init script generators ( was: Re: proper handling of communication channels in debian)

[Erich Schubert]

Hi,
> If the different init systems could be installed simultaneously (with
> /etc/alternatives deciding the dominant one) you wouldn't even need to
> do this.  just look for the registered hint files (in
> /usr/share/initsystem, by analogy with /usr/share/menu?).

Please don't forget the switching issues. alternatives is NOT
suiteable for switching init.
Because the init switch will take effect on reboot, not immediately.

Each init system should ship /etc/init-tools/methods/foobar
Which will be invoked to generate an init script for the appropriate
init system.
When installing a new init script, update-init or so (or maybe this
could be integrated with update-rc.d?) should be called in postinst.
All this is similar to update-menus

Some things to note:
- init scripts should be generated for all installed init systems
(because one might be running right now and needs appropriate shutdown
methods, and a different one might be 'scheduled' to be used after
reboot)
- auto-generation of init scripts only needs to cover 90% of cases; we
can write optimized init scripts for the remaining 10% that are
special one way or another (e.g. mysql)
- generate-init scripts should only overwrite auto-generated init
scripts; for example a package might ship a sysvinit and the meta-init
description; in that case the sysvinit generator should remain
inactive.
- switching init should be supported by using the init=foobar kernel parameter.

I posted a proposal to the list here to use /proc/1/exe for detecting
which init system is currently running (and then invoking the
appropriate /etc/init-tools/invoke/foobar etc. commands). I don't know
if anyone has investigated this closer.

best regards,
Erich Schubert
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