[Dev] HOWTO write a daemon

[Paul D. Boyle]

> 
> Just curious but what is wrong with just writing a program that doesn't
> put out any text to the console and starting it with a script with a
> command like this:
> 
> mydaemon&
> 
> Besides the fact that it's a little less elegant?

What distinguishes a daemon from a "regular" process (either foreground
or background) is that the process becomes (according to Stevens) a
session leader of a new session, it becomes a process group leader of
a new process group, and it has no controlling terminal.  In addition,
very often daemon change their current working directory to a specific
directory (often, but not always, "/"), so that filesystems can be
unmounted while the daemon is running (did you ever try to unmount a
file system and got a 'device busy' message?).  

Under Unix (Linux) all processes automatically open three I/O streams,
stdin, stdout, stderr, these are often closed in a daemon process.

Paul

-- 
Paul D. Boyle			    |	boyle@laue.chem.ncsu.edu
Director, X-ray Structural Facility |	phone: (919) 515-7362
Department of Chemistry - Box 8204  |	FAX:   (919) 515-5079
North Carolina State University     | 
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