LINUX-FAQS.INFO

Sometimes it can useful to prevent non-root users from logging into the system for example during a maintainance. If you, as root, create a new file /etc/nologin and write a message in it. Any non-root user is refused to login and the message written in /ect/nologin will be displayed. Change back to normal and allow other users to login again, by deleting /etc/nologin