Re: How to confirm GRUB is installed and used in a device?

[Markus Kolb]

Am 23.07.2020 15:43, schrieb Anthony Cheng:
> Hello,
>
> Can someone tell me how I can confirm that GRUB is installed and used 
> in a
> device?
>
> I see that I have a /boot folder with grub in this folder, and also
> grub.conf file, so I have fairly convinced that grub is installed, but 
> not
> sure if it is used.

Hi,

you have to know if your BIOS is using UEFI or legacy boot sector.

The boot sector could be checked with

# dd if=/dev/sda bs=512 count=1 | xxd

* /dev/sda is a sample device and needs to be adjusted to your 
environment.
* xxd is a binary dump tool, hexdump -C is alternative.

There you should be able to read something about grub.

If your system boots with UEFI, there is a directory efi/EFI on the 
first partition of boot disk. This boot partition has a kind of FAT 
filesystem.
In this diretory is a subdirectory for bootloaders.
Which one is booted depends on the selection of your system and how 
(which key combination) you can check this depends on the hardware.
If you have only one subdir with file e.g. grub.efi in it and your 
system is using UEFI then it should be booted with grub.

With a default grub config you will also enter the grub boot menu when 
pressing escape key at the beginning of boot phase (after bios phase). 
There should be a short time window of 2 or 3 seconds for accepting the 
escape key.

Hope it helps
Markus