The BIOS (Basic Input Output System) is located in a memory chip of the motherboard and is the program that is started when the PC boots. It performs checks and signals failures with beeps but also puts error codes to the IO port address 80 that can be captured using special PC cards. After a successful boot, it looks for a disk drive as a hard disk and reads there the 512 Byte big Master Boot Record (boot sector) and starts it. This program from the 512 Byte boot sector then can read a partition and load more code into memory and then start it. Boot loaders as Grub will get alive like this.

Boot loaders are therefore limited to understand partition schemes (MBR) and reading filesystems. Therefore it is common for a simple Linux system to have 2 partitions.

/dev/sda1 the boot partition about 128MByte size ext2 formatted to hold the bootloader and the Linux kernels to be read and loaded by the boot loader.

/dev/sda2 then is better more advanced as ext4 formatted and can hold all the data and is called the root partition.

More partitions can be added as a swap partition. However in the time of having SSD swapping to SSD might not be desired. It should also be noted that a swap file can be used instead of a swap partition. Often the swap partition is /dev/sda2 so the root partition will be /dev/sda3. It is also common to split the root partition into more partition or having more than on physical drive (a SSD drive and a big hard disk).

No Floppy drive, no CD drive (or BIOS does not support it), no Windows, no DOS just Linux and the BIOS update comes with a DOS program?

Download (and unzip) a boot-able floppy image as from http://www.bootdisk.com/bootdisk.htm

https://www.finnix.org/Balder

http://www.linurs.org/download/floppy.img.gz.

To create a boot-able floppy image yourself you should have a computer with a floppy disk drive. But having a floppy disk drive makes updating the BIOS easy and the following steps would not be necessary. However the time will come when you probably do not have a floppy disk drive anymore and storing the created floppy image is much easier than storing historic computer hardware. Therefore here the instructions. Create or find a bootable floppy disk. If you do not have a Microsoft operating system available, then use alternatives as the CD from http://www.freedos.org/. When having a boot-able floppy it can be converted into a floppy image file: cat /dev/fd0 ><name of floppy image>

Copy the floppy image to /boot and add the following to your grub.conf:

title=Freedos
root (hd0,0)
kernel /memdisk
initrd /<name of floppy image>

Note: /boot/memdisk might be necessary in the path, depending how your Linux is setup

memdisk is the floppy emulator and can be obtained by emerge syslinux and cp /usr/share/syslinux/memdisk /boot.

Now its worth to try out FreeDOS, boot it and you should find yourself in DOS. When done, the good old Ctrl Alt Del brings you back.

Reboot the PC in Linux and add the BIOS update utility to FreeDos. To do this create a mounting point mkdir /mnt/floppy and mount the image:

mount -o loop /boot/<name of floppy image> /mnt/floppy

Now cd /mnt/floppy and copy the DOS BIOS utility (e.g. AWDFLASH.EXE) and the new BIOS (e.g. M2N-SLI-Deluxe-1701.BIN or rename it to have it DOS style 8 characters and character extension) to the floppy image. Check where the floppy is mounted cat /etc/mtab and then unmount it umount /dev/loop<n>, reboot from FreeDos and update the BIOS.

When done it is wise to mount -o loop /boot/boot/<name of floppy image> /mnt/floppy and delete the BIOS update utility from there, since updating BIOS is a critical task that can badly hurt your PC when it crashes, or gets interrupted by a power failure.

If BIOS update was successful but the motherboard does not start, try to reset the CMOS setup as documented in the motherboard manual or remove the battery.

Unified Extensible Firmware Interface (UEFI) replaced Extensible Firmware Interface (EFI) and therefore the classic BIOS. https://en.wikipedia.org/wiki/Unified_Extensible_Firmware_Interface. https://blog.uncooperative.org/blog/2014/02/06/the-efi-system-partition/

The partition is GPT this means GUID Partition Table and GUID stands for Globally Unique Identifier.

