GRUB_DISTRIBUTOR and the other variables are set in /etc/default/grub on a normal system, but it seems you have inadvertently broken this file. I suggest having a look at that and fixing it, and reaching out to one of the support forums if you need further assistance.
GRUB_DISTRIBUTOR and the other variables are set in /etc/default/grub on a normal system, but it seems you have inadvertently broken this file. I suggest having a look at that and fixing it, and reaching out to one of the support forums if you need further assistance.