Process Creation

Parent processes can create child processes. Every process has an ID (PID) which it managed through.

There are different options for how parent and child processes can share resources (or not):

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

There are also options for how processes can be executed:

• Parent and child are executed concurrently.
• Parent waits for child to terminate.

The child process can be a duplicate of the parent or it can have a new program loaded into it.

• fork — Creates new process
• exec — Syscall after fork to replace processes' memory with a new program.
• wait — Lets parent wait for child termination. Provides child state information to parent.
• exit — Terminates process and returns state information to parent.
• abort — Called by parent to terminate a child process.

The OS may or may not allow child processes to exist without a parent. If it does not, it will use cascaded termination to terminate all child processes when their parent is terminated.

If a child terminates and the parent has already terminated without calling wait, the child is a Zombie process.

If the parent of a child terminates without calling wait, the children of that process are Orphan processes.