Handle `Error: no DISPLAY environment variable specified` automatically

Question

Handle `Error: no DISPLAY environment variable specified` automatically

Closed this issue 2 months ago · 13 comments

Running Firefox in Arch TTY with Wayland, but no X11 and no display manager, gives this error:

$ firefox
Error: no DISPLAY environment variable specified

Running cage firefox in the same TTY starts Firefox in graphical mode, no problem.

The problem

The problem is to prepend cage to every command that needs graphical mode.

The question

Is it possible to intercept application calls that result in Error: no DISPLAY environment variable specified message?
And if yes, is it possible to run cage to handle these calls? Without manually prepending cage to each command.

EDIT: This is pure Wayland system with no X11.
EDIT2: Rewrite of the explanation.

Answer 1 · 2024-11-11T15:41:20.000Z

If cage is compiled with Xwayland support, it will set the DISPLAY env var for processes started inside it.

Answer 2 · 2024-11-11T15:44:44.000Z

@emersion for processes inside cage this message doesn't appear.

Answer 3 · 2024-11-11T15:47:40.000Z

If you want to make a process started outside of cage connect to the X11 server started inside of cage, you'll need to set DISPLAY to the same value as the one set inside cage (note, the value might change).

Answer 4 · 2024-11-11T15:52:11.000Z

@emersion I don't have X11 server at all and do not want to connect to it.

Answer 5 · 2024-11-11T15:53:43.000Z

@emersion I've updated the issue description to clarify it is pure Wayland system with no X11.

Answer 6 · 2024-11-11T15:54:51.000Z

Alright, then the same applies to Wayland with the WAYLAND_DISPLAY env var.

Answer 7 · 2024-11-11T15:58:34.000Z

@emersion who produces Error: no DISPLAY environment variable specified error? I believe I've seen this message with other apps too.

If is it lib or kernel, can it execute cage instead of showing this message? Because I believe cage is not started at this point.

Answer 8 · 2024-11-12T09:02:55.000Z

@abitrolly, I don't get it. Could you try to be a bit more extensive in your description?
Executing cage firefox will set the correct environment variables for the Firefox process you are launching, among them WAYLAND_DISPLAY or even DISPLAY if Cage supports XWayland and everything is fine to start it.

If you don't start Firefox as a Cage argument, you can set the variables by yourself first.

If you try to add arguments to Firefox on Cage command line, use -- to split Firefox options to Cage ones: cage firefox -- -kiosk.

Answer 9 · 2024-11-12T11:46:31.000Z

@joggee-fr I've rewritten the explanation. Hopefully it makes sense now.

Answer 10 · 2024-11-12T16:02:56.000Z

@abitrolly, I think I understand a bit your case.
For me, you can't handle this error but I don't think you need to.
Use -s option for Cage to enable VT switching. Start Cage in VT7 and go back to VT1 for example. In this VT, export WAYLAND_DISPLAY=wayland-0. Consequently, when you will start a Wayland client, it will attach to running compositor. Switch to VT7 to see it. Note that Cage primary client can be a simple script doing a sleep infinity.
Is it what you are looking for?

Answer 11 · 2024-11-14T14:28:44.000Z

That doesn't sound like a kiosk use case. :D I would prefer to have only one application active in a single TTY. The same way vim starts in console and gets exclusive mode.

Answer 12 · 2024-11-14T14:38:56.000Z

I gave you one possibility but I don't really know your use case.
Back to the topic of this issue i.e. handling DISPLAY or better WAYLAND_DISPLAY not set in environment, it exists hacky way to do this. But for non-child process of Cage, it is outside of the compositor business.

Answer 13 · 2024-11-14T14:47:43.000Z

Closing this as out-of-scope.