On 10/30/2017 06:20 AM, Vladimir Mosgalin wrote:
> Hi ToddAndMargo!
> 
>   On 2017.10.27 at 16:57:38 -0700, ToddAndMargo wrote next:
> 
>> I was wondering why one would go through all the effort
>> to do a "ExecStop" in systemd if shutdown was going to send
>> SIGTERM to everyone anyway.  Well because the process might
>> not have long enough to shutdown before the SIGKILL or have
>> all its sub process complete properly either.
> 
> There are lots of reasons to have ExecStop (especially for databases).
> First is handling the case when database can't accept SIGTERM correctly
> and needs specific command to shutdown instead (e.g. Oracle DB). Second
> is need to do some pre/post shutdown cleanup, e.g. you want to send some
> notification to someone else before shutdown. Third is manual picking of
> process to terminate, systemd can either kill very first process with
> SIGTERM or kill all, but there are cases when you need to kill something
> else. For example, this is tree of running processes:
> 
> (1) wrapper
>      |
>      (2) control manager
>          |
>          (3) child 1
>          (4) child 2
>          (5) child 3
> 
> systemd can kill either (1) or (1-5) depending on settings, but killing
> (1) is useless and killing (3-5) directly might harm the service state,
> the only way to correctly shutdown is to send signal to (2) (or 1 and 2
> at once).  Here you'll need ExecStop again.
> 
> I'd say that the only annoyance here is that ExecStop must be
> synchronous, it must actually wait till everything shutdowns before
> returning, otherwise systemd will treat it as failed shutdown attempt
> and kill the service remains right after ExecStop returns. So if you're
> going to stop by sending SIGTERM to some specific process, you need a
> wrapper script for ExecStop which waits till everything has shutdown
> properly. You can't use one that calls shutdown in background and
> returns without waiting.
> 
> 
> Anyhow, just like ExecStop allows these kinds of customizations, you can
> also define "TimeoutStopSec" parameter (e.g. TimeoutStopSec=5min) and
> systemd will wait that time either after sending SIGTERM (if there is no
> ExecStop) or after ExecStop and before sending SIGKILL (ExecStop command
> will be aborted in that case when the time has ran out).
> 

Wow!  Thank you!