In case of modifying grub settings by editing /etc/default/grub, you need to run update-grub. But in kaos I faced:
bash: update-grub: command not found
So I manually created one as beow:
sudo nano /usr/sbin/update-grub
In opened empty file added:
#!/bin/sh
set -e
exec grub-mkconfig -o /boot/grub/grub.cfg "$@"
Then I ran:
sudo chown root:root /usr/sbin/update-grub
sudo chmod 755 /usr/sbin/update-grub
This way I manually created an update-grub commmand just like in ubuntu. Then I ran:
update-grub
And it worked. Hope it helps :)