use POSIX qw(setsid);

defined(my $pid = fork)   or die "Can't fork: $!";
exit 0 if $pid;

chdir '/'                 or die "Can't chdir to /: $!";
umask 0;
setsid()                  or die "Can't start a new session: $!";

print "Started $0 daemon OK\n\n";

# now finish of by redirecting I/O stuff

# we want to ignore STDIN
open STDIN, '/dev/null'   or die "Can't read /dev/null: $!";

# send STDOUT, STDERR wherever...
open STDOUT, '>/dev/null' or die "Can't write to /dev/null: $!";
open STDERR, '>/dev/null' or die "Can't write to /dev/null: $!";