blkid --match-types has no effect

[bdrung]

blkid --match-types seems to have no effect:

$ blkid
/dev/vda2: UUID="a89f4e16-bf48-4c85-8555-04f2fa8a6eb7" BLOCK_SIZE="4096" TYPE="ext4" PARTUUID="62d912c9-c2f0-4b8d-b1f2-bf0dba2787f5"
$ sudo blkid -p /dev/vda2
/dev/vda2: UUID="a89f4e16-bf48-4c85-8555-04f2fa8a6eb7" VERSION="1.0" FSBLOCKSIZE="4096" BLOCK_SIZE="4096" FSLASTBLOCK="6277888" FSSIZE="25714229248" TYPE="ext4" USAGE="filesystem" PART_ENTRY_SCHEME="gpt" PART_ENTRY_UUID="62d912c9-c2f0-4b8d-b1f2-bf0dba2787f5" PART_ENTRY_TYPE="0fc63daf-8483-4772-8e79-3d69d8477de4" PART_ENTRY_NUMBER="2" PART_ENTRY_OFFSET="2203648" PART_ENTRY_SIZE="50223104" PART_ENTRY_DISK="253:0"
$ sudo blkid -p --match-types swap /dev/vda2 || echo $?
/dev/vda2: PART_ENTRY_SCHEME="gpt" PART_ENTRY_UUID="62d912c9-c2f0-4b8d-b1f2-bf0dba2787f5" PART_ENTRY_TYPE="0fc63daf-8483-4772-8e79-3d69d8477de4" PART_ENTRY_NUMBER="2" PART_ENTRY_OFFSET="2203648" PART_ENTRY_SIZE="50223104" PART_ENTRY_DISK="253:0"

I expect blkid will fail if the type does not match.

This behavior is the same on Ubuntu 22.04, Ubuntu 24.04, Ubuntu 24.10 (util-linux 2.39.3-9ubuntu6), and Debian unstable (util-linux 2.40.1-9).

Bug-Ubuntu: https://bugs.launchpad.net/ubuntu/+source/util-linux/+bug/2071807

[karelzak]

It works as expected; maybe the man page should be more accurate.

The option disables/enables the probing functions in the libblkid. This means that when you restrict it to "swap," it can detect only a swap area, and other filesystems are invisible to the prober. It's not an error if nothing is detected. Yes, the name of the option is not ideal ...

Anyway, it returns "2" if nothing is detected on the device:

# blkid -p --match-types vfat /dev/sda1 --no-part-details; echo $?
/dev/sda1: SEC_TYPE="msdos" LABEL_FATBOOT="EFI" LABEL="EFI" UUID="F2BC-BFEC" VERSION="FAT16" FSBLOCKSIZE="4096" BLOCK_SIZE="512" FSSIZE="209715200" TYPE="vfat" USAGE="filesystem"
0

# blkid -p --match-types swap /dev/sda1 --no-part-details; echo $?
2

If you want to filter devices by filesystem type, it's better to use lsblk --fs | grep or, in recent releases, lsblk -Q 'FSTYPE=="swap"'.

[bdrung]

Thanks for the explanation. The man page mislead me. It would be nice if the man page could be clarified.