我正在尝试使用以下命令在 Ubuntu Server 12.04 上安装 tomcat 7：
sudo apt-get install tomcat7
大多数网站和指南都告诉我这样做，但我立即收到了这个答案：
Reading 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:
tomcat7 : Depends: …