Here's some code to daemonize a program. With the test daemon I've provided, it is easy to confirm that the code runs even if you log off.

Here is the daemonizing code: 

#!/usr/bin/perl -w
use strict;
use warnings;
use diagnostics;

use POSIX qw(setsid);

my $cmd = qq{./perl_delayer.pl};
fork_daemon($cmd);
exit 0;

#################################################
# Daemonize!
#################################################
sub fork_daemon
{
    my ($cmd) = @_;   # Pass a string or an array reference

    my $pid_c = fork();     # Parent spawns Child
    die "Cannot fork: $!" if !defined $pid_c;
    if ($pid_c)
    {
        # ==== Parent ====
        waitpid($pid_c, 0); # Zombies not allowed
        return;             # No attachment to grand-child
    }

    # ==== Child ====
    my $pid_gc = fork();     # Child spawns Grand-Child
    die "Cannot fork: $!" if !defined $pid_gc;
    exit (0) if $pid_gc;     # Child exits immediately

    # ==== Grand-Child ====
    # Grand-Child continues, now parented by init.

    # Detach from controlling terminal and create new process group.
    setsid() || die "Can't start a new session: $!";

    # Close std* streams.
    close STDIN;
    close STDOUT;
    close STDERR;
    open STDIN , "< /dev/null";
    open STDOUT, "> /dev/null";     # could use "> nohup.out"
    open STDERR, "> /dev/null";     # could use ">> nohup.out"

    # There is no reason to ignore SIGHUP.
    # Since we've detached from the terminal, we won't
    # be getting one when the user logs out.
    # $SIG{HUP} = 'IGNORE';

    exec(ref($cmd) eq "ARRAY" ? @$cmd : $cmd);  # Run command
    exit(0);
}

[download]

Here is the test daemon code, "perl_delayer.pl". You will observe that the file created ("delayer.out") gets the full countdown and is not affected by a logout. 

#!/usr/bin/perl -w
use strict;
use warnings;

my $fname = "delayer.out";
open(OUT,">",$fname) || die("Cannot open $fname: $!");
select OUT;    $| = 1;      # make unbuffered
select STDOUT; $| = 1;      # make unbuffered

my $count = 60;
while ($count--)
{
    my $str = "$count: The time is now ".localtime()."\n";
    print $str;
    print OUT $str;
    sleep 1;
}

[download]

In reply to Re: Run Perl script in perl program with new process group by gmargo
in thread Run Perl script in perl program with new process group by veshwar

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