[systemd-devel] restart vs. stop/start

[Christian Boltz]

Hello,

Am Montag, 23. Mai 2016, 11:24:06 CEST schrieb Lennart Poettering:
> On Fri, 20.05.16 21:50, Christian Boltz wrote:
> > it looks like
> > 
> >     systemctl restart foo
> > 
> > is internally mapped to a sequence of
> > 
> >     systemctl stop foo; systemctl start foo
> > 
> > Unfortunately, this behaviour causes quite some trouble for me.
> > 
> > I need a way to know if "restart "or "stop" was used because the
> > mapping to stop / start gives my service a completely different
> > behaviour than expected on restart.
> 
> We don't support that as our logic permits merging of jobs. This means
> that if two clients enqueue two stop or two start jobs at the same
> time, then we will only actually run one. In fact, this merging of
> jobs goes even further: restart and start can be merged. And that
> means there's really no clear concept of "My service is being stopped
> for a restart", as your service might actually be stopped on request
> of 7 clients, where 4 wanted to start it, 1 wanted to stop it, and 2
> wanted to restart it....

I'm mostly interested in catching manual restarts done by an admin (the 
RPM %post scripts already use reload as they should [1]), so this 
wouldn't be a problem.

> > Is there a way to find out if "stop" or "restart" was used?
> 
> No, not really... Except that you could misuse the fd store logic for
> this, as you already found out...

So you are saying that I'll need to add a small keep-the-fd-open daemon 
to find out if restart was used?

I'm not too keen on doing this, and would really like to have an 
"official" way to find this out. Especially since systemd already knows 
this, so making that information available to the service should be 
trivial.

> Usually mapping issues like what you are running into indicate though
> that the mapping is skewed, and you are trying to make the "restart"
> verb something that the "reload" verb actually exists for.

You are right that "reload" is what people _should_ use.

However, as I already wrote in another mail, accidently using "restart" 
will make the system insecure, so I'd like to change the restart 
behaviour to do something sane (for AppArmor, it should reload the 
profiles).


Regards,

Christian Boltz

[1] I had to override the default RPM macros for that ;-)
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