pam_krb5 is a Kerberos 5 (Heimdal) authentication module.
pam_nologin checks for /etc/nologin and does the "usual stuff"
if it is found, otherwise it silently succeeds.
pam_rootok silently succeeds if the user is root, otherwise
it fails.
pam_wheel silently succeeds if the user is a member of group
"wheel" (or another nominated group), and fails
otherwise.
There is an issue with kerberosIV and kerberos5 - if both are
being built, then static linking fails with duplicate symbols.
This will take a bit of work to sort out in the kerberii.
