https://bugs.debian.org/784368 shows that initramfs-tools is looking for /sbin/fsck.btrfs, but btrfs-tools ships it in /bin/.
Ben Hutchings suggested back in May that btrfs-tools was going to put fsck.btrfs back into /sbin in the "next version", though i can't tell from the bug log which version that was, but 4.1.2-1 came out in August. Maybe we could add the following line to debian/btrfs-tools.links: bin/fsck.btrfs sbin/fsck.btrfs Regards, --dkg