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, schedules execution, manages memory, controls devices, implements networking and filesystems, and enforces access checks. A Linux distribution combines this kernel with user-space libraries, services, tools, and applications.

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 into the kernel image or loaded later as modules. This arrangement makes subsystem interaction efficient, but a defective kernel component can corrupt shared state or stop the system.

The control path

A user-space program requests kernel work through a system call. The processor switches privilege level, 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. A network send crosses the socket and protocol stacks before a driver queues data to hardware. The kernel returns a result or an error and resumes user-space execution.

Linux Kernel Fundamentals

The control path

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