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)