Saturday 2 February 2019

Linux Academy

Legacy GRUB

Grand Unified Bootloader
boot.img (first 512 bytes) -> core.img to find partition with /boot/
/boot/grub/ contains grub.conf (Redhat) or menu.lst (Debian) and device.map
now linux kernel gets read and system boots
install grub with grub-install <device>
- device can be /dev/sda or /dev/hd0 or '(hd0)'. Use findmnt /boot to find the device
running grub-install is dangerous on a system that is already up and running
the grub shell treats \boot as its root directory

GRUB2

Master Boot Record (with legacy GRUB)
- supported 26 partitions
- partition limited to 2 TB
GPT (GUID Partition Table)
- supports 128 partitions, around a ZB each
- needs UEFI (Unified Extensible Firmware Interface) to boot
  - replacement for traditional BIOS
  - requires 64 bit OS
  - prevents unauthorized OS from booting on the system
UEFI BIOS -> master boot loader boot.img --> GPT header --> partition entry array --> core.img --> /boot/efi on a vfat or FAT32 volume (no other volume types) -> /boot/grub2 which has grubenv and themes files
On Redhat, we use grub2-<command>, whereas on Debian we use grub-<command>
do not directly edit files in the /boot/grub directory
grub2-editenv list to view default boot entry for the grub configuration file
grub2-mkconfig cretaes or updates a /boot/grub2/grub.cfg file
update-grub updatesd the grub2 configuration after changes to \etc\default\grub have been made

Interact With the GRUB Bootloaders