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An Intro to Linux

An Intro to Linux. References: Slides “ Iinux ”, Dr. Farid Farahmand, Fall 2014 http://en.wikipedia.org/wiki/Linux http ://en.wikipedia.org/wiki/Unix http://en.wikipedia.org/wiki/ GNU https://en.wikipedia.org/wiki/ Comparison_of_text_editors https://en.wikipedia.org/wiki/ Gedit

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An Intro to Linux

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  1. An Intro to Linux References: Slides “Iinux”, Dr. Farid Farahmand, Fall 2014 http://en.wikipedia.org/wiki/Linux http://en.wikipedia.org/wiki/Unix • 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.freebsdsoftware.org/shells/ 6/23/2015

  2. It All Started With UNIX • Linux, an Operating System based on Unix • Unix was developed in 1970 by AT&T Lab (Later known as Bell Lab) • 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 Berkeley Software Distribution Unix • SVR4 (System V Release 4) combines all Berkeley enhancements & original features • Unix was essentially for workstations 9/15/15

  3. Then Came Linux • Created in 1991 by Linus Torvalds , a software developer who became the chief architect of the Linux kernel • Small computers & PC-based operating system • Released in 1994 as Version 1 • Initially was developed for 80 & x86 processors (8080, 8086, .. i386) architecture processors) • Today it supports various processor & servers • AMD, Motorola 6800, Power PC, etc. • Runs on embedded systems, firmware, routers, mobile phones (Android), tablets, video game consoles 9/15/15

  4. Linux Distros = Linux Distribution • Each distro is a package including the OS & different applications • Different distros 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 Distro 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 distro can be through ready made packages over the net or buying the CD or just compiling a version 9/15/15

  5. Linux Distros - 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 UNIX code 9/15/15

  6. Red Hat & Fedora Core • Fedora Project was introduced in 1993 to take over Red Hat Linux • Red Hat 9 was the last version • The new Linux distro called Fedora Core • A new version every six months! • 2004  Fedora Core 3 • 2005  Fedora Core 4 • New applications include OpenOffice, FireFox, GIMP (GNU Image Manipulation Program) • 2007  Fedora Core 6 • Fedora comes installed with Firefox 9/15/15

  7. Linux, Layered Views User User Application Programs Shell/Photo/WP/FTP/Telnet/ Web Browser User request Application Programmer Interface (API)- C/C++/Java/Fortran SHELL Application Operating System (Kernel) Lower Level Utilities Computer Hardware, I/O devices, Memory, CPU, Storage Devices LINUX KERNEL Computer Hardware 6/23/2015

  8. 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 • 1.x.y  Major. minor. patch • 2.6 is one of the most improved • Linux 2.6 Version improvements • Supports more hardware • Higher Stability • Supports 4 billion users & 16 TB File System! • Handles external devices better (supporting Hot Plug Devices, USB) • Supports many new devices (Wireless, USB-based, different storage devices using IDE, SCSI, ..) • Sound system • Higher security  Using SELinux (Security Enhanced Linux) 6/23/2015

  9. 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 9/15/15

  10. Linux Platform • A Linux shell, also called "the command line“ • Provides the traditional user interface for the Linux OS • Contains standard commands for Unix • Command are the instructions for the computer to do certain things • Good learning tool to learn Unix! • Basic Shells applications are • BASH, Bourne Shell • BASH is similar to Bourne Shell in Unix • C Shell, tcsh (TENEX C Shell), scsh (Scheme Shell) • http://www.freebsdsoftware.org/shells/ has list of various shells & their differences 9/15/15

  11. Basic Security In Linux • Without SELinux (Security Enhanced Linux) • Domains are divided into Users & Group IDs • The ROOT has absolute control • With SELinux • Domains are divided into Subjects & Objects • Even with Super-user privilege access to some files & devices maybe denied Logon as ROOT 9/15/15

  12. Linux Text Editors • A text editor is a type of program used for editing plain text files • 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 • Come in form of Terminal Command Line Interface (CLI) or Graphic User Interface (GUI) • “vi”, CLI. developed by Bill Joy in C programing language for Unix OS, & Linux uses keyboard • Can put together with many commands, lines of code, to make a program. • “gedit”, CLI & GUI, like Windows Notepad uses mouse & keyboard, friendly 9/15/15

