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running on Linux Mint, I had to make a slight modification as Mint is not fully supported and the Ubuntu repos are out of date for PostgreSQL 9.4; though Ubuntu is, so I just used that version and everything works fine.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 http://apt.postgresql.org/pub/repos/apt/ $(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 http://apt.postgresql.org/pub/repos/apt/ trusty-pgdg main" > /etc/apt/sources.list.d/pgdg.list'
Install their key:
$ wget --quiet -O - https://www.postgresql.org/media/keys/ACCC4CF8.asc | sudo apt-key add - $ sudo apt-get update $ sudo apt-get install pgadmin3