1. UMBC CMSC 104 – Section 01, Fall 2016
Operating Systems

2. Saw This On Reddit…

3. Notes & Announcements
Thursday will be a lab day. We will do part 1 of Project 1 together.
If you can’t make it, the project will be posted after class
Next Tuesday we will not have class.
…but it’s a great time to do part 2 of Project 1 if you haven’t finished it by then.
Next Monday I will be giving a talk at the Microsoft office in Elkridge (15 minutes from here) from 7-9 PM
Topic: Getting started with Universal Windows Platform development
Open to the public. Also, Pizza!
More info & registration: aka.ms/uwpdevtalk

4. Fractions in Alternate Number Systems
A7.BC16 10 x
161
160 7 11
16-1
.6875 12
16-2

5. Operating Systems Overview
Topics
What is an Operating System?
Types of Operating Systems
Interacting with an Operating System
Linux Overview
Frequently Used Linux Commands
Emacs

6. What is an Operating System (OS)?

7. What is an Operating System (OS)?
The base software that makes your computer work
Performs many operations, such as:
Allows you to communicate with the computer (tell it what to do)
Controls access (login) to the computer
Keeps track of all processes currently running
Has code to do common tasks like writing to disk, displaying a graphic, etc.
At this point, your main concern is how to communicate with the computer using the OS

8. Major Operating Systems
Microsoft Windows
UNIX Variants
Apple macOS / iOS
Built on Darwin, a UNIX variant
Linux
Chromium
Android

9. Lesser-known Operating Systems
DOS variants
MS DOS, PC DOS, FreeDOS
Still used often in Point of Sale systems
UNIX variants
BSD, AIX, IRIX
Mostly for servers
OS/2
ReactOS
Haiku
TempleOS

10. Interacting with an OS Two primary types of OS Interfaces
Typically the user is able to interact directly with the OS using I/O devices
Keyboard, Mouse, Touchscreen, Microphone, etc.
Two primary types of OS Interfaces
Command Line Interface (CLI)
Graphical User Interface (GUI)

11. The Command Line Interface
Text-only
Main method of interaction for first PCs
Still frequently used by power users
A fast, efficient way to perform certain tasks
Great for scripting and repeatable tasks
Create 10,000 empty files. 2 minutes via CLI, HOURS via GUI
A favorite for programmers, and our focus for this class
No need to complicate things…

12. The Graphical User Interface
Text + Graphics
Often uses a mouse or touchscreen
Point & Click or Tap & Swipe
More User-friendly
Easier for novice users
Provided by nearly all modern OSes, although it is often optional
Yes, you can still run Windows, macOS, and Linux without a GUI!

13. The Shell The Shell is the part of the OS that you interact with GUI
CLI
Windows
Explorer
DOS/PowerShell
macOS
Aqua
BASH, others
Linux
GNOME, others

14. Remote Connectivity
One advantage to CLI interfaces is they provide a very low bandwidth way to connect remotely
Works great even with a slow or high-latency connection
telnet is a very simple protocol that provides connectivity to the CLI of a remote machine
Instead of sending characters and control data to the local computer's screen, send it over a network connection
Very simple, but also very insecure -- anyone "listening" can see everything!
Secure Shell (SSH) is like telnet, but with encryption
Similar simplicity to telnet, much more secure
We will be using SSH for this class

15. Linux

16. A Brief History of Linux
Started in 1991 by Linus Torvalds while he was a student at University of Helsinki
Initially envisioned as a free replacement for MINIX
MINIX was a minimal UNIX-like OS for PCs targeted at students with freely available source code but expensive licensing terms
Originally not licensed for commercial distribution; later changed to GNU GPL license
Quickly embraced and extended by the community

