[systemd-devel] Waiting for all jobs to finish

[Lennart Poettering]

On Mi, 27.04.22 18:29, Barry Scott (barry at barrys-emacs.org) wrote:

> I have two target files that I use.
>
> prod.target is used to start up all the production services.
> When I use systemctl start prod.target it blocks until all the
> services are running.
>
> I also have prod-upgrade.target that is used to stop service
> via Conflicts=. When I use systemctl start prod-upgrade.target
> it returns immediately but there are stop jobs running.
>
> I believe that this is expected as all the services that need to
> be started have been.
>
> Is there a systemctl command that will wait for all the stop jobs
> without the need to poll for the systemctl list-jobs to be empty?

There is not.

But the correct way to solve this is by combining Conflicts= with an
order dep (After= or Before=).

In systemd the ordering deps After=/Before= control three things:

1. The literally define the start-up order if two units are started,
   i.e. this is the obvious case: if b.service has After=a.service
   this means a.service has to finish startup first, before b.service
   is started.

2. If two units are stopped they define the order too, but in
   reverse. if b.service has After=a.service this hence means that if
   both are shutdown, then b.service has to stop *before* a.service is
   stopped, i.e. the opposite order of the start-up order.

3. If one unit is started and one is stopped then the existance of an
   ordering dep means the stopped unit must complete stopping first,
   before the starting of the other is initiated. Note that it doesn't
   mattre if you set After= or Before= here, that doesn#t matter. What
   matters is that you ordered the unit at all, regardless in which
   direction.

Now, this third rule is what matters here: if your target unit has
Conflicst= on some service, then the target unit should not enter
active state until the service fully shutdown. Thus you can place
After= *or* Before= between the two (your choice) and get the desired
behaviour.

Lennart

--
Lennart Poettering, Berlin