passwd [ name ]
passwd changes the specified user’s password. Only the superuser is allowed to change other users’ passwords. If the user is not root, then the old password is prompted for and verified.
A new password is prompted for twice, to avoid typing mistakes. Unless the user is the superuser, the new password must have more than six characters, and must have either both uppercase and lowercase letters, or nonletters. Some passwords that are similar to the user’s name are not allowed.