[systemd-devel] systemctl start second.service first.service

[Uoti Urpala]

On Thu, 2018-01-11 at 15:34 +0100, Reindl Harald wrote:
> Am 11.01.2018 um 15:25 schrieb Uoti Urpala:
> > I'd guess this is due to systemctl starting each listed unit
> > independently rather than as a single transaction. Thus, the second
> > version first starts second.service without first.service being active
> > at all. Since there's only an After relationship, not Wants/Requires,
> > second.service will immediately start. Then systemctl starts
> > first.service; since second.service is already running, there's nothing
> > the After relationship could affect
> 
> but why?
> 
> the one "After=" should be enough to have a clear ordering of stop/start 
> both as it happens in shutdown/boot

At boot, both would be started as part of the same transaction (same
would happen here if you started a third.service that depended on both
first.service and second.service, then second.service would always
wait). Here second.service is just started individually, and systemd
has no idea at that time that first.service is going to be running at
all. Given that, it really can't behave any differently (it can't delay
the start of second.service to wait for first.service, when as far as
it knows first.service may well never get started at all!). It's only
after second.service is already running that it sees that first.service
will be started, and at that point it's too late to make second.service
wait. There really is nothing the init portion could do differently
given the semantics of bare "After" (the behavior could be changed in
the systemctl binary).