Ubuntu – How to change mirrors in Ubuntu Server from regional to main

This command will get the public key for the repo :

gpg --keyserver pgpkeys.mit.edu --recv-key C90F9CB90E1FAD0C && gpg --export --armor C90F9CB90E1FAD0C | sudo apt-key add -

It works for any repository, you just have to replace the public key number in the command with the one from the error message.

Yes, the name server update does work and if it does work then you've probably updated your IP settings to be static and your server can no longer resolve URLs.

Try the above and if it works, reboot. If it fails after rebooting, then do this:

Edit the template file for the resolv.conf. Ubuntu server rebuilds this every boot.

sudo vi /etc/resolvconf/resolv.conf.d/tail

#add just these two lines >>
nameserver 8.8.8.8
nameserver 8.8.4.4  

Then save the file and restart the service:

sudo /etc/init.d/resolvconf restart

8.8.8.8 and 8.8.4.4 are just Google's Name Servers. You should be able to add in your own ISP's if you want. If you don't like vi, use nano or vim.

I figured it out reading this article. So credit to them for the tip.