DMEVENTD(8)		    System Manager's Manual		   DMEVENTD(8)

NAME
       dmeventd — Device-mapper event daemon

SYNOPSIS
       dmeventd [-d [-d [-d]]] [-e exit_on_path] [-f] [-g seconds] [-h] [-i]
		[-l] [-R] [-V] [-?]

DESCRIPTION
       dmeventd is the event monitoring daemon for device-mapper devices.
       Library plugins can register and carry out actions triggered when
       particular events occur.

OPTIONS
       -d     Repeat from 1 to 3 times (-d, -dd, -ddd) to increase the detail
	      of debug messages sent to syslog.	 Each extra d adds more
	      debugging information.

       -e exit_on_path
	      Specifies the file path whose presence is checked by the daemon
	      when it receives a signal (SIGINT, SIGTERM) and allows it to
	      exit even if there are still monitored devices.  This can help
	      with system shutdown where devices have not been unmonitored
	      properly.	 To disable this behavior set this to the empty string
	      "".  Default value is "/run/nologin".

       -f     Don't fork, run in the foreground.

       -g seconds
	      Set the grace period for monitoring thread cleanup (0-300
	      seconds, default: 10).  During this period, monitoring threads
	      that have finished processing events will wait for potential
	      reuse rather than immediately terminating.  If the same device
	      and plugin combination is registered again within the grace
	      period, the existing thread is reused, significantly reducing
	      overhead. Set to 0 to disable thread reuse.

       -h     Show help information.

       -i     Query the running daemon instance for the status information.
	      The format is internal and unstable and it is targeted for
	      developers.  Format may change between versions.

       -l     Log through stdout and stderr instead of syslog.	This option
	      works only with option -f, otherwise it is ignored.

       -?     Show help information on stderr.

       -R     Replace a running dmeventd instance. The running dmeventd must
	      be version 2.02.77 or newer. The new dmeventd instance will
	      obtain a list of devices and events to monitor from the
	      currently running daemon.

       -V     Show version of dmeventd.

LVM PLUGINS
       Mirror Attempts to handle device failure automatically.	See
	      lvm.conf(5).

       Raid   Attempts to handle device failure automatically.	See
	      lvm.conf(5).

       Snapshot
	      Monitors how full a snapshot is becoming and emits a warning to
	      syslog when it exceeds 80% full.	The warning is repeated when
	      85%, 90% and 95% of the snapshot is filled.  See lvm.conf(5).
	      Snapshot which runs out of space gets invalid and when it is
	      mounted, it gets umounted if possible.

       Thin   Monitors how full thin pool data and metadata are becoming and
	      emits a warning to syslog when it exceeds 80% full.  The warning
	      is repeated when more than 85%, 90% and 95% of the thin pool is
	      filled. See lvm.conf(5).	When a thin pool fills over 50% (data
	      or metadata) thin plugin calls configured dmeventd/thin_command
	      with every 5% increase.  With default setting it calls internal
	      lvm lvextend --use-policies to resize thin pool when it's been
	      filled above configured threshold
	      activation/thin_pool_autoextend_threshold.  If the command
	      fails, dmeventd thin plugin will keep retrying execution with
	      increasing time delay between retries up to 42 minutes.  User
	      may also configure external command to support more advanced
	      maintenance operations of a thin pool.  Such external command
	      can e.g. remove some unneeded snapshots, use fstrim(8) to
	      recover free space in a thin pool, but also can use lvextend
	      --use-policies if other actions have not released enough space.
	      Command is executed with environment variable
	      LVM_RUN_BY_DMEVENTD=1 so any lvm2 command executed in this
	      environment will not try to interact with dmeventd.  To see the
	      fullness of a thin pool command may check these two environment
	      variables DMEVENTD_THIN_POOL_DATA and
	      DMEVENTD_THIN_POOL_METADATA.  Command can also read status with
	      tools like lvs(8).

       Vdo    Monitors how full a VDO pool data is becoming and emits a
	      warning to syslog when it exceeds 80% full.  The warning is
	      repeated when more than 85%, 90% and 95% of the VDO pool is
	      filled. See lvm.conf(5).	When a VDO pool fills over 50% vdo
	      plugin calls configured dmeventd/vdo_command with every 5%
	      increase.	 With default setting it calls internal lvm lvextend
	      --use-policies to resize VDO pool when it's been filled above
	      the configured threshold
	      activation/vdo_pool_autoextend_threshold.	 If the command fails,
	      dmeventd vdo plugin will keep retrying execution with increasing
	      time delay between retries up to 42 minutes.  User may also
	      configure external command to support more advanced maintenance
	      operations of a VDO pool.	 Such external command can e.g. remove
	      some unneeded space with fstrim(8), but also can use lvextend
	      --use-policies if other actions have not released enough space.
	      Command is executed with environment variable
	      LVM_RUN_BY_DMEVENTD=1 so any lvm2 command executed in this
	      environment will not try to interact with dmeventd.  To see the
	      fullness of a VDO pool command may check this environment
	      variable DMEVENTD_VDO_POOL.  Command can also read status with
	      tools like lvs(8).

ENVIRONMENT VARIABLES
       DMEVENTD_THIN_POOL_DATA
	      Variable is set by thin plugin and is available to executed
	      program.	Value represents actual usage of thin pool data
	      volume.  Variable is not set when error event is processed.

       DMEVENTD_THIN_POOL_METADATA
	      Variable is set by thin plugin and is available to executed
	      program.	Value represents actual usage of thin pool metadata
	      volume.  Variable is not set when error event is processed.

       DMEVENTD_VDO_POOL
	      Variable is set by vdo plugin and is available to executed
	      program.	Value presents actual usage of VDO pool data volume.
	      Variable is not set when error event is processed.

       LVM_RUN_BY_DMEVENTD
	      Variable is set by thin and vdo plugin to prohibit recursive
	      interaction with dmeventd by any executed lvm2 command from a
	      thin_command, vdo_command environment.

SEE ALSO
       lvm(8), lvm.conf(5), lvextend(8),

       fstrim(8)

Red Hat, Inc.	       DM TOOLS 2.03.35(2) (2025-09-09)		   DMEVENTD(8)