To get SageMath under Ubuntu, you could either
install the Debian package by running in a terminal:
sudo apt install sagemath-jupyter
(this should work under: Debian >= 9; Ubuntu 17.04; Ubuntu >= 18.04;
unfortunately not in Ubuntu 17.10),
install SageMath binary for your Ubuntu system from the
SageMath download page.
- build from source,
- install using Conda,
- install using Docker.
Note that Ubuntu 18.04 was just released which makes it a good time to upgrade.
Building from source is a good way to get the latest version.
If you build from source, I would suggest building the latest development
release, currently SageMath 8.2.rc4.
When SageMath 8.2 is released, it should be nearly identical to SageMath 8.2.rc4.