Study Quesitions #1 - Topic 1-5, Qn#1-50

Question 2

What are the two main kernel categories?

Answer 2

Monolithic Kernels and Microkernels

Question 3

Explain the main differences between the two main kernel categories.

Answer 3

Monolithic Kernels  One very large program Performs every thing by itself Fast and efficient Difficult to design and maintainMicrokernels A much smaller program Performs the most basic tasks only To perform the rest of the functions, a microkernel calls upon a set of other programs (called servers) NB: servers are programs, not machines Slower and less efficient A lot easier to design and maintain

Question 4

What is the difference between copyright and copyleft?

Answer 4

copyright law is used by the author to prohibit reproducing, adapting, or distributing copies of the work by a third party.copyleft law is the right given to third parties to reproduce, adapt, or distribute copies and any resulting copies or adaptations are bound by the same agreement.

Question 5

When was the first Unix operating system developed?

Answer 5

In 1969

Question 6

When was the first Linux operating system developed?

Answer 6

In 1991

Question 7

Where did the word “Unix” come from?

Answer 7

UNiplexed Information and Computing Service (UNICS)later changed to UNIX

Question 8

Where did the word “Linux” come from?

Answer 8

Linux originates from the name Linus

Question 9

Who developed the first Unix operating system?

Answer 9

Ken Thomson

Question 10

Who developed the first Linux operating system?

Answer 10

Linus Torvalds

Question 11

Who were the first to develop the first C compiler?

Answer 11

Dennis Ritchie

Question 12

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

Answer 12

Ken Thomson and Dennis Ritchie

Question 13

What will cat foo foo foo display?

Answer 13

cat utility reads files sequentially, so it will display: foo foo foo

Question 14

Assuming that bar is a directory, explain what the command rm -r bar does. How is the command different from rmdir bar?

Answer 14

rm -r bar removes contents before removing the directory.rmdir removes an empty directory

Question 15

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

Answer 15

c.progs is not emptyc.progs does not existc.progs is in the wrong pathway

Question 16

The command rmdir bar fails with a message saying that the directory is not empty. On running ls bar, no files are displayed. Why did the rmdir command fail?

Answer 16

Hidden files are present

Question 17

Explain the difference between the commands cd ~smart and cd ~/smart.

Answer 17

cd ~smart changes directory to smart directorycd ~/smart changes directory to smart directory from home directory

Question 18

Explain the difference between cd $HOME and pushd $HOME.

Answer 18

cd $HOME changes current directory to $HOMEpushd $HOME saves $HOME directory so it can be returned to any time.

Question 19

Explain what the following commands do: (i) cd (ii) cd $HOME (iii) cd ~ (iv) cd cd

Answer 19

(i) changes directory(ii) changes directory to home directory(iii) changes directory to home directory(iv) changes directory to cd, if it does not exist, nothing will happen

Question 20

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

Answer 20

cd $HOMEcd ~cd

Question 21

How many characters can a Unix filename be?

Answer 21

255

Question 22

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

Answer 22

/

Question 23

Why are we discouraged from having a filename beginning with a hyphen?

Answer 23

maybe confused with other commands

Question 24

Can the files note and Note coexist in the same directory? Why?

Answer 24

yes they can because Unix is case-sensitive

Question 25

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

Answer 25

(i) it will attempt remove all non-hidden files(ii) it will attempt to remove non-hidden files but will ask for verification(iii) it will attempt to remove file or directory and its contents, (iv) will remove file named rm, if it does not exist, nothing will happen

Question 26

How does the Unix shell treat the * when used as an argument to a command like echo *?

Answer 26

it will treat it as an indicator for all files and directories in the directory. echo* lists all files and directories in current directory

Question 27

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

Answer 27

ls will list all files in a directoryls * will list all files in a directory and it’s contents

Question 28

Does ls . match filenames that begin with a dot?

Answer 28

no, it matches filenames that contain a dot.

Question 29

How do you remove only the hidden files in your current working directory? Does rm * remove these files as well?

Answer 29

use the command rm .* (remove files with fullstop in front of their names aka hidden files)rm* will not remove these files

Question 30

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

Answer 30

ls .* displays all hidden files (files beginning with fullstops) and all non-hidden filesls * will display all files with a full stop at the end of the filenamels -d .* shows information about a symbolic link or directory of hidden filesls -d *. does the same for files ending with “.”

Question 31

Explain when mv *.bat *.bit will work without producing any error

Answer 31

If “.bat” and “.bit” match exactly two file names, then the “mv” command will rename the first file to the second one (the second file will be overridden)

Question 32

What does the command ls -d [3-h]* mean?

Answer 32

list symbolic link or directory of file or directory beginning with a “3”, “h”, or any characters lexically in between in its filename

Question 33

When will the command cd * work?

Answer 33

When there is a directory named *

Question 34

. How do you remove all ordinary files in the current directory that(i) are hidden;(ii) begin and end with *;(iii) have numerals as the first three characters;(iv) have single-character extensions?

Answer 34

(i) all hidden items begin with a “.” to delete them, simply use rm .*(ii) /**/(iii) [0-9][0-9][0-9](iv) *.?

Question 35

Match the filenames chapa, chapb, chapc, chapx, chapy, and chapz with a wild-card expression

Answer 35

chap*[a-z]

Question 36

Devise wild-card patterns to match the following filenames: (i) fool, foo2 and foo5; (ii) quit.c, quit.o and quit.h;(iii) all filenames that begin with a dot and end with swp.

