use POSIX qw( setsid );

print "Content-Type: text/plain\n";
print "\n";
print "1";

my $pid = fork();
exit(0) if !defined($pid) || $pid;

open STDIN,  '</dev/null' or die;
open STDOUT, '>/dev/null' or die;
open STDERR, '>&STDOUT'   or die;
setsid();

... handle request ...