[OpenWrt-Devel] Wait on syslog-ng

[Eneas Queiroz]

On Fri, Sep 27, 2019 at 8:05 AM W. Michael Petullo <mike at flyn.org> wrote:
>
> A daemon I wrote for OpenWrt depends on a running syslogd. I use
> syslog-ng, and I have noticed that its init script completes before the
> daemon begins to listen on /dev/log. This causes my daemon to terminate
> if it starts quickly after syslog-ng.
>
> There are a few obvious solutions:
>
>         (1) My daemon could sleep and try again if its connection to
>         syslogd fails.
>
>         (2) My daemon's init script could sleep for one second before
>         running the daemon.
>
>         (3) Syslog-ng's init script could sleep for one second after
>         executing syslog-ng and before exiting.
>
> (3) seems the most universal, but all of these feel a little kludgy due
> to the reliance on a timeout. I say this becasue you cannot precisely
> predict what the timeout value should be (in practice a second or so
> seems to suffice).
>
> Does the init system provide a more general way to solve this problem?
> The START=n statements seem to impose only the ordering of init script
> execution and have no bearing on whether the services the scripts run
> are ready. Do I have this right?
>
> I did see sleep in a few other scripts such as network.

How about something like this?

#!/bin/sh

exitservice() {
  if [ -n "$!" ]; then
    echo Killing timout
    kill $! 2> /dev/null
    wait $! 2> /dev/null
  fi
}

timeout() {
  sleep 10
  echo 'ERROR: socket not open.  Is syslog running?' >&2
  kill $$
  exit 1
}

trap exitservice EXIT
timeout &
while ! grep -q /dev/log /proc/net/unix; do
  sleep 1
done
exit 0

Cheers,

Eneas

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