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 nullok
69 The default action of this module is to not permit the user access
70 to a service if their official password is blank. The nullok
71 argument overrides this default.
72 try_first_pass
74 Before prompting the user for their password, the module first
75 tries the previous stacked module's password in case that satisfies
76 this module as well.
77 use_first_pass
79 The argument use_first_pass forces the module to use a previous
80 stacked modules password and will never prompt the user - if no
81 password is available or the password is not appropriate, the user
82 will be denied access.
83 nodelay
85 This argument can be used to discourage the authentication
86 component from requesting a delay should the authentication as a
87 whole fail. The default action is for the module to request a
88 delay-on-failure of the order of two second.
89 use_authtok
91 When password changing enforce the module to set the new password
92 to the one provided by a previously stacked password module (this
93 is used in the example of the stacking of the pam_cracklib module
94 documented below).
95 not_set_pass
97 This argument is used to inform the module that it is not to pay
98 attention to/make available the old or new passwords from/to other
99 (stacked) password modules.
100 nis
102 NIS RPC is used for setting new passwords.
103 remember=n
105 The last n passwords for each user are saved in
106 /etc/security/opasswd in order to force password change history and
107 keep the user from alternating between the same password too
108 frequently. Instead of this option the pam_pwhistory module should
109 be used.
110 shadow
112 Try to maintain a shadow based system.
113 md5
115 When a user changes their password next, encrypt it with the MD5
116 algorithm.
117 bigcrypt
119 When a user changes their password next, encrypt it with the DEC C2
120 algorithm.
121 sha256
123 When a user changes their password next, encrypt it with the SHA256
124 algorithm. The SHA256 algorithm must be supported by the crypt(3)
125 function.
126 sha512
128 When a user changes their password next, encrypt it with the SHA512
129 algorithm. The SHA512 algorithm must be supported by the crypt(3)
130 function.
131 blowfish
133 When a user changes their password next, encrypt it with the
134 blowfish algorithm. The blowfish algorithm must be supported by the
135 crypt(3) function.
136 rounds=n
138 Set the optional number of rounds of the SHA256, SHA512 and
139 blowfish password hashing algorithms to n.
140 broken_shadow
142 Ignore errors reading shadow information for users in the account
143 management module.
144 minlen=n
146 Set a minimum password length of n characters. The max. for DES
147 crypt based passwords are 8 characters.
148 no_pass_expiry
150 When set ignore password expiration as defined by the shadow entry
151 of the user. The option has an effect only in case pam_unix was not
152 used for the authentication or it returned authentication failure
153 meaning that other authentication source or method succeeded. The
154 example can be public key authentication in sshd. The module will
155 return PAM_SUCCESS instead of eventual PAM_NEW_AUTHTOK_REQD or
156 PAM_AUTHTOK_EXPIRED.
157 Invalid arguments are logged with syslog(3).
159
161 All module types (account, auth, password and session) are provided.
162
164 PAM_IGNORE
165 Ignore this module.
166
168 An example usage for /etc/pam.d/login would be:
169 # Authenticate the user
171 auth required pam_unix.so
172 # Ensure users account and password are still active
173 account required pam_unix.so
174 # Change the users password, but at first check the strength
175 # with pam_cracklib(8)
176 password required pam_cracklib.so retry=3 minlen=6 difok=3
177 password required pam_unix.so use_authtok nullok md5
178 session required pam_unix.so
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183 login.defs(5), pam.conf(5), pam.d(5), pam(8)
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186 pam_unix was written by various people.
187Linux-PAM Manual 04/11/2018 PAM_UNIX(8)