Lecture 03

Question 1

What are the four possible status codes for a process?

Answer 1

O, S, R, and Z

Question 2

What does the process status code ‘O’ mean?

Answer 2

The process is running on a processor.

Question 3

What does the process status code ‘S’ mean?

Answer 3

The process is sleeping.

It is waiting for an event complete.

Question 4

What does the process status code ‘R’ mean?

Answer 4

Runnable.

The process is on run queue.

Question 5

What does the process status code ‘Z’ mean?

Answer 5

The process is in Zombie State.

It has terminated and the parent is not waiting.

Question 6

What is a process?

Answer 6

A program in execution.

Question 7

What function is used to get a processes id?

Answer 7

getpid()

Question 8

What function is used to create a new process?

Answer 8

fork()

Question 9

Parent and child processes execute:
A - In Parallel
B - In Series

Answer 9

In parallel.

Question 10

What is the return value of fork for the parent process?

Answer 10

The new child’s process id.

Question 11

What is the return value of fork for the child process?

Answer 11

0

Question 12

What function is used to get the process id of a process’ parent?

Answer 12

getppid

Question 13

What happens if a parent terminates before its child process?

Answer 13

The child is assigned the ‘init’ process as its parent.

Question 14

What process id does the ‘init’ process have?

Answer 14

1.

Question 15

What happens to the memory space of a process (in theory), after a fork?

Answer 15

Its entire memory space is copied to the new process so that they both have an independent copy.

Question 16

What function is used to wait on a child process completing?

Answer 16

wait()

Question 17

What does the wait() function do?

Answer 17

Blocks until a child terminates.

Question 18

When will wait return immediately?

Answer 18

When there are no children or a child has already terminated.

Question 19

What happens when a child process terminates but has not been waited on by the parent?

Answer 19

It becomes a zombie state.

Question 20

When a process enters zombie state, what happens to its memory and resources?

Answer 20

They are de-allocated.

Question 21

What does it mean for a Zombie process to be ‘reaped’?

Answer 21

Its parent process has waited on it, so it is now cleared from the ‘process table’.

Question 22

What does the ‘exec’ function do?

Answer 22

Replaces the current program of a process with a new program.

Question 23

What function replaces the current program of a process with a new program?

Answer 23

exec()

Question 24

Using exec to open a new program, what happens to the text, stack, heap, and data of the current process?

Answer 24

They are overwritten.

Question 25

Using exec to open a new program, what happens to the open file descriptors of the current process?

Answer 25

They are retained.

Question 26

What is the difference between exit() and _exit()?

Answer 26

exit flushes the standard buffers and calls registered clean-up function.
_exit just returns immediately to the OS without any clean-up.

Question 27

What function is used to register functions to be called on process exit?

Answer 27

atexit()

Question 28

What is the function prototype for atexit?

Answer 28

int atexit(void (*function)(void));

Question 29

What does the atexit function do?

Answer 29

Registers a function as an exit-handler. It will be called when the process exits.

Question 30

What are Environment Variables stored as?

Answer 30

Key/value pairs.

Question 31

What is the function prototype for getenv?

Answer 31

char* getenv(const char *name);

Question 32

What function is used to get the value of a specific environment variable?

Answer 32

getenv()

Question 33

What command shows the shell environment?

Answer 33

set

Question 34

What is the difference between static and shared libraries, memory-wise?

Answer 34

With static libraries, each program has a copy of the library in memory.
With shared libraries, each program shares one copy of the memory - it’s only kept in memory once.

Question 35

When a static library is changed, programs using it must be ___?

Answer 35

Re-linked.

Question 36

What are the five stages of the static library example?

Page 33

Answer 36

• Declare functions
• Define functions
• Compile, but don’t link
• Create archive
• Link library with application code.

Question 37

What are the five stages of the shared library example?

Page 36

Answer 37

• Declare and define library functions as before
• Compile (but do not link)
• Create shared library archive
• Link library with application code
• Setup the library search path