Why can't ExecStopPre= be used to abort stopping a (broken) service?

[Lennart Poettering]

On Mon, 15.07.13 14:18, Paul Wouters (pwouters at redhat.com) wrote:

> 
> Hi,
> 
> For daemons, it happens that people (or puppet/ansible) makes a config
> change that causes the config file to not load and be invalid. When
> restarting the service, it will stop but not start. Ideally, the stop
> should be aborted.
> 
> I was looking at ExecStopPre= (which is mentioned in the systemd.service
> man page, although it does not have its own section, so is easilly
> missed) but it did not abort the stop on a parse error in the daemon's
> config file.
> 
> I found this note by Lennart: http://osdir.com/ml/fedora-devel-list/2011-05/msg00696.html
> 
> 	No, ExecStopPre= cannot be used for making shutdown of a service
> 	conditional. Even if one of the pre lines fails we will go on with
> 	shutting down the service, however we will store the exit code and the
> 	service will be in "failed" state once fully shut down.
> 
> My question is, why not? Various daemons (libreswan, bind, knot, nsd,
> etc) have a "check config" option that could be used to prevent stopping
> a service if the config file got messed up so it would prevent the
> service from starting.
> 
> I realise that it is not optimal to keep a service running that will fail to
> restart on the next machine boot, but is that preferable over failing
> immediately? If ExecStopPre= would fail and log a message, sysadmins
> would be able to notice the issue and fix it. And there would be 0
> downtime. As opposed to the current behaviour, which kills the service.
> 
> However, if ExecStopPre= would support this, then every maintainer could
> choose for themselves which situation is preferred.

If I grok correctly what you are asking for, you are actually looing for
an ExecRestartPre=, not an ExecStopPre=. You want somthing that is run
before we stop a service when we intend to restart it. But when we
shutdown the system and stop the service for that, or if the user wants
to stop it manually, we shouldn't run it, correct?

If that's what you want, then yes, it is on the TODO list to add
something like this, but ExecStopPre= is not what you want, it would
have very different semantics.

Lennart

-- 
Lennart Poettering - Red Hat, Inc.