Query on S6 system shutdown

Query on S6 system shutdown

[Arjun D R]

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Hi Team,

I am facing an issue at the moment of shutting down the system. Whenever I
reboot the system, it is triggering "s6-rc -v2 -bda change" and stops all
the services. But one service is not responding and it hangs. This blocks
the reboot.

ps -aef | grep s6-rc
root      2770  2707  0 08:24 ?        00:00:00 s6-ipcserverd -1 --
s6-ipcserver-access -v0 -E -l0 -i data/rules -- s6-sudod -t 30000 --
/libexec/s6-rc-oneshot-run -l ../.. --
root      7880  2615  1 08:28 ?        00:00:00 s6-rc -v2 -bda change
root      8603  7880  0 08:28 ?        00:00:00 s6-svlisten1 -D --
/run/s6-rc/servicedirs/critical.service s6-svc -d --
/run/s6-rc/servicedirs/critical.service
root      8755  2620  0 08:28 ttyS0    00:00:00 grep s6-rc

I believe the finish script is not being called by s6-svc. When I run it
manually , the finish script runs and kills the process and graceful
shutdown is happening as expected.

What may be the cause for not triggering the finish script of critical
service.

cat /run/service/critical.service/run.user
#!/bin/execlineb -P
foreground { echo "starting critical service" }
fdmove -c 2 1
envfile -i  /etc/default/critical-env
s6-envdir /etc/s6-rc/source/critical.service/env
<.. many importas commands..>
/usr/bin/critical -b -c /etc/critical/config.json

cat /run/service/critical.service/finish.user
#!/bin/execlineb -P
foreground { echo "Stopping critical service" }
fdmove -c 2 1
backtick -n pid_value { pidof critical }
importas -i pid_value pid_value
/bin/kill -9 -- -${pid_value}


Please help.

Thanks,
Arjun

Re: Query on S6 system shutdown

[Laurent Bercot]

>I believe the finish script is not being called by s6-svc. When I run it
>manually , the finish script runs and kills the process and graceful
>shutdown is happening as expected.
>
>What may be the cause for not triggering the finish script of critical
>service.

  The finish script, which is entirely optional, is not supposed to
kill the process. It is not called by s6-svc, and does not run when
the process is still alive. It is *not* equivalent to the "down"
script of a oneshot. (There is a subtle hint in the fact that the
scripts are named "run" and "finish" instead of "up" and "down".)

  If it exists, the finish script is run by s6-supervise *after* the
service dies. The point is to perform any potentially needed cleanups
that are not automatically performed at service death.

  Your current finish script is entirely incorrect and you should
delete it.

  In order to kill your service, you need to send it a signal. Daemons
normally have a signal that tells them to gracefully exit; for most
daemons, it is SIGTERM, which is what svc -d sends by default.

  If your critical.service does not die on s6-svc -d, it means that
it ignores SIGTERM. Then you need to find out *what* signal it
interprets as a request for a graceful shutdown, and put the name
of this signal in the "down-signal" file in your service definition
directory. Then, when you send s6-svc -d, critical.service will
receive the signal you indicated.

  down-signal can be SIGKILL - this is what you're using at the moment -
but if your service is that critical, chances are it's not the best way
to kill it and you should look for a gentler signal to send it first.
If there are cases where a graceful exit request is ignored or takes
too long, and you want to make sure the service dies at some point,
you can create a "timeout-kill" file, containing a number of 
milliseconds
- if the process is still alive after that duration after receiving
its down-signal, it will be sent a SIGKILL.

--
  Laurent