python下编写守护进程

1、编写守护进程的步骤
python创建守护进程其实和c创建守护进程的方式大同小异了，其实就是那么几个步骤：
（1）创建子进程，父进程退出
（2）改变当前目录为根目录
（3）在子进程中创建新会话
（4）重设文件权限掩码
（5）子进中创建孙子进程，子进程退出，孙子进程成为真正的守护进程
（6）关闭文件描述符

2、定义一个Daemon类，有其他人写好的标准类，可以直接引用
daemon_python.py

#!/usr/bin/env python#coding:utf-8import sys, os, time, atexitfrom 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:                # 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("/")         os.setsid()         os.umask(0)         # 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)         # redirect standard file descriptors        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())        # write pidfile        atexit.register(self.delpid)        pid = str(os.getpid())        file(self.pidfile,'w+').write("%s\n" % 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         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().        """

3、写一个测试的守护进程，每隔两秒向文件中写入数据
test.py

#!/usr/bin/env python#coding:utf-8import sys, os, time, atexitfrom signal import SIGTERM from optparse import OptionParserfrom daemon_python import Daemonclass my_daemon(Daemon):    def run(self):        """        每两秒向文件写入信息        """        while True:            pf = file('/tmp/python_example.txt', 'a+')            pf.write("this is test python daemon\n")            pf.close()            time.sleep(2)if __name__ == "__main__":    newParser  = OptionParser()    newParser.add_option("--action", dest="action", help=u'start|restart|stop daemon')    (args, option) = newParser.parse_args()    if not args.action:        print newParser.print_help()        exit(1)    daemon = my_daemon('/tmp/my_daemon.pid')    if args.action == 'start':        daemon.start()    elif args.action == 'restart':        daemon.restart()    elif args.action == 'stop':        daemon.stop()    else:        print 'unkowm command'

运行结果：

查看程序运行使用方法：

是不是很简单，你们自己也动手试一下吧。
这里用到的命令行解析函数OptionParser()，大家可以自己去查下，这个函数功能很强大