[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 21:35:35 CEST 2016

On 04/06/2016 03:55 AM, Michael Kjörling wrote:
> On 5 Apr 2016 21:25 -0700, from dpchrist at holgerdanske.com (David Christensen):
>> # grep sda2 /etc/crypttab
>> sda2_crypt /dev/sda2                                 /dev/urandom
>> cipher=aes-xts-plain64,size=256,swap
> Since you don't have the "luks" option, Debian does not treat this as
> a LUKS device. So when cryptsetup claims that /dev/sda2 "is not a
> valid LUKS device" it is quite correct.

Thanks for the information.

So, RTFM 'crypttab':  at boot time /sbin/cryptdisks_start will create a 
plain dm-crypt device with target name 'sda2_crypt' 
(/dev/mapper/sda2_crypt) from source device /dev/sda2 with a 256-bit key 
(option 'size') from file /dev/urandom and with cipher aes-xts-plain64 
(option 'cipher'), and then run /sbin/mkswap on the created device 
(option 'swap') (?).

And, as plain dm-crypt devices do not have a LUKS header, 
'luksHeaderBackup' has nothing to back up and the error message I'm 
seeing is expected and correct (?).


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