daemon.py

#!/python3/bin/python3

import sys
import os
import time
import atexit
from 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

    ##  Method: daemonize
    #   Description: initialize script as daemon (service) to run in background
    #       no matter you close shell (your terminal)
    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 as 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 as e:
            sys.stderr.write("fork #2 failed: %d (%s)\n" % (e.errno,
                e.strerror))
            sys.exit(1)

        # redirect standard file descriptors
        with open(self.stdin, 'r') as si:
            os.dup2(si.fileno(), sys.stdin.fileno())
        si.close

        sys.stdout.flush()
        with open(self.stdout, 'wb') as so:
            os.dup2(so.fileno(), sys.stdout.fileno())
        so.close()

        sys.stderr.flush()
        with open(self.stderr, 'wb', 0) as se:
            os.dup2(se.fileno(), sys.stderr.fileno())
        se.close()

        # write pidfile
        atexit.register(self.delpid)
        pid = str(os.getpid())
        with open(self.pidfile, 'w+') as pid_file:
            pid_file.write("%s\n" % pid)
        pid_file.close()

    ## Method: delpid
    #  Description: delete filepid
    def delpid(self):
        os.remove(self.pidfile)

    ## Method: start
    #  Description: start daemon using run and daemonize methods
    def start(self):
        """
        Start the daemon
        """
        # Check for a pidfile to see if the daemon already runs
        try:
            with open(self.pidfile, 'r') as pf:
                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()

    ## Method: stop
    #  Description: stop daemon by killing process id, and removing pidfile
    def stop(self):
        """
        Stop the daemon
        """
        # Get the pid from the pidfile
        try:
            pf = open(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 as 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)

    ## Method: restart
    #  Description: restart daemon, it uses stop and start methods
    def restart(self):
        """
        Restart the daemon
        """
        self.stop()
        self.start()

    ## Method: run
    #  Description: this method should be override or modified with your code
    #      by recomendation override
    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().
        """