[SOLVED] A small error in the 'lsblk' help text.

luvr · 07-15-2019, 08:50 AM

Just a little something I noticed: There’s a small error in the description of the ‘PTUUID’ column in the help text of the ‘lsblk’ command (note that I’m running Slackware64-current on a Legacy BIOS computer with a GPT-partitioned disk):

Code:

$ lsblk --version
lsblk from util-linux 2.34
$ lsblk --help | grep 'UUID  '
        UUID  filesystem UUID
      PTUUID  partition table identifier (usually UUID)
    PARTUUID  partition UUID

That note about PTUUID saying “(usually UUID)” is incorrect, as demonstrated by the following output:

Code:

$ lsblk --output=PATH,UUID,PARTUUID,PTUUID,PARTLABEL --nodeps /dev/sda /dev/sda1 /dev/sda2
PATH      UUID                                 PARTUUID                             PTUUID                               PARTLABEL
/dev/sda                                                                            38ef380d-5a78-4757-a695-f2635093ac5d 
/dev/sda1                                      3e22819f-7030-4d68-b325-7f9fa8ce6b6b 38ef380d-5a78-4757-a695-f2635093ac5d BIOS boot partition
/dev/sda2 feaba671-d648-4b16-b6c5-ba42f39f2312 416e21b4-911a-4733-8866-2924b6da7df0 38ef380d-5a78-4757-a695-f2635093ac5d Linux filesystem

As I understand it:

PTUUID (partition table UUID) is assigned at the time the partition table is created, and remains in effect, no matter how often and how many partitions get created on the disk or removed from it;
PARTUUID (partition UUID) is assigned at the time the partition is created, and remains in effect, no matter how often a filesystem is created on it (i.e., the partition is “formatted”);
UUID (filesystem UUID) is assigned whenever a filesystem is created on the partition, and will change upon each “formatting” operation (unless you explicitly assign the previously existing UUID to the new filesystem).

Thus, these three values are quite distinct, and do not have anything to do with one another. (Granted, nothing earth-shattering, but I just thought I’d mention it here.)

Alien Bob · 07-15-2019, 09:15 AM

I would suggest to write and submit a patch then.
This is the commit that added the text: https://github.com/karelzak/util-lin...30200f6bdb0195

Didier Spaier · 07-15-2019, 09:54 AM

I don't see an error here. UUID means Universally Unique IDentifier and the "universally unique" attribute applies to a kind of object, so the objects partition table, partition and file system have each their own UUID.

That the PTUUID be displayed on a line for a partition should not bother you: it just says that the parent of this partition is a device whose UUID is indicated.

Similarly you can display the field PKNAME, which is the name of the device parent of this partition. So in case of a partition both PKNAME and PTUUID are ways to identify the parent device of this partition.

I don't see how this can be confusing and would classify this as notabug.

Do I miss something?

rknichols · 07-15-2019, 12:34 PM

The help text is attempting to say that the partition table identifier (PTUUID) can be arbitrary text but is usually a UUID, not some UUID displayed in the UUID column. Perhaps that line should read

Code:

      PTUUID  partition table identifier (usually a UUID)

luvr · 07-15-2019, 11:59 PM

Quote:

Originally Posted by rknichols

The help text is attempting to say that the partition table identifier (PTUUID) can be arbitrary text but is usually a UUID, not some UUID displayed in the UUID column.

Ah, I get it now. I never considered the possibility that a column described as “Partition Table UUID” might contain anything but… a UUID. I also didn’t think beyond the common x86 platform and its partition table types (and their UUIDs).

It remains a bit weird that what is called a “Universally Unique Identifier” could ever be set to, perhaps, a “Universally Ambiguous Identifier”, doesn’t it?

Anyway, I’m probably just thinking too deeply about some silly, little, inconsequential detail again…

I’m notorious for doing so every now and then…

In any case, I’ll try and overcome my tendency to be pedantic next time around—but I won’t make any promises.

By the way, I’m attaching a little bash script thingie that demonstrates the documented values that the ‘lsblk’ command can report about a disk device. It will display a dialog that lists the available disk devices, and subsequently list the results for the selected one. Just FYI.

Also, in case you ever need to find a disk partition when given its filesystem label, you could run the ‘findfs’ command—albeit as root:

Code:

# findfs LABEL="${FILESYSTEM_LABEL}"

As a normal (non-root) user, on the other hand, you could do:

Code:

$ readlink --canonicalize-existing /dev/disk/by-label/"${FILESYSTEM_LABEL}"

MrCalvin · 10-14-2020, 01:49 AM

Thanks for clarifying the difference between ptuuid and partuuid :-)