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 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
       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:
       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
	      (/var/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  (/var/run/lvm/lvmetad.socket) and the environment vari-
	      able  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)