use POSIX qw(setsid); 
chdir '/'                 or die "Can't chdir to /: $!"; 
umask 0; 
open STDIN, '/dev/null'   or die "Can't read /dev/null: $!"; 
#open STDOUT, '>/dev/null' or die "Can't write to /dev/null: $!"; 
open STDERR, '>/dev/null' or die "Can't write to /dev/null: $!"; 
defined(my $pid = fork)   or die "Can't fork: $!"; 
exit if $pid; 
setsid                    or die "Can't start a new session: $!"; 
$var=1; 
while(1) { 
   print "TESTING\n"; 
   sleep(20); 
}