GUI over SSH with X11
SSH is awesome, but your options when trying to run a GUI application are a bit limited, especially on headless computers. Luckily there are a few ways to go about handling this problem, even if your computer has no monitor directly connected to it.
SSH into the machine
First of all, you need to ssh into your machine to get everything set up. Now you have a couple options. Some people may have a display (be it a full monitor, a TV screen, a touch display, etc) and others may have nothing it all.
If you have NO display
If you have no display connected to your device such as a headless RPI or a remote server, you can run the following command.
ssh -X user@ip_address
The -X flag tells the connection to forward all display requests to your own computer! This means if you try to run a GUI app on the device, the window will appear on your local machine.
If you want real-time viewing and can’t run locally, use X11 forwarding (ssh -X). This setup is straightforward and preserves the interactivity of the application at hand.
If you DO have a display
If you do in fact have a display connected to your device, you can force the GUI app to run on that display instead. To do so, you need to check the “display” variable. Be sure to run the following NOT over ssh, but directly logged into the machine physically
echo $DISPLAY
Typically, this will return something like :0.
If you cannot run this command, you may assume the output to be :0
Now export this variable in your SSH client. Return to your SSH window and run the following command, replacing :0 with whatever you saw from the previous command.
export DISPLAY=:0
This method ensures that even though you’re SSHed into the Pi, the output is displayed on the physically connected monitor!