问题描述：
每次我尝试下载操作系统（Ubuntu 12.04）的更新时，都会收到以下错误消息列表：
W:Failed to fetch http://extras.ubuntu.com/ubuntu/dists/precise/Release.gpg Something wicked happened resolving 'extras.ubuntu.com:http' (-5 - No address associated with hostname)
, W:Failed to fetch http://ppa.launchpad.net/deluge-team/ppa/ubuntu/dists/precise/Release.gpg Something wicked happened resolving 'ppa.launchpad.net:http' (-5 - No address associated with hostname)
, W:Failed to fetch http://packages.medibuntu.org/dists/precise/Release.gpg Something wicked happened resolving 'packages.medibuntu.org:http' (-5 - No address associated with hostname)
, W:Failed to fetch http://archive.canonical.com/ubuntu/dists/precise/Release.gpg Something wicked happened resolving 'archive.canonical.com:http' (-5 - No address associated with hostname)
, W:Failed to fetch http://ppa.launchpad.net/tualatrix/ppa/ubuntu/dists/precise/Release.gpg Something wicked happened resolving 'ppa.launchpad.net:http' (-5 - No address associated with hostname)
, E:Some index files failed to download. They have been ignored, or old ones used instead.
/etc/apt/sources.list 文件的内容：
# deb cdrom:[Ubuntu 12.04 LTS _Precise Pangolin_ - Release i386 (20120423)]/ precise main restricted
# See http://help.ubuntu.com/community/UpgradeNotes for how to upgrade to
# newer versions of the distribution.
deb http://archive.ubuntu.com/ubuntu precise main restricted
deb-src http://archive.ubuntu.com/ubuntu precise main restricted
## Major bug fix updates produced after the final release of the
## distribution.
deb http://archive.ubuntu.com/ubuntu precise-updates main restricted
deb-src http://archive.ubuntu.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://archive.ubuntu.com/ubuntu precise universe
deb-src http://archive.ubuntu.com/ubuntu precise universe
deb http://archive.ubuntu.com/ubuntu precise-updates universe
deb-src http://archive.ubuntu.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://archive.ubuntu.com/ubuntu precise multiverse
deb-src http://archive.ubuntu.com/ubuntu precise multiverse
deb http://archive.ubuntu.com/ubuntu precise-updates multiverse
deb-src http://archive.ubuntu.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://archive.ubuntu.com/ubuntu precise-security main restricted
deb-src http://archive.ubuntu.com/ubuntu precise-security main restricted
deb http://archive.ubuntu.com/ubuntu precise-security universe
deb-src http://archive.ubuntu.com/ubuntu precise-security universe
deb http://archive.ubuntu.com/ubuntu precise-security multiverse
deb-src http://archive.ubuntu.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
(/etc/apt/sources.list.d) 目录内的文件：
-rw-r--r-- 1 root root 136 Oct 10 16:30 deluge-team-ppa-precise.list
-rw-r--r-- 1 root root 136 Oct 10 16:30 deluge-team-ppa-precise.list.save
-rw-r--r-- 1 root root 285 Oct 10 16:30 medibuntu.list
-rw-r--r-- 1 root root 285 Oct 10 16:30 medibuntu.list.save
-rw-r--r-- 1 root root 132 Oct 10 16:30 tualatrix-ppa-precise.list
-rw-r--r-- 1 root root 134 Oct 10 16:30 tualatrix-ppa-precise.list.save
-rw-r--r-- 1 root root 148 Oct 10 16:30 yannubuntu-boot-repair-precise.list
-rw-r--r-- 1 root root 148 Oct 10 16:30 yannubuntu-boot-repair-precise.list.save
AskUbuntu.com 上此文章的相关链接：
服务器错误（-5 - 没有与主机名关联的地址）
更新时如何修复“-5 没有与主机名关联的地址错误”？
我尝试过在网上搜索解决问题的方法，但没能找出导致这些错误的真正原因。任何可能帮助我解决这个问题的建议、想法或解决方案都将不胜感激。
答案1
该问题的解决方法如下：
步骤1：转到系统 –> 首选项 –> 网络连接。
第2步：接下来，选择您的默认网络接口（eth0）并单击“编辑”。
步骤3：然后选择“IPv4 设置”并选择“仅自动（DHCP）地址”。
步骤4：接下来，在“DNS 服务器”框中输入新的 DNS 服务器地址。使用逗号分隔多个地址，然后单击“应用”保存。
步骤5：选择您喜欢的 DNS 详细信息
OpenDNS ---> 208.67.222.222, 208.67.220.220
Google Public DNS ---> 8.8.8.8, 8.8.4.4
Comodo Secure DNS ---> 156.154.70.22, 156.154.71.22
配置完成后，请上网检查以确保其正常工作。
有关解决类似问题的完整分步教程，请查看：
http://www.liberiangeek.net/2010/08/change-dns-information-ubuntu-10-04-lucid-lynx/
上面的链接解释了如何更改 Ubuntu 中的 DNS 设置。
答案2
我遇到了同样的问题，上述答案都无法解决它。不过，我现在已经解决了。原来我所需要做的就是进入终端并输入sudo apt-get update。运行完成后，我的更新管理器会刷新，给我一份新的要更新的项目列表，然后我单击更新，一切运行正常。不知道这是否会对其他人有所帮助，但我希望它能。
答案3
cat /etc/apt/sources.list
编辑
sudo gedit /etc/apt/sources.list
删除http://packages.medibuntu.org/
然后运行
sudo apt-get update
答案4
如果您有代理，那么此链接有一些答案。
看着那（这设置 apt-get 以使用 http 代理网页内的部分。