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


       The passwd utility is used to update user's authentication token(s).

       This task is achieved through calls to the Linux-PAM and  Libuser  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 global Linux-PAM configuration file for this ser-
       vice would be:

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

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


       -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  performed  by  rendering
              the  encrypted password into an invalid string (by prefixing the
              encrypted string with an !).

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

       -u     This  is  the  reverse  of  the  -l  option - it will unlock the
              account password by removing the ! prefix. This option is avail-
              able  to  root  only.  By default passwd will refuse to create a

       -x     This  will  set  the  maximum password lifetime, in days, if the
              user's account supports password lifetimes.  Available  to  root

       -w     This  will set the number of days in advance the user will begin
              receiving warnings that her password will expire, if the  user's
              account supports password lifetimes.  Available to root only.

       -i     This  will  set  the  number  of  days which will pass before an
              expired password for this account will be taken to mean that the
              account  is  inactive  and  should  be  disabled,  if the user's
              account supports password lifetimes.  Available to root only.

       -S     This will output a short information about  the  status  of  the
              password for a given account. Available to root user only.

Remember the following two principles

       Protect your password.
              Don't  write  down  your password - memorize it.  In particular,
              don't write it down and leave it anywhere, and don't place it in
              an  unencrypted  file!  Use unrelated passwords for systems con-
              trolled by different organizations.  Don't give  or  share  your
              password,  in particular to someone claiming to be from computer
              support or a vendor.  Don't let  anyone  watch  you  enter  your
              password.   Don't  enter  your  password to a computer you don't
              trust or if things "look funny"; someone may be trying to hijack
              your  password.   Use the password for a limited time and change
              it periodically.

       Choose a hard-to-guess password.
              passwd through the calls to the pam_cracklib PAM module will try
              to prevent you from choosing a really bad password, but it isn't
              foolproof; create your password  wisely.   Don't  use  something
              you'd  find  in a dictionary (in any language or jargon).  Don't
              use a name (including that of a spouse, parent, child, pet, fan-
              tasy character, famous person, and location) or any variation of
              your personal or account name.  Don't use accessible information
              about  you  (such as your phone number, license plate, or social
              security number) or your environment.  Don't use a birthday or a
              simple  pattern  (such as "qwerty", "abc", or "aaa").  Don't use
              any of those backwards, followed by a digit, or  preceded  by  a
              digit.  Instead,  use a mixture of upper and lower case letters,
              as well as digits or punctuation.  When choosing a new password,
              make  sure  it's  unrelated  to  any previous password. Use long
              passwords (say at least 8 characters long).   You  might  use  a
              word  pair  with  punctuation  inserted, a passphrase (an under-
              standable sequence of words), or the first letter of  each  word


       Linux-PAM (Pluggable Authentication modules for Linux).


       /etc/pam.d/passwd - the Linux-PAM configuration file


       None known.


       pam(8), pam.d(5), libuser.conf(5), and pam_chauthtok(3).

       For more complete information on how to configure this application with
       Linux-PAM, see the Linux-PAM System Administrators' Guide.


       Cristian Gafton <gafton@redhat.com>

GNU/Linux Sep 24 2009 PASSWD(1)

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