NAME

       libblkid - block device identification library

SYNOPSIS

       #include <blkid.h>

       cc file.c -lblkid

DESCRIPTION

       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.

       The  low-level  part  of  the library also allows to extract infomation about partitions and block device
       topology.

       The high-level part of the library keeps information about block devices in a cache  file  /etc/blkid.tab
       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.

       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).

       The  high-level  part  of  the library supports two methods to evaluate LABEL/UUID.  It reads information
       directly from a block device or read information from /dev/disk/by-* udev symlinks. The udev is preferred
       method by default.

       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.

       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.

CONFIGURATION FILE

       The  standard  location  of the /etc/blkid.conf config file can be overridden by the environment variable
       BLKID_CONF.  The following options control the libblkid library:

       SEND_UEVENT=<yes|not>
              Sends uevent when /dev/disk/by-{label,uuid}/ symlink does not match with  LABEL  or  UUID  on  the
              device. Default is "yes".

       CACHE_FILE=<path>
              Overrides  the  standard  location  of  the  cache  file.  This  setting  can be overridden by the
              environment variable BLKID_FILE. Default is /etc/blkid.tab.

       EVALUATE=<methods>
              Defines LABEL and UUID evaluation method(s). Currently, the libblkid library supports  "udev"  and
              "scan"  methods.  More  than  one  methods  may be specified in a comma separated list. Default is
              "udev,scan". The "udev" method uses udev /dev/disk/by-* symlinks and the "scan" method  scans  all
              block devices from the /proc/partitions file.

AUTHOR

       libblkid  was  written by Andreas Dilger for the ext2 filesystem utilties, with input from Ted Ts'o.  The
       library was subsequently heavily modified by Ted Ts'o.

       The low-level probing code was rewritten by Karel Zak.

FILES

       /etc/blkid.tab    caches data extracted from each recognized block device

       /etc/blkid.conf   configuration file

AVAILABILITY

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

COPYING

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

SEE ALSO

       blkid(8) findfs(8)

util-linux                                          May 2009                                         LIBBLKID(3)