1PAM_UNIX(8) Linux-PAM Manual PAM_UNIX(8)
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6 pam_unix - Module for traditional password authentication
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9 pam_unix.so [...]
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12 This is the standard Unix authentication module. It uses standard calls
13 from the system's libraries to retrieve and set account information as
14 well as authentication. Usually this is obtained from the /etc/passwd
15 and the /etc/shadow file as well if shadow is enabled.
16 The account component performs the task of establishing the status of
18 the user's account and password based on the following shadow elements:
19 expire, last_change, max_change, min_change, warn_change. In the case
20 of the latter, it may offer advice to the user on changing their
21 password or, through the PAM_AUTHTOKEN_REQD return, delay giving
22 service to the user until they have established a new password. The
23 entries listed above are documented in the shadow(5) manual page.
24 Should the user's record not contain one or more of these entries, the
25 corresponding shadow check is not performed.
26 The authentication component performs the task of checking the users
28 credentials (password). The default action of this module is to not
29 permit the user access to a service if their official password is
30 blank.
31 A helper binary, unix_chkpwd(8), is provided to check the user's
33 password when it is stored in a read protected database. This binary is
34 very simple and will only check the password of the user invoking it.
35 It is called transparently on behalf of the user by the authenticating
36 component of this module. In this way it is possible for applications
37 like xlock(1) to work without being setuid-root. The module, by
38 default, will temporarily turn off SIGCHLD handling for the duration of
39 execution of the helper binary. This is generally the right thing to
40 do, as many applications are not prepared to handle this signal from a
41 child they didn't know was fork()d. The noreap module argument can be
42 used to suppress this temporary shielding and may be needed for use
43 with certain applications.
44 The maximum length of a password supported by the pam_unix module via
46 the helper binary is PAM_MAX_RESP_SIZE - currently 512 bytes. The rest
47 of the password provided by the conversation function to the module
48 will be ignored.
49 The password component of this module performs the task of updating the
51 user's password. The default encryption hash is taken from the
52 ENCRYPT_METHOD variable from /etc/login.defs
53 The session component of this module logs when a user logins or leave
55 the system.
56 Remaining arguments, supported by others functions of this module, are
58 silently ignored. Other arguments are logged as errors through
59 syslog(3).
60
62 debug
63 Turns on debugging via syslog(3).
64 audit
66 A little more extreme than debug.
67 quiet
69 Turns off informational messages namely messages about session open
70 and close via syslog(3).
71 nullok
73 The default action of this module is to not permit the user access
74 to a service if their official password is blank. The nullok
75 argument overrides this default.
76 nullresetok
78 Allow users to authenticate with blank password if password reset
79 is enforced even if nullok is not set. If password reset is not
80 required and nullok is not set the authentication with blank
81 password will be denied.
82 try_first_pass
84 Before prompting the user for their password, the module first
85 tries the previous stacked module's password in case that satisfies
86 this module as well.
87 use_first_pass
89 The argument use_first_pass forces the module to use a previous
90 stacked modules password and will never prompt the user - if no
91 password is available or the password is not appropriate, the user
92 will be denied access.
93 nodelay
95 This argument can be used to discourage the authentication
96 component from requesting a delay should the authentication as a
97 whole fail. The default action is for the module to request a
98 delay-on-failure of the order of two second.
99 use_authtok
101 When password changing enforce the module to set the new password
102 to the one provided by a previously stacked password module (this
103 is used in the example of the stacking of the pam_cracklib module
104 documented below).
105 authtok_type=type
107 This argument can be used to modify the password prompt when
108 changing passwords to include the type of the password. Empty by
109 default.
110 nis
112 NIS RPC is used for setting new passwords.
113 remember=n
115 The last n passwords for each user are saved in
116 /etc/security/opasswd in order to force password change history and
117 keep the user from alternating between the same password too
118 frequently. The MD5 password hash algorithm is used for storing the
119 old passwords. Instead of this option the pam_pwhistory module
120 should be used.
121 shadow
123 Try to maintain a shadow based system.
124 md5
126 When a user changes their password next, encrypt it with the MD5
127 algorithm.
128 bigcrypt
130 When a user changes their password next, encrypt it with the DEC C2
131 algorithm.
132 sha256
134 When a user changes their password next, encrypt it with the SHA256
135 algorithm. The SHA256 algorithm must be supported by the crypt(3)
136 function.
137 sha512
139 When a user changes their password next, encrypt it with the SHA512
140 algorithm. The SHA512 algorithm must be supported by the crypt(3)
141 function.
142 blowfish
144 When a user changes their password next, encrypt it with the
145 blowfish algorithm. The blowfish algorithm must be supported by the
146 crypt(3) function.
147 gost_yescrypt
149 When a user changes their password next, encrypt it with the
150 gost-yescrypt algorithm. The gost-yescrypt algorithm must be
151 supported by the crypt(3) function.
152 yescrypt
154 When a user changes their password next, encrypt it with the
155 yescrypt algorithm. The yescrypt algorithm must be supported by the
156 crypt(3) function.
157 rounds=n
159 Set the optional number of rounds of the SHA256, SHA512, blowfish,
160 gost-yescrypt, and yescrypt password hashing algorithms to n.
161 broken_shadow
163 Ignore errors reading shadow information for users in the account
164 management module.
165 minlen=n
167 Set a minimum password length of n characters. The max. for DES
168 crypt based passwords are 8 characters.
169 no_pass_expiry
171 When set ignore password expiration as defined by the shadow entry
172 of the user. The option has an effect only in case pam_unix was not
173 used for the authentication or it returned authentication failure
174 meaning that other authentication source or method succeeded. The
175 example can be public key authentication in sshd. The module will
176 return PAM_SUCCESS instead of eventual PAM_NEW_AUTHTOK_REQD or
177 PAM_AUTHTOK_EXPIRED.
178 Invalid arguments are logged with syslog(3).
180
182 All module types (account, auth, password and session) are provided.
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185 PAM_IGNORE
186 Ignore this module.
187
189 An example usage for /etc/pam.d/login would be:
190 # Authenticate the user
192 auth required pam_unix.so
193 # Ensure users account and password are still active
194 account required pam_unix.so
195 # Change the user's password, but at first check the strength
196 # with pam_cracklib(8)
197 password required pam_cracklib.so retry=3 minlen=6 difok=3
198 password required pam_unix.so use_authtok nullok yescrypt
199 session required pam_unix.so
200
204 login.defs(5), pam.conf(5), pam.d(5), pam(8)
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207 pam_unix was written by various people.
208Linux-PAM Manual 06/08/2020 PAM_UNIX(8)