If you have tried to install docker via the usual instructions, you will find that they’ve not pushed packages for Ubuntu 18.04 “Bionic Beaver” yet:
$ sudo apt install docker-ce [...] E: Unable to locate package docker-ce
This is understandable, as the release day isn’t for a month. But what if you’re a bleeding-edge adopter, such as myself? It’s dead easy:
/etc/apt/sources.list and change the line from:
deb [arch=amd64] https://download.docker.com/linux/ubuntu bionic stable
deb [arch=amd64] https://download.docker.com/linux/ubuntu artful stable
Your install will now work. Just remember to update it once docker start releasing official packages. Remember, this likely isn’t supported, so YMMV.