If you only supply one of the two arguments, passwd checks to see if the other one already exists. If it does not exist, then it defaults it to zero for you. This section applies only to a trusted system. It describes additional capabilities and restrictions. A user-supplied password, subject to length and triviality restrictions.
Passwords can be longer than eight characters.
The system administrator specifies a maximum password length guideline for the 3 system generated options. The minimum password length depends on several parameters that the system administrator sets in the authentication databases. The system warns you if you choose a password that is too short or too long. The system requires a minimum time to elapse before you can change a password. This prevents you from reusing an old password too soon.