主要步骤：
sudo apt-get install pepperflashplugin-nonfree
sudo update-pepperflashplugin-nonfree --install原因：
But this is not the case with Chromium and Ubuntu 14.04 combination. While you can easily play You Tube videos etc on other web browsers such as Firefox, Chrome etc, in Chromium you will see Adobe Flash player missing notice:
Ubuntu14.04下，除了Chromium未能支持Flash播放器的安装外，其余像Firefox, Chrome浏览器都支持Flash播放器的安装。
The reason why this issue occurs only in Chromium is that until now Chromium used Netscape Plugin API for Flash support. Starting from Ubuntu 14.04, Chromium will stop using Netscape Plugin API. Hence, you will face issues with Adobe Flash Player with Chromium.
从14.04起，Chromium不再使用Netscape 插件API。
To fix this issue, we’ll be using Pepper Flash Player, a safer and more stable version of Flash Player from Google. An Adobe Flash Player Pepper installer is available in Ubuntu 14.04 repositories. This installer downloads Google Chrome, extracts Pepper Flash Player and sets it up for Chromium usage.
要解决这个问题，就需要用Pepper Flash Player。它是一个来自于Google的安全稳定的版本。它已经包含在了Ubuntu 软件仓库中。安装它需要下载Chrome，并从中解压出它。
来源：oschina
链接：https://my.oschina.net/u/209016/blog/290067