17. The Origins of Linux
From: (Linus Benedict Torvalds)
Newsgroups: comp.os.minix
Subject: What would you like to see most in minix?
Summary: small poll for my new operating system
Keywords: 386, preferences
Message-ID:
Date: 25 Aug 91 20:57:08 GMT
Organization: University of Helsinki
Lines: 20
Hello everybody out there using minix -
I'm doing a (free) operating system (just a hobby, won't be big and
professional like gnu) for 386(486) AT clones. This has been brewing
since april, and is starting to get ready. I'd like any feedback on
things people like/dislike in minix, as my OS resembles it somewhat
(same physical layout of the file-system (due to practical reasons)
among other things).
I've currently ported bash(1.08) and gcc(1.40), and things seem to work.
This implies that I'll get something practical within a few months, and
I'd like to know what features most people would want. Any suggestions
are welcome, but I won't promise I'll implement them :-)
Linus
PS. Yes - it's free of any minix code, and it has a multi-threaded fs.
It is NOT protable (uses 386 task switching etc), and it probably never
will support anything other than AT-harddisks, as that's all I have :-(.

18. The UNIX Family Tree

19. Linux Today Powers billions of computers worldwide
Every Android & Chromium Device
The majority of modern internet servers
Many supercomputers and special purpose computers
Still directed by Linus Torvalds
Built by contributions from thousands of developers and corporations since 1991

20. Linux on Desktop Computers
As of June 2016…

21. Linux on Mobile Devices
As of August 2016…

22. Linux on Web Servers
As of June 2016…

23. Why Linux? Community Availability Price “Freedom”
Linux has a huge academic and business community built around it
Availability
Linux (and it’s associated source code) is available for nearly every conceivable platform
Price
Because the GNU GPL license specifies that source code must be provided with every distributed copy, Linux is freely available
“Freedom”
Anyone can do anything they want with Linux; you’re free to customize it however you want, as long as you make the source code freely available.

24. Linux Distributions

25. Linux Distributions

26. Logging into Linux On a UMBC Lab PC From Home
Launch VMWare Workstation
Choose Linux VM & power it on
Wait for it to boot
Log in at the prompt
Launch Terminal
From Home
Windows: PuTTY, Bash on Ubuntu on Windows
PuTTY also available on UMBC Lab PCs
macOS: Terminal
See slides from first class

27. Accessing UMBC GL Machines
UMBC provides internet-connected Linux machines for development and general use
Connect via SSH
Note to Windows users: PuTTY is an SSH client
All projects will be tested and graded here
The version of Linux installed in lab machines is NOT guaranteed to be the same as GL
To connect to GL:
Open a Terminal window
Connect via SSH using the following command
ssh

28. Accessing GL Machines (con’t)
When you connect the first time via SSH, you may see a prompt asking you to accept a certificate. Type yes.
A warning screen appears before a password prompt.
When you type your password at the prompt, you will not see any characters or cursor movement. This is for your protection.
After a successful login, you will see your last login date and time (if applicable) and the “Message of the Day” (aka motd).
UMBC’s motd hasn’t changed in years…

29. The Linux Command Prompt
When you log in to the Linux system here, a user prompt will be displayed. It might look like this:
linux#[1]% _
…where # is the number of the Linux server that you have connected to. You may use any of the Linux servers.
The number in the brackets will change as you work. It is the “number” of the command that you are about to type.
If this prompt is not on the screen at any time, you are not in the shell and are not communicating with the OS.

30. Files A file is a sequence of bytes. It can be created by
a text editor (emacs, nano, etc)
a computer program (such as a C program)
It may contain a program, data, a document, or other information .
Files that contain other files are called directories (sometimes called folders).

31. Linux Filenames Restrictions
May not contain certain reserved characters
Have a maximum length
Are case sensitive
Note: This is NOT the case with Windows!
It is best to stick with filenames that contain letters (uppercase or lowercase), numbers, and the underscore ( _ ) for now.

32. Directories
Directories contain files or other directories called subdirectories. They may also be empty.
Directories are organized in a hierarchical fashion.
They help us to keep our files organized.

