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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
   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 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
          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.

   -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)



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