[arch-general] remote poweroff with systemd

[Rodrigo Rivas]

On Tue, Aug 6, 2013 at 5:18 PM, Fons Adriaensen <fons at linuxaudio.org> wrote:

> On Tue, Aug 06, 2013 at 01:56:09PM +0100, Paul Gideon Dann wrote:
>
> > ssh -t remote1 "sudo systemctl poweroff && exit"
> >
> > Technically I guess it's a race condition, but the command should
> terminate
> > and close the SSH session before OpenSSH is shut down, so you shouldn't
> get
> > the hang.
> >
> > Alternatively, you could try "systemctl start poweroff.target" to see if
> that
> > returns quicker.  I'm not sure if the poweroff command returns straight
> away
> > or waits.  Basically, I'm thinking that if you can get the first command
> to
> > return quickly, your shell will close nicely before the shutdown kills
> the
> > connection.
>
> Thanks to all who suggested solutions.
>
> What difference should the '&& exit' make ? The ssh will terminate
> anyway when poweroff returns. Problem is that by then it's too
> late.
>

That's why I suggested "systemctl --no-block poweroff". That should return
immediately and finish the ssh session well within the grace time period
that systemd gives to every service in poweroff.

As I see it, the problem with a simple "systemctl poweroff" (or equivalent)
is not a race-condition, but a dead-lock: systemd waits for the ssh session
to finish to go on with the poweroff, and the ssh session waits for the
poweroff to finish until it returns. And those are precisely the situations
where "--no-block" is useful.

-- 
Rodrigo