CODEWITHSUNDEEP
bashdebianinit.ddebian-based
FrobberOfBits
FrobberOfBits

Reputation: 18022

How to shell script a wrapper for a service

I have a system service, foo that is started and stopped via /usr/sbin/service restart foo. It in turn appears to be controlled by a shell script /etc/init.d/foo

How can I create a "pre-start" hook, so that I can run an extra shell script prior to this service starting? In this case, the pre-start hook is extra config that has to be fetched from a cloud provider metadata catalog, and then jacked into a configuration file necessary for foo to start properly.

I have considered modifying /etc/init.d/foo directly, which would work. But which would complicate expected frequent patch-level upgrades which I will catch by apt-get upgrade. I want to avoid a solution that requires re-establishing the hook.

A second option is that I could create a fooWrapper service, remove foo from all run levels, and then just start/stop fooWrapper. The implementation of that script would just be my secret sauce + invoking /etc/init.d/foo. The trouble with that is again package upgrades, whether foo would re-insert itself into the various runlevels, and I would then end up running two conflicting copies.

Upvotes: 0

Views: 575

Answers (1)

Ljm Dullaart
Ljm Dullaart

Reputation: 4989

Your setup suggests that you use sysv init and not yet systemd. If this is the case, read on. Otherwise ignore this answer.

In general, you will have a link like S20foo in /etc/rc.d/rc3.d. The 20 and 3 may be different for you. Normally, you would create a script /etc/init.d.pre_foo that gets your extra config and link it to /etc/rc.d/rc3.d/S19pre_foo. This will start pre_foo before foo.

Upvotes: 1

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