Double fork a Ruby process.

doublefork.rb

raise 'Must run as root' if Process.euid != 0
p1 = Process.fork {
  # p1 is now running independent of, and parallel to the calling process
  Process.setsid
  p2 = Process.fork {
    # p2 is now running independent of, and parallel to p1
    $0 = 'mydaemon'
    pidfile = File.new('/var/run/mydaemon.pid', 'w')
    pidfile.chmod( 0644 )
    pidfile.puts "#{Process.pid}"
    pidfile.close
    logfile = File.new('/var/log/mydaemon.log', 'a')
    logfile.chmod( 0644 )
    logfile.puts("Starting as pid: #{Process.pid}")
    logfile.fsync
    Dir.chdir '/'
    File.umask 0000
    STDIN.reopen '/dev/null'
    STDOUT.reopen '/dev/null', 'a'
    STDERR.reopen STDOUT
    Signal.trap("USR1") do
      logfile.puts "You sent me a USR1 signal"
      logfile.fsync
    end
    loop {
      sleep(1) # daemon will wake every second...
      # .. to process handler code here
    }
  }
  raise 'Fork failed!' if p2 == -1
  Process.detach(p2) # divorce p2 from parent process (p1)
}
raise 'Fork failed!' if p1 == -1
Process.detach(p1) # divorce p1 from parent process (shell)