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POPython daemon will not run in the background on Ubuntu
 

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    <p>My Python daemon runs fine in the foreground of my Ubuntu system using this command in the terminal:</p> <pre><code>python /opt/my-daemon.py foreground </code></pre> <p>However when I try to call the daemon using the <strong>"start"</strong> command it fails, why?</p> <pre><code>python /opt/my-daemon.py start </code></pre> <p>This is how I call the command in the <code>/etc/rc.local</code> file:</p> <pre><code>python /opt/my-daemon.py start &amp; </code></pre> <p>Herewith the code:</p> <p><strong>1.daemon.py</strong></p> <pre><code>#!/usr/bin/env python import sys, os, time, 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 def daemonize(self): """ Do the UNIX double-fork magic. See Richard 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 &gt; 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 &gt; 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 # 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") &gt; 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(). """ </code></pre> <p><strong>2.my-daemon.py</strong></p> <pre><code>import sys, time from daemon import Daemon import MySQLdb #MySQL libraries #Database parameters config = {"host":"localhost",...} try: conn = MySQLdb.connect(config['host'],... class MyDaemon(Daemon): def run(self): while True: time.sleep(2) #{Do processes, connect to the database, etc....} ... if __name__ == "__main__": daemon = MyDaemon('/tmp/daemon-example.pid') if len(sys.argv) == 2: if 'start' == sys.argv[1]: daemon.start() elif 'stop' == sys.argv[1]: daemon.stop() elif 'restart' == sys.argv[1]: daemon.restart() elif 'foreground' == sys.argv[1]: #This runs the daemon in the foreground daemon.run() else: print "Unknown command" sys.exit(2) sys.exit(0) else: print "usage: %s start|foreground|stop|restart" % sys.argv[0] sys.exit(2) </code></pre>
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    1. USPeter Mortensen
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    1. COWhat exactly happens if you use the `start` command?
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      1. USchryss
    2. COWhat do you mean by "it fails" ?
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      1. USGuillaume Lebourgeois
    3. COFails as in does not run at all. It runs with the foreground command. When i type the "start" command in the terminal with the & at the end I see the PID but then it immediately kills the daemon process.
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