[dm-crypt] Debian 7.10 random key swap Device /dev/sda2 is not a valid LUKS device.

David Christensen dpchrist at holgerdanske.com
Wed Apr 6 07:59:33 CEST 2016

On 04/05/2016 10:38 PM, Milan Broz wrote:
> On 04/06/2016 06:25 AM, David Christensen wrote:
> LUKS device cannot be used with random volume key, so I guess you use
> just plain device without header. (So obviously header backup fails because
> there is no header.)

Thank you for the information.

> You can verify it by checking entry in /etc/crypttab - no luks keyword:
>> # grep sda2 /etc/fstab
>> /dev/mapper/sda2_crypt                    none                    swap
> or running "cryptsetup status sda2_crypt" over unlocked device
> (type is LUKS1 for LUKS devices)

# cryptsetup status sda2_crypt
/dev/mapper/sda2_crypt is active and is in use.
   type:    PLAIN
   cipher:  aes-xts-plain64
   keysize: 256 bits
   device:  /dev/sda2
   offset:  0 sectors
   size:    976896 sectors
   mode:    read/write

So, what I'm seeing is expected and correct, because a random-key 
encrypted swap uses dm-crypt on the raw partition, there is no LUKS 
container, and therefore no LUKS header to back up (?).


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