For questions regarding child-process
In Unix, a child process is typically created as a copy of the parent, using the fork system call. The child process can then overlay itself with a different program (using exec) as required.
Each process may create many child processes but will have at most one parent process; if a process does not have a parent this usually indicates that it was created directly by the kernel.
The inter communication between a child process and a parent process can be done through normal communication schemes such as pipes, sockets, message queues, shared memories.
When a child process terminates, some information is returned to the parent process. When a child process terminates before the parent has called wait, the kernel retains some information about the process, such as its exit status, to enable its parent to call wait later
