passwd —
modify a user's password
  
    | passwd | [ -dfiles |-l] [user] | 
  
    | passwd | [ -dnis |-y] [user] | 
  
    | passwd | [ -dkrb5 |-k] [principal] | 
passwd changes the user's password. First, the user is
  prompted for their current password. If the current password is correctly
  typed, a new password is requested. The new password must be entered twice to
  avoid typing errors.
The new password should be at least six characters long and not
    purely alphabetic. Its total length must be less than
    _PASSWORD_LEN (currently 128 characters). Numbers,
    upper case letters and meta characters are encouraged.
All options may not be available on all systems.
  - -ddatabase
- This option specifies the password database that should be updated. The
      following databases are supported:
    
      - files
- This specifies that the password change should be applied to the local
          password file. When changing only the local password,
          passwduses
          pwd_mkdb(8) to update
          the password databases.
- nis
- This specifies that the password change should be applied to the NIS
          password database. The
          rpc.yppasswdd(8)
          daemon should be running on the master NIS server.
- krb5
- This specifies that the user's Kerberos 5 password should be changed.
          The host must be configured to use Kerberos. See
          krb5.conf(5).
 
- -l
- This is the equivalent of -dfiles.
- -y
- This is the equivalent of -dnis.
- -k
- This is the equivalent of -dkrb5.
If a password database is not specified,
    passwd will change the password database as
    determined by the Pluggable Authentication Module (PAM) library.
The type of cipher used to encrypt the password depends on the
    configuration in
    passwd.conf(5). It can be
    different for local and NIS passwords.
  - /etc/master.passwd
- The user database
- /etc/passwd
- A Version 7 format password file
- /etc/passwd.XXXXXX
- Temporary copy of the password file
Apasswd command appeared in
  Version 6 AT&T UNIX.