From: YANAGAWA Kazuhisa <kjana@...4lab.to>
Date: 2003-12-07T23:37:08+09:00
Subject: Re: Trying to create a Ruby daemon

In Message-Id: <D58DEDEE-28AD-11D8-A981-000393DA3608@humlab.umu.se>
Samuel Kvarnbrink <samuel.kvarnbrink@humlab.umu.se> writes:

> Does anyone here have an example on how to create a Ruby daemon that
> runs as a session leader (without a controlling terminal)? I've tried
> to accomplish that using fork and Process.setpgrp, but the only
> results so far have been zombie processes or processes that exit when
> I close the terminal. I'm quite new to Ruby so I guess that I've
> missed some little detail somewhere... :)

Following is a tiny sample.  You can get more knowledge from other
daemon codes and man pages.  A book like "Advanced Programming in the
UNIX Environment" also helps a lot.

# See Also: daemon(3), setsid(2), setpgrp(2), wait(2), ps(1) and
# tty(4) if needed (on BSD based system, it may contains info around
# TIOCNOTTY).


    # parent process exits to pass child to init(1).
    fork and exit

    # child becomes session leader and disassociates controlling tty.
    # namely do Process.setpgrp + \alpha.
    Process.setsid
    
    # at here already the child process have become daemon. the rest
    # is just for behaving well.

    # ensure no extra I/O.
    File.open("/dev/null", "r+") do
      |devnull|
      $stdin.reopen(devnull)
      $stdout.reopen(devnull)
      $stderr.reopen(devnull)
    end
    
    # ensure daemon process not to prevent shutdown process.
    Dir.chdir("/")


-- 
kjana@dm4lab.to                                 December 7, 2003
Art is long, and time is fleeting.