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My laptop recognises external display devices if I connect them before booting the system, but many times it doesn't if I connect while the system is running. In this case, rebooting naturally solves the problem.

Is there a way to force Ubuntu to detect external displays? Opening up the display menu and pressing "Detect displays" does nothing.

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    Video card and driver in use? Commented Dec 8, 2015 at 17:19
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    From lshw -c video: it's Haswell-ULT Integrated Graphics Controller and the driver is i915. Commented Dec 8, 2015 at 17:53
  • Try logging out, going to a VC (ctrl-alt-F1) and restarting X (askubuntu.com/a/79587/16395). Sometime it works. Without logging out --- I never managed it. Commented Dec 8, 2015 at 21:13
  • Thanks. I was hoping there'd be a way to do that without logging out. Commented Dec 10, 2015 at 19:41
  • I encountered this issue this week, with the fun added factor that rebooting wasn’t doing the trick. What did work was to use the instructions at askubuntu.com/questions/82140/… to boot to an older kernel. Commented Jul 19, 2023 at 16:27

9 Answers 9

Reset to default
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Actually, you don't need to log out. Simply going to a VC with ctrl-alt-F1, restarting x with sudo service sddm restart and and going back to your graphical interface with ctrl-alt-F7 (or F2) should do it.

This way, you don't lose all your windows...

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    This seems like it would work, since restarting my laptop works, but it doesn't. Commented Mar 3, 2017 at 20:14
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    This trick perfectly solved my problem => a case of replacing the current monitor with a new one while Ubuntu 16.04 LTE is running without reboot/logout. I just had to press Ctrl + Alt + F1 while my old monitor is connected, disconnect it and connect my new monitor, press Ctrl + Alt + F7 and it worked instantly! Thank you so much! Commented Apr 19, 2017 at 2:35
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    Nice! before this I was kind of frustrated with 17.10. For me actually just doing Ctrl+Alt+F1 and logging back in is sufficient. Commented Feb 26, 2018 at 17:59
  • I'm also with 17.10, with Gnome replacing Unity. And to get back I used Ctrl+Alt+F2, instead of F7 Commented Apr 9, 2018 at 10:19
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    In Ubuntu 18.04, it seems the default default graphical interface is F1. So I do Ctrl+Alt+F2, then Ctrl+Alt+F1. Commented May 12, 2018 at 13:20
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To enable all outputs in their default mode, run:

$ xrandr --auto

For more information, see:

https://xorg-team.pages.debian.net/xorg/howto/use-xrandr.html

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    xrandr says the display is disconnected, but it works fine in Windows. Commented Dec 9, 2018 at 7:49
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    This one worked for me. My third screen immediately started working. Commented Sep 29, 2019 at 4:37
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I just encountered this issue with my Dell Latitude E5550 using a port extender and two external monitors.

My problems began when I had a power failure. For silly reasons, I could only plug in one of my two monitors, so I opened up the screen display interface and de-activated the screen that didn't have power.

Awesome!

Once the power came back on the process to turn my screen back on was unintuitive. I couldn't see it in the screen display interface even after rebooting or redocking my laptop.

So I tried $ xrandr --auto and got Ubuntu to extend to "one" screen but duplicate to both of my externals (they are two of the same model). Amusing but not useful.

It was only when I clicked on "1 Built-in display" like in the screenshot below that I was able to select my "3rd" screen and turn it on again.

The Screen Display Interface

Doing this flipped the two screens around for some reason and I had to rearrange them but that was easily fixed!

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  • lshw -c video doesn't list monitors it lists your drivers. Commented Mar 11, 2019 at 10:14
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    You're absolutely right! I will edit my answer. Commented Mar 12, 2019 at 11:04
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Adapting Amanda's solution to modern ubuntu with systemd and/or other display manager than sddm : "Actually, you don't need to log out. Simply going to a VC with ctrl-alt-F1, restarting x with sudo systemctl restart <your display manager> (eg gdm or lightdm) and going back to your graphical interface with ctrl-alt-F7 (or F2) should do it.

This way, you don't lose all your windows..."

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  • How do you find out what <your display manager> is? Commented Feb 17, 2023 at 17:10
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    On systems using systemd, try this : systemctl status display-manager. More info on that question here : unix.stackexchange.com/questions/20370/… Commented Feb 18, 2023 at 21:05
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    sudo systemctl restart gdm or sudo systemctl restart gdm3 both killed my GNOME session (I lost my open windows), and didn’t enable my external monitor. (my problem is with external monitor not enabled after resume. Disconnecting and reconnecting the cable enables it, but I don’t want to have to do that every time) Commented Aug 9, 2023 at 0:20
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I also have Dell Latitude E5550, I have one onitor via hdmi, and one via usb-c. Then one via usb-c is not detected sometimes, and for me what it works, is unplug/plug the hdmi port in the monitor, while the rest is connected.

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  • Just solved my issue with Dell XPS 13. Commented May 13, 2021 at 20:22
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Working solution: Disable secure boot in the bios/efi menu.

Hello Everyone, I am coming from a TongFang GK5CN6Z and I had this issue. I noticed it was an issue after having ran the latest updates on Ubuntu. Turns out I had to disable secure boot in order for it to work.

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  • For me it was already disabled. so I enabled it, boot on ubuntu, disabled again and then it worked! Commented Jul 5, 2021 at 17:36
  • why would this work? are there any problems with disabling secure boot? Commented Feb 8, 2024 at 15:16
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I had issues with dual monitors when using prime-select intel when proprietary Nvidia drivers are installed. I guess either uninstalling Nvidia drivers or using only prime-select nvidia works, though Nvidia drivers have their own problems.

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If the external monitor can't be detected by using xrandr --auto, or even by booting to different OS, reboot Ubuntu using a previous kernel. If the computer detects the monitor in the older kernel, you can go back to the latest one without any problems.

I don't know the exact reason why it works, but it definitely worked for me.

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  • xrandr --auto closed my current GUI sessionn ! But afterwards I could use all 3 Displays: Build in Laptop and two external Display. Displays are connected via USB / DisplayLink Commented Oct 10, 2018 at 8:27
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OK I had this very problem last night, in spades. I think I got Microsataned...

What happened: I hooked up a w11 lappy to my HDMI monitor and did some work. Finished up and disconnected it, back to Ubuntu 22.04.

External monitor was black (but detected under System Settings), internal screen fine. Tried both of my other Ubuntu systems (one file server, one games machine). Monitor also black. Tried every solution in this post, and many others, for about an hour. Nada. There is no NVIDIA in this picture, so none of those things applied. Tried just about all the other suggestions though.

My main lappy is dual-boot Ubuntu and W10 (not upgradable, wouldn't anyway), booted to W10, ext. screen worked! Tried more things in ubuntu...nada.

What eventually worked was power cycling the monitor, i.e. pulling out the power cord--deep zero reset, not turning it off and back on, that did nothing. The problem went away and I've had no trouble since.

Conclusion: W11 DID SOMETHING to my monitor which only a power cycle could clear. I have no idea what, but I don't see what other explanation there could be. Does W11 mess around with monitor modes or HDMI signals in a way that Ubuntu can't deal with the resulting state? I dunno. Baffling and annoying, and yet another reason for me to loathe microsoft as if I needed one.

If anyone is interested, system is intel Core I-7 with Mesa Intel gfx. I hope this post helps someone.

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