Process Management 1-2

Question 1

What does fork do in a system process?

Answer 1

It creates a copy of itself, creates a new process by trapping OS and making it mostly duplicate

Question 2

How many times does fork return when called?

Answer 2

Returns twice with each process @ the next instruction)

Question 3

pid_t fork();

Answer 3

a system wide unique process identifier.
childs pid value is returned in the parent and parents pid is returned in the childs.

Question 4

What is a forks order of execution?

Answer 4

nondeterministic , parent and child run concurrently.

Question 5

Post fork, what relation do the parent and child functions have to each other?

Answer 5

They are identical but separate.OS allocates and maintains separate data /state

Question 6

what if fork fails?

Answer 6

most syscalls will return -1 on failure

Question 7

What happens to all terminating processes?

Answer 7

They turn into zombies, They become dead but still tracked by OS. -pid remains in use -exit status can be queried

Question 8

Reaping processes

Answer 8

All processes are responsible for reaping their own immediate children processes

Question 9

How do you kill a zombie process?

Answer 9

By killing/ terminating the parent process

Question 10

What happens when the process is orphaned? ( The parent process is killed)

Answer 10

They are adopted by the OS kernel, reaping its children.

Question 11

Why is it especially important for long running processes to reap their children?

Answer 11

Its important because zombie processes still consume system memory resources. if the parent terminates without reaping the children, then the kernel invokes the init process to reap them

Question 12

Who reaps the parent?

Answer 12

The shell

Question 13

what happens when the process is terminated and has more than 1 child?

Answer 13

reaps a zombie child
- returns reaped child’s pid and exit status
info via pointer

Question 14

what happens when the process has no children when pid_ wait is called?

Answer 14

return -1 immediately populate errno

Question 15

why are fork and exec separate calls?

Answer 15

They are separate because we might want to tweak the process before running a program in it.

Question 16

What are task management features?

Answer 16

They allow the shell to run track and manage multiple processes at once

Question 17

Difference between foreground and background processes?

Answer 17

fg processes: “blocks” additional commands from being run
bg processes can run multiple at once.

Question 18

what are signals and there aspects?

Answer 18

They are messages delivered by the kernel to user processes.
Aspects of signal processing:
1. sending a signal to a process
2. registering a handler for a given signal
3. delivering a signal (kernel mechanism)
4. designing a signal handler

Question 19

What happens if a signal is received as its handler is running?

Answer 19

mark it as pending, but don’t run the
handler again! (signal currently blocked)

Question 20

what happens if a signal is sent many
times before its handler is run?

Answer 20

nothing because we can’t que signals.

Question 21

what happens if a signal is received as
a handler for a lower priority one is
already running?

Answer 21

we preempt the lower priority handler
(and resume it — if possible — later)

Question 22

What operations can signals interrupt?

Answer 22

They can interrupt any non atomic operations.

Question 23

First design goal on signal handlers?

Answer 23

Minimize use of global variables, use mostly primitive data

Question 24

Second design goal for signal handlers?

Answer 24

prefer separate handlers for different signals.

Question 25

what is the importance of a signal handler being re-entrant?

Answer 25

It can be called again when already executing.

Question 26

what are three important lessons to take into consideration for signal handlers?

Answer 26

1. Signals can be delivered at any time
2. Sometimes Causing it to execute in overlapping fashion with itself when handling multiple signals
3. The execution of the sig handlers can overlap , any functions called may have overlapping execution.

Question 27

What is a direct approach that ensures certain sequence of events cannot be interrupted when there is insidious race condition caused by concurrency?
(can’t predict when child will terminate /
when signal will arrive)

Answer 27

block the signal

Question 28

What is another instance in which a signal can be blocked?

Answer 28

when the program is forced to call non- reentrant functions from signal handlers.