Generally speaking, you’ll see that message when repositories can not be reached. The result of the request was a 404 or they didn’t respond in time.
This can happen from time to time, though it can also happen if you’ve made any changes to your apt sources.list file, added repositories, etc.
The default location for your sources file is going to be in
/etc/apt and the main file is:
Other sources files may be contained in this directory:
You can run:
… to view the contents of your main sources file. By default, you should see DigitalOcean pop up as repository sources if you’ve not modified them.
If there are other sources files in the
sources.list.d directory that you’ve added, you’ll want to check those as well.
Without seeing the full output, it’s hard to see which are the main issue though, so if you can run:
and then post the entire output, that’d help us to look in to this further.