Some index files failed to download. They have been ignored, or old ones used instead. in ubuntu 18.04 code example

Example: E: Some index files failed to download. They have been ignored, or old ones used instead.

sudo su 
cd /var/lib/apt/lists/
rm -fr *
cd /etc/apt/sources.list.d/
rm -fr *
cd /etc/apt
sudo cp sources.list sources.list.old
sudo cp sources.list sources.list.tmp
sed 's/ubuntuarchive.hnsdc.com/us.archive.ubuntu.com/' sources.list.tmp | sudo tee sources.list
sudo rm sources.list.tmp*
apt-get clean
apt-get update