libblkid/libblkid.3.adoc

   1 //po4a: entry man manual
   2 ////
   3 Copyright 2001 Andreas Dilger (adilger@turbolinux.com)
   4 This man page was created for libblkid.so.1.0 from e2fsprogs-1.24.
   5 This file may be copied under the terms of the GNU Lesser General Public License.
   6 Created  Wed Sep 14 12:02:12 2001, Andreas Dilger
   7 ////
   8 = libblkid(3)
   9 :doctype: manpage
  10 :man manual: Programmer's Manual
  11 :man source: util-linux {release-version}
  12 :page-layout: base
  13 :lib: libblkid
  14 :firstversion: 2.15
  15
  16 == NAME
  17
  18 libblkid - block device identification library
  19
  20 == SYNOPSIS
  21
  22 *#include <blkid.h>*
  23
  24 *cc* _file.c_ *-lblkid*
  25
  26 == DESCRIPTION
  27
  28 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.
  29
  30 The low-level part of the library also allows the extraction of information about partitions and block device topology.
  31
  32 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*.
  33
  34 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).
  35
  36 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.
  37
  38 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.
  39
  40 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.
  41
  42 == CONFIGURATION FILE
  43
  44 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.
  45
  46 == TAGS
  47
  48 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*():
  49
  50 BLKID_SUBLKS_TYPE::
  51
  52 - TYPE - filesystem type
  53
  54 BLKID_SUBLKS_SECTYPE::
  55
  56 - SEC_TYPE - secondary filesystem type
  57
  58 BLKID_SUBLKS_LABEL::
  59
  60 - LABEL - filesystem label
  61
  62 BLKID_SUBLKS_LABELRAW::
  63
  64 - LABEL_RAW - raw label from FS superblock
  65
  66 BLKID_SUBLKS_UUID::
  67
  68 - UUID - filesystem UUID (lower case)
  69
  70 - UUID_SUB - subvolume uuid (e.g. btrfs)
  71
  72 - LOGUUID - external log UUID (e.g. xfs)
  73
  74 BLKID_SUBLKS_UUIDRAW::
  75
  76 - UUID_RAW - raw UUID from FS superblock
  77
  78 BLKID_SUBLKS_USAGE::
  79
  80 - USAGE - usage string: "raid", "filesystem", etc.
  81
  82 BLKID_SUBLKS_VERSION::
  83
  84 - VERSION - filesystem version
  85
  86 BLKID_SUBLKS_MAGIC::
  87
  88 - SBMAGIC - super block magic string
  89
  90 - SBMAGIC_OFFSET - offset of SBMAGIC
  91
  92 BLKID_SUBLKS_FSINFO::
  93
  94 - FSSIZE - size of filesystem. Note that for XFS this will return the same value
  95   as lsblk (without XFS's metadata), but for ext4 it will return the size with
  96   metadata and for BTRFS will not count overhead of RAID configuration
  97   (redundant data).
  98
  99 - FSLASTBLOCK - last fsblock/total number of fsblocks
 100
 101 - FSBLOCKSIZE - file system block size
 102
 103 The following tags are always enabled::
 104
 105 - BLOCK_SIZE - minimal block size accessible by file system
 106
 107 - MOUNT - cluster mount name (ocfs only)
 108
 109 - EXT_JOURNAL - external journal UUID
 110
 111 - SYSTEM_ID - ISO9660 system identifier
 112
 113 - VOLUME_SET_ID - ISO9660 volume set identifier
 114
 115 - DATA_PREPARER_ID - ISO9660 data identifier
 116
 117 - PUBLISHER_ID - ISO9660 publisher identifier
 118
 119 - APPLICATION_ID - ISO9660 application identifier
 120
 121 - BOOT_SYSTEM_ID - ISO9660 boot system identifier
 122
 123 == AUTHORS
 124
 125 *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.
 126
 127 The low-level probing code was rewritten by Karel Zak.
 128
 129 == COPYING
 130
 131 *libblkid* is available under the terms of the GNU Library General Public License (LGPL), version 2 (or at your discretion any later version).
 132
 133 == SEE ALSO
 134
 135 *blkid*(8),
 136 *findfs*(8)
 137
 138 include::man-common/bugreports.adoc[]
 139
 140 include::man-common/footer-lib.adoc[]
 141
 142 ifdef::translation[]
 143 include::man-common/translation.adoc[]
 144 endif::[]