PAM

"Pluggable Authentication Module." Programs that are aware of PAM use the modules defined in the PAM configuration files for making authentication/access decisions.

Access Control

/etc/pam.d/sshd contains account required pam_access.so.
/etc/security/access.conf contains the rules for who can log into the machine.

Chart of what groups can log onto what machines:

name	restricted by access.conf	nogroup	npg	farm	domain_admins
einstein	no	yes	yes	yes	yes
lentil	no	yes	yes	yes	yes
gourd	yes	no	yes	no	yes
roentgen	yes	no	yes	no	yes
taro	yes	no	yes	no	yes
pepper	yes	no	no	yes	yes
jalapeno	yes	no	yes	no	yes
tomato	yes	no	yes	no	yes
okra	yes	no	yes	no	yes

External Links

pam_access PAM module document