1LIBBLKID(3)                   Programmer's 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 identi‐
17       fiers/serial numbers.  A common use is to allow use of LABEL= and UUID=
18       tags instead of hard-coding specific block device names into configura‐
19       tion files.
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21       The low-level part of the library also allows the extraction of  infor‐
22       mation 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
30       can 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 evaluate
37       LABEL/UUID.  It reads information directly from a block device or  read
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 vis‐
48       ible  devices,  so the use of the cache file is required in this situa‐
49       tion.
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CONFIGURATION FILE

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

57       libblkid was written by Andreas Dilger for the ext2  filesystem  utili‐
58       ties,  with  input from Ted Ts'o.  The library was subsequently heavily
59       modified by Ted Ts'o.
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61       The low-level probing code was rewritten by Karel Zak.
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COPYING

64       libblkid is available under the terms of the GNU Library General Public
65       License (LGPL), version 2 (or at your discretion any later version).
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SEE ALSO

68       blkid(8), findfs(8)
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AVAILABILITY

71       libblkid  is  part  of the util-linux package since version 2.15 and is
72       available from https://www.kernel.org/pub/linux/utils/util-linux/.
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76util-linux                         May 2009                        LIBBLKID(3)
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