grub-set-default

Set the default boot entry permanently

$ sudo grub-set-default [entry_number]

$ sudo grub-set-default --boot-directory /[path/to/boot_directory] [entry_number]

grub-set-default [options] entry

grub-set-default sets the permanent default boot entry for GRUB. Unlike grub-reboot, this setting persists across all subsequent boots until changed.
The entry can be specified as a number (0 for first entry), the full entry name from grub.cfg, or a menu entry identifier. Submenu entries use notation like "1>2" for the third item in the second submenu.

entry

Menu entry number (0-indexed), name, or identifier

Use alternative boot directory instead of /boot

/etc/default/grub

Must contain GRUB_DEFAULT=saved for grub-set-default to take effect.

Requires GRUB_DEFAULT=saved in /etc/default/grub and regenerating the configuration with grub-mkconfig. Without this, the setting in grubenv is ignored. Entry numbers can change when kernels are added or removed.

grub-set-default is part of GRUB 2's saved default functionality. It provides a way to change the boot default without editing configuration files, storing the selection in the grubenv file.

grub-reboot(8), grub-mkconfig(8), grub-editenv(1)