GRUB Bootloader Guide

Enable GRUB Menu

If the GRUB menu is not showing during boot (common on single-OS systems):

Method 1: Show Menu Permanently

1. Edit GRUB configuration:

   sudo nano /etc/default/grub

2. Modify these settings:

   GRUB_TIMEOUT_STYLE=menu
   GRUB_TIMEOUT=10

3. Update GRUB configuration:

   sudo update-grub

Method 2: Show Menu Temporarily

Hold Shift (BIOS) or Esc (UEFI) during boot to access the GRUB menu.

Restore GRUB After Windows Installation

Windows installation often overwrites the bootloader. Here's how to restore GRUB:

For Manjaro/Arch-based Systems

1. Boot into Manjaro live environment

2. Open terminal and access your system via chroot:

   sudo manjaro-chroot -a

3. Install GRUB to the main drive:

   grub-install /dev/sda

   Note: Replace /dev/sda with your actual boot drive (check with lsblk)

4. Verify installation:

   grub-install --recheck /dev/sda

5. Update GRUB configuration:

   update-grub

6. Exit chroot and reboot:

   exit
   reboot

GRUB Configuration

The main GRUB configuration file is /etc/default/grub. Here are common settings:

Key Configuration Options

# Timeout before default boot (seconds)
GRUB_TIMEOUT=10

# Default boot entry (0 = first entry)
GRUB_DEFAULT=0

# Boot menu display style
GRUB_TIMEOUT_STYLE=menu  # or 'hidden'

# Remember last selected entry
GRUB_DEFAULT=saved
GRUB_SAVEDEFAULT=true

# Disable OS prober (faster boot, manual entries only)
GRUB_DISABLE_OS_PROBER=false

After making changes, always update GRUB:

sudo update-grub

Troubleshooting

Common GRUB Issues and Solutions

1. GRUB Rescue Mode

If you see grub rescue> prompt:

# List available partitions
ls

# Find your Linux partition (look for ext4)
ls (hd0,gpt2)/

# Set root and boot
set root=(hd0,gpt2)
set prefix=(hd0,gpt2)/boot/grub
insmod normal
normal

2. Fix Corrupted GRUB Configuration

# Regenerate GRUB configuration
sudo grub-mkconfig -o /boot/grub/grub.cfg

# Or use update-grub (Ubuntu/Debian)
sudo update-grub

3. Check Boot Drive

# List block devices
lsblk

# Check EFI partition (UEFI systems)
sudo efibootmgr -v

# Mount EFI partition
sudo mount /dev/sda1 /boot/efi

4. GRUB Not Detecting Windows

# Install os-prober
sudo apt install os-prober

# Enable OS detection
sudo nano /etc/default/grub
# Set: GRUB_DISABLE_OS_PROBER=false

# Update GRUB
sudo update-grub

Useful GRUB Commands

# Install GRUB to specific device
sudo grub-install /dev/sda

# Install GRUB for UEFI
sudo grub-install --target=x86_64-efi --efi-directory=/boot/efi

# Generate configuration file
sudo grub-mkconfig -o /boot/grub/grub.cfg

# List GRUB modules
ls /usr/lib/grub/x86_64-pc/

# Check GRUB version
grub-install --version