"""Generic linux daemon base class for python 3.x.
Source: https://web.archive.org/web/20160320091458/http://www.jejik.com/files/examples/daemon3x.py"""
import sys
import os
import time
import atexit
import signal
import logging as log
log.basicConfig(level=log.INFO)
logging = log.getLogger(__name__)
[docs]class Daemon:
"""A generic daemon class.
Usage: subclass the daemon class and override the run() method."""
def __init__(self, pidfile):
self.pidfile = pidfile
[docs] def daemonize(self):
"""Deamonize class. UNIX double fork mechanism."""
try:
pid = os.fork()
if pid > 0:
# exit first parent
sys.exit(0)
except OSError as err:
sys.stderr.write('fork #1 failed: {0}\n'.format(err))
sys.exit(1)
# decouple from parent environment
os.chdir('/')
os.setsid()
os.umask(0)
# do second fork
try:
pid = os.fork()
if pid > 0:
# exit from second parent
sys.exit(0)
except OSError as err:
sys.stderr.write('fork #2 failed: {0}\n'.format(err))
sys.exit(1)
# redirect standard file descriptors
sys.stdout.flush()
sys.stderr.flush()
si = open(os.devnull, 'r')
so = open(os.devnull, 'a+')
se = open(os.devnull, 'a+')
os.dup2(si.fileno(), sys.stdin.fileno())
os.dup2(so.fileno(), sys.stdout.fileno())
os.dup2(se.fileno(), sys.stderr.fileno())
# write pidfile
atexit.register(self.delpid)
pid = str(os.getpid())
with open(self.pidfile, 'w+') as f:
f.write(pid + '\n')
[docs] def delpid(self):
os.remove(self.pidfile)
[docs] def start(self):
"""Start the daemon."""
logging.info('Starting server...')
# Check for a pidfile to see if the daemon already runs
try:
with open(self.pidfile, 'r') as pf:
pid = int(pf.read().strip())
except IOError:
pid = None
if pid:
message = "pidfile {0} already exist. " + \
"Daemon already running?\n"
sys.stderr.write(message.format(self.pidfile))
sys.exit(1)
# Start the daemon
self.daemonize()
self.run()
[docs] def stop(self):
"""Stop the daemon."""
logging.info('Stopping server ...')
# Get the pid from the pidfile
try:
with open(self.pidfile, 'r') as pf:
pid = int(pf.read().strip())
except IOError:
pid = None
if not pid:
message = "pidfile {0} does not exist. " + \
"Daemon not running?\n"
sys.stderr.write(message.format(self.pidfile))
return # not an error in a restart
# Try killing the daemon process
try:
while 1:
os.kill(pid, signal.SIGTERM)
time.sleep(0.1)
except OSError as err:
e = str(err.args)
if e.find("No such process") > 0:
if os.path.exists(self.pidfile):
os.remove(self.pidfile)
else:
logging.debug(str(err.args))
sys.exit(1)
[docs] def restart(self):
"""Restart the daemon."""
logging.info('Restarting server...')
self.stop()
logging.info('Server stopped. Now restarting ...')
self.start()
logging.info('Server restarted.')
[docs] def run(self):
"""You should override this method when you subclass Daemon.
It will be called after the process has been daemonized by
start() or restart()."""