🐧 Linux Kernel: How Does Linux Actually Work?

[GIhanvs98]

Discussion Type

Product Feedback

Discussion Content

What is the difference between user mode and kernel mode?

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[sanjayadanushka712]

In Linux, user mode and kernel mode are two privilege levels used to protect the system and its hardware.

User mode is where normal applications run, such as your browser, terminal, text editor, and games. Applications have limited privileges, so they cannot directly access protected kernel memory or freely control hardware.

Kernel mode is where the Linux kernel runs. It has the privileges needed to manage memory, schedule processes, handle hardware, and provide services such as file access and networking.

For example, when a program needs to read a file, it usually cannot access the storage device directly. It requests the operation through a system call (such as open() or read()). The CPU transitions into kernel mode, the kernel checks and performs the requested operation, and control returns to the application in user mode.

The key idea is protection and stability: if an ordinary application crashes, it usually won't crash the entire operating system. A serious kernel bug, however, can affect the whole system because the kernel has much greater privileges.

For further reading, the [Linux Kernel Labs introduction to the kernel](https://linux-kernel-labs.github.io/refs/heads/master/lectures/intro.html) explains user space, kernel space, and system calls with diagrams.