DMEVENTD(8) System Manager's Manual DMEVENTD(8)
NAME
dmeventd — Device-mapper event daemon
SYNOPSIS
dmeventd [-d [-d [-d]]] [-e exit_on_path] [-f] [-h] [-i] [-l] [-R] [-V]
[-?]
DESCRIPTION
dmeventd is the event monitoring daemon for device-mapper devices. Li-
brary plugins can register and carry out actions triggered when particu-
lar 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 debug-
ging 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 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 "". De-
fault value is "/run/nologin".
-f Don't fork, run in the foreground.
-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 develop-
ers. 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 a thin pool data and metadata 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 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_autoex-
tend_threshold. If the command fails, dmeventd thin plugin will
keep retrying execution with increasing time delay between re-
tries 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 free recover space in a thin pool, but also can
use lvextend --use-policies if other actions have not released
enough space. Command is executed with environmental variable
LVM_RUN_BY_DMEVENTD=1 so any lvm2 command executed in this envi-
ronment will not try to interact with dmeventd. To see the full-
ness of a thin pool command may check these two environmental
variables DMEVENTD_THIN_POOL_DATA and DMEVENTD_THIN_POOL_META-
DATA. 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 de-
fault 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 com-
mand 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 mainte-
nance operations of a VDO pool. Such external command can e.g.
remove some unneeded space with fstrim(8), but also can use lvex-
tend --use-policies if other actions have not released enough
space. Command is executed with environmental variable
LVM_RUN_BY_DMEVENTD=1 so any lvm2 command executed in this envi-
ronment will not try to interact with dmeventd. To see the full-
ness of a VDO pool command may check this environmental 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 pro-
gram. Value present 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 pro-
gram. Value present 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 pro-
gram. Value present actual usage of VDO pool data volume. Vari-
able is not set when error event is processed.
LVM_RUN_BY_DMEVENTD
Variable is set by thin and vdo plugin to prohibit recursive in-
teraction 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 2.03.31(2) (2025-02-27) DMEVENTD(8)
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