The document provides a comprehensive overview of the Unix operating system, covering its architecture, file system structure, commands, and file permissions. It describes the components of Unix, such as the kernel and shell, highlights various commands for file manipulation, and explains key concepts related to file types, directory navigation, and permission settings. Additionally, it includes practical examples of command usage and introduces miscellaneous commands for text processing and environment variables.

1. Introduction
 UNIX Architecture
 UNIX file system
 Relative & Absolute path
 File permission
 Directory related commands
 Files related commands
 Miscellaneous commands
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Presented by – Anil Kumar Kapil
February 7, 2014
UNIX

2. INTRODUCTION
What is UNIX?
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Available in different flavors
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An operating system
Invented in 1969 at AT&T Bell Labs
Command Line Interpreter
GUIs (Window systems) are now available
Written in the C programming language.
Multi-user : Several people can use a UNIX computer at the same time
Multi-process : A user can also run multiple programs at the same time
Solaris (Sun),
AIX (IBM)
Linux (open source)
Irix (SGI)
Berkeley
Unix is case-sensitive.
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3. 
The UNIX operating system is made up of
three parts; the kernel, the shell and the
programs.
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Commands and Utilities: There are various
command and utilities which you would use in
your day to day activities. cp, mv, cat and grep
etc.
Shell: Shell is an interface between user and
kernel. Shell interprets your input as
commands and pass them to kernel.
Utilities and Programs
User Interface
Operating System
Computer
Hardware
Unix Kernel
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Kernel : The kernel is the heart of the
operating system. It interacts with hardware
and most of the tasks like memory
management, task scheduling and file
management .
Shell
(sh, bash, tcsh, ksh …)
cp, cat, rm, mv, grep, find, ls etc…
February 7, 2014
UNIX ARCHITECTURE

4. UNIX FILE SUBSYSTEM
All data in UNIX is organized into files. All files are organized into directories. These
directories are organized into a tree-like structure called the filesystem.
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In UNIX, data, directory, process, hard disk etc (almost everything) are expressed as a
file.
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Basic Directory Terms
Home directory
The home directory is a directory assigned to a user. When you log
in, your working directory will be set to your home directory
Root directory
Top of a file tree
Current directory Directory you’re in now
Dot (.)
Another term for the current directory
Dot-dot (..)
Parent of the current directory
Tilde (~)
$HOME directory
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5. UNIX FILE SUBSYSTEM
February 7, 2014
NOTE: Unix file names
are CASE SENSITIVE!
Important
Directories
/bin This contains files that are essential for correct operation of the system. These are
available for use by all users.
/home  This is where user home directories are stored.
/var This directory is used to store files which change frequently, and must be available to be
written to.
/etc  Various system configuration files are stored here
/dev  This contains various devices as files, e.g. hard disk, CD- ROM drive, etc.
/sbin  Binaries which are only expected to be used by the super user.
/tmp Temporary files.

