User:Megavolt/bootloaders
Overview
In order to load the operating system a boot loader is needed. There is not only one boot loader, but many of them which have its benefits and disadvantages.
Common boot loaders are:
- GRUB
- systemd-boot
- rEFInd
- Syslinux
It depends on the computer which boot loader can or should be used. In general there are 2 system: UEFI/EFI and BIOS, while UEFI/EFI has commonly also a legacy mode which is fully compatible with a pure BIOS.
Preparation
Identify the type of system you are attempted to rescue as the commands involved are slightly different. There are 2 types of systems which are not compatible to each other.
Identify the system
Indicators for EFI:
- When you start the computer and you commonly type F8 (or any other key combination) to choose a boot media, you will see 2 different entries of the same media, flagged with either [UEFI] or [legacy].
- Your local Disk has a small vfat (fat16/32) partition (100-300MB).
- Your local Disk has a GPT partition table.
If all of these indicators are not valid to your computer, then it is most likely be a pure BIOS.
BIOS
Old computers have commonly only a pure BIOS.
- Your disk has commonly a MBR/MS-DOS partition table.
- There is only one Master Boot Record for each disk. Which means only one BootLoader can be targeted.
- If you have installed Manjaro along with Windows or another Linux Distribution on the same Disk, then the last installed OS will commonly overwrite the MBR and take itself as the boot target.
- If you have installed 2 Operating-Systems on 2 separate Disks, then you are able to set the boot priority at the BIOS settings, so that it boots the first disk first, if it fails, it boots the second one etc.
EFI
Newer computers have commonly an UEFI. It has also a legacy mode, which is fully compatible with a pure BIOS.
- You disk has commonly a GPT partition table, but it also support MBR/MS-DOS in legacy mode.
- The UEFI has a builtin Bootloader which boots efi files.
- efi files are stored on a partition formatted with vfat (fat16/32) and flagged with "boot" or "esp" or "boot,esp"
- efi files contain at bare minimum, just like MBR, information about which partition should be booted, but there is no limitation of one MBR per Disk, so you create as many efi partitions and efi files as you like
- In your UEFI settings you can set the boot priority just like on a pure BIOS.
- It is possible to use/add a MBR-like behavior in legacy mode on a GPT partition table to be able to boot on both modes. Normally you will see here a 8-10MB non-formatted partition flagged with bios_grub.
Go to Identify the system for indicators of which system you use.
Load Manjaro Installation Media
In order to boot with a Manjaro Installation Media you need to create it, if not done yet.
Identify partitions
To identify your partitions and their designated use you need to run a partition manager. Depending on environment there is various tools. GTK based ISO offers GpartEd, QT based ISO offers KParted and common to all is the CLI tools.
More comprehensive information can be found using fdisk (requires superuser) and you can limit the probed device e.g. /dev/sda or /dev/nvme0n1
The clues to look for is mbr vs. gpt and the presence of a small partition - usually the first - formatted with the vfat filesystem followed by a larger partition formatted as ext4.
Use root context
When you have loaded the live ISO - depending on environment - open a terminal and switch to root context. Use above mentioned root:password combination.
Chroot environment
Chroot is a method to restrict various tasks to a restricted area e.g. package installation and other system maintenance tasks. Follow the link to read more about chroot on the Arch wiki.
Identify system partitions
From the above we assume you have identified the relevant partitions on your system and this document will refer the partitions as follows. Partitions not needed for this kind of maintenance has intentionally been left out (e.g. home, swap).
| Partition | Usage | / Comment |
|---|---|---|
/dev/sdyA |
EFI system | Required for EFI system and mounted on /boot/efi |
/dev/sdyB |
boot | Optional but mounted on /boot The primary use is when GRUB cannot write to / (eg. f2fs) |
/dev/sdyC |
root | Required and for the root filesystem and mounted on / - usually formatted using ext4 |
Use manjaro-chroot
Manjaro deploys a script called manjaro-chroot takes an optional argument which will search the visible devices - scan the partitions for signs of an operating system. If more than one Linux operating system is found you will get a choice of which system to chroot otherwise the file /etc/fstab from the system is used to mount the partitions and chroot into this system.This script is only available in live iso by default but you can get it in an installed system by installing manjaro-tools-base package.
Manual chroot
(Unnecessary if you have used manjaro-chroot)
Mount the partitions using the designated temporary mountpoint and always start with root
Then - if applicable - mount boot
Then - if applicable - mount efi
Create the chroot environment and use bash as shell
Reinstall GRUB
One possible cause why you are reading this document - is an unfinished update - which in turn can be caused by several situations - situation we will not dive into. To fix what ever caused this you should run a full system update including grub to ensure everything is in place.
When the transaction as completed continue below using the section matching your system
BIOS System
On a BIOS/GPT system there is no MBR and therefore no place to store the loader. The GPT partition specification allows for an unformatted partition of the BIOS boot partition type (0xEF02). The size of this partition can be as small as 1 mebibyte. The Calamares installer uses a fixed size of 32 mebibyte. On a BIOS/MBR system a part of the bootloader is written to the Master Boot Record for the primary disk.
The device is the disk (not a partition)
Make sure the grub configuration is up-to-date
EFI System
Reinstall grub
Update the grub configuration
Verify the existance of an EFI system partition
Verify the efi filesystem is loaded
Exit chroot
Try loading the efi filesystem
Re-enter chroot
Then mount the efi filesystem
Verify the efi filesystem is loaded
If successfull re-run above installation commands
Troubleshooting
Arch Linux is not recognized
If Arch Linux wasn't recognized after an update-grub then probably your Arch installation is missing the package lsb-release.