How many levels of run levels are there in the Linux system?

There are seven run levels in a traditional Linux system, which are used to dictate the state of the operating system. These run levels range from 0 to 6 and include the following:

• Run level 0: Halt the system
• Run level 1: Single-user mode (maintenance mode)
• Run level 2: Multi-user mode without network services
• Run level 3: Multi-user mode with networking
• Run level 4: Unused/User-definable
• Run level 5: Multi-user mode with graphical interface (usually the default run level for systems with a graphical desktop environment)
• Run level 6: Reboot the system

Understanding these run levels is crucial for system administration, as they determine how the system boots and operates. Each run level corresponds to a specific mode for the system, allowing administrators to manage system resources effectively during both normal operation and troubleshooting.