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 ... ]
GRUB_GFXMODE=1024x768x32
GRUB_GFXPAYLOAD_LINUX=keep
[ ... lines deleted ... ]

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

[ ... lines deleted ... ]
GRUB_GFXMODE=1920x1080x32,1024x768x32,auto
GRUB_GFXPAYLOAD_LINUX=keep
[ ... 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:

The vga=XXX directive can go anywhere on the line. I put it near the beginning in this example to make it easy to spot if you're viewing this page on a phone. But it will be easiest for you to add it to the end.
Experiment! Press e at the GRUB menu and add an experimental string, then press <Ctrl>-X to boot. If you get an unwanted mode, or even a totally black screen, cycle the power and try again. Once you find a useful value, you can install it as explained below.
You might see linuxefi as in my example above, or linux, depending on your platform. Leave that alone, you're simply looking for the line with some vmlinuz-X.Y.Z kernel file name.

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 ... ]
GRUB_CMDLINE_LINUX_DEFAULT="quiet splash"
GRUB_CMDLINE_LINUX=""
[ ... 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"
GRUB_CMDLINE_LINUX=""
[ ... 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:

Firmware: With UEFI firmware, this can be fairly high resolution graphics. Then then firmware starts:
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:
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 ... ]
GRUB_GRXMODE=1024x768
[ ... lines deleted ... ]

Then regenerate the GRUB configuration file.

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

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