Advanced Process Management, Memory Layout, and Stack/Heap

Question 1

What command starts a low-priority background process?

Answer 1

nice

Question 2

What command changes the priority of a running process?

Answer 2

renice

Question 3

How do you keep a process running even after logout?

Answer 3

nohup myProgram &

Question 4

What does fork() do?

Answer 4

Creates a child process.

Question 5

What does a return value of < 0 from fork() indicate?

Answer 5

Fork failed.

Question 6

What does a return value of 0 from fork() indicate?

Answer 6

Child process.

Question 7

What does a return value > 0 from fork() indicate?

Answer 7

Parent process (value = child’s PID).

Question 8

What do both parent and child processes share?

Answer 8

stdout

• File descriptors
• Global/static variables (as copies)

Question 9

What does waitpid() do?

Answer 9

Wait for a child process to finish.

Question 10

What can waitpid() wait for?

Answer 10

• A specific child (pid)
• Any child (pid = 0)
• Return immediately if no child has exited (WNOHANG)

Question 11

What does exec() do?

Answer 11

Replaces the current process with a new one.

Question 12

What happens if exec succeeds?

Answer 12

Nothing after it runs.

Question 13

What happens if exec fails?

Answer 13

Handle the error.

Question 14

What does pipe() do?

Answer 14

Facilitates communication between parent and child processes.

Question 15

What are the characteristics of pipes?

Answer 15

• Unbuffered
• Unidirectional
• Must be created before fork()

Question 16

What does SIGINT represent?

Answer 16

Ctrl+C

Question 17

Is SIGTERM catchable?

Answer 17

Yes

Question 18

Is SIGKILL catchable?

Answer 18

No

Question 19

What are SIGUSR1 and SIGUSR2?

Answer 19

Custom user signals.

Question 20

What does SIGSEGV represent?

Answer 20

Segfault

Question 21

What command is used to send a signal?

Answer 21

kill or signal()

Question 22

What tool is used to create a process?

Answer 22

fork()

Question 23

What tool is used to replace a process?

Answer 23

exec()

Question 24

What tool is used to wait for a process?

Answer 24

waitpid()

Question 25

What tool is used for communication?

Answer 25

pipe()

Question 26

What is the virtual address space in a program?

Answer 26

Each program thinks it has full access to memory, but the OS maps it.

Question 27

What are the three main segments of runtime memory?

Answer 27

* Text/code segment * Stack * Heap

Question 28

What is stored in the code/text segment?

Answer 28

The program’s machine instructions.

Question 29

What is stored in the stack?

Answer 29

Local variables, function calls.

Question 30

What is stored in the heap?

Answer 30

Memory from malloc(), calloc(), etc.

Question 31

How is stack memory used during function calls?

Answer 31

Functions use stack frames to store parameters and local variables.

Question 32

What happens when a function is called?

Answer 32

* Save old frame pointer (fp) * Move stack pointer (sp) * Allocate space for locals * Execute function * Restore previous frame and return

Question 33

How does the stack grow in memory?

Answer 33

Stack grows downward from high → low memory addresses.

Question 34

What registers are used for the frame pointer and stack pointer?

Answer 34

* %rbp: Base pointer * %rsp: Stack pointer

Question 35

What is recursion in relation to stack memory?

Answer 35

Each recursive call pushes a new frame on the stack.

Question 36

What occurs if there are too many recursive calls?

Answer 36

Stack overflow!

Question 37

What is heap memory used for?

Answer 37

Dynamic allocation of memory.

Question 38

What functions are commonly used for dynamic memory allocation?

Answer 38

malloc(), calloc()

Question 39

What must be done with memory allocated on the heap?

Answer 39

Must call free() manually.

Question 40

What is a consequence of not freeing heap memory?

Answer 40

Memory leak!