# libblkid

## NAME



           libblkid - block device identification library
    


## SYNOPSIS



           **#include <blkid.h>**
    
           **cc** _file.c_ **-lblkid**
    


## DESCRIPTION



           The **libblkid** library is used to identify block devices (disks) as
           to their content (e.g., filesystem type) as well as extracting
           additional information such as filesystem labels/volume names,
           unique identifiers/serial numbers. A common use is to allow use of
           **LABEL=** and **UUID=** tags instead of hard-coding specific block device
           names into configuration files. See list of all available tags in
           **TAGS** section.
    
           The low-level part of the library also allows the extraction of
           information about partitions and block device topology.
    
           The high-level part of the library keeps information about block
           devices in a cache file and is verified to still be valid before
           being returned to the user (if the user has read permission on the
           raw block device, otherwise not). The cache file also allows
           unprivileged users (normally anyone other than root, or those not
           in the "disk" group) to locate devices by label/id. The standard
           location of the cache file can be overridden by the environment
           variable **BLKID_FILE**.
    
           In situations where one is getting information about a single
           known device, it does not impact performance whether the cache is
           used or not (unless you are not able to read the block device
           directly).
    
           The high-level part of the library supports two methods to
           determine **LABEL/UUID**. It reads information directly from a block
           device or reads information from /dev/disk/by-* udev symlinks. The
           udev is preferred method by default.
    
           If you are dealing with multiple devices, use of the cache is
           highly recommended (even if empty) as devices will be scanned at
           most one time and the on-disk cache will be updated if possible.
    
           In some cases (modular kernels), block devices are not even
           visible until after they are accessed the first time, so it is
           critical that there is some way to locate these devices without
           enumerating only visible devices, so the use of the cache file is
           **required** in this situation.
    


## CONFIGURATION FILE



           The standard location of the _/etc/blkid.conf_ config file can be
           overridden by the environment variable **BLKID_CONF**. For more
           details about the config file see blkid(8) man page.
    


## TAGS



           All available tags are listed below. Not all tags are supported
           for all file systems. To enable a tag, set one of the following
           flags with **blkid_probe_set_superblocks_flags**():
    
           BLKID_SUBLKS_TYPE
    
               •   TYPE - filesystem type
    
           BLKID_SUBLKS_SECTYPE
    
               •   SEC_TYPE - secondary filesystem type
    
           BLKID_SUBLKS_LABEL
    
               •   LABEL - filesystem label
    
           BLKID_SUBLKS_LABELRAW
    
               •   LABEL_RAW - raw label from FS superblock
    
           BLKID_SUBLKS_UUID
    
               •   UUID - filesystem UUID (lower case)
    
               •   UUID_SUB - pool member UUID or device item UUID, etc.
                   (e.g., zfs, btrfs, ...)
    
               •   LOGUUID - external log UUID (e.g. xfs)
    
           BLKID_SUBLKS_UUIDRAW
    
               •   UUID_RAW - raw UUID from FS superblock
    
           BLKID_SUBLKS_USAGE
    
               •   USAGE - usage string: "raid", "filesystem", etc.
    
           BLKID_SUBLKS_VERSION
    
               •   VERSION - filesystem version
    
           BLKID_SUBLKS_MAGIC
    
               •   SBMAGIC - super block magic string
    
               •   SBMAGIC_OFFSET - offset of SBMAGIC
    
           BLKID_SUBLKS_FSINFO
    
               •   FSSIZE - size of filesystem. Note that for XFS this will
                   return the same value as lsblk (without XFS’s metadata),
                   but for ext4 it will return the size with metadata and for
                   BTRFS will not count overhead of RAID configuration
                   (redundant data).
    
               •   FSLASTBLOCK - last fsblock/total number of fsblocks
    
               •   FSBLOCKSIZE - file system block size
    
           The following tags are always enabled
    
               •   BLOCK_SIZE - minimal block size accessible by file system
    
               •   MOUNT - cluster mount name (ocfs only)
    
               •   EXT_JOURNAL - external journal UUID
    
               •   SYSTEM_ID - ISO9660 system identifier
    
               •   VOLUME_SET_ID - ISO9660 volume set identifier
    
               •   DATA_PREPARER_ID - ISO9660 data identifier
    
               •   PUBLISHER_ID - ISO9660 publisher identifier
    
               •   APPLICATION_ID - ISO9660 application identifier
    
               •   BOOT_SYSTEM_ID - ISO9660 boot system identifier
    


## COPYING



           **libblkid** is available under the terms of the GNU Library General
           Public License (LGPL), version 2 (or at your discretion any later
           version).
    


## AVAILABILITY



           The **libblkid** library is part of the util-linux package since
           version 2.15. It can be downloaded from Linux Kernel Archive
           <https://www.kernel.org/pub/linux/utils/util-linux/>. This page is
           part of the _util-linux_ (a random collection of Linux utilities)
           project. Information about the project can be found at 
           ⟨https://www.kernel.org/pub/linux/utils/util-linux/⟩. If you have a
           bug report for this manual page, send it to
           util-linux@vger.kernel.org. This page was obtained from the
           project's upstream Git repository
           ⟨git://git.kernel.org/pub/scm/utils/util-linux/util-linux.git⟩ on
           2025-08-11. (At that time, the date of the most recent commit that
           was found in the repository was 2025-08-05.) If you discover any
           rendering problems in this HTML version of the page, or you
           believe there is a better or more up-to-date source for the page,
           or you have corrections or improvements to the information in this
           COLOPHON (which is _not_ part of the original manual page), send a
           mail to man-pages@man7.org
    
    util-linux 2.42-start-521-ec46  2025-08-09                    _LIBBLKID_(3)
    


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