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NAME
       passwd - update a user’s authentication tokens(s)

SYNOPSIS
       passwd  [-k]  [-l] [-u [-f]] [-d] [-n mindays] [-x maxdays] [-w warndays] [-i inactivedays] [-S] [--stdin] [user-
       name]

DESCRIPTION
       Passwd is used to update a user’s authentication token(s).

       Passwd is configured to work through the Linux-PAM API.  Essentially, it initializes itself as a "passwd" service
       with Linux-PAM and utilizes configured password modules to authenticate and then update a user’s password.

       A simple entry in the Linux-PAM configuration file for this service would be:

        #
        # passwd service entry that does strength checking of
        # a proposed password before updating it.
        #
        passwd password requisite \
                    /usr/lib/security/pam_cracklib.so retry=3
        passwd password required \
                    /usr/lib/security/pam_unix.so use_authtok
        #

       Note, other module-types are not required for this application to function correctly.

OPTIONS
       -k     The  option,  -k,  is  used  to  indicate that the update should only be for expired authentication tokens
              (passwords); the user wishes to keep their non-expired tokens as before.

       -l     This option is used to lock the specified account and it is available to root only. The  locking  is  per-
              formed  by rendering the encrypted password into an invalid string (by prefixing the encrypted string with
              an !).

       --stdin
              This option is used to indicate that passwd should read the new password from standard input, which can be
              a pipe.

# echo '123456789' | passwd --stdin tuser
Changing password for user tuser.
passwd: all authentication tokens updated successfully.