Introduction to Linux: From Unix to Linux and Beyond

1. Department of Engineering ScienceEE 465 (CES 440) - Intro. to Networking & Network Management An Intro to Linux

2. It All Started With UNIX • Linux is an Operating System (OS) based on Unix. • Linux commands come mainly from Unix. • Unix was developed in 1970 by AT&T Bell Labs. • A multi-tasking & multi-user OS • AT&T licensed it to outside & the code of Unix was given to universities including UC Berkeley • UC Berkeley enhanced the existing version called it BSD (Berkeley Software Distribution) Unix. • SVR4 (System V Release 4) combines all Berkeley enhancements & original features. • Unix was essentially for workstations, big computers, & servers, • e.g., Sun Microsystems Workstations Sun Microsystems, founded in 1982, created Java programming language, Solaris OS; was acquired by Oracle Corporation in 2010https://en.wikipedia.org/wiki/Sun_Microsystems

3. Then Came Linux • Created in 1991 by Linus Torvalds, a software developer who became the chief architect of the Linux kernel. • Released in 1994 as Version 1. • Was initially developed for 80 & x86 processors (8080, 8086, .. i386) architecture processors*. • Later for small computers & PC-based operating system. • Today it supports various processor & servers including • AMD, Motorola 6800, Power PC, etc. • Runs on embedded systems, firmware, switches, routers, mobile phones (Android), tablets, video game consoles. • Ubuntu OS is based on Linux OS, & Linux is part of Ubuntu. • Linux programming is free, easy, simple, secure, easy to install, & can be used on micro computers. 8080, 8086, and i386 are the Intel 8-, 16-, & 32-bit processors.

4. Linux, Layered Views http://www.tellmeaboutlinux.com/content/linux-architecture User User Application Programs Shell / Photo / WP / FTP / Telnet / Web Browser User request Application Programmer Interface (API)- C/C++/Java/Fortran Applications SHELL Operating System (Kernel) Lower Level Utilities Computer Hardware, I/O devices, Memory, CPU, Storage Devices LINUX KERNEL Utility software is a small program that configures, maintains & monitors a computer (e.g., print utility). Computer Hardware

5. Linux Kernel • Kernel contains the actual Operating System (OS). • Manages processes in terms of creating, suspending, terminating, & maintenance. • Schedules CPU • Provides inter-process communications & communicates with devices. • Has many different versions • Versions offer improvements in - Support of more hardware - Higher Stability - Support of billions of users & File System - Handle of external devices & plug-ins - Supports many new devices (Wireless, USB-based, different storage devices using IDE, SCSI, ..) - Support of Sound system - Support of higher security Using SELinux (Security Enhanced Linux) IDE = Interactive Development Environment SCSI = Small Computer System Interface

6. Linux Platform • Operating Systems are divided according to • How many users can use the system (logon) at the same time • The number of processors the system can run simultaneously • A process executing a program • Basic categories • Single User / Single Processor (Windows 3.1, DOS) • Single User / Multi Processor (Win NT Workstations, OS/2) • Multi User / Single Processor (Does it exist?) • Multi User / Multi Processor (Linux, Windows NT Server) • High resource utilization using multiplexing • Uses Time Sharing • High Throughput (Number of processes finished in a unit of time) • Uses multi-programming – If the current processes is accessing I/O, the CPU can be assigned to another task

7. Linux Platform • A Linux shell, also called the “Command Line“ • Provides the traditional user interface using terminal and keyboard for the Linux OS. • Contains standard commands for Unix. • Good learning tool to learn Unix! • Basic Shell applications are: • BASH (Bourne Again Shell) • BASH is similar to Bourne Shell in Unix. • Most commonly used • C Shell, tcsh (TENEX C Shell), scsh (Scheme Shell) • http://www.freebsdsoftware.org/shells/ has list of various shells & their differences. • Commands are the instructions for the computer to do certain things.

8. Linux Text Editors • A text editor is a type of program used for editing plain text files. • A Linux program is made of many commands & lines of code. • Text editors are provided with operating systems & software development packages, & can be used to change: • configuration files, documentation files & programming languagesource code • Text editor allows to find, replace, cut & copy, filter, & format text in a program. • There are many text editors that were & are used for Linux. • Wikipedia provides a good comparison • Text editor comes in form of Terminal Command Line Interface (CLI) or Graphic User Interface (GUI). • “vim”, an improved version of “vi” CLI. developed by Bill Joy in C programing language for Unix OS, & Linux. It uses only keyboard. • “gedit”, CLI & GUI, like Windows Notepad uses mouse & keyboard, friendly, text editor in Ubuntu, Mac OS X, & Windows.

