lvm2/man/lvmetad.8.in

.TH LVMETAD 8 "LVM TOOLS #VERSION#" "Red Hat Inc" \" -*- nroff -*-
.SH NAME
lvmetad \(em LVM metadata cache daemon

.SH SYNOPSIS
.B lvmetad
.RB [ \-l
.IR level [,level...]]
.RB [ \-p
.IR pidfile_path ]
.RB [ \-s
.IR socket_path ]
.RB [ \-t
.IR timeout_value ]
.RB [ \-f ]
.RB [ \-h ]
.RB [ \-V ]
.RB [ \-? ]

.SH 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
.BR 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:
.br
.BR lvm.conf (5)
.B global/use_lvmetad

For more information on this setting, see:
.br
.B lvmconfig \-\-withcomments global/use_lvmetad

To ignore disks from LVM at the system level, e.g. lvmetad, pvscan use:
.br
.BR lvm.conf (5)
.B devices/global_filter

For more information on this setting, see
.br
.B lvmconfig \-\-withcomments devices/global_filter

.SH OPTIONS

To run the daemon in a test environment both the pidfile_path and the
socket_path should be changed from the defaults.
.TP
.B \-f
Don't fork, but run in the foreground.
.TP
.BR \-h ", " \-?
Show help information.
.TP
.B \-l \fIlevels
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.
.TP
.B \-p \fIpidfile_path
Path to the pidfile. This overrides both the built-in default
(#DEFAULT_PID_DIR#/lvmetad.pid) and the environment variable
\fBLVM_LVMETAD_PIDFILE\fP.  This file is used to prevent more
than one instance of the daemon running simultaneously.
.TP
.B \-s \fIsocket_path
Path to the socket file. This overrides both the built-in default
(#DEFAULT_RUN_DIR#/lvmetad.socket) and the environment variable
\fBLVM_LVMETAD_SOCKET\fP.  To communicate successfully with lvmetad,
all LVM2 processes should use the same socket path.
.TP
.B \-t \fItimeout_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.
.TP
.B \-V
Display the version of lvmetad daemon.
.SH ENVIRONMENT VARIABLES
.TP
.B LVM_LVMETAD_PIDFILE
Path for the pid file.
.TP
.B LVM_LVMETAD_SOCKET 
Path for the socket file.

.SH SEE ALSO
.BR lvm (8),
.BR lvmconfig (8),
.BR lvm.conf (5),
.BR pvscan (8)