Re: [Buildroot] [PATCH v2 0/6] Update init script style

[Thomas Petazzoni via buildroot <buildroot@buildroot.org>]

Hello Fiona,

On Fri, 12 Jul 2024 14:49:50 +0200
Fiona Klute via buildroot <buildroot@buildroot.org> wrote:

> Fiona Klute (WIWA) (6):
>   docs/manual: describe relying on default options
>   package/busybox: tidy up S01syslogd init script
>   docs/manual: include S01syslogd from source
>   package/openssh: tidy up init script
>   package/dnsmasq: tidy up init script
>   package/network-manager: rewrite init script

Thanks a lot for this, all are applied.

Now, when reviewing this and discussing with Arnout, we thought it
would be nice to have a little bit more documentation. Indeed, while
looking at the different init scripts in this series, we can identify 3
different cases:

- The S01syslogd case, where the daemon doesn't create a PID file, so
  we use --make-pidfile + --background so that start-stop-daemon
  creates the PID file and is in charge of daemonizing the daemon

  We use a loop with start-stop-daemon to check if the service has
  stopped

- The S80dnsmasq case, where the daemon creates its PID file, so we
  don't pass --make-pidfile + --background.

  But dnsmasq doesn't remove its PID file on stop, so we also use a
  start-stop-daemon loop to check if the service has stopped

- The S50sshd or S45NetworkManager cases, where the daemon creates its
  PID file, so we don't pass --make-pidfile + --background (same as
  S80dnsmasq)

  However, those daemons remove their PID file on stop, so we cannot
  use a start-stop-daemon loop, but instead loop until the PID file
  goes away

So essentially, the manual should have guidelines like this:

- If your service doesn't create its own PID file: invoke the daemon in
  foreground mode, and use start-stop-daemon --make-pidfile --background

  snippet of code

- If your service creates its own PID file: pass the --pidfile option
  to both start-stop-daemon *and the daemon itself so they agree on
  where the PID file is

  snippet of code

- If your service removes its PID file on shutdown, use a loop testing
  that the PID file has disappeared on stop, see S50sshd or
  S45NetworkManager for example:
 
  snippet of code

- If your service doesn't remove its PID file on shutdown, use a loop
  of start-stop-daemon, see S01syslogd for example:

  snippet of code

That would be *tremendously* useful to have in the documentation.

Thanks a lot!

Thomas
-- 
Thomas Petazzoni, co-owner and CEO, Bootlin
Embedded Linux and Kernel engineering and training
https://bootlin.com
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