PAM_CRACKLIB(8)		       Linux-PAM Manual		       PAM_CRACKLIB(8)



NAME
       pam_cracklib - PAM module to check the password against dictionary
       words

SYNOPSIS
       pam_cracklib.so [...]

DESCRIPTION
       This module can be plugged into the password stack of a given
       application to provide some plug-in strength-checking for passwords.

       The action of this module is to prompt the user for a password and
       check its strength against a system dictionary and a set of rules for
       identifying poor choices.

       The first action is to prompt for a single password, check its strength
       and then, if it is considered strong, prompt for the password a second
       time (to verify that it was typed correctly on the first occasion). All
       being well, the password is passed on to subsequent modules to be
       installed as the new authentication token.

       The strength checks works in the following manner: at first the
       Cracklib routine is called to check if the password is part of a
       dictionary; if this is not the case an additional set of strength
       checks is done. These checks are:

       Palindrome
	   Is the new password a palindrome?

       Case Change Only
	   Is the new password the the old one with only a change of case?

       Similar
	   Is the new password too much like the old one? This is primarily
	   controlled by one argument, difok which is a number of character
	   changes (inserts, removals, or replacements) between the old and
	   new password that are enough to accept the new password. This
	   defaults to 5 changes.

       Simple
	   Is the new password too small? This is controlled by 6 arguments
	   minlen, maxclassrepeat, dcredit, ucredit, lcredit, and ocredit. See
	   the section on the arguments for the details of how these work and
	   there defaults.

       Rotated
	   Is the new password a rotated version of the old password?

       Same consecutive characters
	   Optional check for same consecutive characters.

       Too long monotonic character sequence
	   Optional check for too long monotonic character sequence.

       Contains user name
	   Optional check whether the password contains the user's name in
	   some form.

       This module with no arguments will work well for standard unix password
       encryption. With md5 encryption, passwords can be longer than 8
       characters and the default settings for this module can make it hard
       for the user to choose a satisfactory new password. Notably, the
       requirement that the new password contain no more than 1/2 of the
       characters in the old password becomes a non-trivial constraint. For
       example, an old password of the form "the quick brown fox jumped over
       the lazy dogs" would be difficult to change... In addition, the default
       action is to allow passwords as small as 5 characters in length. For a
       md5 systems it can be a good idea to increase the required minimum size
       of a password. One can then allow more credit for different kinds of
       characters but accept that the new password may share most of these
       characters with the old password.

OPTIONS
       debug
	   This option makes the module write information to syslog(3)
	   indicating the behavior of the module (this option does not write
	   password information to the log file).

       authtok_type=XXX
	   The default action is for the module to use the following prompts
	   when requesting passwords: "New UNIX password: " and "Retype UNIX
	   password: ". The example word UNIX can be replaced with this
	   option, by default it is empty.

       retry=N
	   Prompt user at most N times before returning with error. The
	   default is 1.

       difok=N
	   This argument will change the default of 5 for the number of
	   character changes in the new password that differentiate it from
	   the old password.

       minlen=N
	   The minimum acceptable size for the new password (plus one if
	   credits are not disabled which is the default). In addition to the
	   number of characters in the new password, credit (of +1 in length)
	   is given for each different kind of character (other, upper, lower
	   and digit). The default for this parameter is 9 which is good for a
	   old style UNIX password all of the same type of character but may
	   be too low to exploit the added security of a md5 system. Note that
	   there is a pair of length limits in Cracklib itself, a "way too
	   short" limit of 4 which is hard coded in and a defined limit (6)
	   that will be checked without reference to minlen. If you want to
	   allow passwords as short as 5 characters you should not use this
	   module.

       dcredit=N
	   (N >= 0) This is the maximum credit for having digits in the new
	   password. If you have less than or N digits, each digit will count
	   +1 towards meeting the current minlen value. The default for
	   dcredit is 1 which is the recommended value for minlen less than
	   10.

	   (N < 0) This is the minimum number of digits that must be met for a
	   new password.

       ucredit=N
	   (N >= 0) This is the maximum credit for having upper case letters
	   in the new password. If you have less than or N upper case letters
	   each letter will count +1 towards meeting the current minlen value.
	   The default for ucredit is 1 which is the recommended value for
	   minlen less than 10.

	   (N < 0) This is the minimum number of upper case letters that must
	   be met for a new password.

       lcredit=N
	   (N >= 0) This is the maximum credit for having lower case letters
	   in the new password. If you have less than or N lower case letters,
	   each letter will count +1 towards meeting the current minlen value.
	   The default for lcredit is 1 which is the recommended value for
	   minlen less than 10.

