Don't Panic - Linux Kernel Fundamentals

The Linux kernel is the privileged program between applications and hardware. Applications run in user space with limited authority. The kernel runs in kernel space: it schedules execution, manages memory, controls devices, implements networking and filesystems, and enforces access checks. A distribution combines this kernel with user-space libraries, services, and tools.

Linux is a modular monolithic kernel. Core subsystems and most drivers share one kernel address space so they can call internal interfaces directly. Features may be built in or loaded later as modules. That efficiency means a defective kernel component can corrupt shared state or stop the system.

A user-space program requests work through a system call. The processor switches privilege, the kernel validates arguments and credentials, and a subsystem performs the operation. A file read can pass through the virtual filesystem, a filesystem implementation, the page cache, the block layer, and a device driver. Hardware can also start work through interrupts, with deferred processing outside the tightest interrupt context. The scheduler chooses which runnable task receives each CPU.

Tasks carry scheduling state, credentials, resources, namespaces, and a virtual address space. Memory management gives each task a virtual map backed by physical pages, file mappings, and reclaim under pressure. Drivers and filesystems sit on those paths; mistakes there look like application failures if you only watch user space.

Read the Intro for the control path and subsystem map. Use the Cheatsheet when you need syscall and module landmarks. Landscape and Timeline place the kernel among related OS technologies; Updates tracks kernel.org release versions.

Don't Panic - Linux Kernel Fundamentals

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