bionic (8) lvmetad.8.gz

Provided by: lvm2_2.02.176-4.1ubuntu3.18.04.3_amd64 bug

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 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 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)