[dm-crypt] how to determine the mapped device from the original device

[dm-crypt] how to determine the mapped device from the original device

[Alvin Thompson]

Hi,

I was wondering if it is possible to determine the mapped device from the original device.  For example, if you used the command:

  cryptsetup luksOpen /dev/sdd1 backup

Can you later determine the mapped device name ('backup' in this case) if all you know is the device (/dev/sdd1)?

Thanks,
Alvin

Re: [dm-crypt] how to determine the mapped device from the original device

[Uwe Menges]

Alvin Thompson wrote:
> I was wondering if it is possible to determine the mapped device from the original device.  For example, if you used the command:
> 
>   cryptsetup luksOpen /dev/sdd1 backup
> 
> Can you later determine the mapped device name ('backup' in this case) if all you know is the device (/dev/sdd1)?

I don't know that, but I use entries in /etc/crypttab like:

backup01 /dev/disk/by-uuid/... /dev/shm/backupkey luks,noauto

and use

# cryptdisks_start backup01

which causes /dev/mapper/backup01 to appear.
Corresponding /etc/fstab entry is:

LABEL=backup01  /backup/disk1 auto noauto,noatime,nodiratime

Maybe this helps you with handling the devices.

Yours, Uwe

Re: [dm-crypt] how to determine the mapped device from the original device

[Milan Broz]

On 12/10/2009 01:37 AM, Alvin Thompson wrote:
> I was wondering if it is possible to determine the mapped device from the original device.  For example, if you used the command:
> 
>   cryptsetup luksOpen /dev/sdd1 backup
> 
> Can you later determine the mapped device name ('backup' in this case) if all you know is the device (/dev/sdd1)?

For really low-level, you can try dmsetup.

If you know the major:minor of that device (ls -l /dev/sdd1) check "dmsetup ls --tree" or similar.
The reverse is "cryptsetup status backup" and see device there.

All active encrypted devices you can see with "dmsetup status --target crypt" (or dmsetup table and check table directly).

Anyway, this seems like good idea to add some new command to cryptsetup, like "cryptsetup deps <dev>" to display
encrypted device mapped to underlying <dev>... add new issue to project page if you want this please.

Milan
--
mbroz@redhat.ocm

Re: [dm-crypt] how to determine the mapped device from the original device

[Arno Wagner]

Here is a way (not pretty):

1. Get a list of all names in /dev/mapper via "dmsetup info"
2. Do a "cryptsetup status" for all of them
3. Search the device you want to know about in the output of 2.

Should be doable in Perl/Python in half an hour or so.

Arno

 


On Wed, Dec 09, 2009 at 07:37:26PM -0500, Alvin Thompson wrote:
> Hi,
> 
> I was wondering if it is possible to determine the mapped device from the original device.  For example, if you used the command:
> 
>   cryptsetup luksOpen /dev/sdd1 backup
> 
> Can you later determine the mapped device name ('backup' in this case) if all you know is the device (/dev/sdd1)?
> 
> Thanks,
> Alvin
> 
> _______________________________________________
> dm-crypt mailing list
> dm-crypt@saout.de
> http://www.saout.de/mailman/listinfo/dm-crypt
> 

-- 
Arno Wagner, Dr. sc. techn., Dipl. Inform., CISSP -- Email: arno@wagner.name 
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----
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"news" is "something that hardly ever happens." -- Bruce Schneier 

Re: [dm-crypt] how to determine the mapped device from the original device

[Mario 'BitKoenig' Holbe]

Alvin Thompson <alvin@thompsonlogic.com> wrote:
> Can you later determine the mapped device name ('backup' in this case) if all you know is the device (/dev/sdd1)?

There is no way to do this offline, i.e. as long as the mapped device is
not created. LUKS does not store information about "preferred names" or
something like that.

If the device is online, you can try
ls -l /sys/block/dm-*/slaves/*

Just modify the pattern to your needs, like /sys/block/dm-*/slaves/sdd1

The mapping from dm-x to the symbolic name could be a bit harder, just
in case the dm-* names don't fit your needs.
I'd go for
ls -l /dev/mapper/* | grep " $(sed -e 's/:/, */' /sys/block/dm-x/dev) "
or something like that. Mind the surrounding spaces to get the pattern
safe or use grep -w.


regards
   Mario
-- 
There are trivial truths and the great truths.
The opposite of a trivial truth is plainly false.
The opposite of a great truth is also true.
                                    -- Niels Bohr