Ubuntu Grub headaches

Today I had to install an Ubuntu 14.04.2 LTS system on a two-disk PC, with software RAID1, which I did many times before.

The disks and raid setup went fine, but when reaching the GRUB install it reports “fatal error”.
I skipped the bootloader install and finished the OS setup. Of course, the system didn’t boot…

After a little googling, I can resolve all booting problems.

I was able to boot from CD in rescue mode, but grub-install didn’t work either:

#grub-install /dev/sda Installing for i386-pc platform.
grub-install: warning: this GPT partition label contains no BIOS Boot Partition; embedding won’t be possible.
grub-install: error: embedding is not possible, but this is required for cross-disk install.

The OS install sets GPT partition automatically but there’s no BIOS boot partition entry created which
is a must for Grub2 second stage. This must be due to the “manual partitioning”.

Luckily, the setup left ~1MB unused space on the drives before the first partition (partition alignment policy), so I can use it for the boot partition.

To edit the partition table I needed the parted tool. After entering the command I got a new prompt.
The following commands can be entered afterwards.

# Select the device (e.g. /dev/sda)
select /dev/sdX

# Prints unused spaces
print free

# Creates a new partition on an unused space
# where N1/N2 is the start/end (e.g. 17.4kB 1049kB).
# Ignore the warning about the best performance complain.
mkpart primary N1 N2

# Print the new partition scheme
print

# Sets the new partition as the Grub boot partition
# where N is the newly created partition number.
set N bios_grub on

Repeat these steps for the second drive in the RAID array (e.g. /dev/sdb) then quit from parted.

After this changes, the new partition list may looks like this:

Number Start  End    Size   File system Name    Flags
  5    17.4kB 1049kB 1031kB             primary bios_grub
  1    1049kB 15.0GB 15.0GB ext3                raid
  2    15.0GB 440GB  425GB  ext3                raid
  3    440GB  470GB  30.0GB ext3                raid
  4    470GB  500GB  30.1GB ext3                raid

Install the Grub2 bootloader into both disks then restart PC:

grub-install /dev/sda
grub-install /dev/sdb

After these changes, I was still unable to boot into Ubuntu Linux. The boot procedure stops at the Grub> prompt. To be able to boot from this point, I entered the following commands:

set root=(md/0)
linux /vmlinuz root=/dev/md0 ro
initrd /initrd.img
boot

I repeated the grub-install commands and update-grub then everything went fine, the OS boots after restart. However, there is one glitch remains. At the boot process the following error message shows for a few seconds:

error: Diskfilter writes are not supported

After a quick search, I found this is a bug: Bug #1274320 “Error: diskfilter writes are not supported”

The solution is to patch the /etc/grub.d/00_header file: link to patch.

I preserve here the complete diff:

diff --git a/util/grub.d/00_header.in b/util/grub.d/00_header.in
index 8dc5592..7ab59e3 100644
--- a/util/grub.d/00_header.in
+++ b/util/grub.d/00_header.in
@@ -102,23 +102,42 @@ function savedefault {
 EOF
 
 if [ "$quick_boot" = 1 ]; then
-    cat <<EOF
+  cat <<EOF
 function recordfail {
   set recordfail=1
 EOF
+
+  check_writable () {
+    abstractions="$(grub-probe --target=abstraction "${grubdir}")"
+    for abstraction in $abstractions; do
+      case "$abstraction" in
+	diskfilter | lvm)
+	  cat <<EOF
+  # GRUB lacks write support for $abstraction, so recordfail support is disabled.
+EOF
+	  return
+	  ;;
+      esac
+    done
+
     FS="$(grub-probe --target=fs "${grubdir}")"
     case "$FS" in
       btrfs | cpiofs | newc | odc | romfs | squash4 | tarfs | zfs)
 	cat <<EOF
   # GRUB lacks write support for $FS, so recordfail support is disabled.
 EOF
+	return
 	;;
-      *)
-	cat <<EOF
-  if [ -n "${have_grubenv}" ]; then if [ -z "${boot_once}" ]; then save_env recordfail; fi; fi
-EOF
     esac
+
     cat <<EOF
+  if [ -n "${have_grubenv}" ]; then if [ -z "${boot_once}" ]; then save_env recordfail; fi; fi
+EOF
+  }
+
+  check_writable
+
+  cat <<EOF
 }
 EOF
 fi