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. 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
	      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
       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 <gafton@redhat.com>



GNU/Linux			  Jun 20 2012			     PASSWD(1)