GRUB Bootloader

Configure and install the GRUB bootloader for Linux systems.

Installation

# Install GRUB to MBR
grub-install /dev/sda

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

# Install to directory (for ISO creation)
grub-install --target=i386-pc --boot-directory=/mnt/boot /dev/sda

Configuration File

Create /boot/grub/grub.cfg:

set timeout=5
set default=0

menuentry "Linux" {
    linux /boot/vmlinuz root=/dev/sda1 ro quiet
    initrd /boot/initrd.img
}

menuentry "Linux (Recovery)" {
    linux /boot/vmlinuz root=/dev/sda1 ro single
    initrd /boot/initrd.img
}

menuentry "Custom Initramfs" {
    linux /boot/bzImage rdinit=/init console=tty0
    initrd /boot/initramfs.cpio.gz
}

Generate Configuration

# Auto-generate config
grub-mkconfig -o /boot/grub/grub.cfg

# Update GRUB after changes
update-grub  # Debian/Ubuntu
grub2-mkconfig -o /boot/grub2/grub.cfg  # RHEL/CentOS

GRUB Modules

# List available modules
ls /usr/lib/grub/i386-pc/

# Common modules
insmod part_msdos  # MBR partitions
insmod part_gpt    # GPT partitions
insmod ext2        # ext2/3/4 filesystem
insmod iso9660     # ISO filesystem
insmod loopback    # Loopback devices

Boot Parameters

# In grub.cfg
linux /boot/vmlinuz \
    root=/dev/sda1 \
    rootwait \
    console=tty0 \
    console=ttyS0,115200 \
    init=/sbin/init

GRUB Rescue

# At GRUB rescue prompt
set root=(hd0,1)
set prefix=(hd0,1)/boot/grub
insmod normal
normal

Create Bootable USB

# Install GRUB to USB drive
grub-install --target=i386-pc --boot-directory=/mnt/usb/boot /dev/sdb