9. Gedit Text Editor • Geditis similar to Windows Notepad & the default GUI text editor in the Ubuntu OS. • Can be invoked also in CLI. • Designed for • Simplicity • Editing source code & structured text such as markup languages • Multi-language spell checking • Extensive support of syntax highlighting, & • A large # of official & 3rd party plugins • Freely available for Linux, Mac & Windows, by several developers. An Ubuntu screen shot of GEDIT page

10. Shell Prompt • Most development work is done at the shell prompt which is the Command-Line Interface, e.g., $. • Remember root is “/” • ls – list files • ls /Documents - lists the files in Folder Documents • cd – change directory • cd /home - go to folder home • mkdir – create a directory • Mkdir homework to make a folder homework • Exercise: How can you go to CLI in: • Windows • Mac

11. Shell Prompt • rmdir – remove a directory • rmdir /Documents (Documents is different than documents) • mv – move or rename a file • mv homework1 assignment1 • cp – copy a file • cphomework1 assignment1 • locate – find a file • locate homework1 • gedit <filename> - start editing a file • gedithomework1 • vim <filename> - start editing a file • vi homework1

12. Linux Directory Hierarchy

13. Linux Directory Hierarchy

14. More Basic Commands Format: Command -optionargument • pwd (print working directory) • cd /bin • ls (List info about file(s)) • ls –l (List detail info about file) • ls –a (show hidden files) • mkdirmyoffice • mkdir /root/mydocuments • rmdir office • wc(print word count) • date • man wc (get more information on wc command) • whatis man • whereistcsh(lists the path) • whoami • hostname • uname(displays system info) • E.g., uname–m (machine) • who (info about current user) • echo (display message on screen) • cat /etc/passwd • more /etc/passwd • man vi |more • cp /etc/passwdmypasswd • mv mypasswdyourpasswd • mv –i sample Make sure you can do these!

15. Finding/Displaying Files, Patterns • grep searches file(s) for words/lines that match a given pattern grep word? filename(? For any word1, word2, word. ) • grep command can display the IP address & machine name • find searches for files that meet a desired criteria find xyz? (? For any xyz1, xyz2, xyz. ) • cat concatenates file & prints on the standard output cat xyz • echo displays message on screen echo hello

16. Exercise • Open shell terminal on Ubuntu • Type the following, observe, & briefly explain what each does: • wc • date • man wc(get more info on wc command) • whatis man • whereiscsh(lists the path) • whoami • hostname • uname(linux) • who (information about current user) Command + Options + Arguments

17. File System Permissions in Linux

18. Linux Permissions • Permissions are set for user, group, & others • Each permission is set with a single decimal digit from 0 to 7 (binary 000 to 111) on the combination of permissions • Examples for user, group, or others: read + write + execute = rwx = 4 + 2 + 1 = 7 - + write + execute = -wx = 0 + 2 + 1 = 3 read + - + execute = r-x = 4 + 0 + 1 = 5 read + write + - = rw- = 4 + 2 + 0 = 6

19. Using chmod to Set Permissions

20. Linux Script Example 1 Scriptis a collection of commands typed in text, stored in a file, read by processor & executed for result. One can use a text editor (e.g., vi or gedit) to make the file. Note: “$” is the Shell prompt & “#” indicates comments. Both need a space. Example 1: Write a Linux script to print sum of two numbers, let's say 6 & 3. $ echo 6 + 3This will print 6 + 3, not the sum 9. To do sum or math operations in shell use expr, syntax is as follows: Syntax: expr   op1   operator   op2 Where, op1 & op2 are any Integer Number (Number without decimal point) & operator can be + Addition- Subtraction/ Division, to find quotient, 20 / 3 = 6 % Modular, to find remainder, 20 % 3 = 2 (Remember its integer calculation)\* Multiplication $ expr 6 + 3 # expr Evaluate expressions Now It will print sum as 9, But$ expr 6+3will not work because space is required between number & operator (See Shell Arithmetic).

