Upgrade Ubuntu 12.04 To 13.04

[stnet253]

sudo sed -i 's/precise/raring/' /etc/apt/sources.list
sudo apt-get update
sudo apt-get dist-upgrade

中途遭遇一次GPG公鎖錯誤訊息
W: A error occurred during the signature verification.
The repository is not updated and the previous index files will be used. GPG error:http://extras.ubuntu.com quantal Release:
The following signatures couldn’t be verified because the public key is not available: NO_PUBKEY 16126D3A3E5C1192
解決方式如下