This article explores the 'blkid' command, whose purpose is retrieving information about block devices, LABEL, UUID, file system type, etc. The useful command can help us to identify or troubleshoot issues related to block devices and their attributes.
Installation
To use 'blkid' command, your Linux system needs to have the 'util-linux' package installed.
blkid: command not found
In case 'blkid' command is not installed on your system yet, run the following commands based on your Linux distro:
On Debian/Ubuntu
$sudo apt-get install util-linux
On CentOS/RedHat
$sudo yum install util-linux-ng
Syntax
blkid [options] [device...]
Options to customize its output
-c, --cache-file <file> read from <file> instead of reading from the default -d, --no-encoding don't encode non-printing characters -g, --garbage-collect garbage collect the blkid cache -o, --output <format> output format; can be one of: -k, --list-filesystems list all known filesystems/RAIDs and exit -s, --match-tag <tag> show specified tag -t, --match-token <token> find device with a specific token -l, --list-one look up only first device with token specified by -t -L, --label <label> convert LABEL to device name -U, --uuid <uuid> convert UUID to device name -p, --probe low-level superblocks probing -i, --info gather information about I/O limits -H, --hint <value> set hint for probing function -S, --size <size> overwrite device size -O, --offset <offset> probe at the given offset -u, --usages <list> filter by "usage" -n, --match-types <list> filter by filesystem type -D, --no-part-details don't print info from partition table
1. Display the attributes of all the block devices
By running 'blkid' command only without any options, you will get all attributes of all block devices in your Linux system.
$ blkid /dev/mapper/vgubuntu-swap_1: UUID="9d3263eb-474e-4aea-a596-93a164093a9c" TYPE="swap" /dev/mapper/vgubuntu-root: UUID="fd23872b-bbb8-4bb3-b7b9-425ed0ae0308" BLOCK_SIZE="4096" TYPE="ext4" /dev/loop1: TYPE="squashfs" /dev/sr0: BLOCK_SIZE="2048" UUID="2022-08-10-16-21-45-00" LABEL="Ubuntu 22.04.1 LTS amd64" TYPE="iso9660" PTTYPE="PMBR" /dev/sda2: UUID="7C04-B053" BLOCK_SIZE="512" TYPE="vfat" PARTUUID="27e3efb3-6f62-463d-85d6-ea15deae4711" /dev/sda3: UUID="3uPfc3-rtSZ-FMbH-PKAo-E7p9-UmiN-53qoJT" TYPE="LVM2_member" PARTUUID="9d1ea21c-d934-434d-9061-f2f065ce7a12"
Note: Sometimes you might have to run blkid with sudo (root privileges) to display all block devices. By default, it includes all the loop devices in the list on ubuntu based systems.
2. View information of specific block device
To display attributes of only one block device, for example '/dev/sda1', run the following command:
$ blkid /dev/sda2 /dev/sda2: UUID="7C04-B053" BLOCK_SIZE="512" TYPE="vfat" PARTUUID="27e3efb3-6f62-463d-85d6-ea15deae4711"
You can also display all information of a specific device by combining the command with option -p and '-o' with format 'udev' as the following command:
$ sudo blkid -p -o udev /dev/sda2 ID_FS_UUID=7C04-B053 ID_FS_UUID_ENC=7C04-B053 ID_FS_VERSION=FAT32 ID_FS_BLOCK_SIZE=512 ID_FS_TYPE=vfat ID_FS_USAGE=filesystem ID_PART_ENTRY_SCHEME=gpt ID_PART_ENTRY_UUID=27e3efb3-6f62-463d-85d6-ea15deae4711 ID_PART_ENTRY_TYPE=c12a7328-f81f-11d2-ba4b-00a0c93ec93b ID_PART_ENTRY_NUMBER=2 ID_PART_ENTRY_OFFSET=4096 ID_PART_ENTRY_SIZE=1050624 ID_PART_ENTRY_DISK=8:0
3. Display only UUIDs of block devices
With option '-s' or '--match-tag' with tag 'UUID', the command will display UUID information of devices as follows:
