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 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
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
libblkid was written by Andreas Dilger for the ext2 filesystem
utilities, 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.
This page is part of the util-linux (a random collection of Linux
utilities) project. Information about the project can be found at
⟨https://www.kernel.org/pub/linux/utils/util-linux/⟩. If you have a
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util-linux May 2009 LIBBLKID(3)