Ubuntu的软件源更新常见问题及解决
最近家里的网可能被天朝了，一直很好用的更新设置，出现各种错误，但在公司可以，所以应该是网络的问题，所以把遇到的问题整理了一下：
问题一：
执行命令
sudo apt-get update
错误描述如下：
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.
解决方法：
将/var/lib/apt/lists/partial/下的所有文件删除，但是这可以解决大部分问题，个别源不能解决，如"/var/lib/apt/lists/partial/extras.ubuntu.com_ubuntu_dists_precise_main_binary-i386_Packages"，无耐进入/var/lib/apt/lists/将对应的文件删除
注：经过长时间的实践，这个解决方法不是万能的，最终解决方法还是FQ吧。
问题二：
无法找到对应的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
解决方法：
使用如下命令：
gpg --keyserver subkeys.pgp.net --recv-keys 40976EAF437D05B5
gpg -a --export 40976EAF437D05B5 | sudo apt-key add -
参考网站：
