Running a systemd service unit at next boot, but not subsequent boots

Question

I have a script that I want to run during my next system boot, but not on subsequent boots. I want to use systemd to launch it, so I created a service file at /usr/lib/systemd/system/myscript.service:

[Unit]
Description=My script.

[Service]
Type=oneshot
ExecStart=/opt/mypackage/bin/myscript

[Install]
WantedBy=multi-user.target

I can tell systemd to run this service at boot using systemctl enable myscript.service.

What do I need to do in order to stop it from running on subsequent boots?

I can add systemctl disable myscript.service to the end of my script, but then that always disables the service. If possible I would like to be able to enable the service, then start it, and still have it execute on next boot.

Answer 1

You may use the ConditionPathExists= directive (see systemd.unit(5)) to conditionally start a unit. This allows you to leave the unit permanently enabled and to (temporarily) disable it by deleting a simple file.

There is no distinction between "started at boot" and "started from systemctl start" in systemd. A workaround would be to check the uptime in your script in order to take the decision to enable/disable the unit on next boot (by deleting/creating the ConditionPathExists= file).

Answer 2

Note: this answer extends the answer by Timothée Ravier _{^{(Timothée previously used the name Siosm on this site)}}, and includes an alternative solution.  If you agree with the first part, please up vote Timothée’s answer instead.

In vein with Timothée Ravier’s answer, use ConditionPathExists= in section [Unit] of the unit’s service file (see systemd.unit(5) at freedesktop.org or at man7.org) in order to make the running of your service conditional.

For instance, if myscript’s responsibility is to create a file or a folder once, add startup conditions that reflect this: ConditionPathExists=!/path/to/folder.  Note the !, which negates (inverts) the sense of the condition; the service unit is started only if the path does not exist.

Conversely, you can have the ConditionPathExists point to a file such as /var/tmp/myscript.on-next-reboot that the script is tasked to remove after running successfully.  You can probably add the removal as the unit’s ExecStartPost= directive.

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In general, though, you should try to work your system so that after-reboot actions are not necessary. Setting things to run at next boot is very "Windows-like" in attitude. Linux users and administrators tend to favor deterministic, modular and previsible boots; having conditional run-time values trigger different paths of boot makes boot system much harder to reason about, and it makes it more prone to breakage.