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When I try to increase the resolution in my virtual machine (Xen), running a debian distribution (Kali/Parrot in this case), I get a black screen. I use xrandr, because in the GUI, the max resolution is not high enough.

I managed to crank it a bit up, but at a certain level, it just shows a black screen.


The commands I used: First we use gtf for calculating the modeline of possible resolutions:

gtf <xres> <yres> <refresh> [-x]

Give the desired values for x-resolution, y-resolution and refresh rate. The flag -x is default and can be omitted. For a portrait resolution 480x640 at 60 Hz you will get the following output:

$ gtf 480 640 60 -x
$ 480x640 @ 60.00 Hz (GTF) hsync: 39.78 kHz; pclk: 24.82 MHz Modeline "480x640_60.00" 24.82 480 504 552 624 640 641 644 663 -HSync +Vsync

From this we can copy & paste the modeline to add it to xrandr list of known resolutions:

xrandr --newmode "480x640_60.00" 24.82 480 504 552 624 640 641 644 663 -HSync +Vsync

and:

xrandr --addmode VBOX0 480x640_60.00

Replace VBOX0 with the appropriate monitor.


  • Are you maybe overdriving either the video card or the monitor? Or - since you've tagged with virtual-machine maybe your vGPU hasn't got enough video memory to run properly? – roaima Mar 13 at 12:18
  • I tried to use a ridiculous low refresh rate to test that, but it doesn't seem to help. – 99DJFKDJFO Mar 13 at 12:49
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    @99DJFKDJFO what user roaima is trying to say is that if your vgpu does not have enough memory to support the resolution you cannot use that resolution. Refresh rate has very little to with that. How much virtual memory does your vm have? Edit your question to include the results of the following commands: – kemotep Mar 13 at 13:05
  • xe vm-param-get uuid=[UUID of the VM in question] param-name="platform" param-key=vga and xe vm-param-get uuid=[UUID of the VM in question] param-name="platform" param-key=videoram – kemotep Mar 13 at 13:06
  • @kemotep Does the xe command also works on Qubes-OS? – 99DJFKDJFO Mar 15 at 11:00

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