Processes

Question 1

Process

Answer 1

Program in Execution. It is the basic unit of execution in an OS.

Question 2

What must a process have to run?

Answer 2

Memory to contain the program code and data, and a set of CPU registers to support execution.

Question 3

Process Control Block

Answer 3

Contains the information needed for a process to run. It is a data structure that defines the process to the OS. Processes are represented as PCBs to the OS.

Question 4

What does a process state consist of?

Answer 4

Code, PC, stack, stack pointer, static data, heap, PID, values of registers, and process execution state.

Question 5

Process Execution State

Answer 5

Can be new, ready, running, blocked, or terminated

Question 6

What happens with the PCB when a process is created?

Answer 6

OS allocates and initializes a new PCB and places the PCB on the state queue. When a process terminates, the PCB is deallocated.

Question 7

What happens when a process is created?

Answer 7

(1) the loader reads and interprets the executable file, (2) it sets up the process’s memory, (3) argv and argc are pushed onto the stack, (4) the loader sets the CPU registers and calls start()

Question 8

How is fork() different in the child and parent?

Answer 8

What fork() returns. 0 in the child and the child’s PID in the parent.

Question 9

What happens to the stack and heap in exec?

Answer 9

Overwritten!

Question 10

Is the result of exec a same process and program?

Answer 10

No! Same process but different program.

Question 11

exit()

Answer 11

deallocates all files and memory. If the process has a parent, it becomes a zombie

Question 12

wait()

Answer 12

waits for the parents children. If there is a zombie process, wait returns immediately and deallocates the zombie.

Question 13

Zombie State

Answer 13

The child is not terminated and instead holds the return value and waits for the parent to reap it.

Question 14

Signals

Answer 14

Are vitrual interrupts. They are kernal-defined and have the signal stack and signal masking in user space

Question 15

Besides signals, what are other forms of inter-process communication?

Answer 15

Pipes, messages, and shared memory

Question 16

Orphan Processes

Answer 16

When a parent terminates, the child gets a new parent: init process. Children can orphan themselves to keep running in the background (nohup command).

Question 17

What process control does the OS have? (3 things)

Answer 17

Priority manipulation, debugging support, and alarms and time.

Question 18

What do CTRL-C and CTRL-Z do?

Answer 18

CTRL-C kills the program while CTRL-Z stops the program. Both are sent through kill().

Question 19

How are processes created and managed?

Answer 19

Through system calls. Fork(), exec(), wait(), etc.