Week 2

Question 1

3 Main OS Tasks

Answer 1

1. Virtualize Resources
2. Managing I/O
3. Making the above easy

Question 2

What does mediate mean

Answer 2

processes cannot interfere with each other

Question 3

What an OS Looks like

Answer 3

Programs/process <-> OS <-> CPU/RAM/Device Drivers

Question 4

What is batch mode?

Answer 4

submit a large computaion, wait for result, then submit another one

Question 5

What did even early machines have?

Answer 5

Libraries of functions (common I/O functions)

Question 6

In the 1960 breakthrough, what was implemented

Answer 6

Separation, given the OPTION to use programs

Question 7

3 ways to implement separation for CPU Virtualization

Answer 7

1. Give CPU 2 execution modes
2. Define a trap –> an instruction to switch into OS code and back
3. Ring of fire –> More flexibility

Question 8

What are the different Ring of Fire levels

Answer 8

Level 0: OS/ Kernel
Level 3: Processes/apps

Question 9

What enabled Multiprogramming?

Answer 9

Memory protection: allowing programs to share a memory / see their own area for memory through VIRTUAL MEMORY

Question 10

What is CPU Virtualization

Answer 10

The art of “slicing” a CPU. An OS should be able to:
1. run and stop a program
2. decide which program should run
3. divide CPU time fairly

Question 11

What is Memory Virtualization

Answer 11

Gives every process the same VIRTUAL ADDRESS SPACE
Each process gets the illusion of having the memory to itself.
Virtual address is mapped to the physical space.
Mapping can change and isn’t always 1:

Question 12

Difference between Concurrency and CPU Virtualization

Answer 12

CPU Virtualization gives the “illusion” of concurrency by taking turns.

Concurrency: Different parts of A SINGLE program cooperate to complete a task.

Question 13

What 2 requirements for Concurrency?

Answer 13

1. Different parts of the program are able to communicate
2. Ability to synchronize access to shared data

Question 14

Virtual Memory vs Shared Disk?

Answer 14

Virtual Memory: works because processes mostly need their own memory space and only sometimes need to share MEMORY data

Shared Disk: Works because it is very common for programs to use / share DISK data

Question 15

What is a command line?

Answer 15

Provided by a utility called a shell, it runs the terminal

Question 16

What is a shell?

Answer 16

A program that presents a prompt and waits for text commands

Question 17

What are commands?

Answer 17

Names of executable programs that you want to run.

Question 18

Detailed Steps of how a shell command works.

Answer 18

1. files are compiled programs called binaries
2. OS loads the binary into memory and executes it
3. OS stores metadata about each process (process ID / PID)

Question 19

What are binaries

Answer 19

compiled programs

Question 20

What is a process?

Answer 20

An executing program/binary. A program that is being executed.

Question 21

What are shell environment variables

Answer 21

Stores configuration information and values for the shell. Which modifies the behavior of the shell.

Question 22

How are shell metadata stored?

Answer 22

Stored as KEY-VALUE pairs. Each pair represents a variable and a value.

Ex: “VAR1_NAME = VAR1_VALUE”

Question 23

Who can modify/read variables?

Answer 23

Shell, programs, and the user

Question 24

what is PATH

Answer 24

Tells the shell which folder it should look for in programs.

Question 25

What is a Working directory?

Answer 25

The place (by default) where programs and data will be looked for. Actions on the command depend on the context of where they are run.

Question 26

Can you run a command in any directory?

Answer 26

Yes, by specifying the FULL / absolute path.

Question 27

Pipe Operand

Answer 27

the " cmd1| cmd2" symbol. Executes the code of cmd1 and takes that output into cmd2

Question 28

command line that prints a string to terminal

Answer 28

$echo

Question 29

when shell encounters these it replaces it with the variable of the value that follows

Answer 29

$

Question 30

looks for a program called mycmd in the CURRENT directory and run it

Answer 30

$./mycmd

Question 31

command line utility that prints current working directory

Answer 31

$pwd

Question 32

command line utility to change the working directory

Answer 32

$cd

Question 33

command line utility to go up the parent directory

Answer 33

$cd ../

Question 34

print the content of into the ternimal

Answer 34

$cat

Question 35

command line utility used for string replacement in the files (used alongside regex)

Answer 35

$sed

Question 36

What file-like objects open whenever a program starts?

