Systemd >=240 sets a clamp of 64MB for RLIMIT_MEMLOCK, too low for some applications.

[Kain]

Systemd >= 240 sets a clamp for RLIMIT_MEMLOCK, which is too low for some realistic applications. This clamp should probably be increased. This breaks a number of current jackd setups, for example.

See upstream bug: https://github.com/systemd/systemd/issues/13331.

This occurs on at Ubuntu Disco and newer, Disco being the first release to ship with systemd >= 240.

[Dan Streetman (ddstreet)]

> This breaks a number of current jackd setups, for example.

please provide steps to reproduce the problem.

[Kain (kain-kain)]

Upon further inspection, this is actually fixed in systemd 241. To reproduce, try setting a LimitMEMLOCK higher than 64mb for the system unit user@.service, OR for any unit executed by a systemd --user process. You will see that the RLIMIT_MEMLOCK is actually clamped to 64MB. This can be observed by using prlimit -p <<any-process-id-inside-or-spawned-by-such-a-unit>>.

You can reproduce by trying to give a user session (via user@.service OR /etc/systemd/user.conf) a LimitMEMLOCK of greater than 64MB and then inside a systemd unit or inside a gnome-terminal (since gnome terminals in at least disco and newer are run under a systemd user-service) try to execute `jackd -d hw:0 -r 48000 -p 256 -n 3 -S`. You may need to suspend/stop pulseadio.

On my system at least (USB audio only), jackd wants to memlock 82280346 bytes (82MBish) of RAM for audio buffers and the like.

[Balint Reczey (rbalint)]

Marking as fixed in Eoan, since it already has systemd v242.

[Kain (kain-kain)]

Fix attached. Works on disco.