the short answer is :
don't use the -p option in useradd
instead, as root, run useradd as above (without the -p My...)
then (still as root)
# passwd tux
you'll get a prompt for a new password followed by a confirmation prompt.
The -p option has a very specialized function which I can't quite recall but is typically for, say, a university server admin that needs to create a lot of accounts at one time.