I’ve had an annoying problem with my Linux VirtualBox Host + Guest combo for some time and have now only just got around to solving it, so hopefully this can help others in the same situation.

My Host runs Ubuntu 11.04 Desktop, but I run this headless. Unfortunately when it’s run headless and you VNC/TeamViewer/Weaponofchoice you get an 800×600 res. The latest version of VirtualBox + guest additions for Windows guests lets you define resolutions up to 6400×1200 without having to resize the guest window from the host GUI of VirtualBox.

Unfortunately my Ubuntu 12.04 guest wasn’t so lucky, and it defaulted to 800×600 even with the guest additions. The resizing of the guest window from the host worked, but in my case my host was at 800×600 and resizing was a massive pain in the ass.

I spent many hours scouring for how to manually resize a guest and came across many answers, none of which worked for me. I’ll throw what didn’t work below just in case anyone tries the same thing.

x90@ban-roy-x90-vm:~$ cvt 1280 102
# 1280×1024 59.89 Hz (CVT 1.31M4) hsync: 63.67 kHz; pclk: 109.00 MHz

Modeline “1280x1024_60.00”  109.00  1280 1368 1496 1712  1024 1027 1034 1063 -hsync +vsync

x90@ban-roy-x90-vm:~$ xrandr –newmode “1280x1024_60.00” 109.00  1280 1368 1496 1712  1024 1027 1034 1063 -hsync +vsync
x90@ban-roy-x90-vm:~$ xrandr –addmode VBOX0 1280x1024_60.00
x90@ban-roy-x90-vm:~$ xrandr –output VBOX0 –mode 1280x1024_60.00

vboxmanage setextradata global GUI/MaxGuestResolution 1280,1024
vboxmanage setextradata “VM name” “CustomVideoMode1” “1280x1024x16”

None of these worked. In the end I had to create a custom xorg.conf file that manually specified the resolution. As newer versions of Ubuntu did away with a default xorg.conf file I created:

/usr/share/X11/xorg.conf.d/20-monitor.conf

Which contained the below:

Section “Device”
Identifier      “Configured Video Device”
Driver   “vboxvideo”
EndSection
Section “Monitor”
Identifier      “Configured Monitor”
Option   “DPMS”
EndSection
Section “Screen”
Identifier      “Default Screen”
Monitor  “Configured Monitor”
Device   “Configured Video Device”
DefaultDepth    24
SubSection      “Display”
Depth   24
Modes   “1280×1024”
EndSubSection
EndSection

I guess I could have restarted gdm but after a reboot everything was finally working as expected without ever having to resize the guest window!