Comment 27 for bug 972077

Hi.
Just to re-iterate what Robie said.

If you are seeing hashsum mismatch errors on 16.04 or later, something is wrong.
That could be:
a.) you have a proxy in your way, and the proxy cached a bad download.
Apt is recognizing this and not installing it.
That is working as designed.
Note, that http proxies can be transparent (ie, no explicit configuration from you).
Your ISP could be providing a proxy service that is simply broken.

b.) You're using a mirror that does not support 'by-hash'.

c.) there could be an error in the official ubuntu publishers. If they updated
the Release file before content that it referenced was complete then
that would cause apt to correctly identify the invalid data.

So, what should you do?

First, rule out the most likely problem... the proxy.
If you have an explicitly configured proxy, then unconfigure it.

You can probably verify there is a proxy in your path via:
wget -q -S http://archive.ubuntu.com/ubuntu/dists/xenial/Release -O/dev/null

If you see 'X-Cache' in the output, then there is a proxy between you and archive.ubuntu.com.

If you are seeing this issue on Ubuntu 14.04, then that is not easily fixed.