X Server – How to Connect from System-Wide Terminal

guiopenboxraspbiantmuxx-server

I am currently trying to make an autonomous drone using the Robot Operating System (ROS). To do this, I have installed Raspbian Lite (Jessie) on a Rasperry Pi 3 and am currently using ROS Kinetic on it. Because it is Raspbian Lite, there were no window managers or desktop environments that came along with the installation. I decided to go with Openbox Window Manager and installed a terminal onto it for convenience. I can just call sudo startx, and the window manager opens up, which can be accesed by Ctrl + alt + F2. Since it is a system-wide terminal, I have also installed tmux for convenience. I am running the xserver on a particular pane and conduct my ROS work on other panes.

Now when I try to run commands that call on a GUI application from my system-wide terminal, I get the error:

QxcbConnection: Could not connect to display
Aborted

Now there are two ways to approach this problem:

Since there is a terminal installed in my Window Manager, I should get ROS working on this? However, I do not know how to change the environment of the terminal emulator inside the window manager so that it is the same as the one on the system-wide terminal. Is it as easy as changing shells?
Actually find a way to send my GUI applications to the tmux pane that is currently running the command sudo startx. How do I switch the parent of a process with another parent?

NOTE: I definitely would prefer the second solution, as it is more elegant and efficient for my workflow.

Best Answer

In a terminal in your GUI environment, type:

xhost +

In the non-GUI environment, type:

export DISPLAY="localhost:0"

Then, graphical applications that you launch from the non-GUI environment will be displayed in the GUI environment.

You can read more in man xhost

See also this answer from: What does this xhost … command do?

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How To Reload xserver After a Change in Keyboard Layout

From here:

To apply new [keyboard] settings, restarting the keyboard-setup service should suffice, otherwise you can try to restart kernel input system via udev:
udevadm trigger --subsystem-match=input --action=change

For completeness, restarting keyboard-setup would look like

# For Ubuntu < 16.04
service keyboard-setup restart
# For Ubuntu >= 16.04
systemctl restart keyboard-setup

Terminal – What is Switching Environments System-Wide Called?

They are kernel virtual terminal devices, multiplexed onto the physical framebuffer and human-input devices by a terminal emulator program that is built into the kernel itself. To applications programs running on top of the kernel, they look like any other terminal devices, such as a serial terminal device. (They have a line discipline, but no modem control.)

The system implements terminal login by dint of running a getty program (or equivalent) and a login program that accept user credentials and invoke login sessions.

The X server program also needs to use the physical framebuffer and human-input devices. It needs to negotiate sharing them with the kernel terminal emulator. It does so by allocating one virtual terminal and telling the kernel to disconnect that from the kernel terminal emulator.

Hence why it appears that the X server "runs" on a particular terminal. When the kernel terminal emulator sees the hotkey chord for switching to the allocated virtual terminal, it cedes control of the framebuffer and human-input devices to to the X server. When the X server sees the hotkey chord for switching to another virtual terminal, the X server cedes control back.

These hotkey chords are not necessarily symmetrical. On one of my systems the hotkey chord implemented by the kernel terminal emulation program for switching to virtual terminal #2 is Alt+F2 whereas the hotkey chord implemented by the X server for the same action is Ctrl+Alt+F2.

When it comes to graphical login, a display manager handles starting up X servers with greeter programs. You're just starting an X server directly and not using a display manager, of course. Once the user credentials have been authenticated, a desktop manager displays a desktop environment, which comprises a set of X client applications of varying degrees of complexity. For complex desktop environments, there is a whole bunch of server programs interconnected via a desktop bus. (On one of my systems, the so-called "small and lightweight" GNOME Editor requires a D-BUS broker and nine other server programs to be running.)

Some of those X client programs can be other terminal emulators, userspace ones, such as LXTerminal, Unicode RXVT, GNOME Terminal, Terminate, roxterm, evilvte, xterm, and so forth. These do not directly use physical framebuffer and human-input devices, and they make use of pseudo-terminal devices.

Best Answer

Related Solutions

How To Reload xserver After a Change in Keyboard Layout

Terminal – What is Switching Environments System-Wide Called?

Further reading

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