Ubuntu repository does not have a Release file

Solution 1:

The third line from the bottom in your /etc/apt/sources.list seems to be wrong:

deb http://archive.ubuntu.com xenial universe

I think that line is what's causing the error, so I'd suggest that you remove it.

After doing so there may be a need to clean up the package cache, which you can do by running:

sudo rm -r /var/lib/apt/lists/*

and then:

sudo apt update

Solution 2:

In my case the issue was really dumb. I had no network access outside my server. It took me quite a while to realize that was my problem ;-)

Solution 3:

In my case (16.04 LTS) the remote download server must have had some problems under the hood. I received notifications that it was an Undocumented error. I changed the download server and it worked. I have documented this solution in this other post.