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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 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.

OPTIONS
       -k, --keep
              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, --lock
              This  option  is  used to lock the password of specified account
              and it is available to root only. The locking  is  performed  by
              rendering the encrypted password into an invalid string (by pre-
              fixing the encrypted string with an !). Note that the account is
              not  fully  locked - the user can still log in by other means of
              authentication such as the ssh public  key  authentication.  Use
              chage -E 0 user command instead for full account locking.

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

       -u, --unlock
              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
              passwordless  account  (it  will  not unlock an account that has
              only "!" as a password). The force option -f will override  this
              protection.

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

       -e, --expire
              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.

       -f, --force
              Force the specified operation.

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

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

       -w, --warning DAYS
              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, --inactive DAYS
              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, --status
              This  will  output  a  short information about the status of the
              password for a given account. The status information consists of
              7  fields.  The first field is the user's login name. The second
              field indicates if the user account has a locked password  (LK),
              has  no  password (NP), or has a usable password (PS). The third
              field gives the date of the last password change. The next  four
              fields  are  the  minimum  age, maximum age, warning period, and
              inactivity period for the password. These ages are expressed  in
              days.
              Notes:  The date of the last password change is stored as a num-
              ber of days since epoch. Depending on the current time zone, the
              passwd -S username may show the date of the last password change
              that is different from the real date of the last password change
              by +-1 day.
              This option is available to root 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
              in a passphrase.

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

EXIT CODE
       The passwd command exits with the following codes:
       0
           success
       1
           passwd/libuser operation failed
       2
           unknown user
       252
           unknown user name
       253
           bad arguments or passwordless account
       254
           invalid application of arguments
       255
           libuser operation failed
       Error messages 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 <gafton AT redhat.com>

GNU/Linux                         Jun 20 2012                        PASSWD(1)