====== reboot into OS ======
* Get all entries grep -oP "^((submenu|menuentry)\s')\K(.+?)(?=\')" /boot/grub/grub.cfg
* ...and subentries grep -oP "^((submenu|menuentry|\tmenuentry)\s')\K(.+?)(?=\')" /boot/grub/grub.cfg
* now count from 0 and run grub reboot '1>2'
* reboot