What is the difference between the kernel space and the user space?

linux-kernel operating-system kernel terminology
kc3 picture kc3 · May 11, 2011 · Viewed 121.9k times · Source

What is the difference between the kernel space and the user space? Do kernel space, kernel threads, kernel processes and kernel stack mean the same thing? Also, why do we need this differentiation?

Answer

Jerry Coffin picture Jerry Coffin · May 11, 2011

The really simplified answer is that the kernel runs in kernel space, and normal programs run in user space. User space is basically a form of sand-boxing -- it restricts user programs so they can't mess with memory (and other resources) owned by other programs or by the OS kernel. This limits (but usually doesn't entirely eliminate) their ability to do bad things like crashing the machine.

The kernel is the core of the operating system. It normally has full access to all memory and machine hardware (and everything else on the machine). To keep the machine as stable as possible, you normally want only the most trusted, well-tested code to run in kernel mode/kernel space.

The stack is just another part of memory, so naturally it's segregated right along with the rest of memory.

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