Operating Systems

1. UMBCCMSC 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

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 • 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

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: torv...@klaava.Helsinki.FI (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: <1991Aug25.205708.9541@klaava.Helsinki.FI> 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 (torv...@kruuna.helsinki.fi) 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 • 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 • 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 sshuserid@linux.gl.umbc.edu

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 directoryis 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, • make a subdirectory for CMSC104 • make subdirectories for each project CMSC104 project1 project2 . . . 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 Commands • cd • 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 • Absolute or Relative paths

41. File Viewing Commands • cat • 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 Commands • cp • Copy (cp <source> <destination>) • Works with absolute and relative paths • mv • Move (mv <source> <destination>) • Works with absolute and relative paths • Also useful for renaming • rm • Remove (aka delete) • Works with absolute and relative paths • 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