Installing the latest version of pgAdminIII can be challenging; here is a cheat sheet.

The pgAdmin wiki has all the steps contained here, but to get pgAdminIII running on Linux Mint, I had to make a slight modification as Mint is not fully supported and the Ubuntu repos are out of date for PostgreSQL 9.4; though Ubuntu is, so I just used that version and everything works fine.

Add the repository (If running Ubuntu this will work fine):

sudo sh -c 'echo "deb $(lsb_release -cs)-pgdg main" > /etc/apt/sources.list.d/pgdg.list'

If running Linux Mint (I’m on 17.2), edit the lsb_release to just say trusty (or your Ubuntu codename):

sudo sh -c 'echo "deb trusty-pgdg main" > /etc/apt/sources.list.d/pgdg.list'

Install their key:

$ wget --quiet -O - | sudo apt-key add -

$ sudo apt-get update

$ sudo apt-get install pgadmin3