Apt-Get cannot be downloaded. Some URLs are not found 404

Apt-Get cannot be downloaded. The website reports not found 404 because of a problem with the apt Software Download source.

1. Replace the content in/etc/APT/source. List.

Copy the file to overwrite the file on another Ubuntu machine that can download apt, and then run apt-Get update to update the source list.

2. Choose "software update management"> "Settings"> "ubuntu software"> "Download from" to modify the software download source.

Apt-Get cannot be downloaded. Some URLs are not found 404