cryptsetup refuses to luksFormat?

[Josef Wolf]

On Sat, Oct 14, 2023 at 01:51:06AM +0200, Josef Wolf wrote:
> I want to encrypt the whole disk (including boot) on ubuntu-2204 as described on
> https://discourse.maas.io/t/deploying-servers-with-full-disk-encryption-luks2/3286
> 
> So I enter following commands:
> 
>    # mount -o remount,ro /boot
>    # install -m0600 /dev/null /tmp/boot.tar
>    # tar -C /boot --acls --xattrs --one-file-system -cf /tmp/boot.tar .
>    # umount /boot/efi
>    # umount /boot
>    # cryptsetup -y luksFormat --type luks1 /dev/nvme0n1p3
>    WARNING: Device /dev/nvme0n1p3 already contains a 'ext4' superblock signature.
>    
>    WARNING!
>    ========
>    This will overwrite dataon /dev/nvme0n1p3 irrevocably.
>     
>    Are you sure? (Type 'yes' in capital letters); YES
>    Device /dev/nvme0n1p3 is in use. Cannot proceed with format operation.
> 
> Uh, not what I expected. So i start to investigate:
> 
>    # grep /dev/nvme0n1p3 /proc/mounts
>    # lsof | grep /dev/nvme0n1p3
>    # lsof /dev/nvme0n1p3
>    # fuser /dev/nvme0n1p3
> 
> So:
> - umount succeeded
> - /proc/mounts, lsof, fuser don's show any sign that the partition is in use
> 
> BUT:
> 
>     strace cryptsetup luksFormat --type luks1 /dev/nvme0n1p3 2>&1 | \
>       egrep '(nvme0n1p3|close)'
> 
> shows
> 
>     openat(AT_FDCWD, "/dev/nvme0n1p3", O_RDONLY|ODIRECT) = 3
>     close(3)
>     openat(AT_FDCWD, "/dev/nvme0n1p3", O_RDONLY|O_NONBLOCK|OCLOEXEC) = 3
>     close(3)
>     openat(AT_FDCWD, "/dev/nvme0n1p3", O_RDWR|OEXCL) = -1 EBUSY (Device or resource busy)
> 
> So there must be something holdig a hand on the partition.
> 
> Any idea what that might be?

No ideas on this one?

-- 
Josef Wolf
jw at raven.inka.de