How to see grub boot menu at startup (to choose boot alternative)

If you want to customize the Grub Menu Entries on your Droplet, you can edit the /etc/default/grub configuration file. To display the Grub boot menu during the Droplet’s startup, you should modify the following options:

GRUB_TIMEOUT: Set the time (in seconds) that the menu will be displayed before automatically booting the default entry. For example, GRUB_TIMEOUT=10 shows the menu for 10 seconds. GRUB_HIDDEN_TIMEOUT: Set this to a non-zero value if you want the menu to be hidden unless the Shift key is pressed during the startup. GRUB_HIDDEN_TIMEOUT_QUIET: Set this to false if you want to show a countdown while waiting for the Shift key to be pressed.

After modifying the configuration, you should run sudo update-grub to apply your changes. Note that making changes to these settings may increase the risk of making your Droplet unbootable, so proceed with caution.

Don’t forget to create a snapshot of your customized Droplet to create your Custom Droplet Boot Image. For more information about custom images, visit the DigitalOcean documentation: https://docs.digitalocean.com/products/images/custom-images

Hope that this helps!