33. Directories (con’t) /afs/umbc.edu/users/j/d/jdoe28 junk recipes notes
pies cookies CMSC104
apple peach choc_chip

34. Directories (con’t) Directory Structure of jdoe28 jdoe28 junk recipes
pies
apple
peach
cookies
choc_chip
notes
CMSC104

35. Directories (con’t)
Your home directory is where you are located when you log in (e.g., /afs/umbc.edu/users/j/d/jdoe28).
Tip: type cd at the shell prompt (with no arguments) to return to your home directory
The current directory is where you are located at any time while you are using the system.
Files within the same directory must be given unique names.
Remember that Linux filenames are case sensitive. Hello.txt and hello.txt are two different files!
Paths allow us to give the same name to different files located in different directories.
Each running program has a current directory and all filenames are implicitly assumed to start with the name of that directory unless they begin with a slash.

36. Subdirectories Are used for organizing your files For example, CMSC104
make a subdirectory for CMSC104
make subdirectories for each project
CMSC104
project project project8

37. Moving in the Directory Tree
. (dot) is the current directory.
. . (dot-dot) is the parent directory.
Use the Linux command cd to change directories.
Use dot-dot to move up the tree.
Use the directory name to move down.
Use the complete directory name (path name) to move anywhere.

38. Frequently Used Linux Commands
pwd, ls, cd – Directory Viewing
mkdir, rmdir – Directory Manipulation
cat, more – File Viewing
cp, mv, rm, touch – File Manipulation
clear, man, history , who
ctrl-c, ctrl-z
References:
Linux man page
Links from the 104 homepage
Books and the Internet

39. Directory Viewing Commandscd
Change Directory
Can change to absolute path (beginning with /) or relative path (beginning without /)
pwd
Print Working Directory
Displays full path of your current directory ls
List files in directory
Use ls –al to get more detailed view

40. Directory Manipulation Commands
mkdir
Make Directory
Absolute or Relative paths
rmdir
Remove Directory

41. File Viewing Commands cat more Short for concatenate
Dumps file contents to terminal
more
Displays file on terminal, one page at a time
Use Page Up and Page Down, arrow keys, etc. to scroll
Press q to quit

42. File Manipulation Commandscp
Copy (cp <source> <destination>)
Works with absolute and relative paths mv
Move (mv <source> <destination>)
Also useful for renaming rm
Remove (aka delete)
touch
Creates a blank file if one does not exist
Updates timestamp on existing file

43. Miscellaneous Commands
clear
Clears the terminal screen
man
Manual Page
Shows you instructions on how to use a command
e.g. man ls
history
Shows you commands you have previously run
Cycle through your previous commands using the up arrow
who
Displays users logged into system and what they are running

44. Wildcard Characters
You will find wildcard characters useful when manipulating files (e.g., listing or moving them).
The wildcard characters are * and ?
? is used to represent any single character.
* is used to represent 0 or more characters.

45. Text Editors in Linux
Because the command line is text based, there are a number of text editors available
Generic
nano
Special-purpose
emacs / xemacs
vi / vim

46. Using nano
The nano text editor works like you would expect any standard text editor to.
Arrow keys to move around, tabs with tabstops, etc.
Shortcut options (like save and exit) are available at the bottom of the screen. In this context, the ^ character represents the Ctrl button.

47. Using emacs
The emacs editor provides a lot more functionality, especially for programming
It’s also a lot more complicated…
Emacs also has a GUI frontend. If you’re in the lab and running Linux via VMWare, this should appear. Otherwise the text-only version will appear
Launching emacs with no parameters will display the help screen

48. Emacs

49. Emacs Shortcuts Emacs shortcuts typically begin with C- or M-
C- means Ctrl, then the specified key
M- means Meta (aka Escape), then the specified key
You can quit emacs at any time using C-x C-c
That’s Ctrl-x then Ctrl-c
If you’re working on an unsaved file, you will be prompted to save.
I’ve posted a list of common emacs shortcuts on the class webpage

50. What Editor Should I Use?
You can use whatever editor you want for this class.
If you plan on taking more CMSC courses, it may behoove you to learn emacs
A purpose-built editor like emacs makes adhering to the coding standards easier

51. Questions?