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UNIX Basics

UNIX Basics. What is UNIX?. Operating System An  operating system  ( OS ) is software that enable the computer to function Developed in 1960’s at Bell Laboratories OS for servers Fundamental building block of the Internet Characteristics Multi-user, multi-tasking Powerful & efficient

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UNIX Basics

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  1. UNIX Basics Internet Technology

  2. What is UNIX? • Operating System • An operating system (OS) is software that enable the computer to function • Developed in 1960’s at Bell Laboratories • OS for servers • Fundamental building block of the Internet • Characteristics • Multi-user, multi-tasking • Powerful & efficient • Reliable & robust • First “open” system • Freeware → created to develop as a public collaboration • A command line interface • Types (flavors) of Unix • BSD (Berkley): most well-known • System V (AT&T) : first commercial Unix • Linux: Unix on PC • Mac OS X: Unix by Apple Internet Technology

  3. Unix Basics • Unix: The Good, Bad & Ugly • It does what you say • no prompting, "Are you sure?" • It's not intuitive • Designed by & for engineers • It's CASE SENSITIVE • Unix Fundamentals • Know the difference between a directory and a file • Know what directory you are in • When in directory doubt, type ‘pwd‘ Internet Technology

  4. Unix Basics: File System • Hierarchical Naming • No explicit disk drives • e.g., /home/kiyang (vs. C:\Document and Settings\kiyang) • Top level is called the root (e.g. cd /) • Absolute (full) vs. relative path (filename) • Full path: /home/kiyang/file1.txt • Relative path: file1.txt (current directory = /home/kiyang) • Navigation • No graphical interface or desktop utility • Command line using Unix commands • Command line using Unix commands • pwd (where am I?) • ls -l (what are the files in the current directory?) • cd dirname(move to a directory named dirname) Internet Technology

  5. Unix: Directories • File and directory paths use the forward slash “/” • / "root" directory • /home/kiyang subdirectory “home” → subdirectory “kiyang” root ~ Home directory shorthand ~kiyang = /home/kiyang ~batman = /home/stud/batman ~/ = user’s home directory ~/public_html/ = user’s web directory ~/IT/homework/ = user’s homework directory home usr stud kiyang batman catwoman /home/stud/catwoman/public_html (http://widit.knu.ac.kr/~catwoman/) public_html IT IT public_html homework ithw homework symbolic link created by ‘ln –s’ command /home/stud/batman/IT/homework Internet Technology

  6. Unix: Command Syntax • Unix command syntax: command[space]option switches [space] arguments • To get help on a command • Type ‘man command’ • e.g., man ls (example) ls -l/home/kiyang/share Internet Technology

  7. Unix Basics: lsCommand • ls lists files in a directory • Default argument = current directory • Common options: • -a → list all files including dot files • -l→ display detailed info • -sh → list files sizes • Options can be combined, for example: ls–la • List detailed info of all files (including dot files) in current directory • ls-al • List detailed info of hw1.txt in kiyang’s share directory • ls-l /home/kiyang/share/hw1.txt • List detailed info of files that starts with hw in current directory • ls-l hw* Internet Technology

  8. Unix Basics: cdCommand • cd dir_name • Change directory to the directory named dir_name • To change to userid’s homework directory • cd/home/stud/userid/IT/homework • cd~userid/IT/homework • To change to your own homework directory • cd~/IT/homework • cdIT/homework (from home directory) • cdhomework (from IT directory) • Default argument = home directory • e.g., cd (change to home directory) • .. parent directory • e.g., cd .. (change to parent directory) Internet Technology

  9. Unix Basics: OtherCommand • cp file1 file2copy file1 to file2 • mv file1 file2rename file1 to file2 • rm file1delete file1 • mkdir dir_name to create a directory named dir_name • rmdir dir_name to delete a directory named dir_name • cat filenamedisplay the content of filename • more filenamedisplay filename content a screen at a time • less filenamesame as more & scroll back Internet Technology

