Starting from Scratch: Learn the Differences between Linux Run Levels

Learning the Linux operating system is one of the essential basic knowledge for every system administrator or programmer. Among them, understanding the differences between various operating levels of Linux is crucial to mastering system management and troubleshooting. This article will start from scratch and delve into the concept of Linux run levels and how to set up and control them accordingly in actual operations.

What is a Linux run level?

In the Linux system, runlevel (runlevel) refers to the execution mode of the operating system in different states. Each runlevel has specific services and functions. There are a total of 7 running levels (0-6) in Linux, and each level represents a different system working mode. The main role of the run level is to determine which services and programs run when the system starts.

The difference between various Linux operating levels:

1. Running level 0 (shutdown) : The system will perform a shutdown operation, stop all services and programs, and safely shut down the system .
2. Run level 1 (single-user mode): The system enters single-user mode, only the most basic services are started, and system maintenance and repair operations can be performed.
3. Running level 2 (no network support): At this level, the system starts basic services, but there is no network support, suitable for local development and testing environments.
4. Running level 3 (multi-user, no graphical interface): The system starts all basic services, including network services, but does not load the graphical interface, suitable for server environments.
5. Run level 4 (reserved) : In most Linux systems, run level 4 has no specific purpose and is usually left empty.
6. Running level 5 (multi-user, with graphical interface): The system starts all services and loads the graphical interface, suitable for desktop users.
7. Run level 6 (restart): The system will perform a restart operation, shut down all services and programs, and then restart the system.

How to switch Linux run level?

In Linux systems, you can switch the run level by modifying the /etc/inittab file or using the systemctl command. The following are specific operation examples:

1. By modifying the /etc/inittab file:

First, open the terminal and use Edit the /etc/inittab file with a text editor:

sudo nano /etc/inittab

Find the following line:

id:5:initdefault:

Modify 5 to the run level you want to switch number, save and exit the editor.

2. Through the systemctl command:

Use the following command to switch the run level (taking switching to run level 3 as an example) :

sudo systemctl isolate multi-user.target

Summary:

Through the introduction of this article, we have learned about the differences and switching methods of various operating levels of Linux. Proficient in the concepts and operations of run levels can help us better manage Linux systems and improve system stability and security. I hope this article will be helpful to you in the process of learning Linux!

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