How can I update Ubuntu if the update servers are blocked?

Solution 1:

Ubuntu uses HTTP to update, which is the same protocol used to access most websites (including Ask Ubuntu). Therefore, it seems likely that the particular server you're trying to upgrade from is blocked or (perhaps more likely) otherwise inaccessible due to network problems.

If this is the case, then updating normally with the Update Manager could succeed, if you change your mirror.

You can do this in the Ubuntu Software tab of the Software Sources window. Change the selection in the Download from drop-down menu.

One way to open the Software Sources window is by clicking Settings... in the Update Manager.

Solution 2:

There are ways that involve manually downloading packages, but an easier solution might be to switch to a different mirror.

Ubuntu's updates are 'mirrored' onto a number of different servers around the world. So whilst http://archive.ubuntu.com/ is not accessible to you, there is likely to be a mirror with a URL that you can access.

For an easy way of selecting a fast mirror, look at this Ask Ubuntu answer.