Understanding Linux Runlevels: A Simple Analogy for DBAs

Hello there,

If you're a DBA, you might have heard the term "runlevel" in Linux. Have you ever wondered what it means or does? Let's dive into it with a simple analogy.

Imagine a village called Comature, where a hardworking father named Osur lives with his six sons: Zerom, Onem, Tooky, Thre, Fire, Fiven, and Sixer.

Since Osur was always busy, he assigned specific tasks to each son:

• Zerom and Onem made sure Osur kept working, even when he slowed down.

• Sixer protected Osur's work if thieves tried to steal it.

• Tooky, Thre, and Fire managed supplies on the field.

• Fiven handled supplies, packed them neatly, and delivered them to customers.

Each son had a specific role to help Osur manage everything smoothly.

Now, let’s relate this to Linux:

• The village (Comature) is like a computer.

• The father (Osur) is the Linux operating system.

• The six sons represent the six runlevels (0, 1, 2, 3, 4, 5, 6).

Here’s a table to help you understand what each runlevel does:

System-State Targets	Equivalent Run-Level Targets	Description
graphical.target	runlevel5.target	Set up a multi-user system with networking and display manager.
multi-user.target	runlevel2/3/4.target	Set up a non-graphical multi-user system with networking.
poweroff.target	runlevel0.target	Shut down and power off the system.
reboot.target	runlevel6.target	Shut down and reboot the system.
rescue.target	runlevel1.target	Set up a rescue shell.

To check the current "runlevel" of the system:

[root@analyzenow ~]# runlevel

N 3

[root@analyzenow ~]#