1PAM_UNIX(8)                    Linux-PAM Manual                    PAM_UNIX(8)
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NAME

6       pam_unix - Module for traditional password authentication
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SYNOPSIS

9       pam_unix.so [...]
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DESCRIPTION

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
17       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
27       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
32       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.
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45       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.
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50       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
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54       The session component of this module logs when a user logins or leave
55       the system.
56
57       Remaining arguments, supported by others functions of this module, are
58       silently ignored. Other arguments are logged as errors through
59       syslog(3).
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OPTIONS

62       debug
63           Turns on debugging via syslog(3).
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65       audit
66           A little more extreme than debug.
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68       quiet
69           Turns off informational messages namely messages about session open
70           and close via syslog(3).
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72       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
77       try_first_pass
78           Before prompting the user for their password, the module first
79           tries the previous stacked module's password in case that satisfies
80           this module as well.
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82       use_first_pass
83           The argument use_first_pass forces the module to use a previous
84           stacked modules password and will never prompt the user - if no
85           password is available or the password is not appropriate, the user
86           will be denied access.
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88       nodelay
89           This argument can be used to discourage the authentication
90           component from requesting a delay should the authentication as a
91           whole fail. The default action is for the module to request a
92           delay-on-failure of the order of two second.
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94       use_authtok
95           When password changing enforce the module to set the new password
96           to the one provided by a previously stacked password module (this
97           is used in the example of the stacking of the pam_cracklib module
98           documented below).
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100       authtok_type=type
101           This argument can be used to modify the password prompt when
102           changing passwords to include the type of the password. Empty by
103           default.
104
105       nis
106           NIS RPC is used for setting new passwords.
107
108       remember=n
109           The last n passwords for each user are saved in
110           /etc/security/opasswd in order to force password change history and
111           keep the user from alternating between the same password too
112           frequently. The MD5 password hash algorithm is used for storing the
113           old passwords. Instead of this option the pam_pwhistory module
114           should be used.
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116       shadow
117           Try to maintain a shadow based system.
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119       md5
120           When a user changes their password next, encrypt it with the MD5
121           algorithm.
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123       bigcrypt
124           When a user changes their password next, encrypt it with the DEC C2
125           algorithm.
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127       sha256
128           When a user changes their password next, encrypt it with the SHA256
129           algorithm. The SHA256 algorithm must be supported by the crypt(3)
130           function.
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132       sha512
133           When a user changes their password next, encrypt it with the SHA512
134           algorithm. The SHA512 algorithm must be supported by the crypt(3)
135           function.
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137       blowfish
138           When a user changes their password next, encrypt it with the
139           blowfish algorithm. The blowfish algorithm must be supported by the
140           crypt(3) function.
141
142       rounds=n
143           Set the optional number of rounds of the SHA256, SHA512 and
144           blowfish password hashing algorithms to n.
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146       broken_shadow
147           Ignore errors reading shadow information for users in the account
148           management module.
149
150       minlen=n
151           Set a minimum password length of n characters. The max. for DES
152           crypt based passwords are 8 characters.
153
154       no_pass_expiry
155           When set ignore password expiration as defined by the shadow entry
156           of the user. The option has an effect only in case pam_unix was not
157           used for the authentication or it returned authentication failure
158           meaning that other authentication source or method succeeded. The
159           example can be public key authentication in sshd. The module will
160           return PAM_SUCCESS instead of eventual PAM_NEW_AUTHTOK_REQD or
161           PAM_AUTHTOK_EXPIRED.
162
163       Invalid arguments are logged with syslog(3).
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MODULE TYPES PROVIDED

166       All module types (account, auth, password and session) are provided.
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RETURN VALUES

169       PAM_IGNORE
170           Ignore this module.
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EXAMPLES

173       An example usage for /etc/pam.d/login would be:
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175           # Authenticate the user
176           auth       required   pam_unix.so
177           # Ensure users account and password are still active
178           account    required   pam_unix.so
179           # Change the user's password, but at first check the strength
180           # with pam_cracklib(8)
181           password   required   pam_cracklib.so retry=3 minlen=6 difok=3
182           password   required   pam_unix.so use_authtok nullok md5
183           session    required   pam_unix.so
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SEE ALSO

188       login.defs(5), pam.conf(5), pam.d(5), pam(8)
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AUTHOR

191       pam_unix was written by various people.
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195Linux-PAM Manual                  05/11/2019                       PAM_UNIX(8)
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