1LIBBLKID(3)                Library Functions 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, etc.  A common use is to allow use of LABEL=  and
18       UUID= tags instead of hard-coding specific block device names into con‐
19       figuration files.
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21       Block  device  information  is  normally   kept   in   a   cache   file
22       /etc/blkid/blkid.tab  and  is  verified  to still be valid before being
23       returned to the user (if the user has read permission on the raw  block
24       device,  otherwise not).  The cache file also allows unprivileged users
25       (normally anyone other than root, or those not in the "disk" group)  to
26       locate  devices  by  label/id.  The standard location of the cache file
27       can be overridden by the environment variable BLKID_FILE.
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29       In situations where one is getting information  about  a  single  known
30       device, it does not impact performance whether the cache is used or not
31       (unless you are not able to read the block device  directly).   If  you
32       are  dealing  with  multiple devices, use of the cache is highly recom‐
33       mended (even if empty) as devices will be scanned at most one time  and
34       the  on-disk cache will be updated if possible.  There is rarely a rea‐
35       son not to use the cache.
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37       In some cases (modular kernels), block devices  are  not  even  visible
38       until  after  they  are accessed the first time, so it is critical that
39       there is some way to locate these devices without enumerating only vis‐
40       ible  devices,  so the use of the cache file is required in this situa‐
41       tion.
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CONFIGURATION FILE

44       The standard location of the /etc/blkid.conf config file can  be  over‐
45       ridden  by  the environment variable BLKID_CONF.  The following options
46       control the libblkid library:
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48       SEND_UEVENT=<yes|not>
49              Sends uevent when /dev/disk/by-{label,uuid}/  symlink  does  not
50              match with LABEL or UUID on the device. Default is "yes".
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52       CACHE_FILE=<path>
53              Overrides  the standard location of the cache file. This setting
54              can  be  overridden  by  the  environment  variable  BLKID_FILE.
55              Default is /etc/blkid/blkid.tab.
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57       EVALUATE=<methods>
58              Defines LABEL and UUID evaluation method(s). Currently, the lib‐
59              blkid library supports "udev" and "scan" methods. More than  one
60              methods  may  be specified in a comma separated list. Default is
61              "udev,scan". The "udev" method uses udev /dev/disk/by-* symlinks
62              and   the  "scan"  method  scans  all  block  devices  from  the
63              /proc/partitions file.
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AUTHOR

66       libblkid was written by Andreas Dilger for the  ext2  filesystem  util‐
67       ties,  with  input from Ted Ts'o.  The library was subsequently heavily
68       modified by Ted Ts'o.
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70       The low-level probing code was rewritten by Karel Zak.
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FILES

73       /etc/blkid/blkid.tab
74                         caches data  extracted  from  each  recognized  block
75                         device
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77       /etc/blkid.conf   configuration file
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AVAILABILITY

80       libblkid is part of the util-linux-ng package since version 2.15 and is
81       available from ftp://ftp.kernel.org/pub/linux/utils/util-linux-ng/.
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COPYING

84       libblkid is available under the terms of the GNU Library General Public
85       License (LGPL), version 2 (or at your discretion any later version).  A
86       copy of the LGPL should be included with this library in the file COPY‐
87       ING.  If not, write to
88              Free Software Foundation, Inc.
89              51 Franklin St
90              Fifth Floor
91              Boston, MA  02110-1301  USA
92
93       or         visit         http://www.gnu.org/licenses/licenses.html#LGPL
94http://www.gnu.org/licenses/licenses.html#LGPL⟩
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SEE ALSO

97       blkid(8) findfs(8)
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101util-linux-ng                      May 2009                        LIBBLKID(3)
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