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

NAME

       pam_unix - Module for traditional password authentication

SYNOPSIS

       pam_unix.so [...]

DESCRIPTION

       This is the standard Unix authentication module. It uses standard calls from the system's libraries to retrieve and set account
       information as well as authentication. Usually this is obtained from the /etc/passwd and the /etc/shadow file as well if shadow is
       enabled.

       The account component performs the task of establishing the status of the user's account and password based on the following shadow
       elements: expire, last_change, max_change, min_change, warn_change. In the case of the latter, it may offer advice to the user on
       changing their password or, through the PAM_AUTHTOKEN_REQD return, delay giving service to the user until they have established a new
       password. The entries listed above are documented in the shadow(5) manual page. Should the user's record not contain one or more of
       these entries, the corresponding shadow check is not performed.

       The authentication component performs the task of checking the users credentials (password). The default action of this module is to
       not permit the user access to a service if their official password is blank.

       A helper binary, unix_chkpwd(8), is provided to check the user's password when it is stored in a read protected database. This binary
       is very simple and will only check the password of the user invoking it. It is called transparently on behalf of the user by the
       authenticating component of this module. In this way it is possible for applications like xlock(1) to work without being setuid-root.
       The module, by default, will temporarily turn off SIGCHLD handling for the duration of execution of the helper binary. This is
       generally the right thing to do, as many applications are not prepared to handle this signal from a child they didn't know was fork()d.
       The noreap module argument can be used to suppress this temporary shielding and may be needed for use with certain applications.

       The password component of this module performs the task of updating the user's password.

       The session component of this module logs when a user logins or leave the system.

       Remaining arguments, supported by others functions of this module, are silently ignored. Other arguments are logged as errors through
       syslog(3).

OPTIONS

       debug
           Turns on debugging via syslog(3).

       audit
           A little more extreme than debug.

       nullok
           The default action of this module is to not permit the user access to a service if their official password is blank. The nullok
           argument overrides this default and allows any user with a blank password to access the service.

       nullok_secure
           The default action of this module is to not permit the user access to a service if their official password is blank. The
           nullok_secure argument overrides this default and allows any user with a blank password to access the service as long as the value
           of PAM_TTY is set to one of the values found in /etc/securetty.

       try_first_pass
           Before prompting the user for their password, the module first tries the previous stacked module's password in case that satisfies
           this module as well.

       use_first_pass
           The argument use_first_pass forces the module to use a previous stacked modules password and will never prompt the user - if no
           password is available or the password is not appropriate, the user will be denied access.

       nodelay
           This argument can be used to discourage the authentication component from requesting a delay should the authentication as a whole
           fail. The default action is for the module to request a delay-on-failure of the order of two second.

       use_authtok
           When password changing enforce the module to set the new password to the one provided by a previously stacked password module (this
           is used in the example of the stacking of the pam_cracklib module documented below).

       not_set_pass
           This argument is used to inform the module that it is not to pay attention to/make available the old or new passwords from/to other
           (stacked) password modules.

       nis
           NIS RPC is used for setting new passwords.

       remember=n
           The last n passwords for each user are saved in /etc/security/opasswd in order to force password change history and keep the user
           from alternating between the same password too frequently.

       shadow
           Try to maintain a shadow based system.

       md5
           When a user changes their password next, encrypt it with the MD5 algorithm.

       bigcrypt
           When a user changes their password next, encrypt it with the DEC C2 algorithm.

       sha256
           When a user changes their password next, encrypt it with the SHA256 algorithm. If the SHA256 algorithm is not known to the crypt(3)
           function, fall back to MD5.

       sha512
           When a user changes their password next, encrypt it with the SHA512 algorithm. If the SHA512 algorithm is not known to the crypt(3)
           function, fall back to MD5.

       blowfish
           When a user changes their password next, encrypt it with the blowfish algorithm. If the blowfish algorithm is not known to the
           crypt(3) function, fall back to MD5.

       rounds=n
           Set the optional number of rounds of the SHA256, SHA512 and blowfish password hashing algorithms to n.

       broken_shadow
           Ignore errors reading shadow information for users in the account management module.

       minlen=n
           Set a minimum password length of n characters. The default value is 6. The maximum for DES crypt-based passwords is 8 characters.

       obscure
           Enable some extra checks on password strength. These checks are based on the "obscure" checks in the original shadow package. The
           behavior is similar to the pam_cracklib module, but for non-dictionary-based checks. The following checks are implemented:

           Palindrome
               Verifies that the new password is not a palindrome of (i.e., the reverse of) the previous one.

           Case Change Only
               Verifies that the new password isn't the same as the old one with a change of case.

           Similar
               Verifies that the new password isn't too much like the previous one.

           Simple
               Is the new password too simple? This is based on the length of the password and the number of different types of characters
               (alpha, numeric, etc.) used.

           Rotated
               Is the new password a rotated version of the old password? (E.g., "billy" and "illyb")

       Invalid arguments are logged with syslog(3).

MODULE TYPES PROVIDED

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

RETURN VALUES

       PAM_IGNORE
           Ignore this module.

EXAMPLES

       An example usage for /etc/pam.d/login would be:

           # Authenticate the user
           auth       required   pam_unix.so
           # Ensure users account and password are still active
           account    required   pam_unix.so
           # Change the users password, but at first check the strength
           # with pam_cracklib(8)
           password   required   pam_cracklib.so retry=3 minlen=6 difok=3
           password   required   pam_unix.so use_authtok nullok md5
           session    required   pam_unix.so

SEE ALSO

       pam.conf(5), pam.d(5), pam(7)

AUTHOR

       pam_unix was written by various people.
 

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