CBT Nugget: Linux Server Administration - 2. GRUB and GRUB2 Bootloaders

2. GRUB and GRUB2 Bootloaders

GRUB (GRand Unified Bootloader) and GRUB2 are widely used bootloaders in Linux systems. Here's a detailed overview of both:

GRUB (Legacy GRUB)

1. Overview:

• GRUB, often referred to as Legacy GRUB, is the original version of the GRUB bootloader.
• It was designed to provide a flexible and powerful way to boot operating systems.

2. Key Features:

• Configuration File: /boot/grub/menu.lst or /boot/grub/grub.conf
• Chainloading: Can boot other bootloaders, allowing it to load various operating systems.
• Filesystem Support: Supports a variety of filesystems natively.
• Command Line Interface: Offers a CLI for manual booting and troubleshooting.
• Partition Detection: Can automatically detect and list available operating systems.

3. Limitations:

• Complex Configuration: The configuration syntax can be cumbersome and error-prone.
• Limited Extensibility: Difficult to add new features or support for newer filesystems and architectures.
• Development: No longer actively developed or maintained.

GRUB2

1. Overview:

• GRUB2 is the successor to Legacy GRUB, designed to address its predecessor's limitations and provide modern features.
• It is the default bootloader in most Linux distributions today.

2. Key Features:

• Configuration File: /boot/grub/grub.cfg
  • This file is not meant to be edited directly. Instead, configuration is done via /etc/default/grub and custom scripts in /etc/grub.d/.
• Modular Architecture: GRUB2 has a modular design, allowing for easier addition of new functionalities.
• Scripting Support: Uses a scripting language that allows for more complex configurations and conditions.
• Graphical Menu: Supports themes and graphical boot menus.
• Improved Filesystem Support: Enhanced support for modern filesystems and new technologies.
• Boot Environment: Provides a flexible and powerful pre-boot environment.

3. Key Commands:

• grub-install: Installs GRUB2 to a device.
• update-grub: Generates the grub.cfg file based on scripts and settings.

4. Advantages Over Legacy GRUB:

• Ease of Use: More user-friendly with automated tools for configuration.
• Extensibility: Easily extensible to support new filesystems and hardware.
• Resilience: Better recovery and debugging tools.

Configuration and Usage

GRUB (Legacy):

• Example Configuration (menu.lst):

  plaintext
  default=0
  timeout=5
  title Linux
    root (hd0,0)
    kernel /vmlinuz root=/dev/sda1
    initrd /initrd.img
  

GRUB2:

• Example Configuration (/etc/default/grub):

  plaintext
  GRUB_DEFAULT=0
  GRUB_TIMEOUT=5
  GRUB_DISTRIBUTOR=`lsb_release -i -s 2> /dev/null || echo Debian`
  GRUB_CMDLINE_LINUX_DEFAULT="quiet splash"
  GRUB_CMDLINE_LINUX=""
  
  

• Generating grub.cfg:

  sh
  sudo update-grub
  

Summary

Both GRUB and GRUB2 serve the fundamental purpose of loading operating systems, but GRUB2 provides a more modern, flexible, and powerful platform, addressing the shortcomings of Legacy GRUB. As a result, GRUB2 is the preferred choice for most modern Linux distributions.