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Linux is a family of open source Unix-like operating systems based on the Linux kernel, an operating system kernel first released on September 17, 1991 by Linus Torvalds. Linux is typically packaged in a Linux distribution (or distro for short).

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How to re-jig screens when I disconnect one (lemmy.ml)

submitted 3 years ago by [email protected] to c/[email protected]

3 comments fedilink hide all child comments

Setup: Ubuntu, Openbox, notebook, occasionally an external screen.

I've set things up so that if an external monitor is attached when I start my notebook, a script (run by Openbox's autostart), xrandr makes that the primary monitor.

What I'd like to do is run that script when I turn off or otherwise disconnect that external monitor, so that I can make the notebook's built-in screen the primary again. Does anyone here have any ideas how to do that automatically?

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[–] [email protected] 0 points 3 years ago (1 children)

there's a file called status in cat /sys/class/drm/card0-CONNECTION where CONNECTION is the name xrandr --listmonitors shows on the right. So e.g. for me it looks like this:

$ xrandr --listmonitors
Monitors: 2
 0: +*DP-3 2560/553x1440/311+0+430  DP-3
 1: +DP-5 1440/553x2560/311+2560+0  DP-5

$ cat /sys/class/drm/card0-DP-3/status 
connected

You can watch this file with inotifywatch -e modify. You can put this in a systemd.path unit which calls your script as a one-shot or with an environment parameter.

You can also use srandrd but IMHO that's a bit overkill when you can do it with pid0 tools 😅

[–] [email protected] 0 points 3 years ago (1 children)

Hmm. Maybe I'm doing something wrong but doing

inotifywatch -e modify /sys/class/drm/card0-HDMI-A-2/status

only gives me "No events occurred." (after ctrl-c stops it). Oddly, I can see the file contents change (connected to disconnected and back again) if I cat it in a separate term window so I don't know what's going on.

[–] [email protected] 1 points 3 years ago* (last edited 3 years ago)

hm, maybe you need another event type. What GPU is it?

Events:
        access          file or directory contents were read
        modify          file or directory contents were written
        attrib          file or directory attributes changed
        close_write     file or directory closed, after being opened in
                        writeable mode
        close_nowrite   file or directory closed, after being opened in
                        read-only mode
        close           file or directory closed, regardless of read/write mode
        open            file or directory opened
        moved_to        file or directory moved to watched directory
        moved_from      file or directory moved from watched directory
        move            file or directory moved to or from watched directory
        move_self               A watched file or directory was moved.
        create          file or directory created within watched directory
        delete          file or directory deleted within watched directory
        delete_self     file or directory was deleted
        unmount         file system containing file or directory unmounted

May be create or delete