Error: unknown command 'gfxmode'. Pressing any key continues [duplicate]

I solved the problem deleting the line:

"gfxmode $linux_gfx_mode"

in "/etc/grub.d/40_custom" file

The grub customizer forgot to put set before gfxmode. Go into /etc/grub.d and run the following command to find out which file has the gfxmode entry: grep gfxmode * Then use whatever text editor you like to just put set in front of it.

A little background on this is that gfxmode is a variable, so it has to be set with the set command, but the customizer tried to use it as a command.

I use boot-repair software to reinstall the GRUB.

Then problem resolved.

You can see my comment on this bug.

https://bugs.launchpad.net/ubuntu/+source/grub2/+bug/998835