Grub2 fallback with 14.04 ... need How-To

Question

• 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'

GRUB_DEFAULT=0
#GRUB_HIDDEN_TIMEOUT=0
GRUB_HIDDEN_TIMEOUT_QUIET=true
GRUB_TIMEOUT=5
GRUB_DISTRIBUTOR=""
GRUB_CMDLINE_LINUX_DEFAULT=""
GRUB_CMDLINE_LINUX=""

# fallback addition
export GRUB_FALLBACK="1 2"
GRUB_DEFAULT=saved
GRUB_SAVEDEFAULT=true



# 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 ...)
#GRUB_BADRAM="0x01234567,0xfefefefe,0x89abcdef,0xefefefef"

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

# 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'
#GRUB_GFXMODE=640x480

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

# Uncomment to disable generation of recovery mode menu entries
GRUB_DISABLE_RECOVERY="true"

# 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)' {
        recordfail
        load_video
        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
        else
          search --no-floppy --fs-uuid --set=root 208a7546-da6b-4d07-82ab-0f04e8db6fd0
        fi
        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
        else
          search --no-floppy --fs-uuid --set=root 89ad84a4-3fe5-4409-a702-96ae698872d2
        fi
        linux /boot/vmlinuz
        initrd /boot/initrd.img
        savedefault fallback
}
### END /etc/grub.d/40_custom ###

Answer 1

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.