Hey James, sorry to hear you're hitting this resolution roadblock with your Kubuntu VM—let's work through some fixes that should get you that 2580×1440 display you want.

First up, let's make sure Oracle VM Guest Additions are properly installed. Kubuntu's Plasma desktop can sometimes have slightly different dependencies than other Ubuntu flavors, so let's cover that base:

• Open up your terminal and install the essential build tools first:

  sudo apt update && sudo apt install build-essential dkms linux-headers-$(uname -r)
  

• Head to the Oracle VM menu bar, click Devices → Insert Guest Additions CD image. A popup should appear asking to run the installer—follow the prompts, and restart your VM once it's done.

If Guest Additions are already set up but you still don't see the resolution option, let's manually create the custom resolution:

1. Generate the mode details for 2580×1440 using cvt in the terminal:

   cvt 2580 1440
   

   You'll get output that looks something like this (the exact numbers might vary a bit):

   2580x1440 59.96 Hz (CVT 3.71M9) hsync: 89.48 kHz; pclk: 325.00 MHz #

   Modeline "2580x1440_60.00" 325.00 2580 2784 3064 3548 1440 1443 1448 1493 -hsync +vsync

2. Copy everything after Modeline, then add this mode to your display setup with xrandr:

   xrandr --newmode "2580x1440_60.00"  325.00  2580 2784 3064 3548  1440 1443 1448 1493 -hsync +vsync
   

3. Find your display's name by running just xrandr—look for something like Virtual1 or VGA-1 (this is your VM's display output). Let's say it's Virtual1, so add the new mode to it:

   xrandr --addmode Virtual1 2580x1440_60.00
   

4. Switch to the new resolution right away:

   xrandr --output Virtual1 --mode 2580x1440_60.00
   

5. To make this stick after reboots, edit the ~/.xprofile file:

   nano ~/.xprofile
   

   Paste the three xrandr commands (newmode, addmode, output) into this file, save with Ctrl+O, hit Enter, then exit with Ctrl+X. Next time you log in, the resolution will apply automatically.

Also, double-check your Oracle VM settings:

• Open your VM's settings window, go to the Display tab. Set the Graphics Controller to VBoxSVGA (this is the most compatible option for high resolutions in modern Ubuntu-based distros), and crank up the Video Memory to its maximum allowed value (usually 128MB or 256MB, depending on your host hardware).

If none of the above works, try updating your Kubuntu system fully to make sure you have the latest kernel and driver fixes:

sudo apt full-upgrade

Reboot after the update, then check again for the resolution option.

Hope one of these steps gets your Kubuntu VM displaying at 2580×1440 smoothly!

备注：内容来源于stack exchange，提问作者James