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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.

Linux-PAM Manual			    05/31/2011				      PAM_UNIX(8)
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