Python实现Linux下守护进程的编写方法

# Core modules importatexit importos importsys importtime importsignal classDaemon(object):   """ A generic daemon class. Usage: subclass the Daemon class and override the run() method """   def __init__(self, pidfile, stdin=os.devnull,          stdout=os.devnull, stderr=os.devnull,          home_dir='.', umask=022, verbose=1):     self.stdin = stdin     self.stdout = stdout     self.stderr = stderr     self.pidfile = pidfile     self.home_dir = home_dir     self.verbose = verbose     self.umask = umask     self.daemon_alive = True   def daemonize(self):     """ Do the UNIX double-fork magic, see Stevens' "Advanced Programming in the UNIX Environment" for details (ISBN 0201563177) """     try:       pid = os.fork()       if pid > 0:         # Exit first parent         sys.exit(0)     except OSError, e:       sys.stderr.write(         "fork #1 failed: %d (%s)/n" % (e.errno, e.strerror))       sys.exit(1)     # Decouple from parent environment     os.chdir(self.home_dir)     os.setsid()     os.umask(self.umask)     # Do second fork     try:       pid = os.fork()       if pid > 0:         # Exit from second parent         sys.exit(0)     except OSError, e:       sys.stderr.write(         "fork #2 failed: %d (%s)/n" % (e.errno, e.strerror))       sys.exit(1)     if sys.platform != 'darwin': # This block breaks on OS X       # Redirect standard file descriptors       sys.stdout.flush()       sys.stderr.flush()       si = file(self.stdin, 'r')       so = file(self.stdout, 'a+')       if self.stderr:         se = file(self.stderr, 'a+', 0)       else:         se = so       os.dup2(si.fileno(), sys.stdin.fileno())       os.dup2(so.fileno(), sys.stdout.fileno())       os.dup2(se.fileno(), sys.stderr.fileno())     def sigtermhandler(signum, frame):       self.daemon_alive = False       signal.signal(signal.SIGTERM, sigtermhandler)       signal.signal(signal.SIGINT, sigtermhandler)     if self.verbose >= 1:       print "Started"     # Write pidfile     atexit.register(       self.delpid) # Make sure pid file is removed if we quit     pid = str(os.getpid())     file(self.pidfile, 'w+').write("%s/n" % pid)   def delpid(self):     os.remove(self.pidfile)   def start(self, *args, **kwargs):     """ Start the daemon """     if self.verbose >= 1:       print "Starting..."     # Check for a pidfile to see if the daemon already runs     try:       pf = file(self.pidfile, 'r')       pid = int(pf.read().strip())       pf.close()     except IOError:       pid = None     except SystemExit:       pid = None     if pid:       message = "pidfile %s already exists. Is it already running?/n"       sys.stderr.write(message % self.pidfile)       sys.exit(1)     # Start the daemon     self.daemonize()     self.run(*args, **kwargs)   def stop(self):     """ Stop the daemon """     if self.verbose >= 1:       print "Stopping..."     # Get the pid from the pidfile     pid = self.get_pid()     if not pid:       message = "pidfile %s does not exist. Not running?/n"       sys.stderr.write(message % self.pidfile)       # Just to be sure. A ValueError might occur if the PID file is       # empty but does actually exist       if os.path.exists(self.pidfile):         os.remove(self.pidfile)       return # Not an error in a restart     # Try killing the daemon process     try:       i = 0       while 1:         os.kill(pid, signal.SIGTERM)         time.sleep(0.1)         i = i + 1         if i % 10 == 0:           os.kill(pid, signal.SIGHUP)     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)     if self.verbose >= 1:       print "Stopped"   def restart(self):     """ Restart the daemon """     self.stop()     self.start()   def get_pid(self):     try:       pf = file(self.pidfile, 'r')       pid = int(pf.read().strip())       pf.close()     except IOError:       pid = None     except SystemExit:       pid = None     return pid   def is_running(self):     pid = self.get_pid()     print(pid)     return pid and os.path.exists('/proc/%d' % pid)   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(). """