Systemd LimitNOFILE capped to 4096

Question

I have a systemd user service with LimitNOFILE set. The value is respected until it hits 4096. After that point, it's capped to 4096. I've also tried increasing DefaultLimitNOFILE in /etc/systemd/user.conf.

It's set correctly in limits.conf, which works for new shells out of the box. Though, I heard systemd doesn't care about that file. What could be the problem?

Solution 1

Late answer; limits.conf is not used when systemd is running (limits.conf is for non-systemd systems).

The file you actually want is; /etc/systemd/system.conf - this is the global config. Then you have /etc/systemd/user.conf - this specifies further per-user restrictions.

Specifically in your case; even though you have configured user.conf with a higher limit, this is not valid as the limit in system.conf is lower, and acts as a cap on the limit in user.conf

O_O

Solution 2

From man systemd.exec:

For system units these resource limits may be chosen freely. For user units however (i.e. units run by a per-user instance of systemd(1)), these limits are bound by (possibly more restrictive) per-user limits enforced by the OS.

Your system probably has a configured hard limit of 4096 open files per process. It would open up a loophole if systemd allowed you to bypass this limit.

Comments

[Free Bullets]

Thanks for the man page reference. I'm not sure that's quite it since I have limits.conf configured, but it should get me further troubleshooting.