Answer 36

(i) foo?(ii) quit.a-z .*swp

Question 37

Explain what these wild-card patterns match: (i) [A-z]????* ; (ii) [0-9]

Answer 37

(i) first letter either “A” or “z” or anything lexically in between(ii) files that contain numerals between the first and last letter of the filename

Question 38

A directory bar contains a number of files including one named -foo. How do you remove this -foo file?

Answer 38

rm – -foo

Question 39

You have a file named * and a directory named My Documents in the current directory. How do you remove them with a single command using (i) escaping, (ii) quotation?

Answer 39

(i) rm * rm -r My\ Documents(ii) rm ‘*’ rm -r ‘My Documents’

Question 40

What will happen when you execute the following Unix commands: (i) mkdir file name, (ii) mkdir ‘file name’ , (iii) mkdir “file name”

Answer 40

(i) creates directories ‘file’ and ‘name’(ii) creates directory ‘file name’(iii) also creates a directory ‘file name’

Question 41

What will happen when you execute the following Unix commands: (i) mkdir filename?, (ii) mkdir ‘filename?’ , (iii) mkdir “filename?”

Answer 41

(i) unable to create ‘filename?’(ii) creates directory ‘filename?’(iii) also creates directory ‘filename?’

Question 42

What difference do you notice when executing the commands echo “$SHELL” and echo ‘$SHELL’?

Answer 42

echo “$SHELL” echoes the current shellecho ‘$SHELL’ echoes the actual string $SHELL

Question 43

How do you display the inode number of a file?

Answer 43

ls -i

Question 44

If ls -i shows two filenames with the same inode number, what does that indicate?

Answer 44

they all link to the same file despite having different names

Question 45

What is the difference between executing ln file1 file2 and ln –s file1 file2 Unix commands? How will each command affect the inode of file2?

Answer 45

creates a link for file1 in file2ls file1 file2 gives them the same inodels -s file1 file2 gives them a different inode number

Question 46

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

Answer 46

true if you checked it, modified it, then checked it again

Question 47

Show the octal representation of these permissions: (i) rwxr-xrw- (ii) rw-r—– (iii) –x-w-r–

Answer 47

basically to calculate: r = 4 w = 2 x = 13 = 2 + 1 therefore 3 = _wx5 = 4 + 1 therefore 5 = r_x6 = 4 + 2 therefore 6 = rw_7 = 4 + 2 + 1 therefore 7 = rwx(i) 756(ii) 640(iii) 124

Question 48

What will the permissions string look like for these octal values? (i) 567 (ii) 623 (iii) 421

Answer 48

(i) r_xrw_rwx(ii) rw__w__wx(iii)r___w___x

Question 49

Use the numeric permission method to change the permission of a file in the current working directory called abc to give the owner user read and write permissions, while giving group users and others read permission only.

Answer 49

chmod 644 abc

Question 50

Use the symbolic permission method to change the permission of a file in the current working directory called abc to give the owner user read and write permissions, while giving group users and others read permission only

Answer 50

u = userg = groupo = otherchmod u=rw,go=r file1

Question 51

Explain and give example showing the difference between numeric absolute, symbolic absolute, and symbolic relative permission methods.

Answer 51

numeric absolute chmod 644symbolic absolute chmod g=r (with equals sign)symbolic relative u+rx or u-rx (adding new permissions or subtracting new permissions)

Question 52

How can you combine absolute and relative permission methods together? Give an example.

Answer 52

absolute and relative permission methods can be appended with commaschmod u=rwx,g-w,o-rwx file1

Question 53

. How do you ensure that all ordinary files that you have created have rw-rw—- as the default permissions?

Answer 53

umask 660

Question 54

What do the r, w, and x letters mean in a regular file permission string?

Answer 54

read permissionswrite permissionsexecute permissions

Question 55

What do the r, w, and x letters mean in a file directory permission string?

Answer 55

listing contentscreating filesaccessing files in the directory

Question 56

How do you assign all permissions of a file to the owner and remove all permissions from others using (i) symbolic relative assignment (ii) symbolic absolute assignment (iii) numeric absolute?

Answer 56

(i) chmod u+rwx,go-rwx file1(ii) chmod u=rwx, go= file1(iii)chmod 700 file1

Question 57

Assuming that a file’s current permission is rw-r-xr–, specify the chmod argument(s) that you should use to change the file permission to (i) rwxrwxrwx (ii) r–r—– (iii) —r–r– (iv) ———, using both relative and absolute methods of assigning permissions.

Answer 57

(i) chmod 777 file1 (numerical absolute) chmod uog=rwx file1 (symbolic absolute) chmod u+x,g+w,o+wx file1 (symbolic relative)(ii) chmod 440 file1 chmod ug=r,o= file1 chmod u-w,g-x,o-r file1(iii) chmod 000 file1 chmod uog= file1 chmod u-rw,g-rx,o-r file1

Question 58

What do you do to ensure that no one is able to see the names of your files?

Answer 58

remove read permissions for groups and others

Question 59

The command cd bar failed where bar is a directory. How can that happen?

Answer 59

reading permissions removed for bar

Question 60

How do you split a long command sequence into multiple lines?

Answer 60

semicolon ;