Linux/grub

related commands

• grub-install
  • note that the target must be a device (e.g. /dev/sdd), not a partition or filesystem (e.g. /dev/sdd1).
• grub-mkconfig creates a new grub.cfg based on what disks and boot options it finds. Run as root and redirect output to the desired file.
• update-grub updates the grub menu
  • bootable drives do not need to be mounted in order to be included

Commmands

rescue mode

these commands are still available in rescue mode; examples are from a system with one hard drive on /dev/hda, 2nd partition is ext4

• ls (hd<drive>,<partition>)
  • Example: ls (hd0,2)
    • Returns: (hd0,2): Filesystem is ext2.
  • Example: ls (hd0,2)/boot/grub
    • Returns: (horizontal list of files)

Notes

• https://askubuntu.com/questions/41930/kernel-panic-not-syncing-vfs-unable-to-mount-root-fs-on-unknown-block0-0/48516#48516 - this actually worked when the Repair Disk did not
• http://community.linuxmint.com/tutorial/view/245
• http://askubuntu.com/questions/420778/i-need-step-by-step-guidence-to-recover-grub
• https://askubuntu.com/questions/142300/how-to-fix-error-unknown-filesystem-grub-rescue
• https://ubuntuforums.org/showthread.php?t=1706090 "Grub error unknown filesystem"
• https://askubuntu.com/questions/5298/grub-help-and-reinstalling-ubuntu

Overall, though, this seems to be the magic tool for fixing broken grub booting: https://help.ubuntu.com/community/Boot-Repair

• https://help.ubuntu.com/community/RecoveringUbuntuAfterInstallingWindows - looks like it might discuss the manual steps Boot Repair does

Other links that may be useful:

• https://access.redhat.com/documentation/en-us/red_hat_enterprise_linux/6/html/installation_guide/s2-grub-whatis-booting-uefi
• https://www.eightforums.com/threads/uefi-doesnt-recognise-my-bootable-usb-device.16780/