module Mixlib::ShellOut::Unix

def run_command

within +timeout+ seconds (default: 60s)
* Chef::Exceptions::CommandTimeout when the command does not complete
in the current $PATH)
* Errno::ENOENT when the command is not available on the system (or not
* Errno::EACCES when you are not privileged to execute the command
=== Raises
populated with results of the command
returns +self+; +stdout+, +stderr+, +status+, and +exitstatus+ will be
=== Returns
to +stdout+ and +stderr+, and saving its exit status object to +status+
Run the command, writing the command's standard out and standard error 
def run_command
  @child_pid = fork_subprocess
  configure_parent_process_file_descriptors
  propagate_pre_exec_failure
  @result = nil
  @execution_time = 0
  write_to_child_stdin
  # Ruby 1.8.7 and 1.8.6 from mid 2009 try to allocate objects during GC
  # when calling IO.select and IO#read. Some OS Vendors are not interested
  # in updating their ruby packages (Apple, *cough*) and we *have to*
  # make it work. So I give you this epic hack:
  GC.disable
  until @status
    ready = IO.select(open_pipes, nil, nil, READ_WAIT_TIME)
    unless ready
      @execution_time += READ_WAIT_TIME
      if @execution_time >= timeout && !@result
        raise CommandTimeout, "command timed out:\n#{format_for_exception}"
      end
    end
    if ready && ready.first.include?(child_stdout)
      read_stdout_to_buffer
    end
    if ready && ready.first.include?(child_stderr)
      read_stderr_to_buffer
    end
    unless @status
      # make one more pass to get the last of the output after the
      # child process dies
      if results = Process.waitpid2(@child_pid, Process::WNOHANG)
        @status = results.last
        redo
      end
    end
  end
  self
rescue Exception
  # do our best to kill zombies
  Process.waitpid2(@child_pid, Process::WNOHANG) rescue nil
  raise
ensure
  # no matter what happens, turn the GC back on, and hope whatever busted
  # version of ruby we're on doesn't allocate some objects during the next
  # GC run.
  GC.enable
  close_all_pipes
end