LVMETAD(8) System Manager's Manual LVMETAD(8)
NAME
lvmetad — LVM metadata cache daemon
SYNOPSIS
lvmetad [-l level[,level...]] [-p pidfile_path] [-s socket_path] [-t timeout_value] [-f] [-h] [-V] [-?]
DESCRIPTION
The lvmetad daemon caches LVM metadata so that LVM commands can read metadata from the cache rather than scan‐
ning disks. This can be an advantage because scanning disks is time consuming and may interfere with the nor‐
mal work of the system. lvmetad can be a disadvantage when disk event notifications from the system are unre‐
liable.
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 automati‐
cally by the next LVM command that's run.
When lvmetad is not used, LVM commands revert to scanning disks for LVM metadata.
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 can‐
not 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:
lvm.conf(5) global/use_lvmetad
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 use:
lvm.conf(5) devices/global_filter
For more information on this setting, see
lvmconfig --withcomments devices/global_filter
OPTIONS
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.
-s socket_path
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.
-t timeout_value
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.
ENVIRONMENT VARIABLES
LVM_LVMETAD_PIDFILE
Path for the pid file.
LVM_LVMETAD_SOCKET
Path for the socket file.
SEE ALSO
lvm(8), lvmconfig(8), lvm.conf(5), pvscan(8)
Red Hat Inc LVM TOOLS 2.02.166(2)-RHEL7 (2016-11-16) LVMETAD(8)
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