I am pasting the error and terminal output above.
the version of UE4 is 4.13.1
I have this packages on my linux system (NixOS linux) :
mono 4.6.0
clang 3.8.1
Dont know what am I doing wrong.

This looks related to the ongoing attack on DNS servers. Probably other URLs (not related to us) also fail to resolve for you.

I am not sure this is the case, could be. I still voted up your response. I tried to download today with the same nix expression which is actually a script for nix package manager. Didnt work, I guess the script was the problem, because if I removed ${linkDeps} from configurePhase and “export http_proxy=”"" , then the downloading started and went past 37%, before it never pased this %. I guess it was me doing something wrong.
For the reader, if you are on nixos linux, I am was doing packageOverrides and overrideDerivation on ue4-4.10.2 package. Pushing it to version 4.13.1 to see if that gives a different error. It seems that dependecies for lower version are different from the 4.13.1, and I guess the dependencies of 4.10.2 nixpkgs/cdn-deps.nix at master · NixOS/nixpkgs · GitHub are not good for 4.13.1. Or am I wrong… Anyway the problem is this but I made a separate topic for this error’s discussion.