Ubuntu 7.10 (Gutsy Gibbon) recently reached EOL (end-of-life). Presumably to discourage people from continuing to use a distro that is officially dead, the package repositories for an EOL release disappear from archive.ubuntu.com, which means that if you try to use apt-get to install or upgrade your software you will get 404 errors.
The recommended action for anyone still running 7.10 is to use the do-release-upgrade command to (relatively) painlessly upgrade to a newer, supported version of Ubuntu (remembering to take a backup first, just in case). The one little catch with this solution is that without access to the package repository, you won’t be able to install the upgrade tool if you don’t already have it.
Fortunately, the Gutsy repository hasn’t been removed completely, it’s just relocated to old-releases.ubuntu.com. So if you edit /etc/apt/sources.list and replace all occurrences of archive.ubuntu.com with old-releases.ubuntu.com, you will again be able to access the packages for 7.10. You should then install the update-manager-core package to enable the upgrade.
sudo vi /etc/apt/sources.list sudo apt-get install update-manager-core
After doing this and before upgrading, it is important to revert the changes made to the sources.list file (i.e. change it back to using archive.ubuntu.com). This is because the distro upgrade will replace all references to ‘gutsy’ with ‘hardy’ (as in Hardy Heron, the Ubuntu 8.04 release) but will not change the repository addresses. Since Hardy is hosted at archive.ubuntu.com, leaving it as old-releases.ubuntu.com will cause the upgrade to fail.
sudo vi /etc/apt/sources.list sudo do-release-upgrade
If all goes well you will end up with a fully functioning Ubuntu 8.04 system. Hardy Heron is the current LTS (Long Term Support) release. You have the option of a further upgrade to 9.04 (Jaunty Jackalope), but although it is a more recent release, it will reach EOL earlier because there is no long term support commitment for Jaunty. Jaunty will reach EOL in October 2010 whereas Hardy will be supported until April 2011 for desktops and April 2013 for servers.