pam_unix -- Module for traditional password authentication
     __________________________________________________________________

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.

   quiet
          Turns off informational messages namely messages about session
          open and close via syslog(3).

   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.

   nullresetok
          Allow users to authenticate with blank password if password
          reset is enforced even if nullok is not set. If password reset
          is not required and nullok is not set the authentication with
          blank password will be denied.

   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 seconds.

   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_passwdqc module documented below).

   authtok_type=type
          This argument can be used to modify the password prompt when
          changing passwords to include the type of the password. Empty by
          default.

   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. The MD5 password hash algorithm is used for storing
          the old passwords. 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.

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

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

   rounds=n
          Set the optional number of rounds of the SHA256, SHA512,
          blowfish, gost-yescrypt, and yescrypt 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 is 8 characters.

   no_pass_expiry
          When set ignore password expiration as defined by the shadow
          entry of the user. The option has an effect only in case
          pam_unix was not used for the authentication or it returned
          authentication failure meaning that other authentication source
          or method succeeded. The example can be public key
          authentication in sshd. The module will return PAM_SUCCESS
          instead of eventual PAM_NEW_AUTHTOK_REQD or PAM_AUTHTOK_EXPIRED.

   Invalid arguments are logged with syslog(3).

EXAMPLES

   An example usage for /etc/pam.d/login would be:
# Authenticate the user
auth       required   pam_unix.so
# Ensure user's account and password are still active
account    required   pam_unix.so
# Change the user's password, but at first check the strength
# with pam_passwdqc(8)
password   required   pam_passwdqc.so config=/etc/passwdqc.conf
password   required   pam_unix.so use_authtok nullok yescrypt
session    required   pam_unix.so

AUTHOR

   pam_unix was written by various people.
