python下编写守护进程

**1、编写守护进程的步骤 **
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
  1. 改变当前目录为根目录
  2. 在子进程中创建新会话
  3. 重设文件权限掩码
  4. 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
  5. 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-8
import 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-8
import 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().
        """

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

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