[systemd-devel] safe and fast shutdown/reboot

[Lennart Poettering]

On Fr, 16.03.18 09:13, prashantkumar dhotre (prashantkumardhotre at gmail.com) wrote:

> Hi
> I see that default reboot/systemctl reboot command issues SIGTERM to my
> apps and hence it is doing graceful stop of apps and this may take some
> time and hence shutdown time may be little longer.
> 
> I am looking for safe and fastest shutdown/reboot method.
> 
> 
> a) It is OK if my apps are stopped ungracefully during shutdown .(app
> should not start automatically again after they are killed/stopped during
> shutdown)
> 
> b)  file system and such system level stuff needs to be cleanly shut down
> 
> 1) From my research, I see that 'systemctl reboot --force' is the one I can
> use.
> I understand that this command sends SIGKILL to my apps.
> So this satisfies both (a) and (b) and hence this command should be used to
> reboot faster.
> Could you please confirm ?

That is correct. But note that it will also SIGKILL everything else on
the system, including the journal for example, and that means the
journal files will remain in in a dirty state each time (which
journald will deal with, but is not pretty).

> If this is not right method, please comment on which method to use.
> 
> 2) Also is there a way to limit SIGKILL to only my apps when I do ' 'systemctl
> reboot --force'
> so that rest of the system level services still get stopped
> gracefully

No, for that (as mentioned elsewhere), use KillSignal=SIGKILL or so.

> 3) If  'systemctl reboot --force' is correct command to use in my case,
> then during shutdown , will my apps get restarted
> due to 'Restart'/'StartLimitBurst'/'StartLimitInterval' settings in service
> file ? I dont want my apps to get restarted if they are stopped/killed
> during system shutdown

No. "systemctl reboot --force" means that PID 1 gets replaced by the
"systemd-shutdown" process right away, which has no notion of
services, and will just go on a killing spree and SIGKILL/umount
everything that is left.

Lennart

-- 
Lennart Poettering, Red Hat