http://askubuntu.com/questions/633919/how-install-postgresql-9-4
This command installs the recent version for your distribution:
sudo apt-get install postgresql
postgresql-9.4
is available since Utopic.
Here is a step by step guide to install Postgesql 9.4 for your Ubuntu (Utopic, Trusty, Precise, Lucid) version.
sudo add-apt-repository "deb https://apt.postgresql.org/pub/repos/apt YOUR_UBUNTU_VERSION_HERE-pgdg main"
For trusty:
sudo add-apt-repository "deb https://apt.postgresql.org/pub/repos/apt/ trusty-pgdg main"
To get your ubuntu version:
lsb_release -sc
Now import the public key and install:
wget --quiet -O - https://postgresql.org/media/keys/ACCC4CF8.asc | sudo apt-key add -
sudo apt-get update
sudo apt-get install postgresql-9.4