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LIBBLKID(3) Programmer's Manual LIBBLKID(3)
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 identi-
fiers/serial numbers. A common use is to allow use of LABEL= and UUID=
tags instead of hard-coding specific block device names into configura-
tion files.
The low-level part of the library also allows to extract information
about partitions and block device topology.
The high-level part of the library keeps information about block
devices in a cache file 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 vis-
ible devices, so the use of the cache file is required in this situa-
tion.
CONFIGURATION FILE
The standard location of the /etc/blkid.conf config file can be over-
ridden by the environment variable BLKID_CONF. For more details about
the config file see blkid(8) man page.
AUTHOR
libblkid was written by Andreas Dilger for the ext2 filesystem util-
ties, 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.
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)
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/.
util-linux May 2009 LIBBLKID(3)
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