  10. UNIX Shortcuts • Up arrow • Cycles through previous commands • Tab key after partial filename • Completes the filename if enough has been typed (like auto-complete) • Aliases (~/.aliases) • Use shorter commands in place of longer one. • Syntax: alias short_cmd=‘long command’ • e.g., alias dir='ls -al |more' alias cdit='cd ~/IT/homework' alias cdw='cd ~/public_html' alias chmo='chmod 755 ~/IT/homework/*' Internet Technology

  11. Unix Basics: Working with Files • Files have owners and permissions • Owner = person who created the file • Permission • read, write, execute by owner, group, everyone • Cannot "more" all files • read permission needed • Special files • Dot files: ls –a to list • Symbolic links: ls –I to list the original file • "ls" to list • "cp" to copy • "mv" to rename. • "rm" to delete • "more" (less, cat) to view the content Internet Technology

  12. Unix Basics: Working with Directories • Directories are special types of files • Unix filesystem is hierarchical • use "cd" and "ls" to get around • cannot "cd" everywhere due to file access restrictions • execute permission needed • ~/  your home directory • ~/public_html = /home/kiyang/public_html • "cd" to change directory • "mkdir" to create • "rmdir" to remove • "pwd" to print current working cirectory Internet Technology

  13. Unix Basics: Permissions • The system administrator sets the default permissions • Permissions allow you to share or protect information • Set up into three user groups • owner, group, and world. • chmod to change permissions • e.g., chmod 755 hw1.txt Internet Technology

  14. Unix Permissions Unix file permissions are represented in octal (based on binary) 1 -rwxr-xr-- 1 kiyang users 30 May 25 16:17 80test 000 = 0 = --- 001 = 1 = --x 010 = 2 = -w- 011 = 3 = -wx 100 = 4 = r-- 101 = 5 = r-x 110 = 6 = rw- 111 = 7 = rwx owner group world - rwx r-x r-- 1=Allowed 0=Not Allowed 111 101 100 7 5 4 In decimal number So, the permissions for the file 80test are 754. Internet Technology

  15. Unix Permissions • Shows files and directories, owners, file sizes, last modified date, and permissions • File hw1.txt has read, write, and execute permissions for owner (yangk) and read permissions for group (users) and the world • test is a directory • ithw is a symbolic link to ~/IT/homework WIDIT: ~/public_html -> ls -l total 118 -rwxr--r-- 1 robin robin 30 2013-03-19 16:17 hw1.txt -rw-r-xr-x 1 robin robin 221 2013-03-19 16:19 index.htm -rw-r--r-- 1 robin robin 28672 2013-03-22 16:21 lab1.doc lrwxrwxrwx 1 robin robin 15 2013-03-22 16:20 ithw -> ../IT/homework/ drwx--x--x 2 robin superG 4096 2013-03-31 16:21 test file type permission owner group size last modified date name Internet Technology

  16. Changing Unix File Permissions • Use the chmodcommand • Syntax: chmod permissionsfilename • e.g., chmod 644hw1.txt • This would change the permissions to?(Hint: 6 = 110, 4 = 100 in binary) • Important in web authoring • Web pages • Must be world readable → chmod 644 index.htm • Server-side Programs • Must be executable → chmod 755 roster.cgi • User group depending on web server configuration • Directories • Must be world executable → chmod 711 public_html Internet Technology

  17. Unix Permissions: In English • Whose permission? • u (owner), g (group), o (world), a (all) • What action? • + (give), - (take away) • What rights? • r (read), w (write), x (execute) • Syntax • chmod who+action+rights • Examples • chmod u+rwx file (give owner read, write, execute rights) • chmod go+rx file (give group & world read and execute rights) • → after both of these commands have executed, the file rights will be 755. Internet Technology

  18. UNIX Network Tools • nslookup • UNIX command for a DNS name look up • Translates hostname to IP address • Syntax: nslookup hostname • e.g., nslookup widit.kmu.ac.kr • Ping • Utility for determe if an Internet host is alive & responding • e.g. ping –c 5 www.knu.ac.kr Internet Technology

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