1 - Shell (Part 1)

Question 1

What does information on a process include:

Answer 1

1) Process Stack: includes temporary data (function parameters, return addresses and local variables)
2) Data Selection: Includes global variables
3) Heap: Memory that is dynamically allocated during process run-time

Question 2

What are the 4 states a process can have:

Answer 2

1) New
2) Running
3) Waiting
4) Terminated

Question 3

How is a process represented in the operating system?

Answer 3

A process control block.

Question 4

What information does a process control block include?

Answer 4

Information related to program execution including:

• PID
• state
• program counter
• CPU registers
• CPU-scheduling information
• Memory-management information
• I/O Status Information

Question 5

Examples of operating system services from user-perspective:

Answer 5

1) User interface (CLI or GUI)
2) Program execution
3) I/O Operations
4) File-system manipulation

Question 6

What is the command interpreter?

Answer 6

A program that accepts commands from the user and interprets the commands (type of user interface).

Question 7

What is a system call?

Answer 7

Allows a command to request a service from the operation system.

Question 8

When a command is executed, what carries out the execution?

Answer 8

A separate process from the shell process - a child process will execute the command.

Question 9

What does the fork() command do?

Answer 9

Creates a child process that is a duplicate of the parent.

Question 10

What are the properties of a child process created by fork()?

Answer 10

• Child inherits state from parent process (same program instructions, variables have the same value)
• Parent and child have separate copies of that state
• Child has the same open file descriptors from the parent (might be from 2208)

Question 11

Switching between the parent and child depends on many factors such as:

Answer 11

• machine load

- system process scheduling

Question 12

How many processes are created by 4 consecutive fork commands?

Answer 12

Draw out process tree.

Question 13

Does this code produce a tree or a chain?
pid_t childpid = 0;
for (i=1;i

Answer 13

Tree.

Question 14

Does this code produce a tree or a chain?
pid_t childpid = 0;
for (i=1;i 0)
break;

Answer 14

Chain of child processes.

Question 15

How many times does a fork() command return and what does it return?

Answer 15

A fork system call returns twice: 1) returns a zero to the child. 2) returns the child process ID (PID) to the parent)

Question 16

What gets copied when you use a fork() command?

Answer 16

The file descriptor table. Thus, the parent and child point to eh same entry in the system file table.

Question 17

What does the term Exec refer to?

Answer 17

A family of functions where each of the functions replace a process’s program (the one calling one of the exec functions) with a new loaded program.

Question 18

A call to a function from exec loads what type of file into memory?

Answer 18

A binary file.

Question 19

What happens to the original the original memory image of the programming calling the exec function?

Answer 19

It destroys the memory image image of the program calling it.

Question 20

Referring to the exec function family: Functions with “p” in their name do what? ex. execvp, execlp

Answer 20

Search for the program in the path indicated by the PATH environment variable; functions without p must be given full path

Question 21

Referring to the exec function family: Functions with “v” in their name do what? ex. exec, execvp, execve

Answer 21

They differ from functions with l (execl, execlp, execle) in the way arguments are passed.

Question 22

Referring to the exec function family: Functions with “e” in their name do what?

Answer 22

Functions with “e” accept array of environment variables.

Question 23

True or false: The child return to the old program if exec succeeds.

Answer 23

False! Child will not retune to the old program unless exec fails. This is an important point to remember.

Question 24

True or false: File descriptors are not preserved when a child calls an exec onto itself.

Answer 24

False, file descriptors ARE preserved.