Linux.com: Limiting Linux Logins

“I’m sometimes surprised at the complex solutions administrators
come up with to keep out users whenever that course becomes
necessary when a simple, built-in solution to their problem already
exists. In this article, we’ll look at a few different mechanisms
used to keep out intruders either temporarily, or on a more
permanent basis.

“Most obviously, Linux offers single user mode, in which only
the system administrator can log on. You can get to single user
mode in a number of ways. Typing init 1 at a shell
prompt as root will do it nicely, and do it immediately before you
go into single user mode…”

Complete
Story