新安装的Ubuntu在使用sudo apt-get update更新源码的时候出现如下错误：
W: GPG 错误：http://ppa.launchpad.net precise Release: 由于没有公钥，无法验证下列签名： NO_PUBKEY 3EE66BD3F599ACE3
W: GPG 错误：http://ppa.launchpad.net precise Release: 由于没有公钥，无法验证下列签名： NO_PUBKEY 6AF0E1940624A220
W: 无法下载 bzip2:/var/lib/apt/lists/partial/mirrors.163.com_ubuntu_dists_precise_main_binary-i386_Packages Hash 校验和不符
W: 无法下载 bzip2:/var/lib/apt/lists/partial/mirrors.163.com_ubuntu_dists_precise-security_main_binary-i386_Packages Hash 校验和不符
W: 无法下载 bzip2:/var/lib/apt/lists/partial/extras.ubuntu.com_ubuntu_dists_precise_main_binary-amd64_Packages Hash 校验和不符
W: 无法下载 bzip2:/var/lib/apt/lists/partial/extras.ubuntu.com_ubuntu_dists_precise_main_binary-i386_Packages Hash 校验和不符
E: Some index files failed to download. They have been ignored, or old ones used instead.
解决方法很简单，下载导入公钥就行，下载导入key的命令如下：
sudo apt-key adv --keyserver keyserver.ubuntu.com --recv-keys 6AF0E1940624A220 #此处6AF0E1940624A220需要是错误提示的key
此时继续更新发现没有公钥错误提示，但是还是效验存在问题，此时需要打开软件源的界面，将其他软件选项中的Canpnical合作伙伴/独立等四个选项取消勾选，再执行sudo apt-get update
此时发现可以顺利更新了。
sanbo@ubuntu:~/dev$ sudo apt-get update
命中 http://mirrors.163.com precise Release.gpg
命中 http://mirrors.163.com precise-updates Release.gpg
命中 http://mirrors.163.com precise-security Release.gpg
命中 http://mirrors.163.com precise Release
命中 http://mirrors.163.com precise-updates Release
命中 http://mirrors.163.com precise-security Release
命中 http://mirrors.163.com precise/main Sources
命中 http://mirrors.163.com precise/restricted Sources
命中 http://mirrors.163.com precise/universe Sources
命中 http://mirrors.163.com precise/multiverse Sources
命中 http://mirrors.163.com precise/main amd64 Packages
命中 http://mirrors.163.com precise/restricted amd64 Packages
命中 http://mirrors.163.com precise/universe amd64 Packages
命中 http://mirrors.163.com precise/multiverse amd64 Packages
命中 http://mirrors.163.com precise/main i386 Packages
命中 http://mirrors.163.com precise/restricted i386 Packages
命中 http://mirrors.163.com precise/universe i386 Packages
命中 http://mirrors.163.com precise/multiverse i386 Packages
命中 http://mirrors.163.com precise/main TranslationIndex
命中 http://mirrors.163.com precise/multiverse TranslationIndex
命中 http://mirrors.163.com precise/restricted TranslationIndex
命中 http://mirrors.163.com precise/universe TranslationIndex
命中 http://mirrors.163.com precise-updates/main Sources
命中 http://mirrors.163.com precise-updates/restricted Sources
命中 http://mirrors.163.com precise-updates/universe Sources
命中 http://mirrors.163.com precise-updates/multiverse Sources
命中 http://mirrors.163.com precise-updates/main amd64 Packages
命中 http://mirrors.163.com precise-updates/restricted amd64 Packages
命中 http://mirrors.163.com precise-updates/universe amd64 Packages
命中 http://mirrors.163.com precise-updates/multiverse amd64 Packages
命中 http://mirrors.163.com precise-updates/main i386 Packages
命中 http://mirrors.163.com precise-updates/restricted i386 Packages
命中 http://mirrors.163.com precise-updates/universe i386 Packages
命中 http://mirrors.163.com precise-updates/multiverse i386 Packages
命中 http://mirrors.163.com precise-updates/main TranslationIndex
命中 http://mirrors.163.com precise-updates/multiverse TranslationIndex
命中 http://mirrors.163.com precise-updates/restricted TranslationIndex
命中 http://mirrors.163.com precise-updates/universe TranslationIndex
命中 http://mirrors.163.com precise-security/main Sources
命中 http://mirrors.163.com precise-security/restricted Sources
