grub-reboot:tldr:d453f

This command is used to set the default entry in the GRUB bootloader menu, which is used to choose which operating system to boot into on a dual-boot system or to access different boot options.

Here is a breakdown of the command:

• sudo: This is a command that allows a user with administrative privileges to execute a command as a superuser or root user. It prompts for the user's password before running the command.
• grub-reboot: This is the command executed by sudo. It is a utility provided by GRUB (GRand Unified Bootloader) to set the default boot menu entry.
• ${entry_number}: This is a placeholder for the actual entry number you want to set as the default. Replace ${entry_number} with the number corresponding to the desired boot menu entry.

By running the command with the desired entry number, the default entry in the GRUB menu will be changed. This means that upon system restart, the specified entry in the menu will be automatically selected as the default boot option.