I have a warning sign on the upper bar, a red triangle and an exclamation inside. I click this icon and I am informed that there are updates and the "Show updates" option is available. I click on "Show updates" and I am informed that the package information was last updated 78 days ago. I am prompted to click the check button for new updates. I click the check button and it says "updating cache" and after a moment a "Failed to download repository information" message appears.
This was the result of the execution of"sudo apt-get update | grep NO_PUBKEY:
W: Failed to fetch ppa.launchpad.net/openjdk/ppa/ubuntu/dists/oneiric/main/source/… 404 Not Found W: Failed to fetch ppa.launchpad.net/openjdk/ppa/ubuntu/dists/oneiric/main/… 404 Not Found E: Some index files failed to download. They have been ignored, or old ones used instead.
This situation has been happening often. What should I do?