1. UNIX Basics
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2. What is UNIX? Operating System Characteristics Types (flavors) of Unix
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
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3. Unix Basics Unix: The Good, Bad & Ugly Unix Fundamentals
9/14/2018
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‘
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4. Unix Basics: File System
9/14/2018
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
pwd (where am I?)
ls -l (what are the files in the current directory?)
cd dirname (move to a directory named dirname)
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5. Unix: Directories File and directory paths use the forward slash “/”
9/14/2018
Unix: Directories
File and directory paths use the forward slash “/”
/ "root" directory
/home/kiyang subdirectory “home” → subdirectory “kiyang”
root
~ Unix Home directory shorthand
~kiyang = /home/kiyang
~batman = /home/stud/batman
~/ = (current) user’s home directory
~/public_html/ = user’s web directory
~/IT/homework/ = user’s homework directory
home
usr
kiyang
stud
batman
catwoman IT
public_html IT
/home/stud/catwoman/public_html (
public_html
homework
homework
ithw
/home/stud/batman/IT/homework
symbolic link created by ‘ln –s’ command
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6. Unix: Command Syntax Unix command syntax:
9/14/2018
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
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7. Unix Basics: ls Command
9/14/2018
Unix Basics: ls Command
ls lists files in a directory
Default argument = current directory
Common options:
-a → list all files including dot files
-s → list files sizes
-l → display detailed info
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*
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8. Unix Basics: cd Command
9/14/2018
Unix Basics: cd Command
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
cd IT/homework (from home directory)
cd homework (from IT directory)
Default argument = home directory
e.g., cd (change to home directory)
..  parent directory
e.g., cd (change to parent directory)
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9. Unix Basics: Other Command
9/14/2018
Unix Basics: Other Command
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
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10. UNIX Shortcuts Up arrow Tab key after partial filename
9/14/2018
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/*'
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11. Unix Basics: Working with Files
9/14/2018
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
Try:
ls -l /etc/motd
Try "cp" to copy:
cp /etc/motd ~/motd.my.copy
Try "mv" to rename:
mv motd.my.copy blah
Try "rm" to delete (forever):
rm blah
Directories are special types of files
mkdir blahdir ("rmdir" to remove)
cp /etc/motd ~/blahdir ("ls blahdir" to view)
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12. Unix Basics: Working with Directories
9/14/2018
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
"cd" alone brings you home (RUBY slippers!)
"cd ~" and "cd ~username" brings you home (or to "username's" home)
"cd.." brings you down a directory
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13. Unix Basics: Permissions
9/14/2018
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 hw1.txt
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14. Unix Permissions - rwx r-x r-- 111 101 100 7 5 4
9/14/2018
Unix Permissions
Unix file permissions are represented in octal (based on binary)
-rwxr-xr-- 1 kiyang kiyang 30 May 25 16:17 hw1.txt
000 = 0 = - - -
001 = 1 = - - x
010 = 2 = - w -
011 = 3 = - w x
100 = 4 = r - -
101 = 5 = r - x
110 = 6 = r w -
111 = 7 = r w x
owner
group
world
- rwx r-x r--
1=Allowed
0=Not Allowed
In decimal number
So, the permissions for the file hw1.txt are 754.
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15. 9/14/2018
Unix Permissions
WIDIT: ~/public_html -> ls -l
total 118
-rwxr--r-- 1 robin superG :17 hw1.txt
-rw-r-xr-x 1 robin robin :19 index.htm
-rw-r--r-- 1 robin robin :21 lab1.doc
lrwxrwxrwx 1 robin robin :20 ithw -> ../IT/homework/
drwx--x--x 2 robin robin :21 test
file type
permission
owner
group
size
last modified date
name
Shows files and directories, owners, file sizes, last modified date, and permissions
File hw1.txt has read, write, and execute permissions for owner (robin) and read permissions for group (superG) and the world
test is a directory
ithw is a symbolic link to ~/IT/homework
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16. Changing Unix File Permissions
9/14/2018
Changing Unix File Permissions
Use the chmod command
Syntax: chmod permissions filename
e.g., chmod hw1.txt
This would change the permissions to?
Important in web authoring
Web pages
Must be world readable → chmod (rw- r-- r--) index.htm
Server-side Programs
Must be executable → chmod (rwx r-x r-x) roster.cgi
User group depending on web server configuration
Directories
Must be world executable → chmod (rwx --x --x) public_html
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17. Unix Permissions: In English
9/14/2018
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 file1.txt (give owner read, write, execute rights)
chmod go+rx file1.txt (give group & world read and execute rights)
→ after both of these commands have executed, the file rights will be 755.
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18. UNIX Network Tools nslookup Ping UNIX command for a DNS name look up
9/14/2018
UNIX Network Tools
nslookup
UNIX command for a DNS name look up
Translates hostname to IP address
Syntax: nslookup hostname
e.g., nslookup widit.knu.ac.kr
Ping
Utility for determe if an Internet host is alive & responding
e.g. ping –c 5
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