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 password component of this module performs the task of updating the
46 user´s password.
47 The session component of this module logs when a user logins or leave
49 the system.
50 Remaining arguments, supported by others functions of this module, are
52 silently ignored. Other arguments are logged as errors through
53 syslog(3).
54
56 debug
57 Turns on debugging via syslog(3).
58 audit
60 A little more extreme than debug.
61 nullok
63 The default action of this module is to not permit the user access
64 to a service if their official password is blank. The nullok
65 argument overrides this default.
66 try_first_pass
68 Before prompting the user for their password, the module first
69 tries the previous stacked module´s password in case that satisfies
70 this module as well.
71 use_first_pass
73 The argument use_first_pass forces the module to use a previous
74 stacked modules password and will never prompt the user - if no
75 password is available or the password is not appropriate, the user
76 will be denied access.
77 nodelay
79 This argument can be used to discourage the authentication
80 component from requesting a delay should the authentication as a
81 whole fail. The default action is for the module to request a
82 delay-on-failure of the order of two second.
83 use_authtok
85 When password changing enforce the module to set the new password
86 to the one provided by a previously stacked password module (this
87 is used in the example of the stacking of the pam_cracklib module
88 documented below).
89 not_set_pass
91 This argument is used to inform the module that it is not to pay
92 attention to/make available the old or new passwords from/to other
93 (stacked) password modules.
94 nis
96 NIS RPC is used for setting new passwords.
97 remember=n
99 The last n passwords for each user are saved in
100 /etc/security/opasswd in order to force password change history and
101 keep the user from alternating between the same password too
102 frequently.
103 shadow
105 Try to maintain a shadow based system.
106 md5
108 When a user changes their password next, encrypt it with the MD5
109 algorithm.
110 bigcrypt
112 When a user changes their password next, encrypt it with the DEC C2
113 algorithm.
114 sha256
116 When a user changes their password next, encrypt it with the SHA256
117 algorithm. If the SHA256 algorithm is not known to the crypt(3)
118 function, fall back to MD5.
119 sha512
121 When a user changes their password next, encrypt it with the SHA512
122 algorithm. If the SHA512 algorithm is not known to the crypt(3)
123 function, fall back to MD5.
124 blowfish
126 When a user changes their password next, encrypt it with the
127 blowfish algorithm. If the blowfish algorithm is not known to the
128 crypt(3) function, fall back to MD5.
129 rounds=n
131 Set the optional number of rounds of the SHA256, SHA512 and
132 blowfish password hashing algorithms to n.
133 broken_shadow
135 Ignore errors reading shadow information for users in the account
136 management module.
137 Invalid arguments are logged with syslog(3).
139
141 All module types (account, auth, password and session) are provided.
142
144 PAM_IGNORE
145 Ignore this module.
146
148 An example usage for /etc/pam.d/login would be:
149 # Authenticate the user
151 auth required pam_unix.so
152 # Ensure users account and password are still active
153 account required pam_unix.so
154 # Change the users password, but at first check the strength
155 # with pam_cracklib(8)
156 password required pam_cracklib.so retry=3 minlen=6 difok=3
157 password required pam_unix.so use_authtok nullok md5
158 session required pam_unix.so
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163 pam.conf(5), pam.d(5), pam(8)
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166 pam_unix was written by various people.
167Linux-PAM Manual 06/29/2009 PAM_UNIX(8)