dinit

dinit
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v0.1

What is it?
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"dinit" is destined to eventually become a replacement "init" program for
Linux (and possibly other) systems. But it's not there yet.

However, dinit can be used as a general service monitor. Specifically it
can launch multiple services (generally, "daemon" processes, but see notes
below) in parallel, with dependency management (i.e. if one service's
operation depends on another, the latter service will be started first).

For "process" services (the only kind of service that v0.1 supports) dinit
can monitor the process corresponding to the service, and re-start it if it
dies. It does this in an intelligent way, first "rolling back" all dependent
services (which it will later re-start, if configured to do so).

Notes on services
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The only type of service supported in v0.1 are "process" services. Process
services are so named because they run as a process which dinit launches
and monitors directly (this is opposed to "scripted" services, scheduled for
v0.5, which will be started and stopped with the aid of a script or other
program, and which cannot be directly monitored by dinit).

Many programs that you might want to run under dinit's supervision can run
either "in the foreground" or as a daemon ("in the background"), and the
choice is dictated by a command line switch (for instance the -D and -F
switches to Samba's "smbd"). Although it might seem counterintuitive,
the "foreground" mode should be used for programs registered as process
services in dinit; this allows dinit to monitor the process.

Process services are attractive due to the ease of monitoring (and
restarting) the service, however, they have one inherent problem, which is
that dinit cannot tell when the service is truly started. Once the process
has been launched, dinit assumes that the service has started, but in fact
there will be a short delay before the process sets itself up, starts
listening on sockets, etc; during this time any other process (including
one from a service listed as dependent) which tries to contact it will not
be able to do so.


Things to document about current implementation
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* logfiles won't work until filesystem mounted (/dev/null should, though)