[Solved] Highest Resolution for Linux Guest?

[PeterE]

I am running Arch Linux in a VirtualBox 6.1.0 Guest VM. My monitor is a 4K UHD. The highest resolution I can set for the guest windows is 2560 x 1600. I have used this command in a Windows cmd:

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VBoxManage setextradata "Arch Linux" "CustomVideoMode1" "3000x2000x24"

Then I have edited the /etc/default/grub file:

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GRUB_GFXMODE=3000x2000x24

And I have run:

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grub-mkconfig -o /boot/grub/grub.cfg

When I start the VM the Grub goes to the size 3000 x 2000 until Linux starts booting. Afterwards I am back to 2560 x 1600. What can I do to get my window size?

I can also not go to seamless mode. And if I drag on the frame of my VM window the area for my Linux guest doesn't get bigger.

[mpack]

You choose display resolutions inside the guest OS, just as you did in grub. All that your earlier setextradata command does is enable a video mode, it doesn't force the guest OS to choose it. Hardware doesn't dictate to an OS how the hardware is to be used.

Incidentally, unless your host OS is running a 24bpp graphics mode, doing so in the guest is a bad move leading to poor performance. Host and guest should use the same graphics mode (usually 32bpp RGBA).

[socratis]

My monitor is a 4K UHD

You never said what's the exact resolution of the monitor, as there are several definitions of what that can mean, see 4K resolution » Resolutions from Wikipedia.

I noticed that 2560×1600 = (3840×2400)÷1.5, which could be a weird coincidence given the fact that 3840×2400 is one valid 4K resolution, or it could be what your monitor conveys. Why your Guest/VirtualBox gives a maximum of 2560×1600 could depend on several factors. But, can you try going to "VirtualBox Preferences" » "Display" » "Maximum Guest Screen Size", and change it to "Hint", with "Width" and "Height" set to 3840 and 2400 respectively?

BTW, if you're trying to set custom modes, I wouldn't select 2979x1983 for example, I would try something more "computer friendly". And never give it the actual screen size, that mode should be reserved for Full-Screen mode...

'mpack' already addressed the 24 bpp. No, no, no...

[PeterE]

Let me answer both replies in one post:
I understand what the setextradata command does.

My monitor has a resolution of 3840 × 2160. In the Wikipedia article it is called 4K UHD.
My Monitor has a color depth of 8bits only. I couldn’t find out how many colors my host OS (Windows 10) has. The graphic card is a MSI GT 1030 DDR5.

While I am running the VM the highest resolution I can set is 2560 x 1600. This is a 16/10 ratio, but my monitor has a 16/9 ratio.

I have set the "Maximum Guest Screen Size" to "Hint" and 3840 × 2160, but I still cannot set a higher resolution in the VM.

May I ask again why I can't get seamless mode?

[scottgus1]

if I drag on the frame of my VM window the area for my Linux guest doesn't get bigger.

This is a Vitualbox behavior in Windows guests, too, if you don't have the official Guest Additions from the GAs ISO that came with Virtualbox installed or you don't have "Auto-resize Guest Display" checked in the guest window's 'View' menu.

Arch Linux

Note that the above comments about Guest Additions may not apply if your guest is a text-only terminal. You may have to make a setting change to your Arch terminal to force your desired resolution like you did with grub. Google for how to do this. (It seems common for Linux OS's to change text resolution in the text boot-up process.)

While I am running the VM the highest resolution I can set is 2560 x 1600....I can also not go to seamless mode.

If you have a GUI guest with a desktop, zip and post a guest vbox.log using the forum's Upload Attachment tab, so we can see if you have the correct GAs installed. Start the guest from cold boot, not save-state, run until log-in and try the resolution changes. Then shut down from within the guest OS, then when the guest Virtualbox window is gone, zip and post the log.

[PeterE]

I am running Xfce as my GUI system.
The "Auto-resize Guest Display" is grey, so I cannot check it.
The "Seamless Mode" is also grey.

I have attached the VBox.log file from my last session. I hope it helps.

[scottgus1]

00:00:01.245433 VirtualBox VM 6.1.0 r135406 win.amd64 (Dec 10 2019 14:34:16) release log
00:07:03.689329 VMMDev: Guest Additions information report: Version 6.0.0 r127566 '6.0.0'

00:00:01.357011   VRamSize <integer> = 0x0000000002100000 (34 603 008, 33 MB)

Your Guest Additions seem out of date, and your video memory seems just barely able to squeeze that high-res you want.

Bump that video ram slider up to 128MB. Uninstall the GAs in your guest OS, reboot, and install the GAs from the Device menu, Insert Guest Additions CD Image, and run the installer from the guest's CD drive. Note any errors you may see, and if none happen reboot the guest and try the desired screen setups.

[mpack]

Did you fix that problem with 24bpp? I doubt you'll get seamless mode working if not. The latest log still has an attempt to select 24bpp, though that may just have been the guest restoring the last mode before you changed it.

[socratis]

My Monitor has a color depth of 8bits only.

Let me doubt that, I'm sorry. Maybe you mean 8 bytes and not bits? Even then, I'm not sure how you got that conclusion, can you elaborate?

What's your monitor? Make/model/version, the whole thing please so I can track it down...

[PeterE]

I have done a lot of testing again.
First of all, my VM is running in 3000 x 2000, now. Increasing the video ram to 128MB was the most important point.
I have tried different resolutions and 24 or 32bpp in /etc/default/grub and my .vbox file. 32bpp does not work. I have tried a 4:3 ratio like 2800:2100 (maybe too high) and 2760:2070, but it didn’t work.
The list of modules reports the Guest Additions in version 6.1.0. I have uninstalled them and tried to install the GA from the .ISO, but I didn’t succeed.
Seamless mode is still not working, but I don’t need it.
After a boot of my Linux system I get a big terminal window with many lines, but also with lines on the right half of my screen. I think this can be fixed with a setting for the terminal.

When I pause the VM, it looks normal, now. On another VM I get the following screen:
How can I add an image?
After leaving the GUI I get a totally black screen without any prompt. The only thing I could do was to type blind: poweroff.

My monitor is a Samsung LU32R590CWNXZA.

Thank you all for your support.

[socratis]

First of all, my VM is running in 3000 x 2000, now. Increasing the video ram to 128MB was the most important point.

Thank you for the feedback. Marking as [Solved].

As for the rest of your issues, we like to observe the "One issue, one thread" rule...