luks and logical volumes

manyrootsofallevil · 02-18-2011, 01:15 PM

Not sure whether I should post this on the newbie forum, at any rate.

I'm bit confused as to what is going on with LUKS and Logical Volumes (LV(s) henceforth)

I created a Luks encrypted partition on my VM test machine and that is straight forward enough.

using:

Code:

cryptsetup luksFormat /dev/sdb
 cryptsetup luksOpen /dev/sdb crypto

and then adding to /etc/crypttab the following:

Code:

crypto /dev/sdb none

So far so good

I get prompted on start up for the passphrase and I can mount the partition without any problem , e.g. mount /dev/sdb /mydirectory, works a treat.

Now, I created a volume group (vol1, I like original names) out of two partitions, and then used it to create a logical volume (lv1)

So armed with a logical volume, I proceed with the same steps as above, namely:

Code:

cryptsetup luksFormat /dev/vol1/lv1
 cryptsetup luksOpen /dev/vol1/lv1 cryptlv

and then adding to /etc/crypttab the following:

Code:

cryptlv /dev/vol1/lv1 none

I can mount this with:

Quote:

mount /dev/mapper/cryptlv

The thing is that I did blkid and there is an extra device

/dev/mapper/crypto: UUID="2204caa6-08a1-4c9b-bb1e-d35f6acaa03a" TYPE="ext4"
/dev/mapper/vol1-lv1: UUID="7f54aaf2-8fd6-428c-be12-a059d5df4650" TYPE="crypto_LUKS"
/dev/mapper/cryptlv: UUID="5f7fa55f-09fc-4b29-88e7-b4ddcd5a21b8" TYPE="ext4" LABEL="cryptlv"

I cannot mount this extra device, I tried:

Code:

mount  /dev/mapper/vol1-lv1 /mydir

and

Code:

mount  -t crypto_LUKS /dev/mapper/vol1-lv1 /mydir

but both return

Code:

mount: unknown filesystem type 'crypto_LUKS'

My questions are as follows:

Why is there a new device?
How was it created (I certainly did not do it manually)?
How do I get rid of it?

TIA

rayfordj · 02-19-2011, 07:38 AM

Quote:

Originally Posted by manyrootsofallevil

Why is there a new device?

Because LVM leverages device-mapper to map the underlying [physical volume] block device(s)'s physical-extents to the logical-extents that comprise the logical volume.

Quote:

Originally Posted by manyrootsofallevil

How was it created (I certainly did not do it manually)?

Ah, but you did when you created the logical-volume named lv1.

Quote:

Originally Posted by manyrootsofallevil

How do I get rid of it?

remove the logical volume...

Code:

# umount /dev/mapper/cryptlv 
# cryptsetup luksClose /dev/vol1/lv1
# # Be sure you no longer want to utilize the encrypted LV before proceeding.
# # This will delete the LV; remove or comment its line in /etc/crypttab.
# lvchange -an /dev/vol1/lv1
# lvremove /dev/vol1/lv1

manyrootsofallevil · 02-21-2011, 01:58 AM

Quote:

Originally Posted by rayfordj

Because LVM leverages device-mapper to map the underlying [physical volume] block device(s)'s physical-extents to the logical-extents that comprise the logical volume.

Ah, but you did when you created the logical-volume named lv1.

remove the logical volume...

Code:

# umount /dev/mapper/cryptlv 
# cryptsetup luksClose /dev/vol1/lv1
# # Be sure you no longer want to utilize the encrypted LV before proceeding.
# # This will delete the LV; remove or comment its line in /etc/crypttab.
# lvchange -an /dev/vol1/lv1
# lvremove /dev/vol1/lv1

Thanks for the reply

I had actually worked it all out, after I posted, just too lazy to answer my own post.

It's amazing what happens when one stops and reads documentation