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#!/usr/bin/env python
#
# Daemon.py: this file is part of the GRS suite
# Copyright (C) 2015 Anthony G. Basile
#
# This program is free software: you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation, either version 3 of the License, or
# (at your option) any later version.
#
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
# GNU General Public License for more details.
#
# You should have received a copy of the GNU General Public License
# along with this program. If not, see <http://www.gnu.org/licenses/>.
import atexit
import os
import sys
class Daemon:
""" Adopted from Sander Marechal's "A simple unix/linux daemon in Python"
See: http://www.jejik.com/articles/2007/02/a_simple_unix_linux_daemon_in_python/
To use, inherit by a subclass which overrides run() and does all the
work. You start the daemon with
d = MyDaemon(pidfile, foo='1', bar='2') # Any **kwargs after pidfile
d.start() # to start the daemon
All signal handling should be defined in a subfunction within run().
Note: This isn't completely general daemon code as it doesn't close stdout/stderr.
Rather these are redirected to /var/log/grs/grs-daemon-<pid>.err to capture any
exceptions for debugging.
"""
def __init__(self, pidfile, **kwargs):
# Since this will be used as a super class, we'll accept any **kwargs
# and insert them to our internal __dict__.
self.pidfile = pidfile
for k in kwargs:
self.__dict__[k] = kwargs[k]
def daemonize(self):
try:
pid = os.fork()
if pid > 0:
sys.exit(0)
except OSError as err:
sys.stderr.write('fork #1 failed: %s\n' % err)
sys.exit(1)
os.chdir('/')
os.setsid()
os.umask(0o22)
try:
pid = os.fork()
if pid > 0:
sys.exit(0)
except OSError as err:
sys.stderr.write('fork #2 failed %s\n' % err)
sys.exit(1)
# Dup stdin to /dev/null, and stdout and stderr to grs-daemon-<pid>.err
si = open(os.devnull, 'r')
os.dup2(si.fileno(), sys.stdin.fileno())
os.makedirs('/var/log/grs', mode=0o755, exist_ok=True)
se = open('/var/log/grs/grs-daemon-%d.err' % os.getpid(), 'a+')
sys.stdout.flush()
os.dup2(se.fileno(), sys.stdout.fileno())
sys.stderr.flush()
os.dup2(se.fileno(), sys.stderr.fileno())
# Use atexit to remove the pidfile when we shutdown.
# No matter where the exit is initiated, eg from Execute.py
# we are sure that atexit() will run and delete the pidfile.
atexit.register(self.delpid)
with open(self.pidfile, 'w') as pf:
pf.write('%d\n' % os.getpid())
def delpid(self):
os.remove(self.pidfile)
def run(self):
pass
def start(self):
# If there's a pidfile when we try to startup, then:
# 1) If the pidfile is stale, remove it and startup as usual.
# 2) If we're already running, then don't start a second instance.
try:
with open(self.pidfile, 'r') as pf:
pid = int(pf.read().strip())
except IOError:
pid = None
if pid:
if not os.path.exists('/proc/%d' % pid):
sys.stderr.write('unlinking stale pid file %s\n' % self.pidfile)
os.unlink(self.pidfile)
else:
sys.stderr.write('process running with pid = %d\n' % pid)
return
self.daemonize()
self.run()
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