pam_unix

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.

       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 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_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 are 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).

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 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



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

AUTHOR
       pam_unix was written by various people.



Linux-PAM Manual                   11/10/2020                        PAM_UNIX(8)