That does not turn out to be as simple as it seems at first.
I put the following in custom-cont-init.d/test:
#!/bin/bash
echo "**** CUSTOM ****"
ls -alF /run/s6/services/sabnzbd/
cp /config/run-sabnzbd /run/s6/services/sabnzbd/run
chmod 755 /run/s6/services/sabnzbd/run
where run-sabnzbd is just the adaptated run script to change the port.
While this seems reasonable simple, it results in the following when the container is started:
[cont-init.d] 99-custom-scripts: executing...
[custom-init] files found in /config/custom-cont-init.d executing
[custom-init] run-sabnzbd-without-fixed-port.sh: executing...
**** CUSTOM ****
ls: cannot access '/run/s6/services/sabnzbd/': No such file or directory
cp: cannot create regular file '/run/s6/services/sabnzbd/run': No such file or directory
chmod: cannot access '/run/s6/services/sabnzbd/run': No such file or directory
[custom-init] run-sabnzbd-without-fixed-port.sh: exited 1
[cont-init.d] 99-custom-scripts: exited 0.
[cont-init.d] done.
it seems that the path /run/s6/services/sabnzbd/ is not yet existing at that point of time.
Help appreciated.