nologin(5)

NAME
nologin - prevent unprivileged users from logging into the system

DESCRIPTION
If the file /etc/nologin exists and is readable, login(1) will allow access only to root. Other users will be shown the contents of this file and their logins will be refused. This provides a simple way of temporarily disabling all unprivileged logins.

FILES
/etc/nologin

SEE ALSO
login(1), shutdown(8)