gistfile1.rb

require 'daemons'

# This file will contain all System calls by the program.
# (ie : Launching a programm, monitoring it)

# Returns the pid of the child that executes the cmd
module Monitor
  module System
    extend self
    def daemonize(cmd, options = {})
      rd, wr = IO.pipe

      #the fork call returns twice, once in the parent, returning the process ID of the child, and once in the child, returning nil. The child process can exit using Kernel.exit
      if child = Daemonize.safefork
       #We are in the parent, Process.detach register disinterest in their status; otherwise, the operating system may accumulate zombie processes.
        ::Process.detach(child)

        wr.close

        daemon_id = rd.read.to_i
        rd.close

        return daemon_id if daemon_id > 0

      else
        # child
        rd.close
        set_user(options[:utilisateur]) if !options[:utilisateur].nil?
        to_daemonize = lambda do
          Dir.chdir(ENV['PWD'] = options[:working_dir].to_s) if options[:working_dir]
          ::Kernel.exec(*Shellwords.shellwords(cmd))
          exit
        end

        daemon_id = Daemonize.call_as_daemon(to_daemonize, nil, cmd)

        File.open(options[:pid_file], 'w') {|f| f.write(daemon_id)}
        wr.write daemon_id
        wr.close

        exit
      end

      #Launch the program as a specific User.
      def set_user(uid)
        if ::Process::Sys.geteuid == 0
          uid_num = Etc.getpwnam(uid).uid if uid
          ::Process::Sys.setuid(uid_num) if uid
        end
      end
    end
  end
end