Background processes

Let's start with an intuitive definition of a background process, and define it as a process with no interaction with the terminal it is launched from. This practically means that a background process has no interaction with the user and that's it. Technically, we can say that a background process is the one whose process ID group differs from the one of the terminal it has been launched from. We can define a process group as a bunch of processes sharing the same process group ID, which is an identifier allowing the system to manage all the processes as a whole. A process group ID is determined by the process ID of the first process of the group, also called process group leader; each subsequent process in the group will be the process group ID drawn from the process ID of the leader; and each child process is placed in the process group ID of its...