Answer 36

1. standard output 2. standard input 3. standard error

Question 37

How to access standard input? (code)

Answer 37

Through the “read” function. bytesread = read(0, input, sizeof(input)) if (bytesread < 1) return -1;

Question 38

How to access standard output? (code)

Answer 38

Through the “write” function. write(1, input, strlen(input) - 1) // output the stuff received by the input

Question 39

command to search for a string in each line of input

Answer 39

$grep

Question 40

command to count the number of characters/words/lines in the input

Answer 40

$wc

Question 41

command to save standard OUTPUT to a new file, filename

Answer 41

command > filename

Question 42

command to save standard ERROR to a new file, filename

Answer 42

command 2> filename

Question 43

command to APPEND to an EXISTING file.

Answer 43

command >> filename

Question 44

command to redirect the standard error to the standard output

Answer 44

2>&1

Question 45

command to redirect the standard output to standard error

Answer 45

1>&2

Question 46

What are Manual (man) pages

Answer 46

- Describes different command line utilities and their options - Standard C/C++ functions - Can be accessed with $man

Question 47

What does grep do?

Answer 47

parses a file / standard input and return ALL LINES THAT MATCH (or do not match) a string.

Question 48

A few grep parameters

Answer 48

-i: case insensitive -v: return lines that do NOT match -c: print number of matching lines per file -l: print names of files with matches

Question 49

What is a regular expression?

Answer 49

a pattern that describes a set of strings and uses special characters to describe sets of characters in a string.

Question 50

a regex to match any character ex: matches "a1b", "aAb", "a-b", etc.

Answer 50

. ex: a.b

Question 51

A regex to match a sequence of any length of the preceding character ex: matches "", "a", "aa", "aaa", etc

Answer 51

* ex: a*

Question 52

A regex to match one or more of the preceding characters ex: matches "a", "aa", "aaa", but not ""

Answer 52

+ ex: a+

Question 53

A regex to match zero or one occurence of the preceding character ex: "", "a"

Answer 53

? ex: a?

Question 54

a regex that matches any single character from a set of characters ex:matches "a", "b", or "c"

Answer 54

[] ex: [abc]

Question 55

a regex to match any character within a range ex: matches any lowercase letter from "a" to "z"

Answer 55

[a-b] ex: [a-z]

Question 56

a regex that matches either one pattern or the other ex: matches "cat" or "dog"

Answer 56

( | ) ex: (cat|dog)

Question 57

file system operation to create an empty file

Answer 57

touch

Question 58

file system operation to display size of files

Answer 58

du

Question 59

text processing command to extract fields from content

Answer 59

cut

Question 60

text processing command to invert text

Answer 60

rev

Question 61

text processing command to parce/process text

Answer 61

awk

Question 62

text processing command to sort all input lines numerically/alphabetically

Answer 62

sort

Question 63

text processing command to remove all dupe lines

Answer 63

uniq

Question 64

What 2 types of programs can shell run and how?

Answer 64

Executable Files Interpreted Scripts All ran with $./program_name

Question 65

What are Interpreted Scripts?

Answer 65

A bunch of text which gets passed as an input to an interpreter.

Question 66

What are the UNIX Permissions and to what entities?

Answer 66

Each file has 3 permissions: read, write, execute Each permission can be specified for 3 entities: user, group, all users

Question 67

Does each script must be given permission to execute?

Answer 67

Yes. Use chmod $ chmod a+x [.sh file]

Question 68

What do the back-ticks in shell programming mean? ` `

Answer 68

"replace the string with the output of the expression"

Question 69

How to do expressions in shell programming?

Answer 69

expr keyword VAR = `expr $VAR + 1`

Question 70

Basic structure of conditional blocks for shell programming?

Answer 70

if [ ] then fi --> specifies the end of a conditional block

Question 71

Basic structure for loops in shell programming?

Answer 71

while [ ] do loops done to specify the end of a loop block.