gsettings set org.gnome.settings-daemon.plugins.power button-power shutdown

will change your the behaviour of the power button of your system from interactive (default) to immediate normal shutdown.

The command is gsettings set org.gnome.settings-daemon.plugins.power button-power <option>

Available options are:

• Blank: does nothing
• Suspend: makes your system suspend
• Shutdown: starts a normal issued shutdown procedure
• Hibernate: hibernates your system
• Nothing: does nothing
• Log out: log your user out

参考链接：http://askubuntu.com/questions/430776/how-can-i-modify-the-power-button-behaviour

修改ubuntu按下关机键触发的事件