passwd - Change login password
passwd [ name ]
Passwd changes (or installs) a password associated with the user name (your own name by default).
The program prompts for the old password and then for the new one, and the new password must be typed twice, to forestall mistakes.
New passwords must be at least four characters long if they use a sufficiently rich alphabet and at least six characters long if monocase.
Only the owner of the name or the root-user may change a password; the owner must prove he knows the old password.
If “none” is selected for the new password, the user will not be asked to enter a password when logging in (this is desirable for public accounts).