.B 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, etc.
+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.
.P
-Block device information is normally kept in a cache file
+The low-level part of the library also allows to extract infomation about
+partitions and block device topology.
+.P
+The high-level part of the library keeps information about block devices
+in a cache file
.I /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 standard location of the cache file can be overridden by the
environment variable BLKID_FILE.
.P
-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). If you are dealing with
+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).
+.P
+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.
+.P
+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. There is rarely a reason not to use the cache.
+updated if possible.
.P
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
.SH COPYING
.B libblkid
is available under the terms of the GNU Library General Public License (LGPL),
-version 2 (or at your discretion any later version). A copy of the LGPL
-should be included with this library in the file COPYING. If not, write to
-.RS
-Free Software Foundation, Inc.
-.br
-51 Franklin St
-.br
-Fifth Floor
-.br
-Boston, MA 02110-1301 USA
-.RE
-.PP
-or visit
-.UR http://www.gnu.org/licenses/licenses.html#LGPL
-http://www.gnu.org/licenses/licenses.html#LGPL
-.UE
+version 2 (or at your discretion any later version).
.SH "SEE ALSO"
.BR blkid (8)
.BR findfs (8)