passwd — Update a user’s authentication details.
Passwd is used to update a user’s authentication tokens, like password, lifetime, etc.. Passwd is configured to work through the Linux-PAM API.
$ passwd — Ask new passwd for your account.
# passwd user1 — Ask new passwd for user1’s account.
# passwd -l user1 — Lock user1 account.
# passwd -u user1 — Unlock user1 account.
# passwd -d user1 — Remove password for user1.
# passwd -S user1 — Show short info about user1’s password.
# passwd -n 30 user1 — Set 30days as the min lifetime of the user1’s password.
All new users should read the following topic in the man page
A) Protect your password & B) Choose a hard-to-guess password.
Read: man passwd, pam