Systemd path units

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These are the notes of a training course on systemd I gave as part of my work with Truelite.

This kind of unit can be used to monitor a file or directory for changes using inotify, and activate other units when an event happens.

For example, this activates a unit that manages a spool directory, which activates another unit whenever a .pdf file is added to /tmp/spool/:

[Unit]
Description=Monitor /tmp/spool/ for new .pdf files

[Path]
Unit=beeponce.service
PathExistsGlob=/tmp/spool/*.pdf
MakeDirectory=true

This instead activates another unit whenever /tmp/ready is changed, for example by someone running touch /tmp/ready:

[Unit]
Description=Monitor /tmp/ready

[Path]
Unit=beeponce.service
PathChanged=/tmp/ready

And beeponce.service:

[Unit]
Description=Beeps once

[Service]
Type=oneshot
ExecStart=/usr/bin/aplay /tmp/beep.wav