How to Configure Bootloaders with the 'grubby' Command (with examples)

Grubby is a versatile command-line tool that allows users to modify bootloader configurations, specifically for grub and zipl. Its most common use cases involve adding, removing, or listing kernel boot arguments within the bootloader menu entries. With the ability to manage these entries effectively, grubby proves invaluable for system administrators seeking direct control over kernel boot parameters, offering both flexibility and precision.

Use case 1: Add kernel boot arguments to all kernel menu entries

Code:

sudo grubby --update-kernel=ALL --args 'quiet console=ttyS0'

Motivation:

A system administrator may want to modify the boot parameters across all kernel entries for uniform behavior. Adding arguments such as quiet minimizes console output during boot, providing a cleaner boot sequence. Specifying console=ttyS0 directs console output to the first serial port, which is particularly useful for systems managed via remote terminals or in headless environments, ensuring that kernel messages are routed correctly.

Explanation:

• sudo: Runs the command with superuser privileges, necessary for modifying boot configurations.
• grubby: The command-line tool being used to manage the bootloader.
• --update-kernel=ALL: Indicates that the update should be applied to all kernel entries, ensuring consistent configurations across the board.
• --args 'quiet console=ttyS0': Specifies the arguments to be added. quiet reduces the amount of output displayed during boot, while console=ttyS0 redirects the console output to a specified serial port.

Example Output:

Although the grubby command may not provide output on success, changes to the bootloader configuration can be verified by listing kernel entries to see if new arguments appear under the kernel options.

Use case 2: Remove existing arguments from the entry for the default kernel

Code:

sudo grubby --update-kernel=DEFAULT --remove-args quiet

Motivation:

If excessive boot-time suppression or specific configurations are causing issues, removing arguments like quiet from the default kernel entry can help in troubleshooting. Displaying all boot messages provides visibility into what might be causing start-up problems and can be instrumental in debugging system behavior.

Explanation:

• sudo: Ensures the command is executed with necessary administrative rights to alter boot configurations.
• grubby: The tool employed to adjust bootloader settings.
• --update-kernel=DEFAULT: Targets the default kernel entry for updates, which is the kernel used by default when the system starts.
• --remove-args quiet: Specifies which argument(s) to be removed from the default kernel’s boot parameters. Removing quiet allows full boot message visibility, which is advantageous for diagnostics.

Example Output:

The output might not display specific changes directly on execution but can be confirmed by reviewing kernel entries through listing tools to see removed arguments.

Use case 3: List all kernel menu entries

Code:

sudo grubby --info=ALL

Motivation:

Listing all kernel menu entries allows a system administrator or user to review the current boot options configuration. This information is essential for ensuring consistency across entries, which can aid in determining if further modification is necessary for system stability or performance optimization.

Explanation:

• sudo: Provides the required permissions to access bootloader settings.
• grubby: The command line utility being used.
• --info=ALL: Requests information about all available kernel entries. This parameter outputs details like kernel version, kernel arguments, and configurations, providing comprehensive insight into the system’s boot environment.

Example Output:

The output will display detailed entries for each installed kernel, including:

index=0
kernel=/boot/vmlinuz-5.x.x-xx-generic
args="ro quiet splash"
root=/dev/sda1
initrd=/boot/initrd.img-5.x.x-xx-generic
title=Ubuntu, with Linux 5.x.x-xx-generic
...

Conclusion:

The grubby command offers significant power for modifying and managing bootloader configurations, allowing users to adeptly add, remove, or review kernel menu entries. These functionalities are particularly useful for system administrators and users who require precise control over the system’s boot behavior for reasons ranging from operational efficiency to troubleshooting. Understanding these operations facilitates enhanced system management and stability.