# pam_unix

## 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
    


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