• Ubuntu server 14.04 efi-gpt disk with three partitions, 1=boot, 2=main, 3=recovery
  • I want: default boot on gpt2, grub fallback to gpt3, and grub-reboot to reboot into recovery from main.

  • What I get is no boot at all, just an instant reboot loop.

I am a bit confused by the GNU docs. And I need to be able to do all changes from the 40_custom file and /etc/default/grub to be repeatable and robust.

heres some links: http://www.gnu.org/software/grub/manual/grub.html#Simple-configuration https://www.gnu.org/software/grub/manual/legacy/Booting-fallback-systems.html "wiki.ubuntuusers.de/ GRUB_2/ Skripte/#Fallback-Skript"

here is /etc/default/grub:

# If you change this file, run 'update-grub' afterwards to update
# /boot/grub/grub.cfg.
# For full documentation of the options in this file, see:
#   info -f grub -n 'Simple configuration'


# fallback addition
export GRUB_FALLBACK="1 2"

# Uncomment to enable BadRAM filtering, modify to suit your needs
# This works with Linux (no patch required) and with any kernel that obtains
# the memory map information from GRUB (GNU Mach, kernel of FreeBSD ...)

# Uncomment to disable graphical terminal (grub-pc only)

# The resolution used on graphical terminal
# note that you can use only modes which your graphic card supports via VBE
# you can see them in real GRUB with the command `vbeinfo'

# Uncomment if you don't want GRUB to pass "root=UUID=xxx" parameter to Linux

# Uncomment to disable generation of recovery mode menu entries

# Uncomment to get a beep at grub start
#GRUB_INIT_TUNE="480 440 1


here is the relevant part of grub.cfg:

## BEGIN /etc/grub.d/40_custom ###
# This file provides an easy way to add custom menu entries.  Simply type the
# menu entries you want to add after this comment.  Be careful not to change
# the 'exec tail' line above.

menuentry 'ITH Robot Base Main (on /dev/sda2)' {
        gfxmode $linux_gfx_mode
        insmod gzio
        insmod part_gpt
        insmod ext2
        set root='hd0,gpt2'
        if [ x$feature_platform_search_hint = xy ]; then
          search --no-floppy --fs-uuid --set=root --hint-bios=hd0,gpt2 --hint-efi=hd0,gpt2 --hint-baremetal=ahci0,gpt2  208a7546-da6b-4d07-82ab-0f04e8db6fd0
          search --no-floppy --fs-uuid --set=root 208a7546-da6b-4d07-82ab-0f04e8db6fd0
        linux   /boot/vmlinuz  
        initrd  /boot/initrd.img
        savedefault fallback

menuentry 'ITH Robot Base Recovery(on /dev/sda3)' {
        insmod part_gpt
        insmod ext2
        set root='hd0,gpt3'
        if [ x$feature_platform_search_hint = xy ]; then
          search --no-floppy --fs-uuid --set=root --hint-bios=hd0,gpt3 --hint-efi=hd0,gpt3 --hint-baremetal=ahci0,gpt3  89ad84a4-3fe5-4409-a702-96ae698872d2
          search --no-floppy --fs-uuid --set=root 89ad84a4-3fe5-4409-a702-96ae698872d2
        linux /boot/vmlinuz
        initrd /boot/initrd.img
        savedefault fallback
### END /etc/grub.d/40_custom ###
  • Did you run sudo update-grub after making the changes? It needs to be executed every time you want to apply the grub changes. – E.F. Nijboer Feb 9 '16 at 23:50
  • yes I did run it each time – John Fisher Feb 10 '16 at 0:09
  • Under EFI, partitions are not bootable. Thus, your claim that you want "default boot on gpt2, grub fallback to gpt3" makes no sense from an EFI perspective. Please re-state your requirements in terms of what you want to boot -- different OSes, distributions, or kernels, for instance. The context of your configuration (Boot Info Script output, or at least sudo parted -l output) would be helpful, too. – Rod Smith Feb 10 '16 at 15:28
  • I am going back to see about the EFI/gpt setup; I may have thought I knew something and been wrong, though the initial setup did boot EFI and only refused to boot after I changed Grub settings. Anyway back to the start and double-check. – John Fisher Feb 10 '16 at 17:41
  • this page is very helpful .. askubuntu.com/questions/500359/… ... for one thing I had no idea you could mix and match mbr|gpt vs efi|legacy. I just want a dual-boot with efi-gpt and it looks like I need to experiment a little, then get back to the Grub problem. – John Fisher Feb 10 '16 at 19:33

I solved the issues by making sure that my disk was setup EFI/GPT ( not necessary, but not getting this right made it impossible to follow the instructions when I was already confused), using gparted (or parted) to create the boot EFI partition, and editing the proper files. Here is a guide that might be helpful:

  • To get the disk right use gparted to create a GPT disk table, then create a smallish Fat32 partition with the flag set to "boot" and a mount point /boot/efi. (the mount point is conventional, but I advise following convention).
  • Add your other partitions as required, but root partitions won't have the boot flag as they normally do.
  • After installing Ubuntu, you'll find that Grub has set up all partitions it could find for its boot menu. You may not want this, or you may have customizations.
  • Check /etc/fstab to make sure the /boot/efi mount command is there and the filesystem to make sure there is a /boot/efi mount point.
  • Advice: before you run update-grub make backups of /boot/grub, /etc/default/grub, /etc/grub.d and have a bootable flashdrive or some method of mounting your new partitions so you can fix them when your changes fail to boot.
  • There are only a few things you need to change in /etc/default/grub, the majority of your changes should be in /etc/grub.d/40_custom plus chmodding the 10* 20* 30* scripts as needed to prevent them from doing their thing.
  • You can cut&paste the menu stanza(s) from /boot/grub/grub.cfg into 40_custom
  • Beware Grub( maybe EFI?) counts the disks from zero ( hd0) and the partitions from one.
  • Run update-grub to create the grub.cfg file
  • You don't need to do anything with the Fat32 boot partition
  • Beware: I got a problem on a system with two bootable flashdrives and a HD where the HD used the boot EFI partition off the flashdrive instead of on itself. This is all about having extraneous drives connected- try to disconnect anything that you don't want to change.
  • Beware: if you are saving and restoring multiple drives, you'll have to reset the UUIDs using tune2fs, else you'll get a collision.

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