runit integration

["depuis" <pascal.dupuis@worldonline.be>]

Hello,

I've read yesterday the article on linux today about runnit - tried it - I
find it interesting, and I would like to comment a bit...

My background: linux hacker since 1996 (Slackware 3), today using debian etch
on a laptop, rebooting the system each day, so optimising the start phase is a
big win. Furthermore, I use laptop-net to configure programs and services
based upon the network environment: at home, at work, if a WIFI is available, ...

I think that runit should provide some compatibility mechanism with the
existing rc runlevels and /etc/init.d/ scripts. Maintainers carefully polished
those scripts, some are very elaborate, and providing a drop-in for these
scripts is a lot of work: compatibility issues, following the latest version,
and so on.

What does they have in common ? Most use the start-stop-daemon program in
order to control the processes. What about providing some alternative to this
program? But let's think first about what has to be adapted ? Not a lot.
Mostly program invocation. start-stop-daemon expects the called program to
detach(). In the runit context, this should be avoided. A possible solution is
to write a wrapper, like f.i. for gpm:
#!/bin/sh
sv start devfsd || exit 1
EXTRA_ARG="-D" /etc/init.d/gpm start

The idea is to define two environnement vars:
REMOVE_ARG which contains arguments that have to be removed from the final
command line ('--daemon' f.i.)
EXTRA_ARG is a supplemental arg which prevents the called program to detach
itself (program dependent)

The global idea would thus to provide some substitue for start-stop-daemon,
with some wrapper permitting to use the /etc/init.d script "as is". This
substitute would be a mix of runsv and chpst, as the start-stop-daemon can
alter the process state (-u, -g, ...). All the glue logic (this program must
wait that program before starting) would also be concentrated at the same level.

This way, the compatibility would be achieved as:
1) for each entry in /etc/rc2.d, place a symbolic link in /etc/runit/runsvdir/
default/ to a wrapper in /etc/sv
2) for each entry in /etc/init.d, provide a wrapper in /etc/sv wich add and
remove the required args so that the invoqued program does not detach,
together with the required dependencies on other programs.

This way, runit would be a replacement for sysvinit, minimising the migration
and maintenance burden.

I am not subscribed to this list, but I'll follow this discussion through the
archive.

Best regards

Pascal Dupuis



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