https://blog.toright.com/posts/1266/%e5%9c%a8-linux-gdm-gnome-display-manager-%e4%b8%8b%e5%95%9f%e5%8b%95%e5%9c%96%e5%9e%8b%e4%bb%8b%e9%9d%a2%e6%87%89%e7%94%a8%e7%a8%8b%e5%bc%8f