On 07/13/18 15:36, Pascal Hambourg wrote:
Le 13/07/2018 à 03:13, David Christensen a écrit :
file(1) -- no:

2018-07-12 17:55:01 root@po ~
# file /dev/sda1
/dev/sda1: block special (8/1)

You must add the option -s so that file looks into the special device file contents.

2018-07-13 17:39:48 root@po ~
# file -s /dev/sda1
/dev/sda1: BTRFS Filesystem label "po_boot", sectorsize 4096, nodesize 16384, leafsize 16384, UUID=6ff0dd1d-8d46-454b-bb35-a09afc47145a, 65490944/999292928 bytes used, 1 devices

2018-07-13 17:39:51 root@po ~
# file -s /dev/sda2
/dev/sda2: data

2018-07-13 17:39:59 root@po ~
# file -s /dev/sda3
/dev/sda3: LUKS encrypted file, ver 1 [aes, xts-plain64, sha256] UUID: 0152d2e2-4cfb-42c4-a121-6fb832962e47


The output for /dev/sda2 is not very informative (e.g. clues that it has dm-crypt, random key, and swap).


I have been using /dev/disk/by-id/* successfully [in /etc/crypttab] for a while, but

Did the installer automatically wrote this in /etc/crypttab or did you replace the original device name ?

I edited /etc/crypttab.


/dev/disk/by-partuuid sounds even better -- this will prevent confusion if and when I move partitions or images to other devices.

Beware that unlike a UUID or LABEL, a PARTUUID or PARTLABEL is stored in the partition table, not in the partition data. Also note that a DOS partition table entry does not contain a UUID nor LABEL, and the PARTUUID is artificially built by combining the 32-bit "disk identifier" field in the MBR and the partition number. So if the partition number or the disk identifier changes, the PARTUUID changes.

In short :
- if you move the disk contents (including the partition table) to another disk, the PARTUUID is preserved ; - if you move the partition contents to another partition, the PARTUUID is not preserved.

Thanks for the warning. My typical use-case is to move the entire system drive image between various 16+ GB devices, so PARTUUID should work.


There is a hackish way to add a UUID to a plain dm-crypt partition : write metadata of any kind at the beginning of the partition (ext2, swap, LUKS...) and specify an offset for dm-crypt data beyond the metadata.

Okay.


David

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