使用 Ubuntu 14.04 系统在安装 mysql-server 时出现如下报错信息：
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-5.5 but it is not going to be instaed
E: Unable to correct problems, you have held broken packages.
可以看到报错是无法解决 mysql-server 安装时的依赖关系导致的。
因为用户是使用 apt-get 的方式安装的，那么这种安装方式通常是能够自动解决依赖关系。
写回答
因为系统自带的安装源无法解决安装包依赖问题，更换为新的安装源，解决包依赖问题，安装软件。
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
执行 apt-get update 更新一下列表
1.下载 apt-get 更新源脚本
wget http://oss.aliyuncs.com/aliyunecs/update_source.tgz
2.解压并赋权脚本
tar xvf update_source.tgz
chmod 777 update_source.sh
3.执行该脚本
./update_source.sh
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