On a Ubuntu host I run in Virtualbox a win10 client, but the screen size is limited

Question

I use the software with versions:

• Ubuntu host : 18.04
• Virtualbox: 6.1
• Virtualbox client: win10

I installed this and Win10 client runs, but wit limited screen size. My monitor has 1680 * 1050 pixels, but Windows Client shows only 1024 * 768 pixels. In Windows client I selected the Virtualbox menu -> View -> Virtual screen 1 which shows a disabled list with multiple monitor sizes with 1024* 768 selected. But I can not change this value.

I read I have to install Guest addition ISO but on https://www.virtualbox.org/manual/UserManual.html#additions-windows I could not find this file. Nor on https://www.virtualbox.org/wiki/Linux_Downloads

I have read How to copy between guest OS (Windows 7) running inside Oracle virtual machine 5.0 to host OS (CentOS Release 4.0 final) and Thorian93 answer, but he pointed to a pages where I could not found the guest additions.

My questions:

• Can the Win10 screen size be resized to full screen, without Guest Additions? If so how?
• If this is not possible, where can the proper guest additions be found?

Update 1 :

I installed from page https://www.virtualbox.org/wiki/Download "VirtualBox 6.1.18 Oracle VM VirtualBox Extension Pack" which has "Guest additions" in it. Which seems to be successful.

In VirtualBox server, I selected the Win10 client -> Settings _. Storage -> And added VBoxGuestAdditions.iso as optical storage.

I started Win10 VBoxVlient -> VirtualBox menu -> Devices -> Optical Devices. And I saw a list with VBoxGuestAdditions.iso in it with a selected checkbox. So this seems to be ok.

But the screen size is not full screen yet.

In Win10 VBoxClient -> VirtualBox menu -> View -> Virtual Screen 1, still I different screen sizes where disabled.

Update 2:

To see if the extension pack was properly installed I run:

bernard@p10:~$ VBoxManage list extpacks
Extension Packs: 1
Pack no. 0:   Oracle VM VirtualBox Extension Pack
Version:      6.1.18
Revision:     142142
Edition:      
Description:  Oracle Cloud Infrastructure integration, USB 2.0 and USB 3.0 Host Controller, Host Webcam, VirtualBox RDP, PXE ROM, Disk Encryption, NVMe.
VRDE Module:  VBoxVRDP
Usable:       true 
Why unusable: 
bernard@p10:~$ 

Update 3:

I checked if the guest addition was really installed on Win10:

VBoxManage showvminfo VBox_Win10

with as (stripped) result:

Video mode:                  1024x768x32 at 0,0 enabled
Guest:

This seems to imply guest additions in known to VirtualBox, is visible in the Client (Virtualbox menu -> Devices -> Optical Drives -> VBoxQuestAdditions.iso is checked) but can not be installed (Virtualbox menu -> Devices -> Insert Guest Addition CD Image does not respond)

Answer 1

Can the Win10 screen size be resized to full screen, without Guest Additions? If so how?

Yes; However, if you still want the guest additions VBoxGuestAdditions.iso should be located within /opt/VirtualBox/additions/. This will allow you to follow the rest of the installation directions in order to install it within the guest OS.

If this is not possible, where can the proper guest additions be found?

As others have pointed out you actually need the VirtualBox Extension Pack.

You can install it with

VBoxManage extpack install Oracle_VM_VirtualBox_Extension_Pack-6.1.18.vbox-extpack

VBoxManage extpack cleanup

and can verify it's actually installed with the following command:

VBoxManage list extpacks

Source: VBoxManage extpack

VirtualBox 6.1.18 Oracle VM VirtualBox Extension Pack

Answer 2

Can the Win10 screen size be resized to full screen, without Guest Additions?

No, not normally or with all flexibility. You need the Guest Extensions installed.

https://www.virtualbox.org/wiki/Downloads

VirtualBox 6.1.18 Oracle VM VirtualBox Extension Pack

 All supported platforms 

Support for USB 2.0 and USB 3.0 devices, VirtualBox RDP, disk encryption, NVMe and PXE boot for Intel cards. See this chapter from the User Manual for an introduction to this Extension Pack.

Here is the link for the file:

https://download.virtualbox.org/virtualbox/6.1.18/Oracle_VM_VirtualBox_Extension_Pack-6.1.18.vbox-extpack

I hope this assists you.

Answer 3

The problem was caused my confusion, solving the confusion was almost solving the problem. With help of https://forums.virtualbox.org/viewtopic.php?f=2&t=101549

My confusion was mixing VirtualBox Extension Pack and VirtualBox Guest Additions. I thought Guest Additions was part of Extension Pack, but they are total different tools. VirtualBox Extension Pack should be installed on the host, if needed. But it is not needed at all.

My VirtualBox Manager was 6.1.16 and the Extension Pack was version 6.1.18 which made thinks worse.

This conflict caused that I could not execute in the VM Virtualbox menu -> Devices -> Insert Guest Addition CD

So I removed it using VirtualBox Manager -> Menu -> File -> Preferences -> Extensions Now there is no conflict between versions. That limits the options and limits the confusion.

VirtualBox Guest Additions it just on the Virtual Machine and can be installed by VM Virtualbox menu -> Devices -> Insert Guest Addition CD Because there is no conflict anymore this could be executed, I could select VBoxGuestAdditions.iso . After doing so, and a reboot, I could set the display to the full screen size.