Re: Init system in Lua

[Jakub Piotr Cłapa <jpc-ml@...>]

On 18.11.11 23:32, clemens fischer wrote:
> You might want to look at runit[1], s6[2] or the daemontools[3], which
> implement managing what they call "services".  A supervisor sends
> signals to a service.  If the services directory structure has
> a subdirectory called ./log, the "run" program in it, which often is
> a regular shell script, execs into a logger.  The supervisor sets up
> a pipe from the services stdout to the loggers stdin and tries its best
> to keep it even when either the service or the logger crashes.  The
> supervisor also restarts programs after a crash.

I second that. The daemontools are really well thought out and worth 
learning from. They offer lots of functionality using no magic and 
schockingly low amounts of code. Even if you find these systems a little 
weird you should still try to learn how they work so you can design 
something better.

I know that being better than the standard tons of crappy SysVinit 
scripts is nice but why stop there?

> These systems can be used as unix process 1 ("init") and they don't need
> dependency checking.  If some service needs another one early, it will
> crash, of course, but it will get restarted.  As long as the dependency
> graph contains no cycles, the system stabilizes pretty fast.  S6
> implements a notifier which can be used for dependency tracking.  Runit
> implements "guarding" scripts which can be used for housekeeping.

Dependency tracking can be done by a small executable which waits for 
the services that were passed to it to start up. Or you can keep the 
dependencies as symlinks in a subfolder and make the supervisor respect 
them. Using inotify or some other file monitoring system for this could 
replace lots of ad-hoc IPC.

Bourne shell is not the best thing for running Unix services but before 
deciding if Lua is you may check out the rc shell (from Plan 9 but it 
has ports to normal old Unix). If want something even simpler then 
execline may be worth a shot.

--
regards,
Jakub Piotr Cłapa