E: Package <packagename> has no installation candidate错误，于是便开始google，寻找原因。但苦苦追寻，能查到的都是一些叫我们输入指令的语句 如sudo apt-get update等之类的命令，但该命令不管用。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
我的终端命令如图：
root@ubuntu：~# sudo apt-get update
来源：https://www.cnblogs.com/xy888/p/5477883.html