System Administration Guide: Basic Administration

When to Use Run Levels or Milestones

Under most circumstances, using the init command with a run level to change the system state is sufficient. Using milestones to change system state can be confusing and can lead to unexpected behavior. In addition, the init command allows for the system to be shutdown, so init is the best command for changing system state.

However, booting a system using the none milestone, can be very useful when debugging startup problems. There is no equivalent run level to the none milestone. See How to Boot Without Starting Any Services for specific instructions.