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GRUB and VGA Modes

VGA Modes and GRUB

Hopefully your Linux kernel will detect the video hardware and select a good video mode.

However, especially on virtualized platforms like Oracle VirtualBox, you may need to help it along.

The modern way to do this is through GRUB variables GRUB_GFXMODE and GRUB_GFXPAYLOAD_LINUX. Add something like the following to /etc/default/grub to set the desired width×height×depth (in pixels×pixels×bits).

[ ... lines deleted ... ]
[ ... lines deleted ... ]

You can set multiple resolutions, including the default auto,, using something like this:

[ ... lines deleted ... ]
[ ... lines deleted ... ]

Then update the GRUB configuration. The GRUB configuration file is in /boot/efi/EFI/distro-name/ or in /boot/grub2 on a system with the EFI firmware in BIOS legacy mode.

# grub2-mkconfig -o $(find /boot -name grub.cfg) 

If the command is instead grub-mkconfig with the configuration file in /boot/grub/ on your distribution (e.g., Oracle, RHEL, CentOS, etc), of course use that instead. If you use command completion and file name completion with the <Tab> key as you should, this wouldn't be a problem and you might not even notice the difference.

But If That Doesn't Work...

You can add a vga= directive to the kernel line in the GRUB file, something like the following:

linuxefi /vmlinuz-X.Y.Z vga=792 root=UUID=77aa6e61-df08-4480-a3ae-73bf40116336 ro 

You will, of course, see something specific in place of X.Y.Z and you can use numbers other than 792. That specific number yields 1024×768 with 65,536 possible colors. See the table below for a variety of choices! But first, some tips:

Available VGA Modes

Color bits Colors 640×480 800×600 1024×768 1280×1024 1400×1050 1600×1200
8 bits 256 colors 769 771 773 775
15 bits 32,768 colors 784 787 790 793
16 bits 65,536 colors 785 788 791 794 834 884
24 bits 16,777,216 colors 786 789 792 795

Installing Your Configuration Change

Do not simply edit the /boot/grub/grub.cfg file!

Changes to that file will be wiped out the next time you install a kernel update.

Edit the file /etc/default/grub and look for lines like this:

[ ... lines deleted ... ]
[ ... lines deleted ... ]

Insert your addition there. If there is only one such line, add it to that string. If there are two lines, add it to the non-empty string:

[ ... lines deleted ... ]
GRUB_CMDLINE_LINUX_DEFAULT="quiet splash vga=792"
[ ... lines deleted ... ]

Now, regenerate the GRUB configuration file. This will insert your addition to every stanza or boot target.

# grub-mkconfig -o $(find /boot -name grub.cfg) 

For example, on a UEFI/GPT/dracut platform, the GRUB configuration file might be under /boot/efi/EFI/. On a BIOS/MBR/isolinux platform, the directory might be /boot/grub2 rather than boot/grub. The precise location depends on your distribution.

If you instead find a file named grub.conf, then you're on a very old system with the legacy GRUB 0.99 instead of GRUB 2.

Also, there may be a "2" in the command name: grub2-mkconfig.

What About The GRUB Menu Resolution?

Yes, there are three operating system environments on your way to what you really want to run:

  1. Firmware: With UEFI firmware, this can be fairly high resolution graphics. Then then firmware starts:
  2. GRUB boot loader: This gets whatever the UEFI has set up, although you can tell it to try a specific resolution. That's useful to change in a virtualized environment, where the boot loader is running within a window on a graphical desktop of a host OS. Then it loads and starts:
  3. Operating system: The above showed how to pass a video resolution request like vga=792 to the OS kernel as it's loaded.

To set the GRUB boot loader resolution: look for a line setting GRUB_GFXMODE within the file /etc/default/grub. Add it if needed, or change what's there. You could use double-quotes around the resolution string but they aren't needed:

[ ... lines deleted ... ]
[ ... lines deleted ... ]

Then regenerate the GRUB configuration file.

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

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