pam_krb5(8) UNIX System V (15 Jan 1999) pam_krb5(8)
NAME
pam_krb5 - Kerberos 5 PAM module
SYNOPSIS
/usr/lib32/security/pam_krb5.so
DESCRIPTION
The Kerberos 5 service module for PAM,
/usr/lib/security/pam_krb5.so, provides functionality for
three PAM categories: authentication, account management,
and password management. It also provides null functions
for session management. The pam_krb5.so module is a shared
object that can be dynamically loaded to provide the
necessary functionality upon demand. Its path is specified
in the PAM configuration file.
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 sucessful 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 level.
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
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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>.
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
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server.
The following options may be passed to the password
management module:
debug syslog(3) debugging information at 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).
~/.k5login file containing Kerberos principals that
are allowed access.
SEE ALSO
kdestroy(1), passwd(1), pam(8), syslog(3), pam_start(8),
pam.conf(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.
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dtlogin will not successfully authenticate a user who enters
a realm name as part of their username (even if the
authentication module returns success).
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