The Difference Between GRUB_CMDLINE_LINUX and GRUB_CMDLINE_LINUX_DEFAULT in /etc/default/grub

In the world of Linux, there are many configuration files and parameters that can be tweaked to customize your system’s behavior. Among them, the /etc/default/grub file plays a crucial role in the boot process. In this article, we will focus on two specific parameters within this file: GRUB_CMDLINE_LINUX and GRUB_CMDLINE_LINUX_DEFAULT. By understanding the difference between these two, you can better manage your system’s boot process.

Understanding GRUB

Before we delve into the specifics, it’s important to have a basic understanding of GRUB. GRUB, or the Grand Unified Bootloader, is a program that loads the Linux kernel into the system’s memory so that the system can start. It is highly configurable, allowing users to control various aspects of the boot process.

The configuration file for GRUB is located at /etc/default/grub. This file contains several settings that control how GRUB behaves during the boot process. Two of these settings are GRUB_CMDLINE_LINUX and GRUB_CMDLINE_LINUX_DEFAULT.

GRUB_CMDLINE_LINUX

The GRUB_CMDLINE_LINUX parameter is used to pass options to the Linux kernel during the boot process. These options are applied in both normal boot and recovery mode.

For example, if you have the following line in your /etc/default/grub file:

GRUB_CMDLINE_LINUX="acpi_backlight=vendor"

This option will be effective in both normal boot and recovery mode. The acpi_backlight=vendor option is a common setting used to fix issues with screen brightness control on some laptops. This option tells the system to use the vendor-specific driver (if available) for controlling the backlight.

GRUB_CMDLINE_LINUX_DEFAULT

On the other hand, the GRUB_CMDLINE_LINUX_DEFAULT parameter is used to pass options to the Linux kernel that are only applied during a normal boot. These options are not applied when booting in recovery mode.

For instance, you might see something like this in your /etc/default/grub file:

GRUB_CMDLINE_LINUX_DEFAULT="quiet splash"

The quiet option suppresses most boot messages, and splash enables the splash screen during boot. These options make the boot process less verbose and more visually appealing, but they are not necessary when booting in recovery mode, which is why they are specified under GRUB_CMDLINE_LINUX_DEFAULT rather than GRUB_CMDLINE_LINUX.

The Difference

The main difference between GRUB_CMDLINE_LINUX and GRUB_CMDLINE_LINUX_DEFAULT is when and how their options are applied. GRUB_CMDLINE_LINUX applies its options in both normal boot and recovery mode, while GRUB_CMDLINE_LINUX_DEFAULT applies its options only during normal boot.

This difference is important because it allows you to specify options that should always be applied, regardless of the boot mode, as well as options that should only be applied during a normal boot. This gives you a great deal of flexibility in customizing your system’s boot process.

Conclusion

In conclusion, GRUB_CMDLINE_LINUX and GRUB_CMDLINE_LINUX_DEFAULT are two important parameters in the /etc/default/grub file that allow you to pass options to the Linux kernel during the boot process. Understanding the difference between these two parameters can help you better manage your system’s boot process.

For more information on GRUB and its configuration, you can refer to the GRUB2 documentation. Additionally, if you are troubleshooting backlight issues, you can check the Ubuntu Wiki for debugging tips.