Avoid missing changes with PathChanged while unit is running

Feuermurmel

5/17/24, 5:44 PM

I want to monitor a file and run a command that applies the content of the file to my system, whenever the file it changes. I'm currently using a path unit triggering a service unit to do that. In the example below, the command simply copies the contents of /somefile to /otherfile:

# /etc/systemd/system/example.unit
[Service]
ExecStart=/usr/bin/cp /somefile /otherfile

# /etc/systemd/system/example.path
[Path]
PathChanged=/somefile

[Install]
WantedBy=default.target

The problem I'm facing is that /somefile might be changed/replaced while the command is running. To make sure that /otherfile always ends up with the same content as /somefile, the service would need to be restarted after it completes in that case, but I couldn't find a directive for path units that does that.

Even if the command would check that /somefile hasn't changed while copying, there is a window between that check and the service unit terminating, where the file could be changed without the unit being restarted.

How can I implement this using systemd?

0 + 0

systemd

Elon Musk

I sit in a Tesla and translated this thread with Ai:

EN: Avoid missing changes with PathChanged while unit is running

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