6. UNIX FILE SUBSYSTEM
In UNIX there are three basic types of files:
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Directory is a special file that contains the names of other files and/or
subdirectories..
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Regular file holds ASCII text, binary data, image data, databases, applicationrelated data, and more
Symbolic link. A type of file that point to another file
Every file has a data structure (record) known as an I-node that stores
information about the file, and the filename is simply used as a reference to
that data structure.
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7. UNIX FILE TYPE
Regular file :
Most common file type found in the Solaris Operating
Environment
 Store different kinds of data.
 Regular files can hold ASCII text, binary data, image data,
databases, application-related data, and more.
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8. UNIX FILE TYPE
Directory file :
Directories store information that associates file names with
inode numbers.
 Unlike regular files that can hold many different kinds of data,
directories can hold only one kind
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9. UNIX FILE TYPE
Symbolic link :
A symbolic link is a file that points to another file.
 Like directories, symbolic links contain only one kind of data.
 A symbolic link contains the pathname of the file to which it
points.
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10. RELATIVE & ABSOLUTE PATH
Path means a position in the directory tree.
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Relative path
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Absolute path
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starts from current working directory
If you are already in the users directory, the
Relative pathname for file1 is usern/file1
start from root (/) and follow the tree
The absolute pathname for file1 is
/users/usern/file1
Specifying Paths
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What is the absolute path to index.html?
What is the relative path to index.html
(assuming that usern is your pwd)?
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11. LISTING FILES
ls: To list the files and directories stored in the current directory.
Syntax: ls [<file> … ]
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ls - short listing
ls -l - long listing
ls -a  list all the files including hidden files that start with . .
ls –lt  list all files names based on the time of creation, newer files bring first.
ls –R lists all the files and files in the all the directories, recursively.
Example: ls –l backup
-rw-r--r-drwxr-xr-x
lrwxr-xr-x
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1 ian wheel
4 ian admin
1 ian admin
9218
136
16
21
17
6
Aug 14:49
Jan 16:31
Jan 19:31
support.dat
talk-others
w -> /shared/w
In the ls -l listing example, every file line began with a d, -, or l. These characters indicate
the type of file
Prefix
Description
-
Regular file, such as an ASCII text file, binary executable, or hard link.
D
Directory file that contains a listing of other files and directories.
L
Symbolic link file. Links on any regular file.
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12. FILE PERMISSION
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Suppose you type in ls -l and the result is
Typesrwx r-x r--access supported22:28UNIX.
of file 1 hans doc 858 Aug 22 by hw1
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r – read only permission
What do all these symbols mean?
w –write permission
x –execute permission
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in case of directory, “x” grants permission to list directory contents. It signifies whether you are
permitted to search files under the directory
Unix users can be classified into these categories:
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User – the user who created the file.
Group – the group owns the file.
Other – the rest of the world
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13. 
Chmod  Change the access mode of one or more
files
Symbolic mode
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Whose (user, group, or others) permissions you want to change
What (+ to add, - to subtract, = to equal) operation you want to
perform on the permission
The permission (r, w, x)
Numeric modes
Permissions are stored in the UNIX system in octal numbers.
An octal number is stored in UNIX system using three bits
 Bit 1, value 0 or 1 (read permission) , weight 4
 Bit 2, value 0 or 1 (write permission), weight 2
 Bit 3, value 0 or 1 (defines execute permission),
weight 1
For example, a value of 101 will be 5. (The value of
binary 101 is (4 * 1) + (0 * 1) + (1 * 1) = 5.)
Examples:
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umask: Each time a file is created, its initial file mode
is defined by applying the current value of the file
creation mask
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chmod o+r file.txt
chmod u+x file.txt
chmod u=rwx, g=r, o=wr my_file
umask  Show see the current value of the file creation mask
umask 077  To change the value of the file creation mask
chgrp: change group of the file
chown: change owner of the file
Examples
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chmod 751 my_file
-R recursively descend through directory changing
group of all files and subdirectories
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FILE PERMISSION

14. 
pwd: the absolute pathname of your current working directory
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cd: Change directory
Examples:
 cd backups/unix-tutorial
 cd ../class-notes
 cd ~
 cd ..
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WORKING WITH DIRECTORIES

15. 
cat: Display the contents of file
Syntax: cat <file>
Examples:
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cat /export/home/xyz.txt  cat displays a file with no page breaks
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cat file1 file2 >file3  concatenates file1 and file2, and writes the results in
file3. If no input file is given, cat reads
from the standard input file.
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cat /dev/null/ > message.log  To Cleanup a file content :
# /dev/null/ acts as a black hole from where anything directed to or read from is set as Null.
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more: displays a file one screenful at a time
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more file1
cp: Copy file
Syntax: cp [options] <sources> <destination>
Options:
-i Interactive. cp prompts for confirmation whenever the copy would overwrite an existing target. A Y answer means that the
copy should proceed. Any other answer prevents cp from overwriting target.
-r  Recursive. cp copies the directory and all its files, including any subdirectories and their files to target.
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cp tutorials.txt tutorial.txt.bak
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cp –r dir1 /export/home/bsarda/dir2
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touch: update the access and modification times of given file
touch a.txt
-a - Changes the access time of file.
-m Changes the modification time of file.
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February 7, 2014
FILES RELATED COMMANDS

