On Linux systems, run levels are operational levels that describe the state of the system with respect to what services are available. One run level is restrictive and only used for maintenance; network connections will not be operational, but admins can log in through a console connection. Others allow anyone to log in and work, but maybe with some differences in the available services. This post examines how run levels are configured and how you can change the run level interactively or modify what services are available.
The default run state on Linux systems — the one that will be used when the system starts up (unless instructed otherwise) — is usually configured in the /etc/inittab file which generally looks something like this:
From: Network World