我刚刚安装了 Ubuntu 15.04 和 Gnome 3 桌面环境。如果我尝试从命令行运行 GUI 程序（例如 Gedit），我会得到：
XXXXX:~$ gedit
No protocol specified
** (gedit:3299): WARNING **: Could not open X display
No protocol specified
gdk_mir_display_open
Failed to connect to Mir: Failed to connect to server socket: No such file or directory
Unable to init server: Could not connect: Connection refused
(gedit:3299): Gtk-WARNING **: cannot open display: :0
But, if I launch gedit from the gnome "search" window, it comes up fine.
I have some custom GUIs I use and I typically start them from the command line.
附言：由于 Nvidia 硬件问题，我无法使用 Ubuntu 桌面环境。