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I have VirtualBox instance of Centos 5. The screen size is quite small (800*600) and I'd like to increase it to 1280*1080. Under the Gnome preferences for "Screen Resolution" I only get the option for 600*800 or 640*480.

I've tried editing my xorg.conf (based on this tutorial http://paulsiu.wordpress.com/2008/09/08/creating-and-managing-centos-virtual-machine-under-virtualbox/) but it doesn't seem to have made a difference. Here is a snippet from the edited section:

Section "Screen"
    Identifier "Screen0"
    Device     "Card0"
    Monitor    "Monitor0"
    DefaultDepth     24
    SubSection "Display"
        Viewport   0 0
        Depth     24
        Modes   "1280x800"
    EndSubSection
EndSection

Does anyone know how to do this?

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1  
How much video memory have you allocated to the graphics card in VB? Have you installed guest additions? –  Gilles Nov 23 '11 at 23:42
    
According to the Device Manager it's the VirtualBox Graphics Adapter - looking into this now. EDIT - it looks like it may be an option under the Guest Additions (virtualbox.org/manual/ch04.html#idp11274368), so I'm looking into that now - thank you for the tip. –  Aaron Newton Nov 23 '11 at 23:45
    
This seems to have solved my problem. For those looking for the ISO it is available here as VBoxGuestAdditions_4.1.6.iso - download.virtualbox.org/virtualbox/4.1.6. I mounted this using the VirtualBox Devices > CD/DVD > Choose DVD Disk File menu and ran "sh VboxLinuxAdditions.run" from the media/<nameofdisk> directory –  Aaron Newton Nov 24 '11 at 1:31

2 Answers 2

up vote 5 down vote accepted

A maximum resolution of 800x600 suggests that your X server inside the virtual machine is using the SVGA driver. SVGA is the highest resolution for which there is standard support; beyond that, you need a driver.

VirtualBox emulates a graphics adapter that is specific to VirtualBox, it does not emulate a previously existing hardware component like most other subsystems. The guest additions include a driver for that adapter. Insert the guest additions CD from the VirtualBox device menu, then run the installation program. Log out, restart the X server (send Ctrl+Alt+Backspace from the VirtualBox menu), and you should have a screen resolution that matches your VirtualBox window. If you find that you still need manual tweaking of your xorg.conf, the manual has some pointers.

There's a limit to how high you can get, due to the amount of memory you've allocated to the graphics adapter in the VirtualBox configuration. 8MB will give you up to 1600x1200 in 32 colors. Going beyond that is mostly useful if you use 3D.

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Thank you - marked as the correct answer as installing the VirtualBox Guest additions seems to have solved my problem. See my note above if you don't have the installation CDs. –  Aaron Newton Nov 24 '11 at 1:55

You need Virtual Box guest extensions.

In order to install them you first need the RPMForge repository added for yum, follow these instructions:

http://wiki.centos.org/AdditionalResources/Repositories/RPMForge#head-5aabf02717d5b6b12d47edbc5811404998926a1b

Then run this command in a terminal:

yum install dkms
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Thank you, but I already marked this as the answer last November. –  Aaron Newton May 2 '13 at 12:49
1  
@AaronNewton, I totally understand. I just had to go through more research to get it working for me. If I have to do that, I usually post. Not to answer your question as much to maybe help out someone else that comes along and has the same questions with the accepted answer as I did. –  Beachhouse May 2 '13 at 15:17

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