pythonデーモン

#!/usr/bin/python
# -*- coding: utf-8 -*-
import sys, os, time, atexit
from signal import SIGTERM
class Daemon:
    """
 A generic daemon class.
 
 Usage: subclass the Daemon class and override the _run() method
 """
    def __init__(self, pidfile, stdin='/dev/null', stdout='/dev/null', stderr='/dev/null'):
        self.stdin = stdin
        self.stdout = stdout
        self.stderr = stderr
        self.pidfile = pidfile

    def _daemonize(self):
        """
 do the UNIX double-fork magic, see Stevens' "Advanced 
 Programming in the UNIX Environment" for details (ISBN 0201563177)
 http://www.erlenstar.demon.co.uk/unix/faq_2.html#SEC16
 """

        #     
        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))
            sys.exit(1)

        #    
        os.setsid()
        #         
        os.chdir("/")
        #        
        os.umask(0)

        #   fork，            
        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()
        si = file(self.stdin, 'r')
        so = file(self.stdout, 'a+')
        se = file(self.stderr, 'a+', 0)
        #       /  /  
        os.dup2(si.fileno(), sys.stdin.fileno())
        os.dup2(so.fileno(), sys.stdout.fileno())
        os.dup2(se.fileno(), sys.stderr.fileno())

        #          ，   pid  
        atexit.register(self.delpid)
        pid = str(os.getpid())
        file(self.pidfile,'w+').write("%s
" % pid)

    def delpid(self):
        os.remove(self.pidfile)
    def start(self):
        """
 Start the daemon
 """
        # 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

        if pid:
            message = "pidfile %s already exist. Daemon already running?
"
            sys.stderr.write(message % self.pidfile)
            sys.exit(1)

        # Start the daemon
        self._daemonize()
        self._run()
    def stop(self):
        """
 Stop the daemon
 """
        # Get the pid from the pidfile
        try:
            pf = file(self.pidfile,'r')
            pid = int(pf.read().strip())
            pf.close()
        except IOError:
            pid = None

        if not pid:
            message = "pidfile %s does not exist. Daemon not running?
"
            sys.stderr.write(message % self.pidfile)
            return # not an error in a restart
        # Try killing the daemon process 
        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):
        """
 Restart the daemon
 """
        self.stop()
        self.start()
    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().
 """

class MyDaemon(Daemon):
    def _run(self):
        while True:
            time.sleep(1)

if __name__ == "__main__":
    daemon = MyDaemon('/tmp/daemon-example.pid')
    if len(sys.argv) == 2:
        if 'start' == sys.argv[1]:
            daemon.start()
        elif 'stop' == sys.argv[1]:
            daemon.stop()
        elif 'restart' == sys.argv[1]:
            daemon.restart()
        else:
            print "Unknown command"
            sys.exit(2)
        sys.exit(0)
    else:
        print "usage: %s start|stop|restart" % sys.argv[0]
        sys.exit(2)

簡単に説明すると、クラス全体で実現される機能:1.プロセスが親プロセスおよびターミナルバインドから離れる
2.プロセス一意性保証
3.標準入出力/エラーリダイレクト