Customizing GRUB – the basics

Customizing GRUB is quite easy to do. Do note the following:

• The following steps are to be carried out on the "target" system itself (not on the host); in our case, the Ubuntu 18.04 guest VM.
• This has been tested and verified on our Ubuntu 18.04 LTS guest system only.

Here's a quick series of steps for our customization:

1. Let's be safe and keep a backup copy of the GRUB bootloader config file:

sudo cp /etc/default/grub /etc/default/grub.orig

The /etc/default/grub file is the user-configuration file in question. Before editing it, we make a backup to be safe. This is always a good idea. 

2. Edit it. You can use vi(1) or your editor of choice:

sudo vi /etc/default/grub 

3. To always show the GRUB prompt at boot, insert this line:

GRUB_HIDDEN_TIMEOUT_QUIET=false

On some Linux distros, you might instead have the GRUB_TIMEOUT_STYLE=hidden directive; simply change it to GRUB_TIMEOUT_STYLE=menu to achieve...