What is "grub" command/program? Does it tweak GRUB2 as well or only GRUB legacy

Question

From my terminal:

heer@heer-Latitude-D620:~$ grub --help
The program 'grub' is currently not installed.  You can install it by typing:
sudo apt-get install grub
heer@heer-Latitude-D620:~$ 

Answer 1

GRUB (package name: grub), also known as GRand Unified Bootloader (Legacy version) is the predecessor of GRUB2 (package name: grub-pc), also known as GRand Unified Bootloader, version 2 (PC/BIOS version). So, grub it doesn't tweak with nothing GRUB2, but replaces GRUB2:

$ sudo apt-get install grub
Reading package lists... Done
Building dependency tree       
Reading state information... Done
Suggested packages:
  grub-legacy-doc mdadm
The following packages will be REMOVED:
  grub-gfxpayload-lists grub-pc grub2-common
The following NEW packages will be installed:
  grub
0 upgraded, 1 newly installed, 3 to remove and 0 not upgraded.

Since with version 9.10 of Ubuntu, this has used GRUB 2 as the default boot loader for clean installs (prior to this it was GRUB).

See which are some differences here:

• Differences between GRUB, GRUB2 and BURG
• GRUB vs GRUB 2

Answer 2

• GRUB is the boot loader (and Ubuntu loader) program which loads Ubuntu from the disk to the Memory to be run. So, yes, Such a program is essential to have Ubuntu and it is Grub by default. But there are other bootloader too, such as LILO (LInux LOader) and recent BURG.
  

• To learn Grub command, You can use the Grub manual here.

• Grub Customizer is a graphical interface to configure the GRUB2/BURG settings and menu entries.

  sudo add-apt-repository ppa:danielrichter2007/grub-customizer
  sudo apt-get update
  sudo apt-get install grub-customizer