Kernel

Core Idea

The kernel is the privileged core of the operating system that manages processes, memory, filesystems, devices, and networking.

What The Kernel Does For Your Commands

• Creates and stops processes.
• Reads program files from disk.
• Connects stdin, stdout, stderr, pipes, and redirection.
• Enforces file permissions.
• Schedules CPU time.
• Maps memory.
• Sends packets through the network stack.

Commands To Try

uname -a
uname -r
cat /proc/version

uname -r prints the running kernel release. /proc/version exposes kernel build information through the proc filesystem.

Kernel Space And User Space

Kernel code runs with high privilege. Normal commands run in user space and ask the kernel for services through syscalls. This separation is why a bug in grep should not be able to directly overwrite another user’s memory or disk files.

Common Confusions

• Linux is technically the kernel, but people often say Linux to mean the whole operating system stack.
• Bash, git, curl, Caddy, and Python are user-space programs.
• Root is a powerful user account, not the same thing as the kernel.
• A kernel module is not the same thing as a package installed with apt.

Proof Check

Run uname -r and identify the kernel release. Then run ps -p 1 -o comm= and identify the first user-space process on this system.

Docs Pointers

• Run man uname and man proc.
• Read kernel.org: What is Linux?.
• Read User Space and Syscall next.