Keep the following in mind when you shut down a system:
Use the init and shutdown commands to shut down a system. Both commands perform a clean system shutdown, which means that all system processes and services are terminated normally.
Use the shutdown command to shut down a server. Logged-in users and systems that mount resources from the server are notified before the server is shut down. Additional notification of system shutdowns by electronic mail is also recommended so that users can prepare for system downtime.
You need superuser privileges to use the shutdown or init command to shut down a system.
Both shutdown and init commands take a run level as an argument. The three most common run levels are as follows:
Run level 3 – All system resources are available and users can log in. By default, booting a system brings it to run level 3, which is used for normal day-to-day operations. This run level is also known as multiuser level with NFS resources shared.
Run level 6 – Stops
the operating system and reboots to the state that is defined by the initdefault entry in the /etc/inittab file.
Run level 0 – The operating system is shut down, and it is safe to turn off power. You need to bring a system to run level 0 whenever you move a system, or add or remove hardware.
Run levels are fully described in Chapter 14, Managing Services (Overview).