Chapter 5. System Calls

The kernel provides a set of interfaces by which processes running in user-space can interact with the system. These interfaces give applications access to hardware and other operating system resources. The interfaces act as the messengers between applications and the kernel, with the applications issuing various requests, and the kernel fulfilling them (or telling the application to go away). The fact that these interfaces exist, and that applications are not free to do directly whatever they please, is key to providing a stable system and avoiding a big mess.

System calls provide a layer between the hardware and user-space processes. This layer serves three primary purposes. First, it provides an abstracted hardware interface ...

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