1、打开终端运行命令：gsettings set com.canonical.Unity.Launcher launcher-position Left
如果OK，那就OK了
2、如果出现错误提示：
GLib-GIO-Message: Using the ‘memory‘ GSettings backend. Your settings will not be saved or shared with other applications.
则运行如下命令：export GIO_EXTRA_MODULES=/usr/lib/x86_64-linux-gnu/gio/modules/
再运行命令1即可