daemon.py

import sys
import os
import time
import atexit

from signal import SIGTERM

class Daemon:
  def __init__(self, pidfile, stdin='/dev/null', stdout='/dev/null', stderr='/dev/null'):
    self.pidfile  = pidfile
    self.stdin    = stdin
    self.stdout   = stdout
    self.stderr   = stderr

  def background(self):
    try:
      pid = os.fork()

      if pid > 0:
        sys.exit(0)

    except OSError, e:
      sys.stderr.write("Fork #1 failed: %d (%s)" % (e.errno, e.strerror))

    os.chdir('/')
    os.setsid()
    os.umask(0)

    try:
      pid = os.fork()

      if pid > 0:
        sys.exit(0)

    except OSError, e:
      sys.stderr.write("Fork #2 failed: %d (%s)" % (e.errno, e.strerror))
      sys.exit(1)

    sys.stdout.flush()
    sys.stderr.flush()

    input   = file(self.stdin, 'r')
    output  = file(self.stdout, 'a+')
    error   = file(self.stderr, 'a+', 0)

    os.dup2(input.fileno(), sys.stdin.fileno())
    os.dup2(output.fileno(), sys.stdout.fileno())
    os.dup2(error.fileno(), sys.stderr.fileno())

    atexit.register(self.delete_pid)

    pid = str(os.getpid())

    file(self.pidfile, 'w+').write('%s\n' % pid)

  def delete_pid(self):
    os.remove(self.pidfile)

  def start(self):
    try:
      pid_file  = file(self.pidfile, 'r')
      pid       = int(pid_file.read().strip())

      pid_file.close()

      sys.stderr.write("Pid file %s already exist. Already running?\n" % self.pidfile)
      sys.exit(1)

      return

    except IOError:
      pid = None


    self.background()
    self.run()

  def stop(self):
    try:
      pid_file  = file(self.pidfile, 'r')
      pid       = int(pid_file.read().strip())

      pid_file.close()
    except IOError:
      pid = None

      sys.stderr.write("Pidfile %s does not exist. Not running?" % self.pidfile)
      return

    try:
      while 1: os.kill(pid, SIGTERM)
      time.sleep(0.1)
    except OSError, err:
      err = str(err)

      if err.find('No such process') > 0:
        if os.path.exists(self.pidfile):
          os.remove(self.pidfile)
      else:
        print str(err)
        sys.exit(1)

  def restart(self):
    self.stop()
    self.start()


  def run(self):
    """ Override in subclass """