[Solved] Systemd OnFailure= Clarification

Question

I have a service unit, B, that I want to trigger if another one, A, fails.
The systemd.unit man page says this about OnFailure
OnFailure=
           Lists one or more units that are activated when this unit enters the 'failed' state.
I have this in the A.service file:
[Unit]
Conflicts=B.service
Before=B.service
OnFailure=B.service
There is also a corresponding Conflicts and After in B.service file.
I have tried with both B enabled and disabled, and each time I get the following error if A fails:
Sep 05 15:08:16 SKANKY systemd[1]: Unit A.service entered failed state.
Sep 05 15:08:16 SKANKY systemd[1]: Triggering OnFailure= dependencies of A.service.
Sep 05 15:08:16 SKANKY systemd[1]: Failed to enqueue OnFailure= job: File exists
I've obviously misunderstood something and misconfigured something, but I can't see what. Web and forum searches don't help.
I can post the actual files, but my misunderstanding seems to be more general than specific here, so I'd like to avoid sidetracks into the specifics of the services involved.
Last edited by skanky (2013-09-08 10:15:42)

Answer 1

Thanks for the reply. 
I got the need for Before/After from the manual, though I might be misunderstanding it :
Conflicts=
           Configures negative requirement dependencies. If a unit has a Conflicts= setting on
           another unit, starting the former will stop the latter and vice versa. Note that this
           setting is independent of and orthogonal to the After= and Before= ordering
           dependencies.
           If a unit A that conflicts with a unit B is scheduled to be started at the same time
           as B, the transaction will either fail (in case both are required part of the
           transaction) or be modified to be fixed (in case one or both jobs are not a required
           part of the transaction). In the latter case the job that is not the required will be
           removed, or in case both are not required the unit that conflicts will be started and
           the unit that is conflicted is stopped.
Why isn't OnFailed enough?
It might be, I can't remember if I tried that on its own. I was hoping the error message would suggest a course though, as there's a lot of combinations of settings here that all seem valid and don't seem to ruled out by the documentation. Some of which have thrown up that error message. I'm trying new things out though, as I get a chance.
EDIT:
Okay, I removed all the conflicts stuff and it worked. I'll mark as solved, though I'm still not quite sure I'm completely sure how it all ties together - eg why having Conflicts etc. stops OnFailure working.
Thanks for the nudge though.
Last edited by skanky (2013-09-08 10:15:25)