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130 lines
4.2 KiB
Plaintext
130 lines
4.2 KiB
Plaintext
.TH LVMETAD 8 "LVM TOOLS #VERSION#" "Red Hat Inc" \" -*- nroff -*-
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.SH NAME
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lvmetad \(em LVM metadata cache daemon
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.SH SYNOPSIS
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.B lvmetad
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.RB [ -l
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.IR level [,level...]]
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.RB [ -p
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.IR pidfile_path ]
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.RB [ -s
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.IR socket_path ]
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.RB [ -t
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.IR timeout_value ]
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.RB [ -f ]
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.RB [ -h ]
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.RB [ -V ]
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.RB [ -? ]
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.SH DESCRIPTION
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The lvmetad daemon caches LVM metadata so that LVM commands can read
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metadata from the cache rather than scanning disks. This can be an
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advantage because scanning disks is time consuming and may interfere with
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the normal work of the system. lvmetad can be a disadvantage when disk
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event notifications from the system are unreliable.
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lvmetad does not read metadata from disks itself. Instead, it relies on
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an LVM command, like pvscan --cache, to read metadata from disks and
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send it to lvmetad to be cached.
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New LVM disks that appear on the system must be scanned before lvmetad
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knows about them. If lvmetad does not know about a disk, then LVM
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commands using lvmetad will also not know about it. When disks are added
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or removed from the system, lvmetad must be updated.
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lvmetad is usually combined with event-based system services that
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automatically run pvscan --cache on disks added or removed. This way,
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the cache is automatically updated with metadata from new disks when they
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appear. LVM udev rules and systemd services implement this automation.
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Automatic scanning is usually combined with automatic activation. For
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more information, see
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.BR pvscan (8).
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If lvmetad is started or restarted after disks have been added to the
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system, or if the global_filter has changed, the cache must be updated.
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This can be done by running pvscan --cache, or it will be done
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automatically by the next LVM command that's run.
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When lvmetad is not used, LVM commands revert to scanning disks for LVM
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metadata.
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In some cases, lvmetad will be temporarily disabled while it continues
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running. In this state, LVM commands will ignore the lvmetad cache and
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revert to scanning disks. A warning will also be printed which includes
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the reason why lvmetad is not being used. The most common reasons are the
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existence of duplicate PVs (lvmetad cannot cache data for duplicate PVs),
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or an 'lvconvert --repair' command has been run (the lvmetad cache may
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not be reliable while repairs are neeeded.)
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Once duplicates have been resolved, or repairs have been completed,
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the lvmetad cache is can be updated with pvscan --cache and commands
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will return to using the cache.
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Use of lvmetad is enabled/disabled by:
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.br
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.BR lvm.conf (5)
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.B global/use_lvmetad
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For more information on this setting, see:
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.br
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.B lvmconfig --withcomments global/use_lvmetad
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To ignore disks from LVM at the system level, e.g. lvmetad, pvscan use:
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.br
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.BR lvm.conf (5)
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.B devices/global_filter
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For more information on this setting, see
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.br
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.B lvmconfig --withcomments devices/global_filter
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.SH OPTIONS
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To run the daemon in a test environment both the pidfile_path and the
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socket_path should be changed from the defaults.
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.TP
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.B -f
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Don't fork, but run in the foreground.
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.TP
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.BR -h ", " -?
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Show help information.
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.TP
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.B -l \fIlevels
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Specify the levels of log messages to generate as a comma separated list.
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Messages are logged by syslog.
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Additionally, when -f is given they are also sent to standard error.
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Possible levels are: all, fatal, error, warn, info, wire, debug.
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.TP
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.B -p \fIpidfile_path
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Path to the pidfile. This overrides both the built-in default
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(#DEFAULT_PID_DIR#/lvmetad.pid) and the environment variable
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\fBLVM_LVMETAD_PIDFILE\fP. This file is used to prevent more
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than one instance of the daemon running simultaneously.
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.TP
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.B -s \fIsocket_path
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Path to the socket file. This overrides both the built-in default
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(#DEFAULT_RUN_DIR#/lvmetad.socket) and the environment variable
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\fBLVM_LVMETAD_SOCKET\fP. To communicate successfully with lvmetad,
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all LVM2 processes should use the same socket path.
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.TP
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.B -t \fItimeout_value
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The daemon may shutdown after being idle for the given time (in seconds). When the
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option is omitted or the value given is zero the daemon never shutdowns on idle.
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.TP
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.B -V
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Display the version of lvmetad daemon.
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.SH ENVIRONMENT VARIABLES
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.TP
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.B LVM_LVMETAD_PIDFILE
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Path for the pid file.
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.TP
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.B LVM_LVMETAD_SOCKET
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Path for the socket file.
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.SH SEE ALSO
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.BR lvm (8),
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.BR lvmconfig (8),
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.BR lvm.conf (5),
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.BR pvscan (8)
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