Control: tags -1 wontfix Control: close -1 On Tue, 22 Jun 2021 08:32:12 +0200 Helmut Grohne <[email protected]> wrote: > 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.
This is tracked upstream, and also as mentioned there it can't really be done because we lack the kernel APIs to check things without triggering automounts. -- Kind regards, Luca Boccassi
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