最近家里的網可能被天朝了，一直很好用的更新設置，出現各種錯誤，但在公司可以，所以應該是網絡的問題，所以把遇到的問題整理了一下：
問題一：
執行命令
sudo apt-get update
錯誤描述如下：
W: Failed to fetch http://mirrors.sohu.com/ubuntu/dists/precise/universe/i18n/Index No Hash entry in Release file /var/lib/apt/lists/partial/mirrors.sohu.com_ubuntu_dists_precise_universe_i18n_Index W: Failed to fetch bzip2:/var/lib/apt/lists/partial/mirrors.sohu.com_ubuntu_dists_precise-updates_main_binary-i386_Packages Hash Sum mismatch W: Failed to fetch bzip2:/var/lib/apt/lists/partial/extras.ubuntu.com_ubuntu_dists_precise_main_binary-i386_Packages Hash Sum mismatch E: Some index files failed to download. They have been ignored, or old ones used instead.
解決方法：
將/var/lib/apt/lists/partial/下的所有文件刪除，但是這可以解決大部分問題，個別源不能解決，如"/var/lib/apt/lists/partial/extras.ubuntu.com_ubuntu_dists_precise_main_binary-i386_Packages"，無耐進入/var/lib/apt/lists/將對應的文件刪除
注：經過長時間的實踐，這個解決方法不是萬能的，最終解決方法還是翻牆吧。
問題二：
無法找到對應的KEY
W: GPG error: http://mirrors.sohu.com precise Release: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 40976EAF437D05B5 W: GPG error: http://mirrors.sohu.com precise-updates Release: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 40976EAF437D05B5 W: GPG error: http://mirrors.sohu.com precise-proposed Release: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 40976EAF437D05B5 W: GPG error: http://archive.canonical.com precise Release: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 40976EAF437D05B5 W: GPG error: http://security.ubuntu.com precise-security Release: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 40976EAF437D05B5
解決方法：
使用如下命令：
gpg --keyserver subkeys.pgp.net --recv-keys 40976EAF437D05B5
gpg -a --export 40976EAF437D05B5 | sudo apt-key add -
參考網站：