External monitor not detected

I had my laptop working with an external monitor and the HDMI port for a long time. My laptop doesn’t sleep (another issue I need to resolve) and I forgot to plug it in last night. After booting it didn’t detect my external monitor. I tried a reboot and a second monitor, no luck.

EDIT: solved this… one more reboot did the trick :wink:

I’m posting a response in case anyone else encounters this issue. This was happening to me, but multiple reboots did not seem to fix the issue.

Searching the web I saw and attempted various proposed solutions. The one that seemed to work for me was to run sudo dpkg-reconfigure gdm3 and then reboot again.

Before that I tried installing lightdm (a different display manager), attempted reconfigure and reboot, but that did not work, so I uninstalled.

The other popular recommendation to purge and install nVidia drivers seemed like a bad idea on Purism hardware, as they are private & non-free.

It would be great if someone more knowledgeable about display managers might chime in and make other recommendations to help troubleshoot and fix this if it happens again in the future. A few questions I have:

  • I have been having issues with my battery. Is this problem related to power management? Is it recommended to leave the laptop plugged in while connected to an external monitor? (I typically unplug my laptop when the battery reaches 100% charge, then let it drain for awhile and plug it back in again.)
  • Is this a hardware or software issue? What video drivers do we use in Purism laptops / PureOS?
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I’ve just had this happen to me after performing a full upgrade via apt. I tried the dpkg-reconfigure advice above, but without success.

Interestingly, the gnome update manager says there are packages related to Gnome to be updated, but sudo apt update && apt list --upgradable yields no results, so my theory that that the former is a front-end for the latter must be false!

Anyway, upgrading those packages makes no difference. I still have no external monitor

It happened to me 2 times. Once after carrying a laptop in a briefcase, another time for no reason, in the morning. It scared me a lot, because I work with an external monitor more than 50% of the time. But fortunately, this did not happen again.

I think this might be a hardware issue because the monitor is detected again with zero software changes, and none of the posts in this thread seem to have any criteria linking them.

I didn’t really “do” anything to get it working again. My monitor was still not being detected after coming into work this morning, so I unplugged it, blew out the port like it was an old NES cartridge and tried again. Still no joy, so I restarted the laptop, just for the hell of it, and this time the monitor was detected.

I don’t think blowing out the port did anything. My guess is that it was necessary to restart the laptop in order for the OS to re-register the HDMI port. I also note that the monitor detection was lost after an OS restart, as it was for the author of this thread, fredpastiat.

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I noticed something similar, but I just have to log out and log back in my desktop.

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