how to install PostgreSQL on ubuntu

1. This installs the database server/client, some extra utility scripts and the pgAdmin GUI application for working with the database.

$ sudo apt-get install postgresql postgresql-client postgresql-contrib
$ sudo apt-get install pgadmin3

2. Now we need to reset the password for the ‘postgres’ admin account for the server, substitute in the password you want to use for your administrator account.

$ sudo su postgres -c psql template1
template1=# ALTER USER postgres WITH PASSWORD 'password';
template1=# \q

3. That alters the password for within the database, now we need to do the same for the unix user ‘postgres’.

$ sudo passwd -d postgres
$ sudo su postgres -c passwd

4. Set-up the PostgreSQL admin pack that enables better logging and monitoring within pgAdmin.

$ sudo su postgres -c psql < /usr/share/postgresql/9.1/extension/adminpack--1.0.sql

5. Edit the postgresql.conf file.

$ sudo gedit /etc/postgresql/9.1/main/postgresql.conf

Change the line:
#listen_addresses = 'localhost'
to
listen_addresses = '*'
and also change the line:
#password_encryption = on
to
password_encryption = on

6. Define who can access the server. This is all done using the pg_hba.conf.

$ sudo gedit /etc/postgresql/8.3/main/pg_hba.conf

add this text to the bottom of the file:
host all all [ip address] [subnet mask] md5
add in your subnet mask (i.e. 255.255.255.0) and the IP address of your server (i.e. 138.250.192.115).
Note:if you have some password error, please change all "md5" to "trust" in this file.

7. Now all you have to do is restart the server.

$ sudo /etc/init.d/postgresql restart

Reference:
http://hocuspokus.net/2008/05/install-postgresql-on-ubuntu-804/