This snippets shows you how to create a daemon process out of an ordinary Ruby script.

First you’ll need the daemons gem:

   1  gem install daemons

Then you’ll need the daemon script, for example daemon.rb:

   1  require 'rubygems'
   2  require 'daemons'
   3  
   4  pwd  = File.dirname(File.expand_path(__FILE__))
   5  file = pwd + '/../lib/background_service.rb'
   6  
   7  Daemons.run_proc(
   8    'background_service', # name of daemon
   9  #  :dir_mode => :normal
  10  #  :dir => File.join(pwd, 'tmp/pids'), # directory where pid file will be stored
  11  #  :backtrace => true,
  12  #  :monitor => true,
  13    :log_output => true
  14  ) do
  15    exec "ruby #{file}"
  16  end

Change the file variable to point to the script you want to daemonize and your good to go.

You can now execute the daemon.rb script without parameters to get a list of available commands for controlling the daemon process:

   1  ERROR: no command given
   2  
   3  Usage: lib/background_service.rb <command> <options> -- <application options>
   4  
   5  * where <command> is one of:
   6    start         start an instance of the application
   7    stop          stop all instances of the application
   8    restart       stop all instances and restart them afterwards
   9    run           start the application and stay on top
  10    zap           set the application to a stopped state
  11  
  12  * and where <options> may contain several of the following:
  13  
  14      -t, --ontop                      Stay on top (does not daemonize)
  15      -f, --force                      Force operation
  16  
  17  Common options:
  18      -h, --help                       Show this message
  19          --version                    Show version

This script tests if nginx exists and is executable. The script prints a warning and exits, if nginx doesn’t exists or isn’t executable:

   1  DAEMON=/usr/local/sbin/nbinx
   2  if [ ! -x $DAEMON ]
   3  then
   4     echo "Couldn't find $DAEMON. Please set path to DAEMON."
   5     exit 0
   6  fi

See man test for more information on how to use the test command.