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

.SH SYNOPSIS
.B lvmetad
.RB [ \-l
.RI { all | wire | debug }]
.RB [ \-p
.IR pidfile_path ]
.RB [ \-s
.IR socket_path ]
.RB [ \-f ]
.RB [ \-h ]
.RB [ \-V ]
.RB [ \-? ]

.SH DESCRIPTION

The lvmetad daemon caches LVM metadata, so that LVM commands can read
metadata without scanning disks.

Metadata caching can be an advantage because scanning disks is time
consuming and may interfere with the normal work of the system and disks.

lvmetad does not read metadata from disks itself.  The 'pvscan \-\-cache'
command scans disks, reads the LVM metadata and sends it to lvmetad.

New LVM disks that appear on the system must be scanned by pvscan 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 new disks.  This way, the lvmetad
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 by
running 'pvscan \-\-cache'.

When lvmetad is not used, LVM commands revert to scanning disks for LVM
metadata.

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
.IR \fB\-l " {" all | wire | debug }
Select the type of log messages to generate.
Messages are logged by syslog.  
Additionally, when \-f is given they are also sent to standard error.
Since release 2.02.98, there are two classes of messages: wire and debug.
Selecting 'all' supplies both and is equivalent to a comma-separated list
\-l wire,debug.
Prior to release 2.02.98, repeating \-d from 1 to 3 times, viz. \-d, \-dd, \-ddd,
increased the detail of messages.
.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 \-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)