How can I run a Perl script as a system daemon in linux?

Question

What's a simple way to get a Perl script to run as a daemon in linux?

Currently, this is on CentOS. I'd want it to start up with the system and shutdown with the system, so some /etc/rc.d/init.d integration would also be nice, but I could always add a custom line to /etc/rc.d/rc.local.

Answer 1

The easiest way is to use Proc::Daemon.

#!/usr/bin/perl  use strict; use warnings; use Proc::Daemon;  Proc::Daemon::Init;  my $continue = 1; $SIG{TERM} = sub { $continue = 0 };  while ($continue) {      #do stuff } 

Alternately you could do all of the things Proc::Daemon does:

1. Fork a child and exits the parent process.
2. Become a session leader (which detaches the program from the controlling terminal).
3. Fork another child process and exit first child. This prevents the potential of acquiring a controlling terminal.
4. Change the current working directory to "/".
5. Clear the file creation mask.
6. Close all open file descriptors.

Integrating with the runlevel system is easy. You need a script like the following (replace XXXXXXXXXXXX with the Perl script's name, YYYYYYYYYYYYYYYYYYY with a description of what it does, and /path/to with path to the Perl script) in /etc/init.d. Since you are using CentOS, once you have the script in /etc/init.d, you can just use chkconfig to turn it off or on in the various runlevels.

#!/bin/bash # # XXXXXXXXXXXX This starts and stops XXXXXXXXXXXX # # chkconfig: 2345 12 88 # description: XXXXXXXXXXXX is YYYYYYYYYYYYYYYYYYY # processname: XXXXXXXXXXXX # pidfile: /var/run/XXXXXXXXXXXX.pid ### BEGIN INIT INFO # Provides: $XXXXXXXXXXXX ### END INIT INFO  # Source function library. . /etc/init.d/functions  binary="/path/to/XXXXXXXXXXXX"  [ -x $binary ] || exit 0  RETVAL=0  start() {     echo -n "Starting XXXXXXXXXXXX: "     daemon $binary     RETVAL=$?     PID=$!     echo     [ $RETVAL -eq 0 ] && touch /var/lock/subsys/XXXXXXXXXXXX      echo $PID > /var/run/XXXXXXXXXXXX.pid }  stop() {     echo -n "Shutting down XXXXXXXXXXXX: "     killproc XXXXXXXXXXXX     RETVAL=$?     echo     if [ $RETVAL -eq 0 ]; then         rm -f /var/lock/subsys/XXXXXXXXXXXX         rm -f /var/run/XXXXXXXXXXXX.pid     fi }  restart() {     echo -n "Restarting XXXXXXXXXXXX: "     stop     sleep 2     start }  case "$1" in     start)         start     ;;     stop)         stop     ;;     status)         status XXXXXXXXXXXX     ;;     restart)         restart     ;;     *)         echo "Usage: $0 {start|stop|status|restart}"     ;; esac  exit 0