One of Unix’s hallmarks is its process model. It is the key to understanding access rights, the relationships among open files, signals, job control, and most other low-level topics in this book. Linux adopted most of Unix’s process model and added new ideas of its own to allow a truly lightweight threads implementation.
What exactly is a process? In the original Unix implementations, a process was any executing program. For each program, the kernel kept track of
The current location of execution (such as waiting for a system call to return from the kernel), often called the program’s context
Which files the program had access to
The program’s credentials (which user and group owned the process, for ...