1PAM_PWQUALITY(8) Linux-PAM Manual PAM_PWQUALITY(8)
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6 pam_pwquality - PAM module to perform password quality checking
7
9 pam_pwquality.so [...]
10
12 This module can be plugged into the password stack of a given service
13 to provide some plug-in strength-checking for passwords. The code was
14 originally based on pam_cracklib module and the module is backwards
15 compatible with its options.
16 The action of this module is to prompt the user for a password and
18 check its strength against a system dictionary and a set of rules for
19 identifying poor choices.
20 The first action is to prompt for a single password, check its strength
22 and then, if it is considered strong, prompt for the password a second
23 time (to verify that it was typed correctly on the first occasion). All
24 being well, the password is passed on to subsequent modules to be
25 installed as the new authentication token.
26 The checks for strength are:
28 Palindrome
30 Is the new password a palindrome?
31 Case Change Only
33 Is the new password the the old one with only a change of case?
34 Similar
36 Is the new password too much like the old one? This is primarily
37 controlled by one argument, difok which is a number of character
38 changes (inserts, removals, or replacements) between the old and
39 new password that are enough to accept the new password.
40 Simple
42 Is the new password too small? This is controlled by 6 arguments
43 minlen, maxclassrepeat, dcredit, ucredit, lcredit, and ocredit. See
44 the section on the arguments for the details of how these work and
45 there defaults.
46 Rotated
48 Is the new password a rotated version of the old password?
49 Same consecutive characters
51 Optional check for same consecutive characters.
52 Too long monotonic character sequence
54 Optional check for too long monotonic character sequence.
55 Contains user name
57 Check whether the password contains the user's name in some form.
58 Dictionary check
60 The Cracklib routine is called to check if the password is part of
61 a dictionary.
62 These checks are configurable either by use of the module arguments or
64 by modifying the /etc/security/pwquality.conf configuration file. The
65 module arguments override the settings in the configuration file.
66
68 debug
69 This option makes the module write information to syslog(3)
70 indicating the behavior of the module (this option does not write
71 password information to the log file).
72 authtok_type=XXX
74 The default action is for the module to use the following prompts
75 when requesting passwords: "New UNIX password: " and "Retype UNIX
76 password: ". The example word UNIX can be replaced with this
77 option, by default it is empty.
78 retry=N
80 Prompt user at most N times before returning with error. The
81 default is 1.
82 difok=N
84 This argument will change the default of 1 for the number of
85 changes in the new password from the old password.
86 The special value of 0 disables all checks of similarity of the new
88 password with the old password except the new password being
89 exactly the same as the old one.
90 minlen=N
92 The minimum acceptable size for the new password (plus one if
93 credits are not disabled which is the default). In addition to the
94 number of characters in the new password, credit (of +1 in length)
95 is given for each different kind of character (other, upper, lower
96 and digit). The default for this parameter is 8. Note that there is
97 a pair of length limits also in Cracklib, which is used for
98 dictionary checking, a "way too short" limit of 4 which is hard
99 coded in and a build time defined limit (6) that will be checked
100 without reference to minlen.
101 dcredit=N
103 (N >= 0) This is the maximum credit for having digits in the new
104 password. If you have less than or N digits, each digit will count
105 +1 towards meeting the current minlen value. The default for
106 dcredit is 0 which means there is no bonus for digits in password.
107 (N < 0) This is the minimum number of digits that must be met for a
109 new password.
110 ucredit=N
112 (N >= 0) This is the maximum credit for having upper case letters
113 in the new password. If you have less than or N upper case
114 letters, each upper case letter will count +1 towards meeting the
115 current minlen value. The default for ucredit is 0 which means
116 there is no bonus for upper case letters in password.
117 (N < 0) This is the minimum number of upper case letters that must
119 be met for a new password.
120 lcredit=N
122 (N >= 0) This is the maximum credit for having lower case letters
123 in the new password. If you have less than or N lower case
124 letters, each lower case letter will count +1 towards meeting the
125 current minlen value. The default for lcredit is 0 which means
126 there is no bonus for lower case letters in password.
127 (N < 0) This is the minimum number of lower case letters that must
129 be met for a new password.
130 ocredit=N
132 (N >= 0) This is the maximum credit for having other characters in
133 the new password. If you have less than or N other characters,
134 each other character will count +1 towards meeting the current
135 minlen value. The default for ocredit is 0 which means there is no
136 bonus for other characters in password.
137 (N < 0) This is the minimum number of other characters that must be
139 met for a new password.
140 minclass=N
142 The minimum number of required classes of characters for the new
143 password. The four classes are digits, upper and lower letters and
144 other characters. The difference to the credit check is that a
145 specific class if of characters is not required. Instead N out of
146 four of the classes are required. By default the check is disabled.
