writing s6 services

writing s6 services

[billa chaitanya]

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Hi Team,
Have few doubts while creating service files in s6.

1) Is there a possibility to add an ENV variable dynamically?
I have a shell script which fills out some variables like
IPADDRESS, SERVER  etc .. which I need to use in starting a process later
as part of starting a service/stopping a service.

2) Does s6-supervise has the intelligence of findingout $MAINPID as the
systemd does?(
https://systemd-devel.freedesktop.narkive.com/dpY7US7K/a-little-help-with-mainpid-please
)

Thanks,
chaitanya

Re: writing s6 services

[Laurent Bercot]

>1) Is there a possibility to add an ENV variable dynamically?
>I have a shell script which fills out some variables like
>IPADDRESS, SERVER  etc .. which I need to use in starting a process later
>as part of starting a service/stopping a service.

  You can do whatever you want in a run script, as long as by the end
of it, the pid of the long-running daemon is the pid your run script
was started as.
  If your run script is a shell script, you can absolutely source the
script that fills out your environment variables. It is not the most
idiomatic or safe way to do it, but it will absolutely work.


>2) Does s6-supervise has the intelligence of findingout $MAINPID as the
>systemd does?(
>https://systemd-devel.freedesktop.narkive.com/dpY7US7K/a-little-help-with-mainpid-please

  Yes, that is the point of a process supervisor.
  You don't need a variable such as $MAINPID because the supervisor 
always
remembers the pid of its child. You don't need a pidfile or anything of
the sort.

--
  Laurent

Re: writing s6 services

[billa chaitanya]

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On Wed, Oct 28, 2020 at 7:31 PM Laurent Bercot <ska-supervision@skarnet.org>
wrote:

> >1) Is there a possibility to add an ENV variable dynamically?
> >I have a shell script which fills out some variables like
> >IPADDRESS, SERVER  etc .. which I need to use in starting a process later
> >as part of starting a service/stopping a service.
>
>   You can do whatever you want in a run script, as long as by the end
> of it, the pid of the long-running daemon is the pid your run script
> was started as.
>   If your run script is a shell script, you can absolutely source the
> script that fills out your environment variables. It is not the most
> idiomatic or safe way to do it, but it will absolutely work.
>
>
> >2) Does s6-supervise has the intelligence of findingout $MAINPID as the
> >systemd does?(
> >
> https://systemd-devel.freedesktop.narkive.com/dpY7US7K/a-little-help-with-mainpid-please
>
>   Yes, that is the point of a process supervisor.
>   You don't need a variable such as $MAINPID because the supervisor
> always
> remembers the pid of its child. You don't need a pidfile or anything of
> the sort.
>                So, Is there any variable we can use inside run or finish
> script of a service equivalent to the pid of the  process started inside
> run script?
> --
>   Laurent
>
>

Re: writing s6 services

[Guillermo]

El mar., 3 nov. 2020 a las 8:48, billa chaitanya escribió:
>
> >                So, Is there any variable we can use inside run or finish
> > script of a service equivalent to the pid of the  process started inside
> > run script?

The PID of the supervised process will be the same as that of the
'run' script if it is correctly written, so it's $$ for a shell
script, and the value of the environment variable specified to the
getpid program for an execline script.

* http://www.skarnet.org/software/execline/getpid.html

It is not available inside the 'finish' script, but even if it was, it
is no longer useful since, if that script is being executed, the
supervised process has already terminated, and the PID it had has been
'released'.

G.