I have installed kali linux on a 32GB USB drive, and i have a 9GB partition for persistence. Also, the Macbook Pro i am running Kali on requires the AMD GPU to be disabled, so i am using this guide  to disable the AMD GPU (Step 3). I want to disable it permanently, but the /etc/default/grub file is missing. I reinstalled GRUB 2.0 and the grub config file was there although there was an error:    error: failed to get canonical path of 'overlay'After editing it , i couldn't get the grub-update command to run. It says that there is no such command. And after rebooting, the file disappeared again.Please help me with this issue. I appreciate your assistance greatly.
Live USB version of Kali Linux GRUB issues
kali linux;grub2;live usb