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:
The following dependencies are added unless DefaultDependencies=no is set:
Path files must include a [Path] section, which carries information about the path(s) it monitors. The options specific to the [Path] section of path units are the following:
PathExists=, PathExistsGlob=, PathChanged=, PathModified=, DirectoryNotEmpty=
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.