I have installed Ubuntu 18.04.1 and was just wondering why there are only 3 repos listed:
vi /etc/apt/sources.list
deb http://archive.ubuntu.com/ubuntu bionic main
deb http://archive.ubuntu.com/ubuntu bionic-security main
deb http://archive.ubuntu.com/ubuntu bionic-updates main
The defaul should look different https://gist.github.com/jackw1111/d31140946901fab417131ff4d9ae92e3
EDIT:
I have used the installer ubuntu-18.04.1-live-server-amd64.iso from http://releases.ubuntu.com/18.04/
This is a known issue, specific to the Server ISOs (specifically the Subiquity based 'live-server' installer ISOs.
From my other answer on a different question that has a related answer and cause:
However, on the latest 18.04.1 Subiquity-based Live Server Installer ISOs, there is a known bug where the ISOs for 18.04(.1) install but don't enable Universe or Multiverse repositories.
For those cases, you have to go back and enable Universe and Multiverse and Restricted; keep in mind that this is a bug in the installer and not typical as it's supposed to enable Universe and Multiverse.
(This has been fixed for future ISOs including the 18.04.2 (hopefully) and 18.10 ISOs that are going to be spun when 18.10 is actually released. (However, the 18.04.1 Server ISOs - but not the Alternate istnaller ISO - are known to be affected by this bug))
Because of this bug, only the Main repos get installed and configured. This is why you only see "three" repositories.
