grub-reboot

Set the default boot entry for the next boot only

$ sudo grub-reboot [entry_number]

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

grub-reboot [options] entry

grub-reboot sets the default boot entry for the next boot only. After booting once, GRUB reverts to the permanent default set by grub-set-default or the configuration file.
The entry can be specified as a number (0 for first entry), the full entry name from grub.cfg, or a menu entry identifier. Use grep menuentry /boot/grub/grub.cfg to see available entries.
This is useful for one-time boots into recovery mode, alternative kernels, or other operating systems without permanently changing the boot order.

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-reboot to function.

Requires GRUB_DEFAULT=saved in /etc/default/grub and subsequent grub-mkconfig to function. The setting is stored in grubenv, which must be writable. Only affects the immediate next boot.

grub-reboot is part of GRUB 2, providing the "boot once" functionality that was present in GRUB Legacy. It enables safe testing of alternative boot configurations with automatic fallback.

grub-set-default(8), grub-mkconfig(8), grub-editenv(1)