Manual Pages  — PAM_KRB5

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.
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.
allow_kdc_spoof
	Allow pam_krb5 to succeed even if there is no host or service key available in a keytab to authenticate the Kerberos KDC's ticket. If there is no such key, for example on a host with no keytabs, pam_krb5 will fail immediately without prompting the user. Warning: If the host has not been configured with a keytab from the KDC, setting this option makes it vulnerable to malicious KDCs, e.g. via DNS flooding, because pam_krb5 has no way to distinguish the legitimate KDC from a spoofed KDC.
no_user_check	Do not verify if a user exists on the local system. This option implies the no_ccache option because there is no secure local uid/gid for the cache file.

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.