Install Ubuntu /Xubuntu 12.04 LTS, see the below link to get detailed installation instructions.

http://www.ubuntu.com/download/desktop/install-ubuntu-desktop

Open Applications > Accessories > Terminal and  apply following commands,

sudo su

apt-get install leafpad

Add Koha package repository

wget -O- http://debian.koha-community.org/koha/gpg.asc | sudo apt-key add -

echo deb http://debian.koha-community.org/koha oldstable main | sudo tee /etc/apt/sources.list.d/koha.list

sudo apt-get update
sudo apt-get upgrade

sudo apt-get install koha-common

Initial Configuration
Create a new file

leafpad /etc/koha/koha-sites.conf

Add the following lines and save.

DOMAIN=".myDNSname.org"  # Change this to be your domain.
INTRAPORT="8080"  # TCP listening port for the administration interface
INTRAPREFIX=""
INTRASUFFIX="-intra"
DEFAULTSQL=""
OPACPORT="80"  # TCP listening port for the users' interface
OPACPREFIX=""
OPACSUFFIX=""
ZEBRA_MARC_FORMAT="marc21"  # Possible values are 'marc21', 'normarc' and 'unimarc'
ZEBRA_LANGUAGE="en"  # Possible values are 'en', 'fr' and 'nb'

Adding ports
Open following file and add ports

sudo leafpad /etc/apache2/ports.conf

Copy paste following line below Listen 80

Listen 8080
 

Restart Apache,

sudo service apache2 restart

Configuration of UTF-8 in MySQL and Apache

Enable UTF-8 at MySQL 
Open a Terminal and type following command, 

sudo su 
leafpad /etc/mysql/my.cnf   

[Under the Basic settings section, add the following,] 

# UTF-8 Defaults for Koha 
init-connect='SET NAMES utf8' 
character-set-server=utf8 
collation-server=utf8_general_ci  

leafpad /etc/apache2/conf.d/charset 
[Add the following two lines in] 
 
AddCharset UTF-8 .utf8
AddDefaultCharset UTF-8

Save the file and close the editor.

Sax parser setup

leafpad /etc/perl/XML/SAX/ParserDetails.ini

Cut and paste the following command to the bottom of the file and save it.

[XML::LibXML::SAX::Parser]
http://xml.org/sax/features/namespaces=1 

Instance creation

sudo apt-get install mysql-server

[Put a password for MySQL Root USER]

Apply following commands,
 

sudo apt-get clean

sudo a2enmod rewrite

sudo service apache2 restart

sudo koha-create --create-db library

Ubuntu MySQL security Tweak

sudo su

mysql -u root -p

[Enter the MySQL Root password when it ask]

Execute the following commands,

USE mysql;
DELETE FROM user WHERE user='';
FLUSH PRIVILEGES;
QUIT

Configuring Apache

Execute the following commands in a terminal. 

sudo a2dissite 000-default

sudo a2enmod rewrite

sudo a2enmod deflate
sudo a2ensite library
sudo service apache2 restart

Start web installation of Koha

The username to log in with will be koha_library and the password will be near the end of /etc/koha/sites/library/koha-conf.xml

Apply the following command to see the koha login password. Note down the password.

sudo xmlstarlet sel -t -v 'yazgfs/config/pass' /etc/koha/sites/library/koha-conf.xml

Open following link in a broswer and proceed with post installation configurations,

http://127.0.1.1:8080

How to change Koha master password?

See the following link

http://kohageek.blogspot.in/2013/05/how-to-change-master-password-of-koha.html

Zebra rebuild command

sudo su

koha-rebuild-zebra -v -f library

Reference

http://wiki.koha-community.org/wiki/Koha_on_ubuntu_-_packages#Enable_Modules_and_Site