[gentoo-dev] Re: Providing a `service` scripts that speaks OpenRC and systemd

[Duncan]

Walter Dnes posted on Sat, 30 Sep 2017 00:20:31 -0400 as excerpted:

> But, how do we reliably detect the currently running init system?  Are
> there running processes, or entries in /sys/ or /proc/ or /dev that are
> unique to to each init system?

In theory at least, that's easy enough, just check the kernel 
commandline's (/proc/cmdline) init= if present, and fall back to matching 
against the path (canonical, to take care of symlink-based init-
switching) of PID 1 if init= isn't present or points to the default
/sbin/init.

In practice I suspect one would need to arrange for each supported init 
system to drop its own detection executable in place, making the script 
something like this:

#!/bin/bash
initdetectpath=/lib/initdetect
if ${initdetectpath}/issystemd ; then
...
elif ${initdetectpath}/isopenrc ; then
...


But, once you're having the initsystems package their own detection 
files, you might as well simply make them their own service scripts 
designed to do the detection as well, returning a specified error code if 
it's not that initsystem, making it as simple as:

#!/bin/bash
notme=<magicreturncode>

for $servicefile in /lib/initservicedir/* ; do
	$servicefile "$@"
	code=$?
	[[ $code = $notme ]] || break
done

[[ $code = $notme ]] && /
	echo "No supported initsystem claimed to be running" > /dev/stderr
exit $code


Then it's up to the initsys packagers whether they want to support the 
scheme or not, what sort of detection they do if they support it, and how 
they translate the passed parameters if necessary, and bugs in how they 
do any of it become the bugs of that initsystem.

-- 
Duncan - List replies preferred.   No HTML msgs.
"Every nonfree program has a lord, a master --
and if you use the program, he is your master."  Richard Stallman