Review Questions

Question 1

Gary Kildall contributions?

Answer 1

Wrote an operating system for the 8080 processor, which was called Control Program for Microcomputer (CP/M)

Question 2

8. What is the difference between copyright and copyleft?

Answer 2

Copyleft = open-source.

Question 3

9. When was the first Unix operating system developed?

Answer 3

Unix was developed in 1969 on a PDP-7 with 8K of RAM

Question 4

10. When was the first Linux operating system developed?

Answer 4

From 1991-present, Linux (Unix based operating system) is
becoming a popular alternative to Windows for many students and
companies

Question 5

11. From where did the word “Unix” come from?

12. From where did the word “Linux” come from?

Answer 5

After Bell Labs dropped out of the MULTICS project, one of its researchers, Ken Thompson (February 4, 1943), was looking around for something to do
􏰁 He decided to implement a small version of MULTICS
(using assembly language) on a discarded PDP-7 minicomputer with 8K RAM
􏰂 Succeeded to do so in 1969 (at age 26)
􏰁 His friend, Brian Kernighan (January 1, 1942) (a Canadian CS), jokingly called this new product UNICS (UNiplexed Information and Computing Service)
Later on, the spelling was changed from UNICS to UNIX

12. based on the name of Linus Torvalds, who created it, and to sound like Unix, since it is a flavor of Unix

Question 6

13. Who developed the first Unix operating system?

Answer 6

Ken Thompson and Dennis Ritchie

Question 7

14. Who developed the first Linux operating system?

Answer 7

Linus Torvalds

Question 8

15. Who were the first to develop the first C compiler?

Answer 8

Dennis Ritchie

Question 9

16. Who were the first to re-write the Unix operating system in C?

Answer 9

Ken Thompson and Dennis Ritchie

Question 10

20. The command rmdir c.progs failed. State three possible reasons for this failure.

Answer 10

1) has files in it

2) it is inside a directory that does not have write permissions enabled

Question 11

23. Which Unix command would you use to delete a directory called dir1 which contains some files and directories in it?

Answer 11

rm -r dir

Question 12

27. List 5 different ways to change the current working directory to your home directory.

Answer 12

1) cd
2) cd absolute path
3) cd ~
4) cd $HOME
5) if you are in a folder that is in your home directory cd ..

Question 13

28. How many characters can a Unix filename be?

Answer 13

255 characters (255 bytes)

Question 14

29. Which character(s) can’t be used in a Unix filename?

Answer 14

forward slash.

Question 15

􏰁 Many commands use “ ” to say there are no more options

Answer 15

–

Ex: obelix[5] > rm – -i

Question 16

32. Explain what the following commands do: (i) rm * (ii) rm -i * (iii) rm -r * (iv) rm rm

Answer 16

1) removes any file in the current directory (star wildcard = any repetitions of a character = any file name
2) -i = interactive promo. Star wildcard = all files
3) rm -r * delete all directories in current directory and their contents
4) deletes a file called rm if it exists

Question 17

34. What is the difference between ls and ls * Unix commands?

Answer 17

Nothing. The list commands list whatever argument you give it:
ls adf
\: adf
ls *
adf adf adf

Question 18

36. How do you remove the hidden files in your current working directory?

Answer 18

rm -rf .*

Question 19

39. Explain what the commands ls .* and ls *. display. Does it make any difference if the -d option is added?

Answer 19

ls -d .*

Question 20

echo “The date and time are date “
echo “The date and time are date “
echo “The date and time are ‘date’ “
echo “The date and time are “date” “

Answer 20

The date and time are data
The date and time are Fri Oct 15.. etc..
The data and time are ‘date’
The date and time are date

Question 21

echo /*

echo*

Answer 21

root directory and all its folders / contents

Question 22

61. When you invoke ls -l foo, the access time of foo changes. True or false? Explain your answer.

Answer 22

No

Question 23

77. Create a file in your home directory and change its permission to 444. Copy this file to another file. Compare the permissions of the two files. Are they the same or not? Explain.

Answer 23

444 = r–r–r–
After copying, ls -l copied file reveals:
only “r– — —”

Thus, strips all permissions from G and O?

Question 24

3. What happens when you execute cat > foo if foo contains data?

Answer 24

error because you can’t direct an output into a file that has content, you can only APPEND output into a file that already has content.

Question 25

20. How do you find out (i) the number of users logged in (ii) the number of directories in your home directory tree?

Answer 25

ls -d \/* | wc -w

Question 26

33. How do you move a Unix job from the foreground to the background?

Answer 26

Suspend job, then resume it in the background using the bg command

Question 27

What is the difference between environment variables and local variables?

Answer 27

• affects current shell & programs invoked from the shell
• affects current shell but not programs invoked from the shell