Starting and Stopping Perl Daemon in Linux

Question

I've been working on a perl daemon for linux and here is its skeleton:

#!/usr/bin/env perl
use File::Copy;
use Socket;
use Sys::Hostname;
use POSIX qw(setsid);
use Env;

use Sys::Info::Constants qw( :device_cpu );

my $daemonName = 'proc';

my $proc;
my $error;
my $file = "Proc.pl";
my $pidfile = ">/var/run/proc.pid";
my $pid2check = "/var/run/proc.pid";
my $pid;


if (!$error) {
    LogMessage("$daemonName  : PID $proc : Begin");
}

if (!$error) {
    LogMessage("$daemonName  : PID $proc : Writing pid information to $pidfile");
    print FILE $proc . "\n";
    close (FILE);
}

$SLEEP_TIME = 5; # seconds

#Main loop of Daemon
while (!$error) {
    sleep($SLEEP_TIME);

}


if ($error) {
    LogMessage("$file : PID $proc : Error $error");
}

LogMessage("$file : PID $proc : END");

exit(0);


sub Daemonize {

if (!(chdir '/')) {
    $error .= "Can't chdir to /: $!";
}
if (!(umask 0)) {
    $error .= "Unable to umask 0";
}

unless (open STDIN, '/dev/null') {
    $error .= "Can't read /dev/null: $!";
}

open(OLD_OUT,">&STDOUT");  

#All print statments will now be sent to our log file
unless (open STDOUT, '>>/var/log/proc.log') {
    $error .= "Can't read /var/log/proc.log: $!";
}
#All error messages will now be sent to our log file
unless (open STDERR, '>>/var/log/proc.log') {
    $error .= "Can't write to /var/log/proc.log: $!";
}

defined($pid = fork);
#Exit if $pid exists (parent)

if ($pid)
{
    print OLD_OUT "Service successfully installed.\n";
    exit(0);
}

#As Child
setsid();
$proc = $$;
return ($proc);
 }


#Prints log messages
sub LogMessage {
my $message = $_[0];
print localtime() . " $message\n";
}

I'm relatively new to perl, and I was wondering what would be the easiest way to start and stop this daemon? Also how would I check to make sure there is not an instance of it already running?

score 6 · Accepted Answer · edited May 23 '17 at 12:20

Generally speaking, daemonisation is done with the double fork method. This is common idiom and there are libraries that do this for you which you should consider using. A pid or lockfile is often used to make sure that only one instance runs at a time.

If you're planning to use this as a system process, it is also possible to use something like upstart or supervisord to do the process management and "only one at time" thing for you.

Starting and Stopping Perl Daemon in Linux

1 Answers1