Useful Grub commands

Setting default option in Grub select-system menu:
We edit /etc/default/grub file and enter default option as GRUB_DEFAULT: GRUB_DEFAULT=option_number - number starting from 0. We save the file and enter following command for changes take place: update-grub

To install Grub as a bootmanager we steps through the following list of commands:

1. Boot from the live CD of our distribution.
2. Open terminal and issue the command: sudo fdisk -l to see which partition is our Linux installed on.
3. Issue command: sudo mount /dev/sdaX /mnt where X is the number of partition found above, to mount the partition in /mnt directory.
4. Issue command: sudo grub-install --root-directory=/mnt /dev/sda to install Grub in the /dev/sda disk's boot-sector.
5. Issue command: sudo update-grub to update the Grub's configuration.
6. Reboot.
7. If during booting the system we see some errors (references to non-existing files), we have to repeat Grub installation process after system startup. So after logging in open the teminal and execute commands: sudo grub-install --root-directory=/ /dev/sda
sudo update-grub

To set background image for Grub's system menu, we edit following file: /etc/grub.d/05_debian_theme and in the line before last line (before line containing: set_default_theme) we enter following lines: # If we haven't found a background image yet, use the default from desktop-base.
if set_background_image "/boot/grub/_b1ocean.tga"; then
exit 0
fi
And next we issue command: update-grub.

After each changing Grub settings we must enter following command for changes to take place: update-grub

How to make GRUB menu to show each time computer is rebooted on the machine with single operating system (Linux)

1. Install GRUB: sudo grub-install --recheck --no-floppy --root-directory=/ /dev/sda
2. Open /etc/default/grub file in your favourite text editor and comment out line GRUB_HIDDEN_TIMEOUT=0 by inserting '#' character on the very first position in the line.
3. Apply the change by issuing command: sudo update-grub
4. Reboot and enjoy with GRUB menu at the system start.