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 maximum length of a password supported by the pam_unix module via
       the helper binary is PAM_MAX_RESP_SIZE - currently 512 bytes. The rest
       of the password provided by the conversation function to the module
       will be ignored.

       The password component of this module performs the task of updating the
       user's password. The default encryption hash is taken from the
       ENCRYPT_METHOD variable from /etc/login.defs

       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.

       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. Instead of this option the pam_pwhistory module should
	   be used.

       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. The SHA256 algorithm must be supported by the crypt(3)
	   function.

       sha512
	   When a user changes their password next, encrypt it with the SHA512
	   algorithm. The SHA512 algorithm must be supported by the crypt(3)
	   function.

       blowfish
	   When a user changes their password next, encrypt it with the
	   blowfish algorithm. The blowfish algorithm must be supported by the
	   crypt(3) function.

       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 max. for DES
	   crypt based passwords are 8 characters.

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

AUTHOR
       pam_unix was written by various people.



Linux-PAM Manual		  08/26/2015			   PAM_UNIX(8)