[Bug 1354730] Re: 14.04 grub-install failed: Wrong number of args: mapdevfs <path>

[TJ]

The failure is due to grub_probe() returning more than one line when
using btrfs. In the case of a 4-device raid1 created with:

make.btrfs  -m raid1 -d raid1 /dev/sda1 /dev/sdb1 /dev/sdc1 /dev/sds1

grub_probe() returns and assigns to $rootfs:

/dev/sda1
/dev/sdb1
/dev/sdc1
/dev/sdd1

which causes calls to mapdevfs to fail since it receives 4 arguments
with error code 1 and message "Wrong number of args: mapdevfs <path>".

The fix is to amend the grub-installer script's grub_probe() function:

 diff -u grub-installer.orig grub-installer
--- grub-installer.orig 2014-08-10 04:22:23.009006148 +0100
+++ grub-installer      2014-08-10 04:22:38.249815612 +0100
@@ -113,7 +113,7 @@
                apt-install grub-common
                is_grub_common_installed=true
        fi
-       $chroot $ROOT grub-probe $@
+       $chroot $ROOT grub-probe $@ | head -1
 }


** Changed in: grub-installer (Ubuntu)
       Status: In Progress => Triaged

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https://bugs.launchpad.net/bugs/1354730

Title:
  14.04 grub-install failed: Wrong number of args: mapdevfs <path>

Status in “grub-installer” package in Ubuntu:
  Triaged

Bug description:
  I was previously able to install ubuntu on a root btrfs filesystem in raid1 mode as I described here:
  http://askubuntu.com/questions/87241/how-to-install-using-btrfs-in-raid10-mode

  So I used gparted to create btrfs partitions on all the disksand left
  1 MB at the beginning of the disks for GRUB. (I also tried 2, and 5)

  Then later I made the btrfs filesystem as follows:
  mkfs.btrfs -m raid1 -d raid1 /dev/sda1 /dev/sdb1 /dev/sdc1 /dev/sdd1
  And performed:
  btrfs dev scan

  Then I went back through normal installation.

  I am now trying to do this again, using Ubuntu 14.04.
  Everything goes fine up to the point that it wants to install grub.
  It mentions the error in the title and fails.

  Apparently, somebody else also reported an error like this with 14.04.
  https://bugs.launchpad.net/ubuntu/+source/grub-installer/+bug/912431 (at the bottom a person mentions that it occurs in 14.04)

  I will attach some files later.

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