.
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 email@example.com. 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) LVMETAD(8)