lvmetad — LVM metadata cache daemon
] [-s socket_path
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
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 LVM
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 reasons are the existence of
duplicate PVs (lvmetad cannot cache data for duplicate PVs), or an 'lvconvert
--repair' command has been run (the lvmetad cache may not be reliable while
repairs are neeeded.) Once duplicates have been resolved, or repairs have been
completed, 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 use:
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.
- Don't fork, but run in the foreground.
- -h, -?
- Show help information.
- -l levels
- 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, debug.
- -p pidfile_path
- 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.
- -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.
- Display the version of lvmetad daemon.
- Path for the pid file.
- Path for the socket file.