5.)
Instead of init.d scripts create systemd units.
https://wiki.debian.org/systemd#Creating_or_altering_services
https://freedesktop.org/wiki/Software/systemd/
So you propose not to use init.d scripts. I usually prefer a simple shell script that is easy to test, systemd is just way to complex. But probably for Debian you are right, if I understood correctly, newer versions do not even support init.d / LSB anymore, so using systemd units seems to be required there.
About your gitlab-runner.service failure:
https://wiki.debian.org/systemd#Failed_units
HINT: Extensive debugging information about systemd is on this
FreeDesktop page. https://freedesktop.org/wiki/Software/systemd/Debugging/
I didn't find anything about init.d or DPKG_MAINTSCRIPT_PACKAGE in these pages.
I just see that I'm supposed to reboot (!) with special parameters to debug a shell script.
Only I found using "status", but this does not help either:
root@node17-0:/etc/init.d# systemctl status gitlab-runner2.service
- gitlab-runner2.service
Loaded: not-found (Reason: No such file or directory)
Active: inactive (dead)
funny that it does not even tell WHICH file was not found and why it was loaded anyway.
I tried "journalctl -b > journal.txt" and found in journal.txt several blocks like that:
09:40:09
node17-0
systemd[1]: Started LSB: gitlab-runner.
09:40:09
node17-0
gitlab-runner[17967]: Starting multi-runner from /local/users/sdettmer/work/_gitlab/config.tom l ... builds=0
...
09:44:08
node17-0
systemd[1]: Stopping LSB: gitlab-runner...
09:44:08
node17-0
gitlab-runner[17967]: WARNING: Requested service stop: terminated builds=0
09:44:08
node17-0
gitlab-runner[17967]: All workers stopped. Can exit now builds=0
09:44:08
node17-0
gitlab-runner[10318]: Stopping GitLab Runner:.
09:44:08
node17-0
systemd[1]: Stopped LSB: gitlab-runner.
which does not give any hint (except that it works with
DPKG_MAINTSCRIPT_PACKAGE set).
The string "gitlab-runner2" does not appear anywhere in the whole file at all.
Any other places where I could look?
What is in gitlab-runner.service on that one server anyways?
There is no such file "gitlab-runner.service" (I tried "find /etc" and "locate").
It seem that some systemd magic applies here. Maybe, if its content is needed for technical reasons, systemd creates some "virtual unit" on the fly, who knows.
Somewhen in 2016-2018 someone on debian planet posted multiple blogs of
a great systemd introduction series, I can't find my bookmark right now
:(
What a pitty, I though init.d scripts would be in support of systemd, but apparently they are not anymore :(
So in future portable packages won't be that easy.
Steffen