DMEVENTD(8)

NAME
dmeventd — Device-mapper event daemon

SYNOPSIS
[-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)