我使用了 xbindkeys 和 xmodkey 两个方式设置键位映射，最终都没有成功。 感觉应该是Gnome 接管了 Keyboard 的设置
上网查到了用gnome-tweak-tool是可以设置 Ctrl 位置的。
13.10+:
Install and use gnome-tweak-tool > Keyboard & Mouse > Keyboard > Additional Layout Options > Caps Lock behavior.
Pre 13.10:
Open the Keyboard Preferences dialog (System -> Preferences -> Keyboard). On the layout tab, click the Options… button. Expand the Ctrl key position section and select Swap Ctrl and Caps Lock.
Those settings should be applied each time you log in, and will only affect your user account.