Abra /etc/apt/sources.list e substitua pk.archive.ubuntu.com por archive.ubuntu.com , após salve o arquivo e execute sudo apt-get update
Acabei de instalar o Ubuntu 12.0.4 LTS (Precise Pangolin). Eu tentei executar sudo apt-get update no shell e ele acaba com os seguintes erros após alguns segundos:
Err http://pk.archive.ubuntu.com precise Release.gpg
Could not connect to pk.archive.ubuntu.com:80 (58.65.218.244), connection timed out
W: Failed to fetch http://pk.archive.ubuntu.com/ubuntu/dists/precise-backports/Release.gpg Unable to connect to pk.archive.ubuntu.com:http:
W: Some index files failed to download. They have been ignored, or old ones used instead.
Abra /etc/apt/sources.list e substitua pk.archive.ubuntu.com por archive.ubuntu.com , após salve o arquivo e execute sudo apt-get update