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PASSWD(1)                       User utilities                       PASSWD(1)



NAME
       passwd - update user's authentication tokens


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



DESCRIPTION
       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 service 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 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.


       -u     This is the reverse of the -l option - it will unlock the account password by  removing  the  !  prefix.
              This  option  is  available to root only. By default passwd will refuse to create a passwordless account
              (it will not unlock an account that has only "!" as a password). The force option -f will override  this
              protection.


       -d     This  is  a  quick  way to delete a password for an account. It will set the named account passwordless.
              Available to root only.


       -e     This is a quick way to expire a password for an account. The user will be forced to change the  password
              during the next login attempt.  Available to root only.


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


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


       -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 pass-
              word 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 controlled 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 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, fantasy 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 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 understandable sequence of words), or the first letter of each word in a passphrase.



       These principles are partially enforced by the system, but only partly so.  Vigilence on your  part  will  make
       the system much more secure.


EXIT CODE
       On  successful  completion  of its task, passwd will complete with exit code 0.  An exit code of 1 indicates an
       error occurred.  Textual errors are written to the standard error stream.


CONFORMING TO
       Linux-PAM (Pluggable Authentication modules for Linux).


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


BUGS
       None known.


SEE ALSO
       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.


AUTHOR
       Cristian Gafton <gaftonATredhat.com>



GNU/Linux                         Jan 26 2012                        PASSWD(1)