Ubuntu in VirtualBox does not stretch to full screen although Guest Additions are installed (SOLVED)

1. Are the Guest Additions actually installed?

First, make sure you actually have Guest Additions installed.

It is recommended to update the guest OS to the latest package versions:

sudo apt update
sudo apt full-upgrade

After the update is complete, restart your computer:

reboot

There is a guest additions package in the standard repositories. It can be installed as follows:

sudo apt update
sudo apt install virtualbox-guest-dkms

2. Enabling full screen mode and resizing the guest OS screen

To switch to full screen mode, press Host+A, or go to Menu → View → Full screen mode.

If this did not help either, then maximize the virtual machine window to the maximum, then go to Menu → View → Auto-resize Guest Display.

3. Changing the type of graphics controller

If that doesn't work, try with different graphics controllers. With the virtual machine turned off, you need to go to its settings, then to the Display tab.

On this tab, you need to set VMSVGA or VboxVGA as the Graphics controller - try different controllers and see which one works with “Auto-resize Guest Display”.

4. Reinstallation and reconfiguration of virtualbox-guest-dkms:

sudo apt remove virtualbox-guest-dkms --purge
sudo apt install virtualbox-guest-dkms
sudo dpkg-reconfigure virtualbox-guest-dkms

5. Increase the video memory size

In the settings of the virtual machine, increase the video memory size to the maximum

6. Manually change the screen resolution settings

Go to the screen resolution settings of your guest virtual machine and select another, more appropriate.

So

Some of these methods should help you. Write in the comments – which one, it will help other users who have encountered the exact same problem.

If all else fails, then it is recommended to update VirtualBox to the latest version, and also make a full system update and reboot:

sudo apt update && sudo apt full-upgrade -y
reboot