module Daemonize

Daemonize Library

February. 4, 2005 Travis Whitton <whitton@atlantic.net>

Daemonize allows you to easily modify any existing Ruby program to run as a daemon. See README.rdoc for more details.

How to install

su to root
ruby install.rb

build the docs if you want to

rdoc --main README.rdoc daemonize.rb README.rdoc

Copying

The Daemonize extension module is copywrited free software by Travis Whitton <whitton@atlantic.net>. You can redistribute it under the terms specified in the COPYING file of the Ruby distribution.

WARRANTY

THIS SOFTWARE IS PROVIDED "AS IS" AND WITHOUT ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED WARRANTIES OF MERCHANTIBILITY AND FITNESS FOR A PARTICULAR PURPOSE.

Purpose

Daemonize is a module derived from Perl's Proc::Daemon module. This module allows you to easily modify any existing Ruby program to run as a daemon. A daemon is a process that runs in the background with no controlling terminal. Generally servers (like FTP and HTTP servers) run as daemon processes. Note, do not make the mistake that a daemon == server. Converting a program to a daemon by hand is a relatively simple process; however, this module will save you the effort of repeatedly looking up the procedure, and it will also insure that your programs are daemonized in the safest and most corrects fashion possible.

Procedure

The Daemonize module does the following:

Forks a child and exits the parent process.

Becomes a session leader (which detaches the program from the controlling terminal).

Forks another child process and exits first child. This prevents the potential of acquiring a controlling terminal.

Changes the current working directory to "/".

Clears the file creation mask.

Closes file descriptors.

Example usage

Using the Daemonize module is extremely simple:

require 'daemonize'

class TestDaemon
  include Daemonize

  def initialize
    daemonize()
    loop do
      # do some work here
    end
  end
end

Credits

Daemonize was written by Travis Whitton and is based on Perl's Proc::Daemonize, which was written by Earl Hood. The above documentation is also partially borrowed from the Proc::Daemonize POD documentation.

Constants

VERSION

Public Class Methods

call_as_daemon(block, logfile_name = nil, app_name = nil) click to toggle source

# File lib/daemons/daemonize.rb, line 142
def call_as_daemon(block, logfile_name = nil, app_name = nil)
  rd, wr = IO.pipe
  
  if tmppid = safefork
    # parent
    wr.close
    pid = rd.read.to_i
    rd.close
    
    Process.waitpid(tmppid)
    
    return pid
  else
    # child
    
    rd.close
    
    # Detach from the controlling terminal
    unless sess_id = Process.setsid
      raise Daemons.RuntimeException.new('cannot detach from controlling terminal')
    end

    # Prevent the possibility of acquiring a controlling terminal
    #if oldmode.zero?
      trap 'SIGHUP', 'IGNORE'
      exit if pid = safefork
    #end

    wr.write Process.pid
    wr.close
    
    $0 = app_name if app_name
    
    Dir.chdir "/"   # Release old working directory
    File.umask 0000 # Insure sensible umask

    # Make sure all file descriptors are closed
    ObjectSpace.each_object(IO) do |io|
      unless [STDIN, STDOUT, STDERR].include?(io)
        begin
          unless io.closed?
            io.close
          end
        rescue ::Exception
        end
      end
    end

    redirect_io(logfile_name)  
  
    block.call
    
    exit
  end
end

daemonize(logfile_name = nil, app_name = nil) click to toggle source

This method causes the current running process to become a daemon

# File lib/daemons/daemonize.rb, line 201
def daemonize(logfile_name = nil, app_name = nil)
  srand # Split rand streams between spawning and daemonized process
  safefork and exit # Fork and exit from the parent

  # Detach from the controlling terminal
  unless sess_id = Process.setsid
    raise Daemons.RuntimeException.new('cannot detach from controlling terminal')
  end

  # Prevent the possibility of acquiring a controlling terminal
  #if oldmode.zero?
    trap 'SIGHUP', 'IGNORE'
    exit if pid = safefork
  #end

  $0 = app_name if app_name
  
  Dir.chdir "/"   # Release old working directory
  File.umask 0000 # Insure sensible umask

  # Make sure all file descriptors are closed
  ObjectSpace.each_object(IO) do |io|
    unless [STDIN, STDOUT, STDERR].include?(io)
      begin
        unless io.closed?
          io.close
        end
      rescue ::Exception
      end
    end
  end

  redirect_io(logfile_name)
  
  #return oldmode ? sess_id : 0   # Return value is mostly irrelevant
  return sess_id
end

redirect_io(logfile_name) click to toggle source

Free file descriptors and point them somewhere sensible STDOUT/STDERR should go to a logfile

# File lib/daemons/daemonize.rb, line 244
def redirect_io(logfile_name)
  begin; STDIN.reopen "/dev/null"; rescue ::Exception; end       
   
  if logfile_name
    begin
      STDOUT.reopen logfile_name, "a" 
      STDOUT.sync = true
    rescue ::Exception
      begin; STDOUT.reopen "/dev/null"; rescue ::Exception; end
    end
  else
    begin; STDOUT.reopen "/dev/null"; rescue ::Exception; end
  end
  
  begin; STDERR.reopen STDOUT; rescue ::Exception; end
  STDERR.sync = true
end

safefork() click to toggle source

Try to fork if at all possible retrying every 5 sec if the maximum process limit for the system has been reached

# File lib/daemons/daemonize.rb, line 97
def safefork
  tryagain = true

  while tryagain
    tryagain = false
    begin
      if pid = fork
        return pid
      end
    rescue Errno::EWOULDBLOCK
      sleep 5
      tryagain = true
    end
  end
end

simulate(logfile_name = nil) click to toggle source

# File lib/daemons/daemonize.rb, line 115
def simulate(logfile_name = nil)
  # NOTE: STDOUT and STDERR will not be redirected to the logfile, because in :ontop mode, we normally want to see the output
  
  Dir.chdir "/"   # Release old working directory
  File.umask 0000 # Insure sensible umask

  # Make sure all file descriptors are closed
  ObjectSpace.each_object(IO) do |io|
    unless [STDIN, STDOUT, STDERR].include?(io)
      begin
        unless io.closed?
          io.close
        end
      rescue ::Exception
      end
    end
  end

  # Free file descriptors and
  # point them somewhere sensible
  # STDOUT/STDERR should go to a logfile
  
  begin; STDIN.reopen "/dev/null"; rescue ::Exception; end       
end