UNIX

Question 1

UNIX

Answer 1

• Multi-user, multi-tasking operating system

- architecture-independent operating system (can work on most things)

Question 2

History

Answer 2

A&T labs
-Thomson and Ritchie 1970
-academic research operation system
-first “portable” (take from one system to another)
Berkeley standard distribution 
-cheap, first standard network support
-Linux, CentOS7
Android
-intro in 2008
-uses Linux/ UNIX

Question 3

Pros and cons of UNIX when made

Answer 3

Pros: flexible, extensive (add new pieces), file sharing
Cons: security, robustness, performance

Question 4

Why use UNIX

Answer 4

Multiuser

• remote processing (use in background)
• stable (safe)
• highly modular (how we group functionality together and how we use it)
• some free (open source)
• large user community
• “tools are mature” (have become efficient, usable)

Question 5

Kernel

Answer 5

• the brain of the system, communication with devices
• is protected core of the OS
• large and complex
• memory allocation, file system

Question 6

Shell

Answer 6

• responsible for communication between user and hardware
• job control (scheduling tasks)
• many shells (sh, bash, ksh)
• interprets your typed commands in order of what you want

Question 7

File system

Answer 7

• organization of files
• mapping blocks of data from physical storage onto logical blocks users can manipulate
• arranged in tree like structures

Question 8

File

Answer 8

An abstraction that allows us to understand it but to the computer it’s just data or memory

Question 9

Directories

Answer 9

• just reference where a file is
• special kind of file and format
• working directory is where we are currently relative pathnames are worked in relation to working directory

Question 10

File attributes

Answer 10

• every file/directory has attributes

- such as username, file size, file type, permissions

Question 11

Input/ output streams

Answer 11

• has three streams
• standard input/ stdin: defaults to the console keyboard
• standard output/ stdout: defaults to the console screen
• standard error/stderr: defaults to the console screen
• shell provides a mechanism for overriding this default behaviour (stream redirection)

Question 12

Stream redirection

Answer 12

Mechanism for overriding default streams

-take input from file cmd output to a file

Question 13

Pipes

Answer 13

• are considered by many to be on of innovations
• route standard output from cmd into input of another cmd
• symbol: |
• able to combine efficiently
• “generator” starts at the head
• eliminates intermediate files
• all cmds run at same time but one error all fails

Question 14

Command sequencing

Answer 14

• multiple commands can be executed sequentially
• ex) date;who;pwd
• you can group commands together and redirect the output

Question 15

Quoting

Answer 15

Strong: all chars inside single pair of quotes are preserved
Weak: some char($,’) inside (“”) are interpreted by the shell
Back: substitute result of evaluation as a command

Question 16

Shell vars

Answer 16

• built in dictionary of variables
• some built in some user-defined
• can add new vars or discard
• no spaces when assigning vars

Question 17

Path

Answer 17

• helps the shell find the cmds you want to execute

- its value is a list of directories separates by :

Question 18

Enviro variables

Answer 18

• subshell: when executing cmd, launches another shell
• inherits from parent
• change vars for short term or long term

Question 19

Shell script

Answer 19

• take all cmds and run as single program
• not always sensible
• wrap a repeated task into a cmd

Question 20

Selection

Answer 20

• test involve file operations

- bash tends to think of everything as a string