libblkid/libblkid.3

   1 .\" Copyright 2001 Andreas Dilger (adilger@turbolinux.com)
   2 .\"
   3 .\" This man page was created for libblkid.so.1.0 from e2fsprogs-1.24.
   4 .\"
   5 .\" This file may be copied under the terms of the GNU Lesser General Public
   6 .\" License.
   7 .\"
   8 .\" Created  Wed Sep 14 12:02:12 2001, Andreas Dilger
   9 .TH LIBBLKID 3 "May 2009" "util-linux" "Programmer's Manual"
  10 .SH NAME
  11 libblkid \- block device identification library
  12 .SH SYNOPSIS
  13 .B #include <blkid.h>
  14 .sp
  15 .B cc
  16 .I file.c
  17 .B \-lblkid
  18 .SH DESCRIPTION
  19 The
  20 .B libblkid
  21 library is used to identify block devices (disks) as to their content (e.g.,
  22 filesystem type) as well as extracting additional information such as
  23 filesystem labels/volume names, unique identifiers/serial numbers.
  24 A common use is to allow use of LABEL= and UUID= tags instead of hard-coding
  25 specific block device names into configuration files.
  26 .P
  27 The low-level part of the library also allows to extract information about
  28 partitions and block device topology.
  29 .P
  30 The high-level part of the library keeps information about block devices in a
  31 cache file and is verified to still be valid before being returned to the user
  32 (if the user has read permission on the raw block device, otherwise not).
  33 The cache file also allows unprivileged users (normally anyone other
  34 than root, or those not in the "disk" group) to locate devices by label/id.
  35 The standard location of the cache file can be overridden by the
  36 environment variable BLKID_FILE.
  37 .P
  38 In situations where one is getting information about a single known device, it
  39 does not impact performance whether the cache is used or not (unless you are
  40 not able to read the block device directly).
  41 .P
  42 The high-level part of the library supports two methods to evaluate LABEL/UUID.
  43 It reads information directly from a block device or read information from
  44 /dev/disk/by-* udev symlinks.  The udev is preferred method by default.
  45 .P
  46 If you are dealing with
  47 multiple devices, use of the cache is highly recommended (even if empty) as
  48 devices will be scanned at most one time and the on-disk cache will be
  49 updated if possible.
  50 .P
  51 In some cases (modular kernels), block devices are not even visible until
  52 after they are accessed the first time, so it is critical that there is
  53 some way to locate these devices without enumerating only visible devices,
  54 so the use of the cache file is
  55 .B required
  56 in this situation.
  57 .SH CONFIGURATION FILE
  58 The standard location of the
  59 .I /etc/blkid.conf
  60 config file can be overridden by the environment variable BLKID_CONF.  For more
  61 details about the config file see
  62 .BR blkid (8)
  63 man page.
  64 .SH AUTHORS
  65 .B libblkid
  66 was written by Andreas Dilger for the ext2 filesystem utilities, with input
  67 from Ted Ts'o.  The library was subsequently heavily modified by Ted Ts'o.
  68
  69 The low-level probing code was rewritten by Karel Zak.
  70 .SH COPYING
  71 .B libblkid
  72 is available under the terms of the GNU Library General Public License (LGPL),
  73 version 2 (or at your discretion any later version).
  74 .SH SEE ALSO
  75 .BR blkid (8),
  76 .BR findfs (8)
  77 .SH AVAILABILITY
  78 libblkid is part of the util-linux package since version 2.15 and is available from
  79 https://www.kernel.org/pub/linux/utils/util-linux/.