[systemd-devel] Requires and After

[Michael Chapman]

On Wed, 2 Jan 2019, Zbigniew Jędrzejewski-Szmek wrote:
> On Sun, Dec 30, 2018 at 12:05:46PM +0100, Olaf van der Spek wrote:
> > Hi,
> > 
> > Evverx suggested I ask here @ https://github.com/systemd/systemd/issues/11284
> > It's about Requires and After. I think a unit in Requires should imply
> > that unit in After too, otherwise the requirement isn't really met.
> > Is there a use case for Requires but not After?
> > If not, would it make sense to change semantics to have Requires imply After?
> 
> The short answer is that Requires without After is mostly meaningless,
> because it's impossible for systemd to actually implement the check,
> so effectively Requires downgrades to Wants.

Only on service activation though.

During deactivation, RequiredBy= dependencies (but not WantedBy= 
dependencies) are followed to enqueue further deactivation jobs.

> Two considerations though:
> - For Wants=, it is OK to not have an ordering dependency.
> 
>   So if we made Requires= imply After=, there'd be an inconsistency
>   between Requires= and Wants=.
> 
> - When .requires/ is used (and .wants/ too), an After= dependency is
>   added automatically.
> 
> I think we could consider making Requires= imply After=, with the
> necessary notices in NEWS, if somebody looks through units (e.g. all
> the ones packaged in Fedora), to verify that this is unlikely to break
> existing units. Elsewhere in the thread, somebody mentioned openstack,
> so that'd be first thing to check.

In my opinion, I don't think the extra inconsistency we get from this is 
worth it. It literally only saves one line in a unit file.