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pam_unix -- Module for traditional password authentication

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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.

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 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

AUTHOR

pam_unix was written by various people.

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