Bug#856985: systemd: Uninstalling systemd-cron hangs/crashes systemd

[Michael Biebl]

Am 06.03.2017 um 22:53 schrieb Andreas Bombe:
> Package: systemd
> Version: 215-17+deb8u6
> Severity: important
> 
> I have a rented virtual server running jessie. The virtualization
> environment is OpenVZ according to hostnamectl.
> 
> There are problems with the jessie version of systemd-cron (crontab
> doesn't work without existing crontab files) so I wanted to switch to
> regular cron.  I think it was at the "processing systemd triggers" stage
> that the installation process hung.
> 

Narrowing it down, I think what happens is:
systemd-cron installs a cron-update.path unit which in turn starts a
cron-update.service whenever there are changes to

 [Path]
 PathChanged=/etc/crontab
 PathChanged=/etc/cron.d
 PathChanged=/etc/anacrontab
 PathChanged=/var/spool/cron/crontabs

cron-update.service runs

 [Service]
 Type=oneshot
 ExecStartPre=/bin/systemctl daemon-reload
 ExecStart=/bin/systemctl try-restart cron.target

cron-update.service
So, upon removal of the package, a start of cron-update.service is
triggered via cron-update.path, i.e. we trigger a daemon-reload at point
when the files are removed underneath systemd.


My suggestion would be, that systemd-cron stops cron-update.path in
prerm on "remove", to disable path triggering at a point where the
package is in an inconsistent state.

This seems to me to be the least invasive fix for jessie by avoiding the
situation which can trigger the crash.

Andreas, can you confirm that stopping the cron-update.path unit prior
to the removal avoids the crash? You will have to edit
/lib/systemd/system/cron-update.path to remove
 RefuseManualStart=true
 RefuseManualStop=true


-- 
Why is it that all of the instruments seeking intelligent life in the
universe are pointed away from Earth?

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