今天帮师弟安装服务器，在安装mysql-server的时候，出现了：
eading package lists... Done
Building dependency tree
Reading state information... Done
Some packages could not be installed. This may mean that you have
requested an impossible situation or if you are using the unstable
distribution that some required packages have not yet been created
or been moved out of Incoming.
The following information may help to resolve the situation:
The following packages have unmet dependencies:
mysql-server : Depends: mysql-server-5.1 but it is not going to be instaed
E: Unable to correct problems, you have held broken packages.
初步估计是系统自带安装源出了问题，在网上搜索了几个安装源来更新都没解决。后来在阿里云帮助中心找到了一个解决方案。
方法一：
cp -a /etc/apt/source.list /etc/apt/source.list.bak //备份/etc/apt/source.list文件
vim /etc/apt/source.list
在最前面添加一下内容：
deb http://mirrors.aliyun.com/ubuntu/ precise main restricted universe multiverse
deb http://mirrors.aliyun.com/ubuntu/ precise-security main restricted universe multiverse
deb http://mirrors.aliyun.com/ubuntu/ precise-updates main restricted universe multiverse
deb http://mirrors.aliyun.com/ubuntu/ precise-proposed main restricted universe multiverse
deb http://mirrors.aliyun.com/ubuntu/ precise-backports main restricted universe multiverse
deb-src http://mirrors.aliyun.com/ubuntu/ precise main restricted universe multiverse
deb-src http://mirrors.aliyun.com/ubuntu/ precise-security main restricted universe multiverse
deb-src http://mirrors.aliyun.com/ubuntu/ precise-updates main restricted universe multiverse
deb-src http://mirrors.aliyun.com/ubuntu/ precise-proposed main restricted universe multiverse
deb-src http://mirrors.aliyun.com/ubuntu/ precise-backports main restricted universe multiverse
sudo apt-get update && sudo apt-get -y upgrade//更新一下列表
方法二：
1.通过wget http://oss.aliyuncs.com/aliyunecs/update_source.tgz 下载update_source的压缩包。
2.tar xvf update_source.tgz解压后予执行权限 chmod 777 update_source.sh。
3.执行该脚本./update_source.sh进行自动变更源操作。
我采用的是方法一，更新了源之后，再输入命令：
sudo apt-get install mysql-server
即可以正常安装mysql。