147 maxrepeat=N
149 Reject passwords which contain more than N same consecutive
150 characters. The default is 0 which means that this check is
151 disabled.
152 maxsequence=N
154 Reject passwords which contain monotonic character sequences longer
155 than N. The default is 0 which means that this check is disabled.
156 Examples of such sequence are '12345' or 'fedcb'. Note that most
157 such passwords will not pass the simplicity check unless the
158 sequence is only a minor part of the password.
159 maxclassrepeat=N
161 Reject passwords which contain more than N consecutive characters
162 of the same class. The default is 0 which means that this check is
163 disabled.
164 gecoscheck=N
166 If nonzero, check whether the individual words longer than 3
167 characters from the passwd(5) GECOS field of the user are contained
168 in the new password. The default is 0 which means that this check
169 is disabled.
170 dictcheck=N
172 If nonzero, check whether the password (with possible
173 modifications) matches a word in a dictionary. Currently the
174 dictionary check is performed using the cracklib library. The
175 default is 1 which means that this check is enabled.
176 usercheck=N
178 If nonzero, check whether the password (with possible
179 modifications) contains the user name in some form. The default is
180 1 which means that this check is enabled. It is not performed for
181 user names shorter than 3 characters.
182 usersubstr=N
184 If greater than 3 (due to the minimum length in usercheck), check
185 whether the password contains a substring of at least N length in
186 some form. The default is 0, which means this check is disabled.
187 enforcing=N
189 If nonzero, reject the password if it fails the checks, otherwise
190 only print the warning. The default is 1 which means that the weak
191 password is rejected (for non-root users).
192 badwords=<list of words>
194 The words more than 3 characters long from this space separated
195 list are individually searched for and forbidden in the new
196 password. By default the list is empty which means that this check
197 is disabled.
198 dictpath=/path/to/dict
200 This options allows for specification of non-default path to the
201 cracklib dictionaries.
202 enforce_for_root
204 The module will return error on failed check even if the user
205 changing the password is root. This option is off by default which
206 means that just the message about the failed check is printed but
207 root can change the password anyway. Note that root is not asked
208 for an old password so the checks that compare the old and new
209 password are not performed.
210 local_users_only
212 The module will not test the password quality for users that are
213 not present in the /etc/passwd file. The module still asks for the
214 password so the following modules in the stack can use the
215 use_authtok option. This option is off by default.
216 use_authtok
218 This argument is used to force the module to not prompt the user
219 for a new password but use the one provided by the previously
220 stacked password module.
221
223 Only the password module type is provided.
224
226 PAM_SUCCESS
227 The new password passes all checks.
228 PAM_AUTHTOK_ERR
230 No new password was entered, the username could not be determined
231 or the new password fails the strength checks.
232 PAM_AUTHTOK_RECOVERY_ERR
234 The old password was not supplied by a previous stacked module or
235 got not requested from the user. The first error can happen if
236 use_authtok is specified.
237 PAM_SERVICE_ERR
239 A internal error occurred.
240
242 For an example of the use of this module, we show how it may be stacked
243 with the password component of pam_unix(8).
244 #
246 # These lines stack two password type modules. In this example the
247 # user is given 3 opportunities to enter a strong password. The
248 # "use_authtok" argument ensures that the pam_unix module does not
249 # prompt for a password, but instead uses the one provided by
250 # pam_pwquality.
251 #
252 password required pam_pwquality.so retry=3
253 password required pam_unix.so use_authtok
254 Another example is for the case that you want to use sha256 password
256 encryption:
257 #
259 # These lines allow modern systems to support passwords of at least 14
260 # bytes with extra credit of 2 for digits and 2 for others the new
261 # password must have at least three bytes that are not present in the
262 # old password
263 #
264 password required pam_pwquality.so \
265 difok=3 minlen=15 dcredit=2 ocredit=2
266 password required pam_unix.so use_authtok nullok sha256
267 And here is another example in case you don't want to use credits:
269 #
271 # These lines require the user to select a password with a minimum
272 # length of 8 and with at least 1 digit number, 1 upper case letter,
273 # and 1 other character
274 #
275 password required pam_pwquality.so \
276 dcredit=-1 ucredit=-1 ocredit=-1 lcredit=0 minlen=8
277 password required pam_unix.so use_authtok nullok sha256
278
280 pwscore(1), pwquality.conf(5), pam_pwquality(8), pam.conf(5), PAM(8)
281
283 Tomas Mraz <tmraz@redhat.com>
284 Original author of pam_cracklib module Cristian Gafton
286 <gafton@redhat.com>
287Red Hat, Inc. 2020-08-03 PAM_PWQUALITY(8)