[systemd-devel] Requested transaction contradicts existing jobs: start is destructive

[Mark Bannister]

I've been trying to find the cause of a 'transaction is destructive' error
from systemd.  I'm testing systemd-219-67.el7_7.4 with the following patch
applied:

https://github.com/systemd/systemd/commit/cf99f8eacf1c864b19a6a02edea78c43f3185cb7

One of the error messages I've been trying to explain is reported like this:

2020-04-22T00:45:47.047710-04:00 jupiter systemd[1]: Requested transaction
contradicts existing jobs: Transaction for session-752473.scope/start is
destructive (user-16027.slice has 'stop' job queued, but 'start' is
included in transaction).
2020-04-22T00:45:47.047985-04:00 jupiter systemd[1]: Removed slice User
Slice of userlp.
2020-04-22T00:45:47.048159-04:00 jupiter systemd-logind[1402]: Failed to
start session scope session-752473.scope: Transaction for
session-752473.scope/start is destructive (user-16027.slice has 'stop' job
queued, but 'start' is included in transaction).


This also coincides with a message from sshd:

2020-04-22T00:45:47.049949-04:00 jupiter sshd[20984]:
pam_unix(sshd:session): session opened for user userlp by (uid=0)
2020-04-22T00:45:51.181665-04:00 jupiter sshd[20984]:
pam_unix(sshd:session): session closed for user userlp


I'm not sure where to begin to troubleshoot the problem.  The systemd error
is occurring sporadically and I haven't yet found a way to reproduce it.  I
also can't say I actually understand the error message or what I'm supposed
to do about it.  How is it even possible for stop and start jobs to clash
like this?

If someone could please provide a little guidance here, your help will be
much appreciated.

Thanks in advance!
Mark
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