Linux Pocket Guide, 2nd Edition

Name

passwd — stdin  stdout  - file  -- opt  --help  --version

Synopsis

passwd [options] [username]

The passwd command changes a login password, yours by default:

$ passwd

or another user’s password if run by the superuser:

# passwd smith

passwd does have options, most of them related to password expiration. Use them only in the context of a well-thought-out security policy.