16. 
rm: remove file
Syntax: rm [options] <file>
Examples:
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rm tutorials.txt
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rm -rf /export/home/anil/dir2/ --This will remove files (write-protected too becoz of –f option) recursively from the
directory. If the dir is write-protected then it cant.
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mv: Move/Rename file/directory
Syntax: mv [options] <sources> <destination>
Examples:
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mv tutorials.txt tutorial2.txt
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mv tutorials.txt /export/home/anil/dir2/
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head: Showing first “n” lines of file, by default will display the first 10 lines of a file
Syntax: head –n file1
Examples:
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head -20 tutorials.txt
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tail: Showing last “n” lines of file, by default will display the last 10 lines of a file
Syntax: tail –n file1
Examples:
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tail -20 tutorials.txt
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wc: counts the characters, words or lines in a file depending upon the option.
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wc -l filename  print total number of lines in a file.
wc -w filename print total number of words in a file.
wc -c filename  print total number of characters in a file.
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diff: compare the two files and print out the differences
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cmp: compare the two files and print out the differences
February 7, 2014
FILES RELATED COMMANDS

17. 
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man: This is help command, and will explains you about
online manual pages
date: Display date and time
date + “%m-%d-%y %H:%M:%S”
date + “%D” -- mm/dd/yy
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date + “%T” --hh:mi:ss
To get year as 2009 in full use „Y‟ otherwise „y „will give 09 only.
# To have a new line in between Date and Time use %n like
$date “+Date : %D %n %T” will give the output as
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Date: 09/19/08
09:29:28
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banner: prints characters in a sort of ascii art poster
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cal: print the calander on current month by default
Examples:
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banner wait
Syntax: tail –n file1
Examples:
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cal 8 1965  print calander of august of 1965
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sleep
Examples:
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sleep 10  Tell a shell script to pause for 10 seconds
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env: See environment variables
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clear: clear the screen
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dircmp: compares two directories.
Example :If i have two directories in my home directory
named dirone and dirtwo and each has 5-10 files in it. Then
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dircmp dirone dirtwo will return this
Dec 9 16:06 1997 dirone only and dirtwo only Page 1
./cal.txt
./fourth.txt
./dohazaar.txt
./rmt.txt
./four.txt
./te.txt
./junk.txt
./third.txt
February 7, 2014
MISCELLANEOUS COMMANDS

18. TEXT PROCESSING COMMANDS
echo
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sort: sort command sort the lines of a file or files, in alphabetical order
Example:
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sort file.txt
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sort -r file.txt
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sort –f file.txt
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sort –n file.txt
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sort -k3 file.txt
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cut: selects a list of columns or fields from one or more files
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-- display in reverse order
-- ignore case
-- numerical order
-- Sorts using the third field of each line
cut –d „ „ -f 1,2,11, 15-20 file.txt
cut –c 1-8 file.txt  it will extract first 8 characters of every line in the file.
uniq: removes duplicate adjacent lines from sorted file while sending one copy of each second file
Examples
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sort names | uniq -d  will show which lines appear more than once in names file
Options:
-c print each line once, counting instances of each.
-d print duplicate lines once, but no unique lines.
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-u print only unique lines
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tee: Put output on screen and append to file
Examples
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who | tee -a > <file>
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19. VIEWING & SETTING ENVIRONMENT VARIABLES
env
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PATH Variable
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Which
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List of places (directories) on the system where the shell should look to locate a command. Each command you type is
physically located as a file somewhere on your file system
To find whether a particular command exists in you search path. If it does exist, which tells directory contains that command
Where
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20. February 7, 2014
QUESTIONS ?

21. February 7, 2014
Thank You ……