Package: systemd Version: 241-7~deb10u7 Tags: upstream Hi,
systemd provides a unit type .automount that is equipped with a parameter TimeoutIdleSec. What that time passed without anything accessing the relevant directory, the automount is umounted. That behaviour mostly works except that there is one thing that keeps accessing all mounts: systemd. Every time a path-restricted unit (i.e. one using InaccessiblePaths/ReadWritePaths/ReadOnlyPaths, e.g. implied by DynamicUser=yes) is started, systemd calls statfs on every mount point. statfs in turn tells autofs that the filesystem is in use (unless specifying the "strictexpire" option, see https://github.com/systemd/systemd/issues/18445). If services are started sufficiently frequently, automounts never expire. A workaround can be listing all automount paths as InaccessiblePaths for frequently started .service units. In any case, this behaviour is far from ideal. We'll only see more and more units making use of these kind of restrictions and with more units using them, automount timeouts become completely useless. I think this needs to be solved on the systemd side for good. I wasn't able yet to reproduce this on a more recent version of systemd. Therefore, I'm not reporting it upstream. I am reasonably confident that this issue persists upstream. Sketch for reproducing: * Create an .automount unit with a TimeoutIdleSec of e.g. 5 minutes. A tmpfs should do. * Create a Type=oneshot .service unit that e.g. runs /bin/true with DynamicUser=true. * Create a matching .timer unit that runs the previous unit once a minute. * Access the automount. * Observe that it never gets umounted. * Optionally strace -e trace=statfs -f -p 1 to see who keeps the filesystem mounted. Helmut
