[systemd-devel] Help regarding service dependency

[Amit Saha]

----- Original Message -----
> From: "Lennart Poettering" <lennart at poettering.net>
> To: "Amit Saha" <asaha at redhat.com>
> Cc: "systemd Mailing List" <systemd-devel at lists.freedesktop.org>
> Sent: Tuesday, March 25, 2014 7:49:08 AM
> Subject: Re: [systemd-devel] Help regarding service dependency
> 
> On Thu, 13.03.14 21:25, Amit Saha (asaha at redhat.com) wrote:
> 
> > Hello,
> > 
> > We have service1 which starts in default.target, and we want it to start
> > After service2
> > (systemd-readahead-done) which starts after the default.target is reached.
> > So, I think what would happen in this case is the After=service2 for
> > service1 is ignored
> > and it is started before service2 since the default.target must be reached.
> > 
> > For more specific info, here is a snippet of the .timer file for service2:
> > 
> > [Unit]
> > Description=Stop Read-Ahead Data Collection 10s After Completed Startup
> > Documentation=man:systemd-readahead-replay.service(8)
> > DefaultDependencies=no
> > Conflicts=shutdown.target
> > After=default.target
> > Before=shutdown.target
> > ConditionVirtualization=no
> > 
> > [Timer]
> > OnActiveSec=30s
> > 
> > 
> > A colleague suggested creating a new target for service1 which
> > the system boots into and has a After=default.target,
> > systemd-readahead-done.service.
> > Even if not exactly how I mention, this idea holds promise.
> > 
> > Also, is there any other suggested solution involving fiddling with the
> > unit dependencies
> > but not the system boot target?
> 
> Note entirely sure I grok what you want to do, but note that if a unit
> is pulled in by a target unit via Wants= and both the unit and the
> target unit DefaultDependencies=yes (which is the default), then you
> will implicitly get an After= added too, so that the target unit is only
> reached after the unit is started.
> 
> Or in other words: if you want to order a unit foo.service *after* a
> target bar.target you want to pull it in from, then you need to set
> DefaultDependencies=no and After=bar.target in it.
> 
> The unit you listed above does exactly that, if you look closely.

Thanks Lennart. That solves what I wanted to achieve.

For the record, here is how my service now looks like:

[Unit]
Description=The Beaker Harness server.
After=network.target NetworkManager-wait-online.service time-sync.target systemd-readahead-done.service multi-user.target
Requires=beah-beaker-backend beah-fwd-backend
DefaultDependencies=no

[Service]
Type=simple
ExecStart=/usr/bin/beah-srv
KillMode=process

The key changes are:

DefaultDependencies=no

And, adding multi-user.target in "After"

After the above, this service starts after the readahead colllection is completed which is what I wanted 
to achieve.


Best,
Amit.