Fixing the black external monitor after login in Linux Mint

Hey everybody! Time for another fix.

This one gave me a real headache: after I logged in in my HP Elitebook 850 using Linux Mint 17.1 Cinnamon Edition, my external VGA monitor went black. Everything was fine while booting (the splash screen appeared on both screens) and in the login screen, but as soon as I logged in, there was nothing. I immediately went to see if my xrandr output and monitors.xml (.config/monitors.xml) file. The monitor didn’t show up in the xrandr, but there were some signs of problems in the monitors.xml, as shown bellow. xrandr:

<code>Screen 0: minimum 320 x 200, current 1366 x 768, maximum 32767 x 32767
eDP1 connected primary 1366x768+0+0 (normal left inverted right x axis y axis) 344mm x 194mm
1366x768       60.0*+   40.0
1360x768       59.8     60.0
1024x768       60.0
800x600        60.3     56.2
640x480        59.9
DP1 disconnected (normal left inverted right x axis y axis)
HDMI1 disconnected (normal left inverted right x axis y axis)
DP2 disconnected (normal left inverted right x axis y axis)
HDMI2 disconnected (normal left inverted right x axis y axis)
VIRTUAL1 disconnected (normal left inverted right x axis y axis)</code>

Extract of monitors.xml:

  <configuration>
      <clone>no</clone>
      <output name="eDP1">
          <vendor>CMN</vendor>
          <product>0x15be</product>
          <serial>0x00000000</serial>
          <width>1366</width>
          <height>768</height>
          <rate>60</rate>
          <x>0</x>
          <y>0</y>
          <rotation>normal</rotation>
          <reflect_x>no</reflect_x>
          <reflect_y>no</reflect_y>
          <primary>yes</primary>
      </output>
      <output name="DP1">
      </output>
      <output name="HDMI1">
      </output>
      <output name="DP2">
          <vendor>???</vendor>
          <product>0x0000</product>
          <serial>0x00000000</serial>
      </output>
      <output name="HDMI2">
      </output>
      <output name="VIRTUAL1">
      </output>
  </configuration>
  

To solve this problem, my solution was:

• Reboot the computer, and wait for grub (you might have to hold shift or other keys to force the grub to appear)
• At the GRUB boot menu select the correct line but don’t press Enter. Press the “E” key to edit.
• Using the Down arrow key, go down to the line that starts with: linux /boot/vmlinuz………….ro quiet splash $vt_handoff
• In the end of that line, write: video=DP2:d
• Press F10
• Wait for the login screen to appear. When it does, press Ctrl+Alt+F1.
• Login in the terminal that appears, and execute this command to cleanup and backup the monitors file: mv .config/monitors.xml .config/monitors.xml.bak
• Logout (exit) and press Ctrl+Alt+F7 (or F8) to come back to the Mint login screen
• Login as usual

This reverted my monitor back to normal.

Now, I only need to make these changes permanent! To do that, I just need to edit /etc/default/grub (with, for instance, the command sudo nano /etc/default/grub and make the changes. After that, I run sudo update-grub to update the grub with the just updated changes.

I hope this helps if anyone else has the same problem! If you need more information or help, please comment bellow. I’ll give my best to provide feedback!