make all the processes of a given user killable by anyone

Give the other users permission to kill the processes as the low priority user through

sudo -u lowpriouser /bin/kill PID

A user can only signal their own processes, unless they have root privileges. By using sudo -u a user with the correct set-up in the sudoers file may assume the identity of the low priority user and kill the process.

For example:

%killers ALL = (lowpriouser) /bin/kill

This would allow all users in the group killers to run /bin/kill as lowpriouser.

See also the sudoers manual on your system.

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On an OpenBSD system, the same can be done through the native doas utility with a configuration like

permit :killers as lowpriouser cmd /bin/kill

Then

doas -u lowpriouser /bin/kill PID

See the manuals for doas and doas.conf.

You shouldn't kill the processes, if they're low priority they'll consume few resources.

To actually make them low priority, either change their priority manually, or use a daemon like autonice that I wrote for DEC OSF/1 many years ago (c. 1994) that looks for long-running jobs and progressively reduces their priority the longer they run.

EDIT there's a package called and that offers this functionality for modern Unices.

I think you approach the issue from the wrong angle: If a process is run at low priority settings (CPU, I/O) it shouldn't affect other processes much because it won't be scheduled to run. As for memory usage, if main memory is tight and the process wasn't scheduled to run in a long time (e. g. due to CPU and I/O constraints), its “clean” pages are dropped and its “dirty” pages are committed or swapped out and no longer affect the performance of other processes.

Conclusion: with the right priority setting and sufficient swap space it should be unnecessary to kill low priority jobs to make “room“ for more important tasks; instead the kernel will take care to put the former to sleep in favour of the latter.