Re: Choosing grub2 video modes

[Jordan Uggla]

On Wed, Jun 10, 2015 at 1:10 PM, Alex Regan <address@hidden> wrote:
> Hi,
>
> I'm confused about how to control the text video mode from grub. I've seen
> references to GRUB_GFXMODE and gfxmode, but I don't understand how it's set.

I assume that by "text video mode" you mean the mode used by linux for
text ttys. Since the advent of kernel mode setting, the video mode
passed by the bootloader is essentially meaningless; The kernel will
(by default) always try to configure the native resolution for your
display, and as it has access to full native graphics drivers (rather
than just VESA) it usually succeeds.

Before KMS the kernel could only use the boot firmware's drivers for
non-Xorg ttys, and so was both limited by available VESA modes and
kept the mode passed to it by grub. That is why GRUB_GFXPAYLOAD (which
defaults to the value of GRUB_GFXMODE) determined the resolution of
your ttys, and still does if you use proprietary drivers or for other
reasons pass "nomodeset" as a kernel parameter to disable KMS.

For kernels using KMS try passing the kernel parameter "video=640x480"
to tell the kernel that that is the mode that you want to use for your
ttys.

>
> I've tried setting it using "set gfxmode=640x480" in /boot/grub2/grub.cfg
> and other variations, but they seem to be ignored.
>
> I've tried setting GRUB_GFXMODE=640x480 in /etc/default/grub then recreating
> grub.cfg, but that also doesn't appear to work.

GRUB_GFXMODE and gfxmode control the mode used by *grub* for its menu.
Is the resolution of your grub menu really not matching what you
entered for GRUB_GFXMODE?

>
> I'd appreciate it if someone could share some examples of how to do it on
> current versions of fedora.
>
> I've also tried using 'vbeinfo' while inside grub, but those numbers (0x114,
> for example) don't seem to have any effect either.
>
> How can I tell what resolution the console is currently set to?

You can tell what mode *grub* is currently set to use by running
"videoinfo" and looking for the asterisk denoting the current mode.

-- 
Jordan Uggla (Jordan_U on irc.freenode.net)