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daemon.py
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daemon.py
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'''
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***
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Modified generic daemon class
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***
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Author: http://www.jejik.com/articles/2007/02/
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a_simple_unix_linux_daemon_in_python/www.boxedice.com
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License: http://creativecommons.org/licenses/by-sa/3.0/
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Changes: 23rd Jan 2009 (David Mytton <david@boxedice.com>)
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- Replaced hard coded '/dev/null in __init__ with os.devnull
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- Added OS check to conditionally remove code that doesn't
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work on OS X
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- Added output to console on completion
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- Tidied up formatting
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11th Mar 2009 (David Mytton <david@boxedice.com>)
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- Fixed problem with daemon exiting on Python 2.4
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(before SystemExit was part of the Exception base)
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13th Aug 2010 (David Mytton <david@boxedice.com>
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- Fixed unhandled exception if PID file is empty
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'''
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# Core modules
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from __future__ import print_function
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import atexit
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import errno
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import os
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import sys
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import time
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import signal
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class Daemon(object):
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"""
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A generic daemon class.
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Usage: subclass the Daemon class and override the run() method
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"""
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def __init__(self, pidfile, stdin=os.devnull,
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stdout=os.devnull, stderr=os.devnull,
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home_dir='.', umask=0o22, verbose=1,
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use_gevent=False, use_eventlet=False):
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self.stdin = stdin
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self.stdout = stdout
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self.stderr = stderr
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self.pidfile = pidfile
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self.home_dir = home_dir
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self.verbose = verbose
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self.umask = umask
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self.daemon_alive = True
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self.use_gevent = use_gevent
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self.use_eventlet = use_eventlet
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def log(self, *args):
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if self.verbose >= 1:
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print(*args)
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def daemonize(self):
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"""
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Do the UNIX double-fork magic, see Stevens' "Advanced
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Programming in the UNIX Environment" for details (ISBN 0201563177)
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http://www.erlenstar.demon.co.uk/unix/faq_2.html#SEC16
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"""
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if self.use_eventlet:
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import eventlet.tpool
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eventlet.tpool.killall()
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try:
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pid = os.fork()
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if pid > 0:
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# Exit first parent
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sys.exit(0)
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except OSError as e:
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sys.stderr.write(
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"fork #1 failed: %d (%s)\n" % (e.errno, e.strerror))
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sys.exit(1)
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# Decouple from parent environment
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os.chdir(self.home_dir)
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os.setsid()
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os.umask(self.umask)
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# Do second fork
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try:
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pid = os.fork()
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if pid > 0:
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# Exit from second parent
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sys.exit(0)
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except OSError as e:
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sys.stderr.write(
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"fork #2 failed: %d (%s)\n" % (e.errno, e.strerror))
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sys.exit(1)
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if sys.platform != 'darwin': # This block breaks on OS X
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# Redirect standard file descriptors
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sys.stdout.flush()
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sys.stderr.flush()
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si = open(self.stdin, 'r')
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so = open(self.stdout, 'a+')
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if self.stderr:
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try:
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se = open(self.stderr, 'a+', 0)
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except ValueError:
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# Python 3 can't have unbuffered text I/O
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se = open(self.stderr, 'a+', 1)
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else:
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se = so
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os.dup2(si.fileno(), sys.stdin.fileno())
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os.dup2(so.fileno(), sys.stdout.fileno())
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os.dup2(se.fileno(), sys.stderr.fileno())
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def sigtermhandler(signum, frame):
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self.daemon_alive = False
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sys.exit()
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if self.use_gevent:
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import gevent
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gevent.reinit()
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gevent.signal(signal.SIGTERM, sigtermhandler, signal.SIGTERM, None)
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gevent.signal(signal.SIGINT, sigtermhandler, signal.SIGINT, None)
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else:
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signal.signal(signal.SIGTERM, sigtermhandler)
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signal.signal(signal.SIGINT, sigtermhandler)
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self.log("Started")
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# Write pidfile
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atexit.register(
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self.delpid) # Make sure pid file is removed if we quit
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pid = str(os.getpid())
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open(self.pidfile, 'w+').write("%s\n" % pid)
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def delpid(self):
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try:
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# the process may fork itself again
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pid = int(open(self.pidfile, 'r').read().strip())
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if pid == os.getpid():
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os.remove(self.pidfile)
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except OSError as e:
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if e.errno == errno.ENOENT:
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pass
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else:
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raise
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def start(self, *args, **kwargs):
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"""
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Start the daemon
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"""
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self.log("Starting...")
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# Check for a pidfile to see if the daemon already runs
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try:
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pf = open(self.pidfile, 'r')
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pid = int(pf.read().strip())
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pf.close()
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except IOError:
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pid = None
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except SystemExit:
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pid = None
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if pid:
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message = "pidfile %s already exists. Is it already running?\n"
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sys.stderr.write(message % self.pidfile)
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sys.exit(1)
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# Start the daemon
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self.daemonize()
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self.run(*args, **kwargs)
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def stop(self):
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"""
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Stop the daemon
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"""
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if self.verbose >= 1:
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self.log("Stopping...")
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# Get the pid from the pidfile
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pid = self.get_pid()
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if not pid:
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message = "pidfile %s does not exist. Not running?\n"
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sys.stderr.write(message % self.pidfile)
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# Just to be sure. A ValueError might occur if the PID file is
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# empty but does actually exist
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if os.path.exists(self.pidfile):
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os.remove(self.pidfile)
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sys.exit(0) # Not an error in a restart
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# Try killing the daemon process
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try:
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i = 0
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while 1:
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os.kill(pid, signal.SIGTERM)
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time.sleep(0.1)
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i = i + 1
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if i % 10 == 0:
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os.kill(pid, signal.SIGHUP)
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except OSError as err:
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if err.errno == errno.ESRCH:
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if os.path.exists(self.pidfile):
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os.remove(self.pidfile)
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else:
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print(str(err))
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sys.exit(1)
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self.log("Stopped")
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def restart(self):
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"""
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Restart the daemon
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"""
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self.stop()
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self.start()
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def get_pid(self):
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try:
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pf = open(self.pidfile, 'r')
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pid = int(pf.read().strip())
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pf.close()
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except IOError:
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pid = None
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except SystemExit:
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pid = None
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return pid
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def is_running(self):
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pid = self.get_pid()
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if pid is None:
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self.log('Process is stopped')
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return False
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elif os.path.exists('/proc/%d' % pid):
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self.log('Process (pid %d) is running...' % pid)
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return True
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else:
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self.log('Process (pid %d) is killed' % pid)
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return False
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def run(self):
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"""
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You should override this method when you subclass Daemon.
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It will be called after the process has been
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daemonized by start() or restart().
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"""
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raise NotImplementedError
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