Updating ubuntu server apt-get gives me - 404 Not Found [duplicate]

I assume the problem is because you are using a relatively old release of Ubuntu. A possible fix would be to open the /etc/apt/sources.list file with an editor of your choice .Change all (xx.)archive.ubuntu.com to old-releases.ubuntu.com.. In your case an example would be ://archive.ubuntu.com/ubuntu/dists/natty/main/source/Sources becomes

://old-releases.ubuntu.com/ubuntu/dists/natty/main/source/Sources

after this, you can try running sudo apt-get update

For you to update your release,you need update-manager-core(sudo apt-get install update-manager-core) and then sudo do-release-upgrade but this will update you to the next release and has to be repeated until you reach say 12.04 LTS which has Long Term Support.

Ubuntu 11.04 was supported for 18 months, and that means it's been unsupported for almost a year. If you have to use it, then you need to switch to old-releases archives, but please keep in mind that you will not get any security upgrades for it and there are known issues.

The correct way to "cleanup this mess" is to upgrade to a current version of Ubuntu. If you don't want to upgrade very often, the best suggestion is to get 12.04.3LTS, which will be supported until April 2017. You can upgrade LTS-releases directly from one to the next. You can't skip versions, so upgrading 11.04 would take a long time.