daemon.py

# Based on http://www.jejik.com/articles/2007/02/a_simple_unix_linux_daemon_in_python/

import atexit
import errno
import logging
import logging.handlers
import os
from signal import SIGTERM
import sys
import time


def go(daemon):
    if len(sys.argv) > 1:
        if "start" == sys.argv[1]:
            daemon.start()
        elif "stop" == sys.argv[1]:
            daemon.stop()
        elif "restart" == sys.argv[1]:
            daemon.restart()
        elif "status" == sys.argv[1]:
            sys.exit(daemon.status())
        else:
            print "Unknown command"
            sys.exit(2)
        sys.exit(0)
    else:
        print "usage: %s start|stop|restart" % sys.argv[0]
        sys.exit(2)


class Daemon:
    """
    A generic daemon class.

    Usage: subclass the Daemon class and override the run() method
    """
    def __init__(self, pidfile, logfile=None):
        self.pidfile = pidfile
        self.logfile = logfile

    def daemonize(self):
        """
        do the UNIX double-fork magic, see Stevens' "Advanced
        Programming in the UNIX Environment" for details (ISBN 0201563177)
        http://www.steve.org.uk/Reference/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()
        null = os.open("/dev/null", os.O_RDWR)
        for i in range(3):
            try:
                os.dup2(null, i)
            except OSError, e:
                if e.errno != errno.EBADF:
                    raise
        os.close(null)

        # write pidfile
        atexit.register(self.delpid)
        pid = str(os.getpid())
        file(self.pidfile,'w+').write("%s\n" % pid)

    def setup_logging(self):
        """Configure the logging module"""
        log = logging.getLogger()
        log.setLevel(logging.INFO)
        handler = logging.handlers.RotatingFileHandler(self.logfile,
                                                       maxBytes=1024*1024,
                                                       backupCount=1)
        handler.setFormatter(logging.Formatter(
                "%(asctime)s %(process)d %(levelname)s %(message)s"))
        log.addHandler(handler)

    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()
        if self.logfile:
            self.setup_logging()
        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)
                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 status(self):
        try:
            pf = file(self.pidfile, "r")
            pid = int(pf.read().strip())
            pf.close()
        except IOError:
            pid = None

        if not pid:
            sys.stderr.write("Daemon not running.\n")
            return 3

        # see if it's running?
        try:
            os.getpgid(pid)
            sys.stderr.write("Daemon (PID %s) is running...\n" % pid)
            return 0
        except OSError, err:
            err = str(err)
            if err.find("No such process") > 0:
                sys.stderr.write("Daemon not running but pidfile exists\n")
                return 1
            else:
                print str(err)
                return 4

    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().
        """