[systemd-devel] failing unmounts during reboot

[Mantas Mikulėnas]

On Thu, Jul 25, 2019 at 12:49 PM Frank Steiner <
fsteiner-mail1 at bio.ifi.lmu.de> wrote:

> Hi,
>
> I'm currently discussing a problem with the SuSE support about failing
> unmounts during reboot. Tyring to debug this I realized that systemd
> is not killing processes left over by some init.d script. E.g. use
> the following script in /etc/init.d/
>
> #!/bin/sh
> #
> ### BEGIN INIT INFO
> # Provides: bla
> # Required-Start: $network $remote_fs sshd
> # Required-Stop: $network $remote_fs sshd
> # Default-Start:  2 3 5
> # Description:    test
> ### END INIT INFO
> case "$1" in
>       start) cd /test; /usr/bin/sleep 99d & ;;
>        stop) true;;
> esac
>
>
> On shutdown, unmounting /test will fail because the sleep process is
> not killed. Shouldn't there be a mechanism in system to kill processes
> spawned by LSB script when shutting these down?
>

I think that's a deliberate decision made in the systemd-sysv-generator.
Note how the generated .service files have "KillMode=process" (and even
"RemainAfterExit=yes"). The default for native services is to kill the
entire cgroup, and IIRC that even was one of the main reasons for using
cgroups.

Most likely it's there to retain compatibility with some of the weirder
init.d scripts – those which don't start any daemons; those which start
several; and so on and so on.


>
> And moreover, wouldn't it make sense to have a mechanism to at least
> try to kill all processes using a filesystem before unmounting it?
> We often see failing unmounts of several local or iscsi fs during
> reboot, and in the support case we are currently working on with SuSE
> failing iscsi fs even cause xfs I/O errors. So it might be a good idea
> to have sth. like a lsof + kill before unmounting a filesystem, maybe
> configurable with a flag to enable or disable it. Even if lsof or kill
> failed, it wouldn't be worse than now.
>

IIRC the idea is that user sessions are killed during shutdown before
unmounting anything anyway, and services have implicit
After=local-fs.target so they get stopped before local filesystems? The
shutdown process is one area that I still know very little about.


>
> As far as I see there is no way to write a drop-in for a mount unit
> that allows to execute commands before the unmount happens, is that
> right? Sth. like "ExecPreUmount=" would help here, especially if there
> was sth. like a umount at .service that would be called for every umount
> with e.g. the mounpoint accessable with a variable.
>

No, there isn't.

-- 
Mantas Mikulėnas
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