UNIX and Linux System Administration Handbook, 5th Edition

11	Drivers and the Kernel

The kernel is the central government of a UNIX or Linux system. It’s responsible for enforcing rules, sharing resources, and providing the core services that user processes rely on.

We don’t usually think too much about what the kernel is doing. That’s fortunate, because even a simple command such as cat /etc/passwd entails a complex series of underlying actions. If the system were an airliner, we’d want to think in terms of commands such as “increase altitude to 35,000 feet” rather than having to worry about the thousands of tiny internal steps that were needed to manage the airplane’s control surfaces. ...