Upgrading Ubuntu 14.04 / Debian 8 "jessie" with CMake 3.x, gcc-5, and g++-5

Ubuntu 14.04 and Debian 8 "jessie" are still relatively popular, especially considering the Ubuntu 14.04.5 LTS release that isn't considered end-of-life until April 2019.

Many low-end VPS providers still have Ubuntu 14.04 as a common OS image. Of course I much prefer Ubuntu 16.04, but when that isn't an option, you have to make do.

These two resources helped greatly, and I will quote them in case they disappear or I can't find them in the future:

Install gcc-5 and g++-5 (from gcc 5 on ubuntu 14.04):

sudo add-apt-repository ppa:ubuntu-toolchain-r/test
sudo apt-get update
sudo apt-get install gcc-5 g++-5

sudo update-alternatives --install /usr/bin/gcc gcc /usr/bin/gcc-5 60 --slave /usr/bin/g++ g++ /usr/bin/g++-5

Install CMake 3.x (from How to install cmake 3.2 on Ubuntu):

sudo apt-get install software-properties-common
sudo add-apt-repository ppa:george-edison55/cmake-3.x
sudo apt-get update

sudo apt-get install cmake