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 - subvolume uuid (e.g. 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

AUTHORS

       libblkid was written by Andreas Dilger for the ext2 filesystem utilities, with input from
       Ted Ts’o. The library was subsequently heavily modified by Ted Ts’o.

       The low-level probing code was rewritten by Karel Zak.

COPYING

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

SEE ALSO

       blkid(8), findfs(8)

REPORTING BUGS

       For bug reports, use the issue tracker at https://github.com/util-linux/util-linux/issues.

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/>.