GRUBDEFAULT

GRUBDEFAULT is a configuration option within the GRUB (Grand Unified Bootloader) system used primarily on Linux distributions to specify the default boot entry during system startup. This setting determines which kernel and initramfs (initial RAM filesystem) are loaded by default when the user does not explicitly select an entry from the GRUB menu.

The `GRUBDEFAULT` entry is typically set in the GRUB configuration file, often located at `/etc/default/grub` or `/boot/grub/grub.cfg`. This file contains various parameters that control GRUB's behavior, including the default boot option. The exact syntax for setting `GRUBDEFAULT` varies slightly depending on the Linux distribution, but it generally follows the format:

`GRUB_DEFAULT=0`

where the number corresponds to the entry number in the GRUB menu. For example, if the first entry is the default kernel, `GRUB_DEFAULT=0` would select it. Some distributions also support a "menu-driven" mode, where `GRUB_DEFAULT=menu` forces GRUB to display the boot menu at every startup, allowing users to manually choose an entry.

Users may adjust `GRUBDEFAULT` to prioritize specific boot configurations, such as a particular kernel version for troubleshooting or performance optimization. However, changes to this setting require a subsequent update of the GRUB configuration, usually done via the `update-grub` command on Debian-based systems or `grub2-mkconfig` on others. Incorrect settings can lead to boot failures, so it is important to verify the correct entry number before making changes.