  13. 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 clients • Was developed at MIT & some computer companies (X.org) • Uses mouse & keyboard • How the actual interface looks or feels depends on the GUI interface 9/15/15

  14. GUI Examples Choosing KDE (K-desktop Environment) at the Login Screen default GNOME Desktop The KDE Desktop (Fedora Core) 6/23/2015

  15. GEDIT Text Editor • Geditis Similar to Windows Notepad & the default GUI text editor in the Ubuntu OS • Can be invloked 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 6/23/2015

  16. Ubuntu on Windows, Multi-OS Environment • 3 ways to install Ubuntu/Linux OS on your PC or laptop with Windows 7 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 OS 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 Windows Linux 9/15/15

  17. Shell Prompt • Most work is done at the shell prompt which is the Command-Line Interface • Remember root is / • ls – list files • ls /mnt/floppy to see contents of floppy • cd – change directory • cd /home to go to folder home • mkdir – create a directory • Mkdirhomework to make a folder homework • Exercise: How can you go to CLI in: • Windows • Mac 9/15/15

  18. Shell Prompt • rmdir – remove a directory • rmdir /mnt/floppy/test • 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 • vi <filename> - start editing a file • vi homework1 9/15/15

  19. 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, default shell in various *BSD flavor unices, used by those who know C programing language Basically most Shell types work basically 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 • Shells can be changed by simply typing the name of the shell at the command prompt • chsh (change shell) 6/23/2015

  20. Linux Directory Hierarchy 6/23/2015

  21. Linux Directory Hierarchy 9/15/15

  22. Some 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! 6/23/2015

  23. Finding/Displaying Files, Patterns • grep searches file(s) for words/lines that match a given pattern • E.g.., grep word? filename • grepcommand can display the IP address & machine name • find searches for files that meet a desired criteria • E.g., find xyz? (? For any xyz1, xyz2, xyz. ) • cat concatenates file & prints on the standard output • E.g., cat xyz • echo displays message on screen • E.g., echo hello 9/15/15

  24. Exercise Command + Options + Arguments • Open a shellterminal • 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) 9/15/15

  25. File System Permissions in Linux 9/15/15

  26. Linux Permissions • Permissions are set for user, group, & others • Each permission is set with a single 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 9/15/15

  27. Using chmod to Set Permissions 9/15/15

  28. Linux Script Examples 1 Scriptis a collection of commands typed in text, stored in a file, read by processor and executed for result. One can use a text editor (e.g., vi) to make the file. Note: “$” is the Shell prompt & “#” indicates comments. Example 1: Write a Linux script to print sum of two numbers, let's say 6 and 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 and op2 are any Integer Number (Number without decimal point) and 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 # exprEvaluate expressions Now It will print sum as 9 , But$ expr 6+3will not work because space is required between number and operator (See Shell Arithmetic). 9/15/15

  29. Linux Script Example2 & 3 Notes: • $ with a space char after is the Linux prompt here • $ with NO space after defines a Linux variable Example 2: How to define two variable x=20, y=5 and then to print division of x and y (i.e. x/y)$ x=20$ y=5$ expr $x / $y Example 3: Modify above and store division of x and y to variable called z$ x=20$ y=5$ z=`expr $x / $y`$ echo $z To execute a program in Linux, type: ./filename, e.g., ./xxx ` (back quote) executes the command 9/15/15

  30. / junks primary secondary my_junk_file my_primary_file my_secondary.log Practice • Read about chmod - Read about LINUX permissions (check the hyperlink) • Find install.log file • For simple examples of scripts go to http://www.freeos.com/guides/lsst/misc.htm#commonvi • Write a shell script & using grep command (or anything else) display the IP address & machine name (use uname) • Create the following directories & files (/ is the root directory): 9/15/15

  31. 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 • Create a new file called YOUR_IP_ADDRESS containing the IP address of your machine  thus, by doing a less YOUR_IP_ADDRESS we should get your IP address • 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! (make sure you try running your program multiple times) 9/15/15

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