$ blkid -s UUID /dev/mapper/vgubuntu-swap_1: UUID="9d3263eb-474e-4aea-a596-93a164093a9c" /dev/mapper/vgubuntu-root: UUID="fd23872b-bbb8-4bb3-b7b9-425ed0ae0308" /dev/sr0: UUID="2022-08-10-16-21-45-00" /dev/sda2: UUID="7C04-B053" /dev/sda3: UUID="3uPfc3-rtSZ-FMbH-PKAo-E7p9-UmiN-53qoJT"
Additionally, you can combine blkid with option -o or --output to display only UUID value as this command:
$ blkid -s UUID -o value 9d3263eb-474e-4aea-a596-93a164093a9c fd23872b-bbb8-4bb3-b7b9-425ed0ae0308 2022-08-10-16-21-45-00 7C04-B053 3uPfc3-rtSZ-FMbH-PKAo-E7p9-UmiN-53qoJT
4. List all devices in a list format
Option -o also gives list output for readability format:
$ blkid -o list
device fs_type label mount point UUID
-----------------------------------------------------------------------------------------------------
/dev/mapper/vgubuntu-swap_1
swap [SWAP] 9d3263eb-474e-4aea-a596-93a164093a9c
/dev/mapper/vgubuntu-root
ext4 / fd23872b-bbb8-4bb3-b7b9-425ed0ae0308
/dev/loop1 squashfs /snap/firefox/2987
/dev/sr0 iso9660 Ubuntu 22.04.1 LTS amd64 (not mounted) 2022-08-10-16-21-45-00
/dev/sda2 vfat /boot/efi 7C04-B053
/dev/sda3 LVM2_member (not mounted) 3uPfc3-rtSZ-FMbH-PKAo-E7p9-UmiN-53qoJT/dev/loop5 squashfs /snap/core18/2785
/dev/sda1 (not mounted)
5. Display only specific filesystem type
You can use -t or --match-token option to output block devices having specific filesystem type by running the following command:
$ blkid -t TYPE=ext4 /dev/mapper/vgubuntu-root: UUID="fd23872b-bbb8-4bb3-b7b9-425ed0ae0308" BLOCK_SIZE="4096" TYPE="ext4"
6. Display attributes for devices by specific labels
Option '-t' can also be used to retrieve which devices match with provided labels by running the below command:
$ blkid -t LABEL="Ubuntu 22.04.1 LTS amd64" /dev/sr0: BLOCK_SIZE="2048" UUID="2022-08-10-16-21-45-00" LABEL="Ubuntu 22.04.1 LTS amd64" TYPE="iso9660" PTTYPE="PMBR"
7. Display first device in the list of specified attribute
In case you need to output only the first device from the retrieved list of a specified attribute, option -l or --list-one can be combined with option '-t', as shown in the following example:
$ blkid -t TYPE=squashfs /dev/loop1: TYPE="squashfs" /dev/loop19: TYPE="squashfs" /dev/loop27: TYPE="squashfs" /dev/loop17: TYPE="squashfs" /dev/loop8: TYPE="squashfs" /dev/loop25: TYPE="squashfs" /dev/loop15: TYPE="squashfs" /dev/loop6: TYPE="squashfs" /dev/loop23: TYPE="squashfs" /dev/loop13: TYPE="squashfs" /dev/loop4: TYPE="squashfs" /dev/loop21: TYPE="squashfs" /dev/loop11: TYPE="squashfs" /dev/loop2: TYPE="squashfs" /dev/loop0: TYPE="squashfs" /dev/loop18: TYPE="squashfs" /dev/loop9: TYPE="squashfs" /dev/loop26: TYPE="squashfs" /dev/loop16: TYPE="squashfs" /dev/loop7: TYPE="squashfs" /dev/loop24: TYPE="squashfs" /dev/loop5: TYPE="squashfs" /dev/loop22: TYPE="squashfs" /dev/loop3: TYPE="squashfs" /dev/loop20: TYPE="squashfs" /dev/loop10: TYPE="squashfs" jayce@Ubuntu-01:~$ blkid -t TYPE=squashfs -l /dev/loop1: TYPE="squashfs"
8. Display I/O Limits of specific block devices
With option '-i' or '--info', the command will give us output device's "I/O Limits" to ensure they are using properly aligned and sized I/O.
$ sudo blkid -i /dev/sda1 /dev/sda1: MINIMUM_IO_SIZE="512" PHYSICAL_SECTOR_SIZE="512" LOGICAL_SECTOR_SIZE="512"
9. Update device list
In some situations, new additional or removable devices have not been updated to device list. Run command with option -g or --garbage-collect to perform an update on device list:
$ blkid -g
Conclusion
Along with 'lsblk' and 'fdisk', the command 'blkid' will make it easier to manage block storage devices in Linux. By practicing the examples mentioned in this article, you will become proficient in using the command.
