pam_nologin man page
pam_nologin — Prevent non-root users from login
pam_nologin.so [file=/path/nologin] [successok]
pam_nologin is a PAM module that prevents users from logging into the system when /var/run/nologin or /etc/nologin exists. The contents of the file are displayed to the user. The pam_nologin module has no effect on the root user's ability to log in.
Use this file instead the default /var/run/nologin or /etc/nologin.
Return PAM_SUCCESS if no file exists, the default is PAM_IGNORE.
Module Types Provided
The auth and acct module types are provided.
The user is not root and /etc/nologin exists, so the user is not permitted to log in.
Memory buffer error.
This is the default return value.
Success: either the user is root or the nologin file does not exist.
User not known to the underlying authentication module.
The suggested usage for /etc/pam.d/login is:
auth required pam_nologin.so
In order to make this module effective, all login methods should be secured by it. It should be used as a required method listed before any sufficient methods in order to get standard Unix nologin semantics. Note, the use of successok module argument causes the module to return PAM_SUCCESS and as such would break such a configuration - failing sufficient modules would lead to a successful login because the nologin module succeeded.
nologin(5), pam.conf(5), pam.d(5), pam(8)
pam_nologin was written by Michael K. Johnson <firstname.lastname@example.org>.