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PAM_KRB5(8)                 System Manager's Manual                PAM_KRB5(8)

NAME
     pam_krb5 -- Kerberos 5 PAM module

SYNOPSIS
     [service-name] module-type control-flag pam_krb5 [arguments]

DESCRIPTION
     The Kerberos 5 service module for PAM provides functionality for three
     PAM categories: authentication, account management, and password
     management.  It also provides null functions for session management.

   Kerberos 5 Authentication Module
     The Kerberos 5 authentication component provides functions to verify the
     identity of a user (pam_sm_authenticate()) and to set user specific
     credentials (pam_sm_setcred()).  pam_sm_authenticate() converts the
     supplied username into a Kerberos principal, by appending the default
     local realm name.  It also supports usernames with explicit realm names.
     If a realm name is supplied, then upon a successful return, it changes
     the username by mapping the principal name into a local username (calling
     krb5_aname_to_localname()).  This typically just means the realm name is
     stripped.

     It prompts the user for a password and obtains a new Kerberos TGT for the
     principal.  The TGT is verified by obtaining a service ticket for the
     local host.

     When prompting for the current password, the authentication module will
     use the prompt ``Password for <principal>:''.

     The pam_sm_setcred() function stores the newly acquired credentials in a
     credentials cache, and sets the environment variable KRB5CCNAME
     appropriately.  The credentials cache should be destroyed by the user at
     logout with kdestroy(1).

     The following options may be passed to the authentication module:

     debug               syslog(3) debugging information at LOG_DEBUG level.

     no_warn             suppress warning messages to the user.  These
                         messages include reasons why the user's
                         authentication attempt was declined.

     use_first_pass      If the authentication module is not the first in the
                         stack, and a previous module obtained the user's
                         password, that password is used to authenticate the
                         user.  If this fails, the authentication module
                         returns failure without prompting the user for a
                         password.  This option has no effect if the
                         authentication module is the first in the stack, or
                         if no previous modules obtained the user's password.

     try_first_pass      This option is similar to the use_first_pass option,
                         except that if the previously obtained password
                         fails, the user is prompted for another password.

     renewable=timeperiod
                         Obtain renewable Kerberos credentials for the user.
                         The renewable time can be specified, or it defaults
                         to one month.  Since spaces are not allowed in the
                         pam configuration time, underscores are used to form
                         parseable times (e.g., 1_month).

     forwardable         Obtain forwardable Kerberos credentials for the user.

     no_ccache           Do not save the obtained credentials in a credentials
                         cache.  This is a useful option if the authentication
                         module is used for services such as ftp or pop, where
                         the user would not be able to destroy them.  [This is
                         not a recommendation to use the module for those
                         services.]

     ccache=name         Use name as the credentials cache.  name must be in
                         the form type:residual.  The special tokens `%u', to
                         designate the decimal UID of the user; and `%p', to
                         designate the current process ID; can be used in
                         name.

   Kerberos 5 Account Management Module
     The Kerberos 5 account management component provides a function to
     perform account management, pam_sm_acct_mgmt().  The function verifies
     that the authenticated principal is allowed to login to the local user
     account by calling krb5_kuserok() (which checks the user's .k5login
     file).

   Kerberos 5 Password Management Module
     The Kerberos 5 password management component provides a function to
     change passwords (pam_sm_chauthtok()).  The username supplied (the user
     running the passwd(1) command, or the username given as an argument) is
     mapped into a Kerberos principal name, using the same technique as in the
     authentication module.  Note that if a realm name was explicitly supplied
     during authentication, but not during a password change, the mapping done
     by the password management module may not result in the same principal as
     was used for authentication.

     Unlike when changing a UNIX password, the password management module will
     allow any user to change any principal's password (if the user knows the
     principal's old password, of course).  Also unlike UNIX, root is always
     prompted for the principal's old password.

     The password management module uses the same heuristics as kpasswd(1) to
     determine how to contact the Kerberos password server.

     The following options may be passed to the password management module:

     debug               syslog(3) debugging information at LOG_DEBUG level.

     use_first_pass      If the password management module is not the first in
                         the stack, and a previous module obtained the user's
                         old password, that password is used to authenticate
                         the user.  If this fails, the password management
                         module returns failure without prompting the user for
                         the old password.  If successful, the new password
                         entered to the previous module is also used as the
                         new Kerberos password.  If the new password fails,
                         the password management module returns failure
                         without prompting the user for a new password.

     try_first_pass      This option is similar to the use_first_pass option,
                         except that if the previously obtained old or new
                         passwords fail, the user is prompted for them.

   Kerberos 5 Session Management Module
     The Kerberos 5 session management component provides functions to
     initiate (pam_sm_open_session()) and terminate (pam_sm_close_session())
     sessions.  Since session management is not defined under Kerberos 5, both
     of these functions simply return success.  They are provided only because
     of the naming conventions for PAM modules.

ENVIRONMENT
     KRB5CCNAME  Location of the credentials cache.

FILES
     /tmp/krb5cc_uid             default credentials cache (uid is the decimal
                                 UID of the user).
     $HOME/.k5login              file containing Kerberos principals that are
                                 allowed access.

SEE ALSO
     kdestroy(1), passwd(1), syslog(3), pam.conf(5), pam(8)

NOTES
     Applications should not call pam_authenticate() more than once between
     calls to pam_start() and pam_end() when using the Kerberos 5 PAM module.

SECURITY CONSIDERATIONS
     The pam_krb5 module implements what is fundamentally a password
     authentication scheme.  It does not use a Kerberos 5 exchange between
     client and server, but rather authenticates the password provided by the
     client against the Kerberos KDC.  Therefore, care should be taken to only
     use this module over a secure session (secure TTY, encrypted session,
     etc.), otherwise the user's Kerberos 5 password could be compromised.

NetBSD 6.1.5                    March 10, 2007                    NetBSD 6.1.5