[dm-crypt] btrfs and "requested offset is beyond real size of device"

Arno Wagner arno at wagner.name
Mon Feb 16 08:24:26 CET 2015

Just one data-point: LUKS does not store device size. It gets 
queried on mapping. What it stores is the data-offset, i.e.
where the data-area starts after they keyslot-area.

Can you reproduce this with strace and a password that is not 
secret? ("strace cryptsetup ...") That should tell us in which 
call the error happens.


On Sun, Feb 15, 2015 at 23:43:22 CET, Jay Sullivan wrote:
> Hi,
> I don't know if this belongs on the btrfs, GRUB, or LUKS mailing list, but
> it is a cryptsetup error, so I figure maybe someone here can help me
> understand what this error means.
> *What I'm doing*
> I'm trying to set up a system with a btrfs /boot partition, and a few
> encrypted btrfs-over-LUKS partitions. Nothing special, except that I'm
> using btrfs for all of my partitions.
> *The Problem*
> I did get the setup "working", I'm able to successfully boot into it.
> Here's the weird part: it only successfully boots about half of the time.
> The other half of the time,  I see this error just after I successfully
> enter my password:
>     requested offset is beyond real size of device
> When this happens, it continues to fail when it prompts me again for my
> password, until I reboot.  It seems to fall into this issue about 50% of
> the boots.
> The culprit seems to be when the /boot partition is btrfs. If I use ext4 as
> /boot, everything works fine and dandy.
> This should be reproducible on any machine, I've tried several times on
> different machines to rule out hardware. I can give complete instructions
> to reproduce if someone wants it, but before I go through the effort, has
> anyone heard of this behavior before? Does anyone have any insight on why
> this may be happening, especially why it only happens sometimes.
> I'm using Ubuntu 14.10's LiveCD to install the operating system, where
> cryptsetup's version says 1.6.1, and btrfs's version is 3.14.1.
> Thanks,
> Jay Sullivan

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Arno Wagner,     Dr. sc. techn., Dipl. Inform.,    Email: arno at wagner.name
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