libblkid(3)

1LIBBLKID(3)                   Programmers Manual                   LIBBLKID(3)
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NAME

6       libblkid - block device identification library
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SYNOPSIS

9       #include <blkid.h>
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11       cc file.c -lblkid
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DESCRIPTION

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

52       The standard location of the /etc/blkid.conf config file can be
53       overridden by the environment variable BLKID_CONF. For more details
54       about the config file see blkid(8) man page.
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TAGS

57       All available tags are listed below. Not all tags are supported for all
58       file systems. To enable a tag, set one of the following flags with
59       blkid_probe_set_superblocks_flags():
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61       BLKID_SUBLKS_TYPE
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63           •   TYPE - filesystem type
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65       BLKID_SUBLKS_SECTYPE
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67           •   SEC_TYPE - secondary filesystem type
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69       BLKID_SUBLKS_LABEL
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71           •   LABEL - filesystem label
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73       BLKID_SUBLKS_LABELRAW
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75           •   LABEL_RAW - raw label from FS superblock
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77       BLKID_SUBLKS_UUID
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79           •   UUID - filesystem UUID (lower case)
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81           •   UUID_SUB - subvolume uuid (e.g. btrfs)
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83           •   LOGUUID - external log UUID (e.g. xfs)
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85       BLKID_SUBLKS_UUIDRAW
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87           •   UUID_RAW - raw UUID from FS superblock
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89       BLKID_SUBLKS_USAGE
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91           •   USAGE - usage string: "raid", "filesystem", etc.
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93       BLKID_SUBLKS_VERSION
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95           •   VERSION - filesystem version
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97       BLKID_SUBLKS_MAGIC
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99           •   SBMAGIC - super block magic string
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101           •   SBMAGIC_OFFSET - offset of SBMAGIC
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103       BLKID_SUBLKS_FSINFO
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105           •   FSSIZE - size of filesystem. Note that for XFS this will return
106               the same value as lsblk (without XFS’s metadata), but for ext4
107               it will return the size with metadata and for BTRFS will not
108               count overhead of RAID configuration (redundant data).
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110           •   FSLASTBLOCK - last fsblock/total number of fsblocks
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112           •   FSBLOCKSIZE - file system block size
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114       The following tags are always enabled
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116           •   BLOCK_SIZE - minimal block size accessible by file system
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118           •   MOUNT - cluster mount name (ocfs only)
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120           •   EXT_JOURNAL - external journal UUID
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122           •   SYSTEM_ID - ISO9660 system identifier
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124           •   VOLUME_SET_ID - ISO9660 volume set identifier
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126           •   DATA_PREPARER_ID - ISO9660 data identifier
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128           •   PUBLISHER_ID - ISO9660 publisher identifier
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130           •   APPLICATION_ID - ISO9660 application identifier
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132           •   BOOT_SYSTEM_ID - ISO9660 boot system identifier
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AUTHORS

135       libblkid was written by Andreas Dilger for the ext2 filesystem
136       utilities, with input from Ted Ts’o. The library was subsequently
137       heavily modified by Ted Ts’o.
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139       The low-level probing code was rewritten by Karel Zak.
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COPYING

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

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

153       The libblkid library is part of the util-linux package since version
154       2.15. It can be downloaded from Linux Kernel Archive
155       <https://www.kernel.org/pub/linux/utils/util-linux/>.
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159util-linux 2.39.2                 2023-06-14                       LIBBLKID(3)