At my work place I connect to internet via proxy (requiring username/password). I've one desktop running Ubuntu 10.04 and wanted to upgrade to 10.10 the latest long term release. Even after applying all the updates shown in Update Manager, I never get to see the availability of new release.
After lot of googling and playing around with proxy settings in Synaptic Package manager and also in Network Proxy, I found no success. On various forums also I see many facing the same problem. After some days of such struggle and trying different options to make update manager "read" my proxy settings I realized that Update Manager correctly detects the proxy settings to show the available updates, but the apt-get which actually checks for availability of new release does not "read" the proxy settings from the same location as Update Manager does.
So as suggested on Ubuntu help pages on setting up proxy, I tried to temporarily setup proxy by exporting http_proxy and then tried sudo apt-get update. Still the result was same. Still no option to upgrade to 10.10 :-(
After this I tried to change the proxy settings in /etc/apt/apt.conf to provide proxy along with the username/password. After saving the changes, apt-get successfully updated all the packages from the repositories and Update Manager showed me the 10.10 availability message.
So even though Ubuntu help page says that you can set the proxy temporarily by exporting http_proxy, it seems apt-get ignores http_proxy and always refers to atp.conf (/etc/apt/apt.conf). Well things are not always as it should be and it applies to worlds one of the best OS too.