[dm-crypt] backup of luks header example in the FAQ has a wrong path

[dm-crypt] backup of luks header example in the FAQ has a wrong path

[.. ink ..]

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using cryptsetup 1.4.1

At the section on how to backup a luks header, the example given is below:

cryptsetup luksHeaderBackup --header-backup-file h /dev/mapper/c1


The usage of "/dev/mapper" path implies running the command on the mapper,
when i do that i get the following output:

[root@mtz build]# cryptsetup luksOpen /dev/sdc1 abc
Enter passphrase for /dev/sdc1:
[root@mtz build]# cryptsetup luksHeaderBackup --header-backup-file
backup.img  /dev/mapper/abc ; echo $?
Device /dev/mapper/abc is not a valid LUKS device.
1

The command errors out when using the mapper address as FAQ suggests.

When i use the device directly, it works as shown below:
[root@mtz build]# cryptsetup luksHeaderBackup --header-backup-file
backup.img  /dev/sdc1 ; echo $?
0

It looks like the command to backup the header is supposed to be run on the
device its self and not on the mapper as the FAQ suggests.

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Re: [dm-crypt] backup of luks header example in the FAQ has a wrong path

[Arno Wagner]

Hi,

On Sat, Jan 14, 2012 at 05:32:27PM -0500, .. ink .. wrote:
> using cryptsetup 1.4.1
> 
> At the section on how to backup a luks header, the example given is below:
> 
> cryptsetup luksHeaderBackup --header-backup-file h /dev/mapper/c1
> 
> 
> The usage of "/dev/mapper" path implies running the command on the mapper,
> when i do that i get the following output:
> 
> [root@mtz build]# cryptsetup luksOpen /dev/sdc1 abc
> Enter passphrase for /dev/sdc1:
> [root@mtz build]# cryptsetup luksHeaderBackup --header-backup-file
> backup.img  /dev/mapper/abc ; echo $?
> Device /dev/mapper/abc is not a valid LUKS device.
> 1
> 
> The command errors out when using the mapper address as FAQ suggests.
> 
> When i use the device directly, it works as shown below:
> [root@mtz build]# cryptsetup luksHeaderBackup --header-backup-file
> backup.img  /dev/sdc1 ; echo $?
> 0
> 
> It looks like the command to backup the header is supposed to be run on the
> device its self and not on the mapper as the FAQ suggests.

Ah, yes. Well spotted. I think I was confused because I usually test 
LUKS on loop-files. Fixed in SVN and Wiki.

Arno
-- 
Arno Wagner, Dr. sc. techn., Dipl. Inform., CISSP -- Email: arno@wagner.name 
GnuPG:  ID: 1E25338F  FP: 0C30 5782 9D93 F785 E79C  0296 797F 6B50 1E25 338F
----
One of the painful things about our time is that those who feel certainty 
are stupid, and those with any imagination and understanding are filled 
with doubt and indecision. -- Bertrand Russell