	   (N < 0) This is the minimum number of lower case letters that must
	   be met for a new password.

       ocredit=N
	   (N >= 0) This is the maximum credit for having other characters in
	   the new password. If you have less than or N other characters, each
	   character will count +1 towards meeting the current minlen value.
	   The default for ocredit is 1 which is the recommended value for
	   minlen less than 10.

	   (N < 0) This is the minimum number of other characters that must be
	   met for a new password.

       minclass=N
	   The minimum number of required classes of characters for the new
	   password. The default number is zero. The four classes are digits,
	   upper and lower letters and other characters. The difference to the
	   credit check is that a specific class if of characters is not
	   required. Instead N out of four of the classes are required.

       maxrepeat=N
	   Reject passwords which contain more than N same consecutive
	   characters. The default is 0 which means that this check is
	   disabled.

       maxsequence=N
	   Reject passwords which contain monotonic character sequences longer
	   than N. The default is 0 which means that this check is disabled.
	   Examples of such sequence are '12345' or 'fedcb'. Note that most
	   such passwords will not pass the simplicity check unless the
	   sequence is only a minor part of the password.

       maxclassrepeat=N
	   Reject passwords which contain more than N consecutive characters
	   of the same class. The default is 0 which means that this check is
	   disabled.

       reject_username
	   Check whether the name of the user in straight or reversed form is
	   contained in the new password. If it is found the new password is
	   rejected.

       gecoscheck
	   Check whether the words from the GECOS field (usualy full name of
	   the user) longer than 3 characters in straight or reversed form are
	   contained in the new password. If any such word is found the new
	   password is rejected.

       enforce_for_root
	   The module will return error on failed check also if the user
	   changing the password is root. This option is off by default which
	   means that just the message about the failed check is printed but
	   root can change the password anyway. Note that root is not asked
	   for an old password so the checks that compare the old and new
	   password are not performed.

       use_authtok
	   This argument is used to force the module to not prompt the user
	   for a new password but use the one provided by the previously
	   stacked password module.

       dictpath=/path/to/dict
	   Path to the cracklib dictionaries.

MODULE TYPES PROVIDED
       Only the password module type is provided.

RETURN VALUES
       PAM_SUCCESS
	   The new password passes all checks.

       PAM_AUTHTOK_ERR
	   No new password was entered, the username could not be determined
	   or the new password fails the strength checks.

       PAM_AUTHTOK_RECOVERY_ERR
	   The old password was not supplied by a previous stacked module or
	   got not requested from the user. The first error can happen if
	   use_authtok is specified.

       PAM_SERVICE_ERR
	   A internal error occurred.

EXAMPLES
       For an example of the use of this module, we show how it may be stacked
       with the password component of pam_unix(8)

	   #
	   # These lines stack two password type modules. In this example the
	   # user is given 3 opportunities to enter a strong password. The
	   # "use_authtok" argument ensures that the pam_unix module does not
	   # prompt for a password, but instead uses the one provided by
	   # pam_cracklib.
	   #
	   passwd  password required	   pam_cracklib.so retry=3
	   passwd  password required	   pam_unix.so use_authtok


       Another example (in the /etc/pam.d/passwd format) is for the case that
       you want to use md5 password encryption:

	   #%PAM-1.0
	   #
	   # These lines allow a md5 systems to support passwords of at least 14
	   # bytes with extra credit of 2 for digits and 2 for others the new
	   # password must have at least three bytes that are not present in the
	   # old password
	   #
	   password  required pam_cracklib.so \
			  difok=3 minlen=15 dcredit= 2 ocredit=2
	   password  required pam_unix.so use_authtok nullok md5


       And here is another example in case you don't want to use credits:

	   #%PAM-1.0
	   #
	   # These lines require the user to select a password with a minimum
	   # length of 8 and with at least 1 digit number, 1 upper case letter,
	   # and 1 other character
	   #
	   password  required pam_cracklib.so \
			  dcredit=-1 ucredit=-1 ocredit=-1 lcredit=0 minlen=8
	   password  required pam_unix.so use_authtok nullok md5



SEE ALSO
       pam.conf(5), pam.d(5), pam(8)

AUTHOR
       pam_cracklib was written by Cristian Gafton <gafton@redhat.com>



Linux-PAM Manual		  06/18/2013		       PAM_CRACKLIB(8)