进程守护

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): 
        try:   
            pid = os.fork()   
            if pid > 0:  
                # 退出父进程
                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("/")   # 修改工作目录
        os.setsid()   # 设置新的会话连接
        os.umask(0)   # 重新设置文件创建权限
      
        # do second fork  
        try:   
            pid = os.fork()   # 第二次fork，禁止进程打开终端
            if pid > 0:  
                sys.exit(0)   
        except OSError, e:   
            sys.stderr.write("fork #2 failed: %d (%s)\n" % (e.errno, e.strerror))  
            sys.exit(1)   
      
        # 重定向所有输出  
        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())  
      
        # 记录pid  
        atexit.register(self.delpid)  # 在最后执行的语句
        pid = str(os.getpid())  
        file(self.pidfile,'w+').write("%s\n" % pid)  
      # 记录pgid
        pgid = getpgid(int(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?\n"  
            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?\n"  
            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)  
                # kill进程组，
                # os.killpg(pgid,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(). 
        """