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

The easiest way is to use Proc::Daemon.

#!/usr/bin/perluse 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/functionsbinary="/path/to/XXXXXXXXXXXX"[ -x $binary ] || exit 0RETVAL=0start() {    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}"    ;;esacexit 0

If you don't have Proc::Daemon as suggested by Chas. Owens, here's how you'd do it by hand:

sub daemonize {   use POSIX;   POSIX::setsid or die "setsid: $!";   my $pid = fork() // die $!; #//   exit(0) if $pid;   chdir "/";   umask 0;   for (0 .. (POSIX::sysconf (&POSIX::_SC_OPEN_MAX) || 1024))      { POSIX::close $_ }   open (STDIN, "</dev/null");   open (STDOUT, ">/dev/null");   open (STDERR, ">&STDOUT"); }

I think the easiest way is to use daemon. It allows you to run any process as a daemon. This means you don't have to worry about libraries if you, for example, decided to change to python. To use it, just use:

daemon myscript args

This should be available on most distros, but it might not be installed by default.