A process is the execution of a command by the Linux kernel. The shell that starts when you log in is a process, like any other. When you specify the name of a utility as a command, you initiate a process. When you run a shell script, another shell process is started, and additional processes are created for each command in the script. Depending on how you invoke the shell script, the script is run either by the current shell or, more typically, by a subshell (child) of the current shell. Running a shell builtin, such as cd, does not start a new process.
fork() system call
Like the file structure, the process structure is hierarchical, with parents, children, and a root. A parent process forks (or spawns) a child process, ...