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NAME | SYNOPSIS | DESCRIPTION | CONFIGURATION FILE | TAGS | AUTHORS | COPYING | SEE ALSO | REPORTING BUGS | AVAILABILITY |
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LIBBLKID(3) Programmers Manual LIBBLKID(3)
libblkid - block device identification library
#include <blkid.h>
cc file.c -lblkid
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.
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.
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
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.
libblkid is available under the terms of the GNU Library General
Public License (LGPL), version 2 (or at your discretion any later
version).
blkid(8), findfs(8)
For bug reports, use the issue tracker
<https://github.com/util-linux/util-linux/issues>.
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)
Pages that refer to this page: open_by_handle_at(2), blkid(8), mount(8), wipefs(8)
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HTML rendering created 2025-09-06 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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