Grub

Resources

• http://www.gnu.org/software/grub/
• https://en.wikipedia.org/wiki/GNU_GRUB
• https://help.ubuntu.com/community/Grub2
• https://wiki.gentoo.org/wiki/GRUB2
• https://www.dedoimedo.com/computers/grub-2.html

Repair/update Grub2

• Repair Grub2
• How to Update Grub on Ubuntu and Other Linux Distributions. Good instruction. Two disks; each with its own Linux distribution. The second disk won't install Grub. So the Linux on the 1st disk needs to update its grub so it can see the Linux on the 2nd disk.
• GRUB Rescue | Repairing GRUB Apr 2019

Not see Grub after re-install/upgrade Windows

Fix Grub Not Showing For Windows 10 Linux Dual Boot

Add a new entry to boot an ISO

• UBUNTU Using GRUB2 to boot to ISO (kind of outdated)
• Custom Grub Boot Menu Feb 2019

Configuration - /etc/default/grub

How to Configure the GRUB2 Boot Loader’s Settings

Configuration options:

• Scripts in /etc/grub.d
• Configuration file at /etc/default/grub

Incorporating changes:

• grub2-mkconfig (or grub-mkconfig for Grub v1) reads configurations and generates a new configuration for /boot/grub2 (or /boot/grub)

Show the grub2 screen

To show the grub2 screen, run sudo nano /etc/default/grub and comment out the line GRUB_HIDDEN_TIMEOUT=0 and change the line GRUB_CMDLINE_LINUX_DEFAULT="quiet splash" to GRUB_CMDLINE_LINUX_DEFAULT="". Remember to run 'sudo update-grub' after any change to grub.

How do I set the grub timeout and the grub default boot entry?

https://askubuntu.com/questions/148095/how-do-i-set-the-grub-timeout-and-the-grub-default-boot-entry

1. gksudo gedit /etc/default/grub
2. Change as you like. Save and closed the file.
   • You can change the default from 0 to any number
   • You can change the "hidden timeout" (no menu)
   • You can force the grub menu to show by commenting out the two GRUB_HIDDEN lines with a # at the beginning of the line
   • set the grub menu timeout (default is 10 seconds)
3. sudo update-grub
4. Reboot

Grub Customizer - GUI program

• How To Change The GRUB Boot Order Or Default Boot Entry In Ubuntu, Linux Mint, Debian, Or Fedora With Grub Customizer
• How to Edit GRUB with GRUB Customizer
• Add a live ISO boot to GRUB menu

Add a splash image

Follow the instruction at https://help.ubuntu.com/community/Grub2/Displays. Note that Grub2 will search the image based on some priority and there are also some minor requirements on the images. To test

sudo apt-get install grub2-splashimages
sudo cp /usr/share/images/grub/Moraine_Lake_17092005.tga /boot/grub/
sudo update-grub

Boot into command line

http://www.linuxandubuntu.com/home/how-to-boot-into-linux-command-line

1. Highlight the first item (default) and press 'e' in the GRUB menu
2. Navigate to the line that starts with ‘linux’, change the runlevel to 3 (at the end of the line). Level 3 means multi-user, command-line only system
3. Press Ctrl+x or F10 to boot into

To switch back to GUI, type sudo init 5. Level 5 is the default.

Where is grub installed

• Where is grub installed and do I need a new one for a separate linux installation?
• https://askubuntu.com/a/30347 which suggests Boot info script. Very useful. We can run it using live USB.
  • The boot files in each partition will be discovered.
  • After running sudo ./bootinfoscript, the result is saved in a text file "RESULTS.TXT".
  • On my system it shows Grub2 is installed in the MBR of /dev/sda. My setup is /dev/sda for Windows 10, /dev/sdb for a backup disk and /dev/sdc for Ubuntu.
  • The RESULTS.txt shows sdc/boot/grub/grub.cfg contains the boot menu I saw when the system boots up.
• https://help.ubuntu.com/community/Boot-Repair

MBR and GPT

• MBR
  • https://en.wikipedia.org/wiki/Master_boot_record
  • MBR
• How to Check if a Disk Uses GPT or MBR, and Convert Between the Two