今天在安装软件的时候出现了Package has no installation candidate的问题，如：

#  apt-get install <packagename>
Reading package lists... Done
Building dependency tree... Done
Package aptitude is not available, but is referred to by another package.
This may mean that the package is missing, has been obsoleted, or
is only available from another source
E: Package <packagename> has no installation candidate

解决方法如下：
# apt-get update
# apt-get upgrade
# apt-get install <packagename>

这样就可以正常使用apt-get了～

添加第三方地址：

sudo add-apt-repository "deb http://archive.canonical.com/ lucid partner"

sudo apt-get update

   但有的时候sudo apt-get update等之类的命令该命令不管用。这是因为在我们的/etc/apt/sources.list文件下，拥有的是只是一些系统初装的源，后期的一些源还是得自己添加的，不然网上的很多资源包都是无法使用的。下面我就贴上我在网站上找到的各种源。

sources.list（源）

位置：/etc/apt/sources.list

常见的源：

1 中国科技大学源

deb http://debian.ustc.edu.cn/ubuntu/ hardy main multiverse restricted universe
deb http://debian.ustc.edu.cn/ubuntu/ hardy-backports main multiverse restricted universe
deb http://debian.ustc.edu.cn/ubuntu/ hardy-proposed main multiverse restricted universe
deb http://debian.ustc.edu.cn/ubuntu/ hardy-security main multiverse restricted universe
deb http://debian.ustc.edu.cn/ubuntu/ hardy-updates main multiverse restricted universe
deb-src http://debian.ustc.edu.cn/ubuntu/ hardy main multiverse restricted universe
deb-src http://debian.ustc.edu.cn/ubuntu/ hardy-backports main multiverse restricted universe
deb-src http://debian.ustc.edu.cn/ubuntu/ hardy-proposed main multiverse restricted universe
deb-src http://debian.ustc.edu.cn/ubuntu/ hardy-security main multiverse restricted universe
deb-src http://debian.ustc.edu.cn/ubuntu/ hardy-updates main multiverse restricted universe

2 北京交大源

deb http://mirror.bjtu.edu.cn/Ubuntu/ hardy main restricted universe multiverse
deb http://mirror.bjtu.edu.cn/Ubuntu/ hardy-backports restricted universe multiverse
deb http://mirror.bjtu.edu.cn/Ubuntu/ hardy-proposed main restricted universe multiverse
deb http://mirror.bjtu.edu.cn/Ubuntu/ hardy-security main restricted universe multiverse
deb http://mirror.bjtu.edu.cn/Ubuntu/ hardy-updates main restricted universe multiverse
deb-src http://mirror.bjtu.edu.cn/Ubuntu/ hardy main restricted universe multiverse
deb-src http://mirror.bjtu.edu.cn/Ubuntu/ hardy-backports main restricted universe multiverse
deb-src http://mirror.bjtu.edu.cn/Ubuntu/ hardy-proposed main restricted universe multiverse
deb-src http://mirror.bjtu.edu.cn/Ubuntu/ hardy-security main restricted universe multiverse
deb-src http://mirror.bjtu.edu.cn/Ubuntu/ hardy-updates main restricted universe multiverse

3 台湾大学源

deb http://ubuntu.csie.ntu.edu.tw/ubuntu/ hardy main restricted universe multiverse
deb-src http://ubuntu.csie.ntu.edu.tw/ubuntu/ hardy main restricted universe multiverse
deb http://ubuntu.csie.ntu.edu.tw/ubuntu/ hardy-updates main restricted universe multiverse
deb-src http://ubuntu.csie.ntu.edu.tw/ubuntu/ hardy-updates main restricted universe multiverse
deb http://ubuntu.csie.ntu.edu.tw/ubuntu/ hardy-backports main restricted universe multiverse
deb-src http://ubuntu.csie.ntu.edu.tw/ubuntu/ hardy-backports main restricted universe multiverse
deb http://ubuntu.csie.ntu.edu.tw/ubuntu/ hardy-security main restricted universe multiverse
deb-src http://ubuntu.csie.ntu.edu.tw/ubuntu/ hardy-security main restricted universe multiverse
deb http://ubuntu.csie.ntu.edu.tw/ubuntu/ hardy-proposed main multiverse restricted universe
deb-src http://ubuntu.csie.ntu.edu.tw/ubuntu/ hardy-proposed main restricted universe multiverse

4 CN99源

deb http://Ubuntu.cn99.com/ubuntu/ hardy main restricted universe multiverse
deb http://Ubuntu.cn99.com/ubuntu/ hardy-security main restricted universe multiverse
deb http://Ubuntu.cn99.com/ubuntu/ hardy-updates main restricted universe multiverse
deb http://Ubuntu.cn99.com/ubuntu/ hardy-proposed main restricted universe multiverse
deb http://Ubuntu.cn99.com/ubuntu/ hardy-backports main restricted universe multiverse
deb-src http://Ubuntu.cn99.com/ubuntu/ hardy main restricted universe multiverse
deb-src http://Ubuntu.cn99.com/ubuntu/ hardy-security main restricted universe multiverse
deb-src http://Ubuntu.cn99.com/ubuntu/ hardy-updates main restricted universe multiverse
deb-src http://Ubuntu.cn99.com/ubuntu/ hardy-proposed main restricted universe multiverse
deb-src http://Ubuntu.cn99.com/ubuntu/ hardy-backports main restricted universe multiverse

5 Lupaworld源

deb http://mirror.lupaworld.com/ubuntu hardy main restricted universe multiverse
deb http://mirror.lupaworld.com/ubuntu hardy-security main restricted universe multiverse
deb http://mirror.lupaworld.com/ubuntu hardy-updates main restricted universe multiverse
deb http://mirror.lupaworld.com/ubuntu hardy-backports main restricted universe multiverse
deb http://mirror.lupaworld.com/ubuntu hardy-proposed main restricted universe multiverse
deb-src http://mirror.lupaworld.com/ubuntu hardy main restricted universe multiverse
deb-src http://mirror.lupaworld.com/ubuntu hardy-security main restricted universe multiverse
deb-src http://mirror.lupaworld.com/ubuntu hardy-updates main restricted universe multiverse
deb-src http://mirror.lupaworld.com/ubuntu hardy-backports main restricted universe multiverse
deb-src http://mirror.lupaworld.com/ubuntu hardy-proposed main restricted universe multiverse

（注释：deb代表的是我们需要的deb软件包，deb-src 是指下载源代码得指示。之后是包的来源地址，再在后面是系统的标记。之后的main代表的是主要软件包，universe是不被官方支持的自由软件。)

                                         如何更改源呢？

1、首先备份Ubuntu 8.04 的当前更新源列表（以备不测）

      sudo cp /etc/apt/sources.list /etc/apt/sources.list.backup （备份下当前的源列表）

2、修改更新源
      sudo gedit /etc/apt/sources.list 
3、在里面我选择在后面添加源；

4、通知Ubuntu 11.10 启用新的更新源
     sudo apt-get update

最后

root@ubuntu：~# sudo apt-get update