Lecture 3: Process / Shell (Part 1) Part 2

Question 1

Every process has a __________

Answer 1

Process File Descriptor Table

Question 2

What does an entry inside a Process File Descriptor Table represent?

Answer 2

Something that can be read from or written to - such as:

• file
• screen
• pipe

Question 3

Where is the System File Descriptor Table maintained? (Who’s memory?)

Answer 3

The OS maintains this table in the OS’s memory.

Question 4

Describe the System File Descriptor Table. What do the entries represent?

Answer 4

• Each entry represents an open file in the system (ie. every open file has at least 1 entry in the table)
• One file can have many entries in the table associated with it (if opened by many processes)

Question 5

What does an entry in the System File Descriptor Table contain?

Answer 5

1) The file descriptor’s permissions
2) # of Links
3) The file offset which is moved by read or write

Question 6

When is an entry removed from the System File Descriptor Table?

Answer 6

When there are 0 links pointing to it.

Question 7

Wait command returns what?

Answer 7

• Returns PID of child process

- Returns -1 if no child process exists (already exited)

Question 8

What is the command you can use at the Shell CLI to obtain a list of processes and their info?

Answer 8

ps -el

Question 9

What does the exec function return?

Answer 9

-1 if it fails. Upon success, it never returns.

Question 10

What is the exec family of functions used for mainly?

Answer 10

A child process can use it to execute some other program other than the parent / overlays a new program on the existing process.