命中 http://mirrors.163.com precise-security/universe Sources
命中 http://mirrors.163.com precise-security/multiverse Sources
命中 http://mirrors.163.com precise-security/main amd64 Packages
命中 http://mirrors.163.com precise-security/restricted amd64 Packages
命中 http://mirrors.163.com precise-security/universe amd64 Packages
命中 http://mirrors.163.com precise-security/multiverse amd64 Packages
命中 http://ppa.launchpad.net precise Release.gpg
命中 http://ppa.launchpad.net precise Release.gpg
命中 http://mirrors.163.com precise-security/main i386 Packages
命中 http://mirrors.163.com precise-security/restricted i386 Packages
命中 http://mirrors.163.com precise-security/universe i386 Packages
命中 http://mirrors.163.com precise-security/multiverse i386 Packages
命中 http://mirrors.163.com precise-security/main TranslationIndex
命中 http://mirrors.163.com precise-security/multiverse TranslationIndex
命中 http://mirrors.163.com precise-security/restricted TranslationIndex
命中 http://mirrors.163.com precise-security/universe TranslationIndex
获取：1 http://mirrors.163.com precise/main Translation-zh_CN [100 kB]
命中 http://mirrors.163.com precise/main Translation-en
获取：2 http://mirrors.163.com precise/multiverse Translation-zh_CN [6,476 B]
命中 http://mirrors.163.com precise/multiverse Translation-en
获取：3 http://mirrors.163.com precise/restricted Translation-zh_CN [2,620 B]
命中 http://mirrors.163.com precise/restricted Translation-en
获取：4 http://mirrors.163.com precise/universe Translation-zh_CN [139 kB]
命中 http://ppa.launchpad.net precise Release
命中 http://mirrors.163.com precise/universe Translation-en
获取：5 http://mirrors.163.com precise-updates/main Translation-zh_CN [100 kB]
命中 http://mirrors.163.com precise-updates/main Translation-en
获取：6 http://mirrors.163.com precise-updates/multiverse Translation-zh_CN [6,476 B]
命中 http://mirrors.163.com precise-updates/multiverse Translation-en
获取：7 http://mirrors.163.com precise-updates/restricted Translation-zh_CN [2,620 B]
命中 http://mirrors.163.com precise-updates/restricted Translation-en
获取：8 http://mirrors.163.com precise-updates/universe Translation-zh_CN [139 kB]
命中 http://mirrors.163.com precise-updates/universe Translation-en
命中 http://mirrors.163.com precise-security/main Translation-en
命中 http://mirrors.163.com precise-security/multiverse Translation-en
命中 http://mirrors.163.com precise-security/restricted Translation-en
命中 http://mirrors.163.com precise-security/universe Translation-en
命中 http://ppa.launchpad.net precise Release
命中 http://ppa.launchpad.net precise/main Sources
命中 http://ppa.launchpad.net precise/main amd64 Packages
命中 http://ppa.launchpad.net precise/main i386 Packages
忽略 http://ppa.launchpad.net precise/main TranslationIndex
命中 http://ppa.launchpad.net precise/main Sources
命中 http://ppa.launchpad.net precise/main amd64 Packages
命中 http://ppa.launchpad.net precise/main i386 Packages
忽略 http://ppa.launchpad.net precise/main TranslationIndex
忽略 http://ppa.launchpad.net precise/main Translation-zh_CN
忽略 http://ppa.launchpad.net precise/main Translation-zh
忽略 http://ppa.launchpad.net precise/main Translation-en_US
忽略 http://ppa.launchpad.net precise/main Translation-en
忽略 http://ppa.launchpad.net precise/main Translation-zh_CN
忽略 http://ppa.launchpad.net precise/main Translation-zh
忽略 http://ppa.launchpad.net precise/main Translation-en_US
忽略 http://ppa.launchpad.net precise/main Translation-en
下载 497 kB，耗时 7秒 (66.3 kB/s)
正在读取软件包列表... 完成
搞定收工！
另外送上一个163源，更新的速度挺不错，品种也挺全的:
