GNU/Linux man pages
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GNU/Linux |
CentOS 4.8 |
i386 |
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libblkid(3) |
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libblkid − block device identification library
#include <blkid/blkid.h>
cc file.c −lblkid
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, etc. A common use is to allow use of LABEL= and UUID= tags instead of hard-coding specific block device names into configuration files.
Block device information is normally kept 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.
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 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.
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.
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.
/etc/blkid.tab
Caches data extracted from each recognized block device.
libblkid is part of the e2fsprogs package since version 1.33 and is available from http://e2fsprogs.sourceforge.net.
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
Free Software Foundation, Inc.
59 Temple Place
Suite 330
Boston, MA 02111-1307 USA
or visit http://www.gnu.org/licenses/licenses.html#LGPL
blkid_get_cache(3), blkid_put_cache(3), blkid_get_dev(3), blkid_probe_all(3), blkid_get_devname(3), blkid_get_tag_value(3), blkid.tab(7)
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libblkid(3) | |