The pam_access module enforces login restrictions defined in the access.conf configuration file, which specifies rules based on combinations of users or groups, the origin (such as a hostname, IP address, or tty), and often the PAM service being used. This allows administrators to build fine- grained login policies, such as allowing a particular user to log in only from specific hosts.
pam_nologin instead simply prevents all non-root logins when the /etc/nologin file is present.