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.\" Copyright 2001 Andreas Dilger (adilger@turbolinux.com)
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.\"
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.\" This man page was created for libblkid.so.1.0 from e2fsprogs-1.24.
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.\"
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.\" This file may be copied under the terms of the GNU Public License.
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.\"
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.\" Created Wed Sep 14 12:02:12 2001, Andreas Dilger
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.TH LIBBLKID 3 "May 2009" "util-linux" "Programmer's Manual"
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.SH NAME
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libblkid \- block device identification library
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.SH SYNOPSIS
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.B #include <blkid.h>
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.sp
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.B cc
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.I file.c
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.B \-lblkid
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.SH DESCRIPTION
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The
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.B libblkid
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library is used to identify block devices (disks) as to their content (e.g.
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filesystem type) as well as extracting additional information such as
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filesystem labels/volume names, unique identifiers/serial numbers.
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A common use is to allow use of LABEL= and UUID= tags instead of hard-coding
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specific block device names into configuration files.
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.P
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The low-level part of the library also allows to extract information about
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partitions and block device topology.
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.P
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The high-level part of the library keeps information about block devices in a
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cache file and is verified to still be valid before being returned to the user
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(if the user has read permission on the raw block device, otherwise not).
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The cache file also allows unprivileged users (normally anyone other
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than root, or those not in the "disk" group) to locate devices by label/id.
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The standard location of the cache file can be overridden by the
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environment variable BLKID_FILE.
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.P
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In situations where one is getting information about a single known device, it
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does not impact performance whether the cache is used or not (unless you are
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not able to read the block device directly).
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.P
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The high-level part of the library supports two methods to evaluate LABEL/UUID.
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It reads information directly from a block device or read information from
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/dev/disk/by-* udev symlinks. The udev is preferred method by default.
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.P
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If you are dealing with
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multiple devices, use of the cache is highly recommended (even if empty) as
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devices will be scanned at most one time and the on-disk cache will be
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updated if possible.
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.P
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In some cases (modular kernels), block devices are not even visible until
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after they are accessed the first time, so it is critical that there is
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some way to locate these devices without enumerating only visible devices,
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so the use of the cache file is
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.B required
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in this situation.
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.SH CONFIGURATION FILE
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The standard location of the
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.I /etc/blkid.conf
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config file can be overridden by the environment variable BLKID_CONF. For more
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details about the config file see
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.BR blkid (8)
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man page.
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.SH AUTHOR
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.B libblkid
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was written by Andreas Dilger for the ext2 filesystem utilties, with input
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from Ted Ts'o. The library was subsequently heavily modified by Ted Ts'o.
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The low-level probing code was rewritten by Karel Zak.
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.SH AVAILABILITY
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.B libblkid
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2010-11-30 04:41:59 -06:00
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is part of the util-linux package since version 2.15 and is available from
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ftp://ftp.kernel.org/pub/linux/utils/util-linux/.
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.SH COPYING
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.B libblkid
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is available under the terms of the GNU Library General Public License (LGPL),
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version 2 (or at your discretion any later version).
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.SH "SEE ALSO"
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.BR blkid (8)
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2009-02-05 17:21:07 -06:00
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.BR findfs (8)
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