[systemd-devel] does "Before=network.target" really work

[Lennart Poettering]

On Fri, 24.06.16 18:41, Xin Long (lucien.xin at gmail.com) wrote:

> On Fri, Jun 24, 2016 at 6:23 PM, Andrei Borzenkov <arvidjaar at gmail.com> wrote:
> > On Fri, Jun 24, 2016 at 1:11 PM, Xin Long <lucien.xin at gmail.com> wrote:
> >> Hi,
> >>
> >> I have a service, and want it to be stopped only after network is
> >> stopped when system shutdown.
> >>
> >> I checked "man systemd.special ", network is a special internal
> >> service for systemd, , and I found "network.target":
> >> "at shutdown, a unit that is ordered after network.target will be
> >> stopped before the network -- to whatever  level it might be set up
> >> then -- is shut down".
> >> That means "After=network.target" can work well.
> >>
> >> But my situation is opposite to that, I need "a unit that is ordered
> >> before network.target will be stopped *after* the network so
> >> shutdown".
> >>
> >> So I added "Before=network.target" to .service file. can it really
> >> work as I expect?
> >>
> >
> > No. That is why systemd was forced to introduce additional
> > network-pre.target to make it possible to explicitly order things
> > before networking is started (or stop after networking has been
> > stopped - assuming of course that all services that implement
> > networking correct order themselves After network-pre.target).
> 
> So you mean "Before=network-pre.target" can work on my case, right ?

Yes, that's what it is for. Also make sure to actually pull in the
target from your service too. Hence you want:

    Before=network-pre.target
    Wants=network-pre.target

n-p.t is a target that is "passive", it needs to be pulled in by the
implementor of such a service, not by the consumer of it. This has the
benefit that as long as no service wants to hook into this nothing is
added to the transactions for bootup and shutdown and thus more can be
parallelized as one synchronization points less is in the queue.

See systemd.special(7) about it as well as
https://www.freedesktop.org/wiki/Software/systemd/NetworkTarget/

> >> I have a service, and want it to be stopped only after network is
> >> stopped when system shutdown
> 
> and since which version "network-pre.target" was introduced ?
> cause I didn't find it in "man systemd.special" in my system.

This has been addedin systemd 214.

Lennart

-- 
Lennart Poettering, Red Hat