Python recipe -- daemon

参考：http://www.tsheffler.com/blog/?p=377

# -*- coding: utf-8 -*-
'''
    This module is used to fork the current process into a daemon.
    Almost none of this is necessary (or advisable) if your daemon
    is being started by inetd. In that case, stdin, stdout and stderr are
    all set up for you to refer to the network connection, and the fork()s
    and session manipulation should not be done (to avoid confusing inetd).
    Only the chdir() and umask() steps remain as useful.
    References:
        UNIX Programming FAQ
            1.7 How do I get my program to act like a daemon?

        Advanced Programming in the Unix Environment
            W. Richard Stevens, 1992, Addison-Wesley, ISBN 0-201-56317-7.

    History:
      2001/07/10 by Jürgen Herman
      2002/08/28 by Noah Spurrier
      2003/02/24 by Clark Evans


'''
import sys, os, time
from signal import SIGTERM

def deamonize(stdout='/dev/null', stderr=None, stdin='/dev/null',
              pidfile=None, startmsg = 'started with pid %s' ):
    '''
        This forks the current process into a daemon.
        The stdin, stdout, and stderr arguments are file names that
        will be opened and be used to replace the standard file descriptors
        in sys.stdin, sys.stdout, and sys.stderr.
        These arguments are optional and default to /dev/null.
        Note that stderr is opened unbuffered, so
        if it shares a file with stdout then interleaved output
        may not appear in the order that you expect.
    '''
    # Do first fork.
    try:
        pid = os.fork()
        if pid > 0: sys.exit(0) # Exit first parent.
    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.umask(0)
    os.setsid()

    # Do second fork.
    try:
        pid = os.fork()
        if pid > 0: sys.exit(0) # Exit second parent.
    except OSError, e:
        sys.stderr.write("fork #2 failed: (%d) %s\n" % (e.errno, e.strerror))
        sys.exit(1)

    # Open file descriptors and print start message
    if not stderr: stderr = stdout
    si = file(stdin, 'r')
    so = file(stdout, 'a+')
    se = file(stderr, 'a+', 0)
    pid = str(os.getpid())
    sys.stderr.write("\n%s\n" % startmsg % pid)
    sys.stderr.flush()
    if pidfile: file(pidfile,'w+').write("%s\n" % pid)

    # Redirect standard file descriptors.
    os.dup2(si.fileno(), sys.stdin.fileno())
    os.dup2(so.fileno(), sys.stdout.fileno())
    os.dup2(se.fileno(), sys.stderr.fileno())

def startstop(stdout='/dev/null', stderr=None, stdin='/dev/null',
              pidfile='pid.txt', startmsg = 'started with pid %s' ):
    if len(sys.argv) > 1:
        action = sys.argv[1]
        try:
            pf = file(pidfile,'r')
            pid = int(pf.read().strip())
            pf.close()
        except IOError:
            pid = None
        if 'stop' == action or 'restart' == action:
            if not pid:
                mess = "Could not stop, pid file '%s' missing.\n"
                sys.stderr.write(mess % pidfile)
                sys.exit(1)
            try:
               while 1:
                   os.kill(pid,SIGTERM)
                   time.sleep(1)
            except OSError, err:
               err = str(err)
               if err.find("No such process") > 0:
                   os.remove(pidfile)
                   if 'stop' == action:
                       sys.exit(0)
                   action = 'start'
                   pid = None
               else:
                   print str(err)
                   sys.exit(1)
        if 'start' == action:
            if pid:
                mess = "Start aborded since pid file '%s' exists.\n"
                sys.stderr.write(mess % pidfile)
                sys.exit(1)
            deamonize(stdout,stderr,stdin,pidfile,startmsg)
            return
    print "usage: %s start|stop|restart" % sys.argv[0]
    sys.exit(2)

def test():
    '''
        This is an example main function run by the daemon.
        This prints a count and timestamp once per second.
    '''
    sys.stdout.write ('Message to stdout...')
    sys.stderr.write ('Message to stderr...')
    c = 0
    while 1:
        sys.stdout.write ('%d: %s\n' % (c, time.ctime(time.time())) )
        sys.stdout.flush()
        c = c + 1
        time.sleep(1)

if __name__ == "__main__":
    startstop(stdout='/tmp/deamonize.log',
              pidfile='/tmp/deamonize.pid')
    test()

使用的时候：

SIGTERM_SENT = False

def sigterm_handler(signum, frame):
    print >>sys.stderr, "SIGTERM handler.  Shutting Down."

    global SIGTERM_SENT
    if not SIGTERM_SENT:
        SIGTERM_SENT = True
        print >>sys.stderr, "Sending TERM to PG"
        os.killpg(0, signal.SIGTERM)

    sys.exit()

def main():
    # set session ID to this process so we can kill group in sigterm handler
    os.setsid()
    signal.signal(signal.SIGTERM, sigterm_handler)

    while True:
        # ... run daemon threads and subprocesses with impunity.

    # ... this function never returns ...

from daemonize import startstop

if __name__== "__main__":
    startstop(stdout="/var/log/example.log",
              pidfile="/var/run/example.pid")
    main()

main函数中的os.setsid()的作用是将daemon进程设为会话ID。然后退出的时候用os.killpg(0, signal.SIGTERM)将进程组杀掉就可以了。