Btrfs – Fixing ‘Sparse File Not Allowed’ Error After Installing on Btrfs Filesystem

bootbtrfs

I've installed Ubuntu without creating a swap partition and with / on a btrfs.# Now I get the message "Sparse file is not allowed" on each boot. This message appears before the splash-screen. Is there a way to kill this warning?

Best Answer

OK after a bit of rummaging around I found a how-to too get rid of this problem at least temporarily it is fairly simple however I don't have my system set-up with btrfs so I can't confirm this fix.

either comment out or remove this line:

if [ -n ${have_grubenv} ]; then save_env recordfail; fi

or

if [ -n "\${have_grubenv}" ]; then if [ -z "\${boot_once}" ]; then save_env \
recordfail; fi; fi

in this file

/etc/grub.d/00_header

then run

update-grub

the reason for not editing /boot/grub/grub.cfg directly is that it will be over written every time grub is updated in this case you would only have to "re do" the fix if the grub common packages is updated.

This is the bug on launchpad if you want to add yourself bug #736743

Quoting Colin Watson from the bug report

This is actually a misleading error message: what's happening is that GRUB's btrfs implementation doesn't implement the file read hook interface for returning blocklists to calling code. I posted to grub-devel about this and the upstream maintainer pointed out that, even aside from multi-device problems, writing to btrfs from GRUB is fundamentally risky because:

the same block may be used by multiple snapshots every tree which uses a given block will contain its checksum, and so on recursively

However, btrfs reserves space at the start for the boot loader. This space is more than GRUB needs to embed itself, and so we could use 1KB of it for an environment block.

In any case, this is not a new problem that arose from using subvolumes, nor does it prevent booting (you get a spurious "Press any key to continue" prompt, but if you just ignore it it'll boot anyway). Downgrading to wishlist.

Hope this helps