Installation of Dspace 5.5 on Ubuntu 14.04 LTS

Open terminal by using [Ctrl+Alt] keys (like a command-cmd prompt in window)

(I assume that your system is 64bit and not under the proxy server)

sudo apt-get update

sudo apt-get install openjdk-7-jdk ant maven

sudo apt-get install tasksel

sudo tasksel

Select the following packages

[*] LAMP server

[*] PostgreSQL database

[*] Tomcat Java server

Create the database user

sudo su postgres
createuser -U postgres -d -A -P dspace

Enter password for new role: [Enter a password e.g. dspace]
Shall the new role be allowed to create more new roles? (y/n) n
[Enter n and press enter button]

Type exit

Allow the database user (dspace) to connect to the database
[If the following command not open, check the postgresql version number and apply in the command]

sudo gedit /etc/postgresql/9.3/main/pg_hba.conf

Add this line to the configuration file at the end:

local all dspace md5

save and close the file

Restart PostgreSQL :

sudo su
/etc/init.d/postgresql restart

Create Dspace user

sudo useradd -m dspace
sudo passwd dspace [enter a password for the new user dspace] 

sudo mkdir /dspace
sudo chown dspace /dspace

Create the PostgreSQL 'dspace' database

sudo -u dspace createdb -U dspace -E UNICODE dspace

save and close the file.
Create Dspace directory

sudo mkdir /build
sudo chmod -R 777 /build
cd /build

Download Dsapce to /build directory
Copy paste following line in the terminal,

wget https://github.com/DSpace/DSpace/releases/download/dspace-5.5/dspace-5.5-src-release.tar.gz


Extracting Dspace package

tar -zxf dspace-5.5-src-release.tar.gz
cd /build/dspace-5.5-src-release
mvn -U package

Enter into Dspace package folder to download packages.

cd dspace/target/dspace-installer
sudo ant fresh_install

Create ADMINISTRATOR for DSpace

/dspace/bin/dspace create-administrator

Stop tomcat service

sudo service tomcat7 stop

Copy webapps xmlui, oai, solr to tomcat

sudo cp -r /dspace/webapps/xmlui/ /var/lib/tomcat7/webapps

sudo cp -r /dspace/webapps/oai/ /var/lib/tomcat7/webapps

sudo cp -r /dspace/webapps/solr/ /var/lib/tomcat7/webapps

Fix Tomcat permissions, and restart the Tomcat server

sudo chown tomcat7:tomcat7 /dspace -R

sudo service tomcat7 start

Test DSpace xmlui  in your browser

That is all that is required to install DSpace on Ubuntu. There are two main webapps that provide a similar turn-key repository interface
http://localhost:8080/xmlui