LVMETAD(8)LVMETAD(8)NAMElvmetad — LVM metadata cache daemon
SYNOPSISlvmetad [-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 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 com‐
mands 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 auto‐
matically 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 automat‐
ically 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
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:
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.
-h, -? Show help information.
-l levels
Specify the levels of log messages to generate as a comma sepa‐
rated list. Messages are logged by syslog. Additionally, when
-f is given they are also sent to standard error. Possible lev‐
els 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_PID‐
FILE. 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.
-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 ALSOlvm(8), lvmconfig(8), lvm.conf(5), pvscan(8)Red Hat Inc LVM TOOLS 2.02.176(2) (2017-11-03) LVMETAD(8)