# deb cdrom:[Ubuntu 12.04.1 LTS _Precise Pangolin_ - Release i386 (20120817.3)]/ precise main restricted
# See http://help.ubuntu.com/community/UpgradeNotes for how to upgrade to
# newer versions of the distribution.
deb http://mirrors.163.com/ubuntu/ precise main restricted
deb-src http://mirrors.163.com/ubuntu/ precise main restricted
## Major bug fix updates produced after the final release of the
## distribution.
deb http://mirrors.163.com/ubuntu/ precise-updates main restricted
deb-src http://mirrors.163.com/ubuntu/ precise-updates main restricted
## N.B. software from this repository is ENTIRELY UNSUPPORTED by the Ubuntu
## team. Also, please note that software in universe WILL NOT receive any
## review or updates from the Ubuntu security team.
deb http://mirrors.163.com/ubuntu/ precise universe
deb-src http://mirrors.163.com/ubuntu/ precise universe
deb http://mirrors.163.com/ubuntu/ precise-updates universe
deb-src http://mirrors.163.com/ubuntu/ precise-updates universe
## N.B. software from this repository is ENTIRELY UNSUPPORTED by the Ubuntu
## team, and may not be under a free licence. Please satisfy yourself as to
## your rights to use the software. Also, please note that software in
## multiverse WILL NOT receive any review or updates from the Ubuntu
## security team.
deb http://mirrors.163.com/ubuntu/ precise multiverse
deb-src http://mirrors.163.com/ubuntu/ precise multiverse
deb http://mirrors.163.com/ubuntu/ precise-updates multiverse
deb-src http://mirrors.163.com/ubuntu/ precise-updates multiverse
## N.B. software from this repository may not have been tested as
## extensively as that contained in the main release, although it includes
## newer versions of some applications which may provide useful features.
## Also, please note that software in backports WILL NOT receive any review
## or updates from the Ubuntu security team.
deb http://mirrors.163.com/ubuntu/ precise-security main restricted
deb-src http://mirrors.163.com/ubuntu/ precise-security main restricted
deb http://mirrors.163.com/ubuntu/ precise-security universe
deb-src http://mirrors.163.com/ubuntu/ precise-security universe
deb http://mirrors.163.com/ubuntu/ precise-security multiverse
deb-src http://mirrors.163.com/ubuntu/ precise-security multiverse
## Uncomment the following two lines to add software from Canonical's
## 'partner' repository.
## This software is not part of Ubuntu, but is offered by Canonical and the
## respective vendors as a service to Ubuntu users.
deb http://archive.canonical.com/ubuntu precise partner
deb-src http://archive.canonical.com/ubuntu precise partner
## This software is not part of Ubuntu, but is offered by third-party
## developers who want to ship their latest software.
deb http://extras.ubuntu.com/ubuntu precise main
deb-src http://extras.ubuntu.com/ubuntu precise main
# codeblock
deb http://ppa.launchpad.net/pasgui/ppa/ubuntu precise main
deb-src http://ppa.launchpad.net/pasgui/ppa/ubuntu precise main
# ubuntu tweak
deb http://ppa.launchpad.net/tualatrix/ppa/ubuntu precise main
deb-src http://ppa.launchpad.net/tualatrix/ppa/ubuntu precise main
==============================================偶尔时刻还是有各种问题，归纳如下================================================
【缺少公钥】
现象：
sudo apt-get update
W: GPG error: http://apt.tt-solutions.com dapper Release: 由于没有公钥，下列签名无法进行验证： NO_PUBKEY 06EA41DE4F6C1E86
解决方法：
gpg --keyserver subkeys.pgp.net --recv 4F6C1E86
gpg --export --armor 4F6C1E86 | sudo apt-key add -
说明：
若缺少其他公钥，则将命令中两处4F6C1E86改为NO_PUBKEY
06EA41DE4F6C1E86中最后8位即可！
如果是Ubuntu PPA的则按照如下方法处理：
sudo apt-key adv --recv-keys --keyserver keyserver.ubuntu.com
【签名错解决办法】
情况一.概率出现的问题，这次有，可能下次就没了，可忽略
By simply waiting. This happens at times during archive updates.
情况二.使用如下方法更新：
$ sudo apt-get update -o Acquire::http::No-Cache=True情况三.
或者
$ sudo apt-get update -o Acquire::BrokenProxy=true
现象：
In a particular case this was caused by a broken file and could get fixed using rescue boot and "fsck -fy /" (http://forum.ubuntuusers.de/goto?post=89197 - german)
解决办法：
fsck -fy /
情况四：
现象：
The fix is just to back up sources.list, delete everything in it and run "apt-get update". After the update replace sources.list with the backup and run "apt-get update" again. You should not get the error then.解决办法：
备份sources.list，然后把sources.list中的东西删空，运行"apt-get update"，然后再用刚刚的备份将"apt-get update"复原，再运行"apt-get update"。
情况五.主旨就是清理缓存
sudo bash
apt-get clean
cd /var/lib/apt
mv lists lists.old
mkdir -p lists/partial
apt-get clean
apt-get update
情况六.缓存代理服务器导致的问题：
如下内容添加到/etc/apt/apt.conf.d/10broken_proxy文件里试试看。
Acquire::http::No-Cache "true";
Acquire::http::Max-Age "0";
情况七
sudo apt-get install medibuntu-keyring