Instead of a boot sector, UEFI is able to read a FAT 32 formated file system acting as the EFI system partition (ESP). There is no mystery about the ESP it is just a FAT32 formated partition on a GTP disk with its boot flag turned on. Unfortunately FAT32 does not support symlinks.

For backward and fallback reasons most motherboards have the CSM, the Compatibility Support Module within UEFI. So a UEFI motherboard can boot as a good old BIOS when using a MBR partitioned disk. GTP partitioned disks with CSM is also possible but more complicated.

The BIOS on the motherboard has boot entries that point to efi applications in the ESP (boot partition formatted with FAT 32). Typically there is a efi directory in the ESP where every efi application has its own subdirectory. If the ESP is after booting mounted to /boot those efi applications appear as /boot/efi/boot/bootx64.efi.

It is possible to communicate after a EFI boot (not a CSM boot) with EFI via the EFI Variables. This requires the Kernel settings Pseudo File System > EFI Variable filesystem. The kernel module might be required to be loaded modprobe efivars to have then access mount -t efivarfs none /sys/firmware/efi/efivars. Finally access is via /sys/firmware/efi/efivars/

To work with the boot entries (add, view, edit, delete) there is the efibootmgr. efibootmgr accesses the efivars this means the PC must have be booted with efi (make sure the live CD supports this and the motherboards BIOS is set to just do a efi boot). efibootmgr -v shows the boot entries. A boot entry needs to know

The following adds a boot entry to the motherboards BIOS on the first hard disks first partition that has the label Gentoo and calls grub efibootmgr --create --disk /dev/sda --part 1 --label "Gentoo" --loader "\efi\boot\grubx64.efi"

Or

efibootmgr --create --disk /dev/sdb --part 1 --label "Gentoo" --loader "\efi\gentoo\grubx64.efi"

To change the order the boot entries try to boot use: efibootmgr -o 2,1,3,0 . The numbers are the (1 or 4 digit) numbers shown by efibootmgr. It is a good sign if writing fails due to read-only file system error. If so, remount the efivars mount -o remount /sys/firmware/efi/efivars -o rw,nosuid,nodev,noexec,noatime

efibootmgr -t 10 set a timout

efibootmgr -T delete the timeout

efibootmgr -b 1 -B to delete the boot entry Boot0001 as shown by efibootmgr

A efi GTP disk and be simply partitioned and formatted as follows

mkfs.fat -F 32 /dev/sda1 to format FAT32 the first partition as ESP with about 128M. Within parted, set 1 boot on turns the boot flag on

/dev/sda2 the ext4 rootfs partition

Once grub starts, grub can call other installed efi applications as the efi shell. As example add to /etc/grub.d/51_efishell the following

#!/bin/sh
exec tail -n +3 $0

menuentry "EFI shell" {
 chainloader /EFI/shell/Shell_Full.efi
}

Secure Boot is used with the Unified Extensible Firmware Interface to restrict booting just from signed bootloaders. For Linux this means no more compiling the bootloader since then it is no more binary equal and therefore not signed. Such signed binary bootloaders are Shim and PreLoader.

The package fwts allows to see what is stored in the BIOS: fwts uefidump - | less

On MBR partitions the boot loader does not fit into the bootsector. The bootsector has just everything necessary to start the bootloader that is somewhere else on the disk. Usually the boot loader starts the operation system and the PC is ready to go. Chainloading is when the boot loader calls an other bootloader instead. As example when doing a major update to a bootloader, it might be advisable to have the old well working bootloader calling the new one, the new one could fails and crash the PC, a simple reboot will bring back the old old bootloader where you could select now to boot directly into the system.

There are different boot loaders available. For booting from hard disks (or any disks except CD/DVD or embedded solutions) grub is mostly used.

GRUB_PLATFORMS="efi-64"

#!/bin/sh
exec tail -n +3 $0

menuentry "FREEDOS" {
 
 root=hd0,0
 linux /memdisk
 initrd (loop)/FDSTD.288
}