daemon.py

'''
    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?
                http://www.erlenstar.demon.co.uk/unix/faq_2.html#SEC16
        Advanced Programming in the Unix Environment
            W. Richard Stevens, 1992, Addison-Wesley, ISBN 0-201-56317-7.

    History:
      2001/07/10 by Juergen Hermann
      2002/08/28 by Noah Spurrier
      2003/02/24 by Clark Evans
      
      http://aspn.activestate.com/ASPN/Cookbook/Python/Recipe/66012
'''
import sys, os, time, signal

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
        except ValueError:
            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,signal.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
        if "reload" == action:
            if not pid:
                mess = "Could not reload, pid file '%s' missing.\n"
                sys.stderr.write(mess % pidfile)
                sys.exit(1)
            os.kill(pid, signal.SIGHUP)
            sys.exit(0)
        
    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()