
\S parent process:  child process \S

Processes have a hierarchical structure like file systems.  Each process
has a parent process and it might also have a child process.  For example,
the shell that started when you logged in is the parent of the commands you
execute.  These commands are in turn child processes of the shell.  When
you execute a program that you wrote, it is a child process of your login
shell.  If you execute a command in the program, the program is a parent
and the command becomes a child process.

