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

daemon, linux, perl, shutdown, startup

Solution

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:

- Fork a child and exits the parent process.

- Become a session leader (which detaches the program from the controlling terminal).

- Fork another child process and exit first child. This prevents the potential of acquiring a controlling terminal.

- Change the current working directory to `"/"`.

- Clear the file creation mask.

- 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

Problem

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`.

Original source