Which command installs the GRUB boot files into the currently active file system?

The command that installs the GRUB (GRand Unified Bootloader) boot files into the currently active file system is the one that targets the entire disk drive rather than a specific partition. When using grub-install, specifying a device like /dev/sda directs the installation of GRUB to the Master Boot Record (MBR) or the EFI System Partition (if in UEFI mode) of that disk. This is essential because GRUB needs to be installed at the disk level to take control of the boot process for the system.

Installing GRUB on the entire drive (like /dev/sda) ensures that it can manage the booting of multiple operating systems or kernels effectively. In contrast, targeting a specific partition (as seen in other options) does not configure GRUB to handle boot priorities for the system, which is why they would not achieve the intended outcome of setting up the boot loader properly for the whole system.

The command assumes that the active filesystem is recognized and that no additional flags or options are needed to specify the context, making it straightforward for typical installations.