SYSTEMD.PATH(5) systemd.path SYSTEMD.PATH(5)
NAME
systemd.path - Path unit configuration
SYNOPSIS
path.path
DESCRIPTION
A unit configuration file whose name ends in ".path" encodes
information about a path monitored by systemd, for path-based
activation.
This man page lists the configuration options specific to this unit
type. See systemd.unit(5) for the common options of all unit
configuration files. The common configuration items are configured in
the generic [Unit] and [Install] sections. The path specific
configuration options are configured in the [Path] section.
For each path file, a matching unit file must exist, describing the
unit to activate when the path changes. By default, a service by the
same name as the path (except for the suffix) is activated. Example: a
path file foo.path activates a matching service foo.service. The unit
to activate may be controlled by Unit= (see below).
Internally, path units use the inotify(7) API to monitor file systems.
Due to that, it suffers by the same limitations as inotify, and for
example cannot be used to monitor files or directories changed by other
machines on remote NFS file systems.
When a service unit triggered by a path unit terminates (regardless
whether it exited successfully or failed), monitored paths are checked
immediately again, and the service accordingly restarted instantly. As
protection against busy looping in this trigger/start cycle, a start
rate limit is enforced on the service unit, see StartLimitIntervalSec=
and StartLimitBurst= in systemd.unit(5). Unlike other service failures,
the error condition that the start rate limit is hit is propagated from
the service unit to the path unit and causes the path unit to fail as
well, thus ending the loop.
AUTOMATIC DEPENDENCIES
Implicit Dependencies
The following dependencies are implicitly added:
• If a path unit is beneath another mount unit in the file system
hierarchy, both a requirement and an ordering dependency between
both units are created automatically.
• An implicit Before= dependency is added between a path unit and the
unit it is supposed to activate.
Default Dependencies
The following dependencies are added unless DefaultDependencies=no is
set:
• Path units will automatically have dependencies of type Before= on
paths.target, dependencies of type After= and Requires= on
sysinit.target, and have dependencies of type Conflicts= and
Before= on shutdown.target. These ensure that path units are
terminated cleanly prior to system shutdown. Only path units
involved with early boot or late system shutdown should disable
DefaultDependencies= option.
OPTIONS
Path unit files may include [Unit] and [Install] sections, which are
described in systemd.unit(5).
Path unit files must include a [Path] section, which carries
information about the path or paths it monitors. The options specific
to the [Path] section of path units are the following:
PathExists=, PathExistsGlob=, PathChanged=, PathModified=,
DirectoryNotEmpty=
Defines paths to monitor for certain changes: PathExists= may be
used to watch the mere existence of a file or directory. If the
file specified exists, the configured unit is activated.
PathExistsGlob= works similarly, but checks for the existence of at
least one file matching the globbing pattern specified.
PathChanged= may be used to watch a file or directory and activate
the configured unit whenever it changes. It is not activated on
every write to the watched file but it is activated if the file
which was open for writing gets closed. PathModified= is similar,
but additionally it is activated also on simple writes to the
watched file. DirectoryNotEmpty= may be used to watch a directory
and activate the configured unit whenever it contains at least one
file.
The arguments of these directives must be absolute file system
paths.
Multiple directives may be combined, of the same and of different
types, to watch multiple paths. If the empty string is assigned to
any of these options, the list of paths to watch is reset, and any
prior assignments of these options will not have any effect.
If a path already exists (in case of PathExists= and
PathExistsGlob=) or a directory already is not empty (in case of
DirectoryNotEmpty=) at the time the path unit is activated, then
the configured unit is immediately activated as well. Something
similar does not apply to PathChanged= and PathModified=.
If the path itself or any of the containing directories are not
accessible, systemd will watch for permission changes and notice
that conditions are satisfied when permissions allow that.
Unit=
The unit to activate when any of the configured paths changes. The
argument is a unit name, whose suffix is not ".path". If not
specified, this value defaults to a service that has the same name
as the path unit, except for the suffix. (See above.) It is
recommended that the unit name that is activated and the unit name
of the path unit are named identical, except for the suffix.
MakeDirectory=
Takes a boolean argument. If true, the directories to watch are
created before watching. This option is ignored for PathExists=
settings. Defaults to false.
DirectoryMode=
If MakeDirectory= is enabled, use the mode specified here to create
the directories in question. Takes an access mode in octal
notation. Defaults to 0755.
TriggerLimitIntervalSec=, TriggerLimitBurst=
Configures a limit on how often this path unit may be activated
within a specific time interval. The TriggerLimitIntervalSec= may
be used to configure the length of the time interval in the usual
time units "us", "ms", "s", "min", "h", ... and defaults to 2s. See
systemd.time(7) for details on the various time units understood.
The TriggerLimitBurst= setting takes a positive integer value and
specifies the number of permitted activations per time interval,
and defaults to 200. Set either to 0 to disable any form of trigger
rate limiting. If the limit is hit, the unit is placed into a
failure mode, and will not watch the paths anymore until restarted.
Note that this limit is enforced before the service activation is
enqueued.
Check systemd.unit(5), systemd.exec(5), and systemd.kill(5) for more
settings.
SEE ALSO
Environment variables with details on the trigger will be set for
triggered units. See the "Environment Variables Set on Triggered Units"
section in systemd.exec(1) for more details.
systemd(1), systemctl(1), systemd.unit(5), systemd.service(5),
inotify(7), systemd.directives(7)
systemd 252 SYSTEMD.PATH(5)
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