This section describes the terminology used in shutting down and booting a system.
Run levels and init states - A run level is a letter or digit representing a system state in which a particular set of system services are available. The system is always running in one of a set of well-defined run levels. Run levels are also referred to as init states because the init process is used to perform transitions between run levels. System administrators use the init(1M) command to initiate a run-level transition. This book refers to init states as run levels.
Interactive boot - You are prompted to provide information about how the system is booted, such as the kernel and device path name.
Reconfiguration boot - The system is reconfigured to support newly added hardware or new pseudo devices.
Recovery boot - The system is hung or an invalid entry is prohibiting the system from booting successfully or from allowing users to log in.