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x SuSE Linux 13.1-RELEASEx
LIBBLKID(3) Programmers Manual LIBBLKID(3)
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
o TYPE - filesystem type
BLKID_SUBLKS_SECTYPE
o SEC_TYPE - secondary filesystem type
BLKID_SUBLKS_LABEL
o LABEL - filesystem label
BLKID_SUBLKS_LABELRAW
o LABEL_RAW - raw label from FS superblock
BLKID_SUBLKS_UUID
o UUID - filesystem UUID (lower case)
o UUID_SUB - subvolume uuid (e.g. btrfs)
o LOGUUID - external log UUID (e.g. xfs)
BLKID_SUBLKS_UUIDRAW
o UUID_RAW - raw UUID from FS superblock
BLKID_SUBLKS_USAGE
o USAGE - usage string: "raid", "filesystem", etc.
BLKID_SUBLKS_VERSION
o VERSION - filesystem version
BLKID_SUBLKS_MAGIC
o SBMAGIC - super block magic string
o SBMAGIC_OFFSET - offset of SBMAGIC
BLKID_SUBLKS_FSINFO
o 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).
o FSLASTBLOCK - last fsblock/total number of fsblocks
o FSBLOCKSIZE - file system block size
The following tags are always enabled
o BLOCK_SIZE - minimal block size accessible by file system
o MOUNT - cluster mount name (ocfs only)
o EXT_JOURNAL - external journal UUID
o SYSTEM_ID - ISO9660 system identifier
o VOLUME_SET_ID - ISO9660 volume set identifier
o DATA_PREPARER_ID - ISO9660 data identifier
o PUBLISHER_ID - ISO9660 publisher identifier
o APPLICATION_ID - ISO9660 application identifier
o 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/>.
util-linux 2.39.3 2023-11-21 LIBBLKID(3)
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