I have recently created a Ubuntu 12.04.2 64 bit virtual machine on VirtualBox, and I am not very used to Linux (I used Linux Mint for a few weeks some time ago), so please refer the full name of stuff, not just "the what-not-command".

The problem is I can't set the full resolution my computer supports (I think it is 1366 by 768),

I have found similar questions and tried most of the respective solutions, thy did not work.

If I type xrandr to the terminal I get:

xrandr: Failed to get size of gamma for output default
Screen 0: minimum 640 x 480, current 1024 x 768, maximum 1024 x 768
default connected 1024x768+0+0 0mm x 0mm
    1024x768       61.0* 
    800x600        61.0  
    640x480        60.0  

As you can see, the maximum is too low. And in the settings of the screen (I mean, with GUI) only 1024x768 and 800x600 appear. I don't remember exactly which answer of those questions, but it was one in the terminal (again, with xrandr) that made the resolution I wanted appear (although it gave an error when selected, not even changing to the 1366x768 resolution first and then back to 1024x768).

  • Ah! Now I remember with all uses of xrandr I got that «xrandr: Failed to get size of gamma for output default» line.
    – JMCF125
    Jun 25 '13 at 20:29
  • 2
    You need the guest additions to change screen geometry.
    – Takkat
    Jun 25 '13 at 20:36
  • @Takkat You should probably post that as an answer.
    – Panther
    Jun 25 '13 at 20:54
  • In the comment you've stated you already have installed the Guest Additions. Please verify this by including the output of lsmod | grep -io vboxguest | xargs modinfo | grep -iw version in your question.
    – gertvdijk
    Jun 25 '13 at 21:36
  • @gertvdijk, I've installed when Takkat and bodhi.zazen commented (about 1 hour ago). The answer came less than half an hour ago.
    – JMCF125
    Jun 25 '13 at 21:48

You'll need to install the VirtualBox Guest Additions in order to be able to use graphics properly. See the Q&A linked below on how to do that.

How do I install Guest Additions in a VirtualBox VM?

Background info

The graphics cards being emulated by the VirtualBox host required optimizations to run properly, smooth and providing integration with the host OS (shared folders, shared clipboard, mouse pointer integration, etc.). These optimizations are accomplished by some cooperation from the driver at the other end of the virtual graphics card: the guest operating system. The Guest Additions contain drivers for several of VirtualBox's features, including the driver (Xorg an kernel module) for the graphics card VirtualBox is emulating.

Without the driver, it's just running in a plain limited VESA mode, without any form of hardware acceleration. You'll notice it's a bit sluggish and you won't be able to use all features like high resolutions.

  • Already done. Thank you very much! Nonetheless, can you answer also why does this happen?
    – JMCF125
    Jun 25 '13 at 21:31
  • @JMCF125 Please include such important information in your question. It would be sad if more answers come in with things you've already tried. And are you sure the guest additions are installed properly? An update of the kernel will render it useless again if you don't have installed DKMS for example.
    – gertvdijk
    Jun 25 '13 at 21:33
  • Please check the comment above. (I'm writing this for third-party viewers, you're already notified).
    – JMCF125
    Jun 25 '13 at 21:51
  • So, did it solve your issue then? I don't quite get what you mean now.
    – gertvdijk
    Jun 25 '13 at 21:52
  • Yes it did. I'd just like you to explain the reason for which this happens before I mark this answer as accepted.
    – JMCF125
    Jun 25 '13 at 22:53

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