[systemd-devel] DBUS API to restart unit by sending sigkill/sighup

[Mantas Mikulėnas]

On Mon, Sep 10, 2018 at 9:44 AM prashantkumar dhotre <
prashantkumardhotre at gmail.com> wrote:

> Hi,
> Is there is dbus API for systemd to restart unit by sending sigkill
> /sighup ?
> https://www.freedesktop.org/wiki/Software/systemd/dbus/
> RestartUnit(in  s name, in  s mode, out o job);
> My requirement is to have a way to restart unit by sending sigkill or
> sighup (user can specify ) also along with sigterm.
>

Most programs use SIGHUP for live reloads, not restarts. If your service
does the same, you can specify
    ExecReload=/bin/kill -HUP $MAINPID
in your service, and use ReloadUnit().


> Since that dbus APi does not seem to exists, to achieve same effect ,
> I can use KillUnit() API to send custom signal and then use  StartUnit().
> KillUnit(in  s name, in  s who,   in  i signal);
> StartUnit(in  s name, in  s mode,  out o job);
>

If you want an *immediate* SIGKILL, then yes, use KillUnit(). But is that
really what you need?

Note that the default StopUnit will first send a SIGTERM first, wait a few
seconds, and send a SIGKILL afterwards. So if the service takes a long time
to stop normally, it will get killed after a timeout. You can reduce this
timeout using TimeoutStopSec=.

But if the service *always* needs an immediate SIGKILL, you can configure
that as the KillSignal= in the .service file, and that will make StopUnit
go straight for the kill.


> Is that correct understanding ?
> One issue with this is how to know when to do  StartUnit() after
> KillUnit() since KillUnit() may not have completed stopping unit yet.
>

KillUnit's purpose isn't stopping the unit; that only happens as a side
effect due to the process exiting.

I would call Subscribe(), then probably KillUnit(), then explicitly use
StopUnit() (which creates a job), then wait for a dbus signal informing
that the stop job has finished.

-- 
Mantas Mikulėnas
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