GRUB 2 (Grand Unified Bootloader version 2) is a popular and flexible bootloader used in many Linux distributions. It serves as the interface between the system’s firmware and the operating system, enabling users to choose which OS or kernel version to boot into. GRUB 2 supports a wide range of operating systems, including Linux, Windows, and others, making it highly versatile. It features a modular design, allowing for customization and expansion through various modules, such as support for different file systems and encryption. GRUB 2 also includes an interactive command-line interface, rescue mode, and configuration options that can be edited to modify boot behavior. This bootloader is crucial for managing multi-boot systems and ensuring that the operating system boots correctly after system updates or changes.
GRUB 2’s ability to fix boot problems has greatly improved over the original GRUB bootloader. This article provides information on options for repairing GRUB 2 boot issues and specific instructions on how to use the GRUB 2 terminal. The instructions are written for GRUB 2.
How does the GRUB 2 prompt look like?
There are basically three error messages or screens when GRUB fails to boot.
grub>: This is the screen mode you see when GRUB has found everything except the configuration file. This file probably will be grub.conf.
grub rescue>: This is the mode when GRUB 2 is unable to find the GRUB folder or its contents are missing/corrupted. The GRUB 2 folder contains the menu, modules and stored environmental data.
GRUB: Just “GRUB” nothing else indicates GRUB 2 failed to find even the most basic information needed to boot the system.
These are the basic errors that may occur during booting. However, a few more errors can be seen on the screen, like a frozen splash screen, Busybox, or Initramfs: GRUB 2 began.
However, each of the GRUB 2 failure modes can be corrected either from the GRUB 2 terminal or the distro’s Live boot CD or DVD. Third-party rescue tools are also available.
Basic commands available.
These are the commands that can be used when you enter the GRUB 2 terminl mode by pressing “c”.
boot (Initiate the boot, also F10 or CTRL-x)
cat (view the contents of config or txt files; cat (hd0,1)/boot/grub/grub.cfg)
configfile (Load a GRUB 2 configuration file such as grub.cfg; configfile (hd0,5)/boot/grub/grub.cfg.)
initrd (Loads the initrd.img, necessary for booting; initrd (hd0,5)/initrd.img.)
insmod (Loads a module; insmod (hd0,5)/boot/grub/normal.mod, or insmod normal.)
linux (Loads the kernel; insmod /vmlinuz root=(hd0,5) ro.)
loop (Mount a file as a device; loopback loop (hd0,2)/iso/my.iso.)
ls (lists the contents of a partition/folder; ls, ls /boot/grub, ls (hd0,5)/, ls (hd0,5)/boot.)
lsmod (List loaded modules.)
normal (Activate the normal module, if loaded.)
search (Search for a device. Type help search for the available options.)
set (Review current settings, or set XXX to set a variable such as colors, prefix, root.)
vbeinfo (Display GRUB 2 available resolutions.)
The Rescue Shell.
If you get a rescue shell, this usually means that GRUB failed to load the “normal” module for some reason. It may be possible to work around this temporarily: for instance, if the reason for the failure is that “prefix” is wrong (perhaps it refers to the wrong device, or perhaps the path to “https://www.howtoforge.com/boot/grub” was not correctly made relative to the device), then you can correct this and enter normal mode manually: Inspect the current prefix (and other preset variables):
set
You will probably have an output more or less like this:
Your output may differ but you get the information required. Find out which devices are available:
ls
Set to the correct value, which might be something like this:
set prefix=(hd0,1)/grub
(this has to be done according to your own drive name)
set root=(hd0,1)
(this has to be performed according to your own drive name.)
insmod normal
normal
The above commands will get you out of the rescue mode to the normal terminal mode. In the terminal mode you have more commands with increased functionality.
After the above commands you can go ahead and start the rest of the settings.
insmod linux
* linux /vmlinuz root=/dev/sdXY ro
(if this doesn’t work try this)
linux /boot/vmlinuz-3.2.0-14-generic root=/dev/sda1 ro
(optional)
initrd /initrd.img
(Selects the initrd image.)
boot
After Booting the system.
Update the GRUB config file.
sudo update-grub
Reinstallation of Grub on the device:
sudo grub-install /dev/sdX
This should be it for the rescue part and your system should be good and running. If not you can save all your trouble by using Boot Repair. This is the tool used to repair your complete boot menu. It can be downloaded directly and used as a Live Boot CD or DVD. Here is the download link.
