grub-mkrelpath

grub-mkrelpath [OPTION]... PATH

-h, --help
    Display a help message and exit.

-V, --version
    Display version information and exit.

grub-mkrelpath is a utility from the GRUB (GRand Unified Bootloader) suite. Its primary function is to convert an absolute filesystem path into a path that is relative to GRUB's active root device and filesystem. This is crucial for GRUB configuration files (grub.cfg) and scripts, as GRUB often operates within its own abstracted filesystem view.

For instance, if GRUB has identified /dev/sda1 as its root filesystem (e.g., (hd0,msdos1) which contains /boot), and a file is located at /boot/grub/grub.cfg, running grub-mkrelpath /boot/grub/grub.cfg might return /grub/grub.cfg. This relative path is then directly usable by GRUB commands like configfile or chainloader without needing to specify the device or partition, making GRUB configurations more robust and portable across different boot environments or system changes where the absolute mount points might vary. It simplifies path management within the GRUB environment.

The "relative" path generated by grub-mkrelpath is specific to GRUB's internal understanding of its root filesystem. This might not always align with the host operating system's perspective of filesystem paths, especially if GRUB's root device differs from the OS's root. Misuse or misinterpretation of the output can lead to GRUB failing to locate essential boot files.

This command is not typically run directly by users on the command line for everyday tasks. Instead, it is primarily employed by GRUB-related scripts, such as grub-mkconfig, during the automatic generation of the grub.cfg configuration file. Its purpose in this context is to ensure that all file paths referenced within the bootloader configuration are correctly resolved relative to GRUB's determined root filesystem, thereby contributing to the creation of robust and portable GRUB configuration files.

grub-mkrelpath is an integral part of the GRUB 2 bootloader project, which began development in the early 2000s as a complete rewrite of GRUB Legacy. This utility likely emerged during the development of GRUB 2's sophisticated filesystem handling capabilities, enabling more flexible and portable configuration files by standardizing path resolution within the GRUB environment itself. It has been a stable part of the GRUB 2 toolchain for many years.

grub-mkconfig(8), grub-install(8), grub-probe(8), grub(8)