My laptop used to display on both. I re-installed, trying to get it to play sound through HDMI. During installation, it detected on both displays. And I had it "mirrored". Then the mirror stopped displaying on the laptop but only on the TV. Now, when I turn it on, there are a few lines on the TV down the sides, but once I log in, it says "no signal" on my TV and only displays on the laptop. I
If I go into the "settings" it doesn't seem to detect the 2nd display.
Ubuntu 18.04.
Here's something else. I left it for most of the day and when I came back and logged in, it was working just they way I had wanted. . . namely, it is displaying on the TV. I don't know if there is something to learn from this but what I will try is if it is not working, I'll try to leave it for a while and see if that works.
Or is there something I can do proactively?
It booted up the same way today . . . not recognizing the TV. I tried the alt-F, r to restart the interface and it didn't work. I tried restarting it and that didn't work. Now, I'll just leave it on to shut down on its own to see if it will recognize the TV later.
xrandr
command show?