pam_krb5(8) manual page

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.

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.

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.

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.

`/tmp/krb5cc_`uid	default credentials cache ( uid is the decimal UID of the user).
`$HOME/.k5login`	file containing Kerberos principals that are allowed access.

Manual Pages — PAM_KRB5

NAME

CONTENTS

SYNOPSIS

DESCRIPTION

Kerberos 5 Authentication Module

Kerberos 5 Account Management Module

Kerberos 5 Password Management Module

Kerberos 5 Session Management Module

ENVIRONMENT

FILES

SEE ALSO

NOTES

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.
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.