21. Linux Script Example 2 & 3 Notes: • $ with a space char after is the Linux prompt here • $ with NO space after defines a Linux variable Example 2: Define two variables x=20, y=5andthen print division of xandy (i.e. x/y).$ x=20$ y=5$ expr $x / $y Example 3: Modify aboveandstore division of xandy to variable called z.$ x=20$ y=5$ z=`expr $x / $y`$ echo $z To execute a program in Linux, type: ./filename, e.g., ./program1 ` (back quote) executes the command

22. / junks primary secondary my_junk_file my_primary_file my_secondary.log Practice • Read about chmod and LINUX permissions (check the hyperlink) • For simple examples of scripts go to http://www.freeos.com/guides/lsst/misc.htm#commonvi • Create the following directories & files (/ is the root directory):

23. References • Slides “Iinux”, Dr. Farid Farahmand, Fall 2014 • https://www.youtube.com/watch?v=IVquJh3DXUA&t=83s • http://en.wikipedia.org/wiki/Linux • http://en.wikipedia.org/wiki/GNU • https://en.wikipedia.org/wiki/Comparison_of_text_editors • https://en.wikipedia.org/wiki/Gedit • http://distrowatch.com/ • http://lifehacker.com/5774997/getting-started-with-linux-how-to-install-linux-on-your-computer • http://www.flexbeta.net/main/printarticle.php?id=70 • http://www.freeos.com/guides/lsst/ch01sec04.html • http://www.freeos.com/guides/lsst/misc.htm#commonvi • http://www.freebsdsoftware.org/shells/

24. Linux Distribution (Linux Distros) • Each distribution is a package including the OS & different applications. • Different distributions provide different applications & require different installations steps. • The package includes: • Core Linux OS (also called Kernel) • X Window System & GUI interfaces • Graphical desktop (e.g., GNOME or KDE) • Different applications • Word Processor, Spreadsheet, etc. • Documentations • Each distribution is under General Public License (GNU) http://en.wikipedia.org/wiki/GNU • Anyone can copy & distribute the software in open source form to others (e.g., Ubuntu “www.ubuntu.com” is an Open Source). • Obtaining a distribution can be through ready made packages on the net or buying the CD or just compiling a version. * https://www.tecmint.com/top-best-linux-distributions-2016/

25. Linux Distribution - GNU • GNU is a free Operating System consisting of a kernel, libraries, system utilities, compilers, & end-user applications. • "GNU's Not Unix", which was chosen because its design is Unix-like, but differs from Unix by being free software & by not containing any exact UNIX code.

26. Basic Security In Linux • Without SELinux (Security Enhanced Linux) • Domains are divided into Users & Group IDs. • The ROOT has absolute control – need to logon as “root”. • With SELinux • Domains are divided into Subjects & Objects. • Even with Super-user privilege access to some files & devices maybe denied.

27. Linux Desktop • Using the terminal commands is boring! • XWindow System or X • Is an open, cross-platform, client/server system. • Provides windowing system for graphic work stations. • Based on a client/server model. • Server handles input & output devices. • Generates graphical displays used by the client. • Was developed at MIT & some computer companies (X.org). • Uses mouse & keyboard. • How the actual interface looks or feels depends on the GUI interface.

28. Ubuntu on Windows, Multi-OS Environment • Three ways to install Ubuntu/Linux OS on your PC or laptop with Windows 7 (or above) or Mac OS. See http://lifehacker.com/5774997/getting-started-with-linux-how-to-install-linux-on-your-computer • Install Linux OS on a flash memory, then select Windows or Ubuntu/Linux as you boot your computer, OR • Install two different OSes in two different partitions, in which case there is no access to each other, OR • Use an emulator, e.g., VMware that can install & run a copy of a second OS (Ubuntu/Linux) on the Hard Drive. VMWare VPC/ WINE Host OS Guest OS PCs in Salazar 2006 Windows Linux

29. Shell Types The Linux Shell has evolved in several types, some are used, & some are not. Used: • bash — Bourne Again SHell, default shell in most Linux distributions, decent features, most common, freeware Shell • zsh — most feature rich, based on Bourne-style, still rarely used due to its complexity; developed by Paul Falstad in 1990 • ksh — default shell in Solaris, AIX & other few other unices; (Korn Shell by David Korn, AT&T) • tcsh — TENEX C shell, used by those who know C programing language Basically most Shell types work the same with similar base commands. Not Used (Historic): • sh — original Bourne shell (released 1977), developed by Steven Bourne, AT&T. Obsoleted by bash • csh — original C shell (released 1978), developed by Bill Joy, UCB. Obsoleted by tcsh & ksh • ash – a Bourne shell clone, light-weight (used in Android phone) by Kenneth Almquist • dash - a clone of ash developed by Debian • Can install & remove different shells using “Software Center” on Ubuntu.

30. Practice (cont) • Write a shell script (called myshell) to perform the following: • Remove all the new directories: junks, primary, secondary. • Backup HOSTS file by creating HOSTS_BACK • Display the IP address of your machine • Change the permission on YOUR_IP_ADDRESS such that can only be viewed by the user & make sure it is readable only. Note: you should be able to run the script multiple times with no errors! To make sure, run your program multiple times.