systemd.path — Path unit configuration
path.path
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.
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.
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.
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 similar, 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 path(s) 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.