1. Parent process creates children processes, which, in turn create other processes, forming a tree of processes.
2. Resource sharing

• Parent and children share all resources.
• Children share subset of parent’s resources.
• Parent and child share no resources.

3. Execution

• Parent and children execute concurrently.
• Parent waits until children terminate.

• Child duplicate of parent.
• Child has a program loaded into it.

• fork system call creates new process
• fork returns 0 to child , process id of child for parent
• exec system call used after a fork to replace the process’ memory space with a new program.

--Process Termination

Process executes last statement and asks the operating system to delete it (exit).

• Output data from child to parent (via wait).
• Process’ resources are deallocated by operating system.n Parent may terminate execution of children processes (abort).
• Child has exceeded allocated resources.
• Task assigned to child is no longer required.
• Parent is exiting.

----------- Operating system does not allow child to continue if its parent terminates.

----------- Cascading termination.

• In Unix, if parent exits children are assigned init as parent