Section: System Administration (8)
Updated: February 2011
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blkid - locate/print block device attributes
program is the command-line interface to working with the
library. It can determine the type of content (e.g. filesystem or swap)
that a block device holds, and also attributes (tokens, NAME=value pairs)
from the content metadata (e.g. LABEL or UUID fields).
has two main forms of operation: either searching for a device with a
specific NAME=value pair, or displaying NAME=value pairs for one or
more specified devices.
The size and offset arguments may be followed by binary (2^N)
suffixes KiB, MiB, GiB, TiB, PiB and EiB (the "iB" is optional, e.g. "K" has the
same meaning as "KiB") or decimal (10^N) suffixes KB, MB, GB, PB and EB.
- -c cachefile
instead of reading from the default cache file
If you want to start with a clean cache (i.e. don't report devices previously
scanned but not necessarily available at this time), specify
Don't encode non-printing characters. The non-printing characters are encoded
by ^ and M- notation by default. Note that -o udev output format uses
a diffrent encoding and this encoding cannot be disabled.
Perform a garbage collection pass on the blkid cache to remove
devices which no longer exist.
Display a usage message and exit.
Display I/O Limits (aka I/O topology) information. The 'export' output format is
automatically enabled. This option can be used together with the -p option.
Look up only one device that matches the search parameter specified with -t.
List all known filesystems and RAIDs and exit.
option. If there are multiple devices that match the specified search
parameter, then the device with the highest priority is returned, and/or
the first device found at a given priority. Device types in order of
decreasing priority are Device Mapper, EVMS, LVM, MD, and finally regular
block devices. If this option is not specified,
will print all of the devices that match the search parameter.
- -L label
Look up the device that uses this label (equal to: -l -o device -t
LABEL=<label>). This lookup method is able to reliably use /dev/disk/by-label
udev symlinks (dependent on a setting in /etc/blkid.conf). Avoid using the
symlinks directly; it is not reliable to use the symlinks without verification.
The -L option works on systems with and without udev.
Unfortunately, the original
from e2fsprogs use the -L option as a
synonym for the -o list option. For better portability, use -l -o device
-t LABEL=<label> and -o list in your scripts rather than the -L option.
- -n list
Restrict the probing functions to the specified (comma-separated) list of
superblock types (names).
The list items may be prefixed with "no" to specify the types which should be ignored.
blkid -p -n vfat,ext3,ext4 /dev/sda1
probes for vfat, ext3 and ext4 filesystems, and
blkid -p -n nominix /dev/sda1
probes for all supported formats except minix filesystems.
This option is only useful together with -p.
- -o format
output using the specified format. The
parameter may be:
print all tags (the default)
print the value of the tags
print the devices in a user-friendly format; this output format is unsupported
for low-level probing (-p or -i)
print the device name only; this output format is always enabled for -L
and -U options
print key="value" pairs for easy import into the udev environment; the keys are
prefixed by ID_FS_ or ID_PART_ prefixes
The udev output returns the ID_FS_AMBIVALENT tag if more superblocks are detected,
and ID_PART_ENTRY_* tags are always returned for all partitions including empty
print key=value pairs for easy import into the environment; this output format
is automatically enabled when I/O Limits (-i option) are requested
- -O offset
Probe at the given offset (only useful with -p). This option can be
used together with the -i option.
Switch to low-level superblock probing mode (bypass cache).
Note that low-level probing also returns information about partition table type
(PTTYPE tag) and partitions (PART_ENTRY_* tags).
- -s tag
For each (specified) device, show only the tags that match
It is possible to specify multiple
options. If no tag is specified, then all tokens are shown for all
In order to just refresh the cache without showing any tokens, use
with no other options.
- -S size
Overwrite device/file size (only useful with -p).
- -t NAME=value
Search for block devices with tokens named
that have the value
and display any devices which are found.
Common values for
If there are no devices specified on the command line, all block devices
will be searched; otherwise only the specified devices are searched.
- -u list
Restrict the probing functions to the specified (comma-separated) list of "usage" types.
Supported usage types are: filesystem, raid, crypto and other. The list items may be
prefixed with "no" to specify the usage types which should be ignored. For example:
blkid -p -u filesystem,other /dev/sda1
probes for all filesystem and other (e.g. swap) formats, and
blkid -p -u noraid /dev/sda1
probes for all supported formats except RAIDs.
This option is only useful together with -p.
- -U uuid
Look up the device that uses this uuid. For more details see the -L option.
Display version number and exit.
- -w writecachefile
Write the device cache to
instead of writing it to the default cache file
If you don't want to save the cache at all, specify
If not specified, it will be the same file as that given with the
Display tokens from only the specified device. It is possible to
options on the command line. If none is given, all devices which
are shown, if they are recognized.
If the specified token was found, or if any tags were shown from (specified)
devices, 0 is returned.
If the specified token was not found, or no (specified) devices could be
identified, an exit code of 2 is returned.
For usage or other errors, an exit code of 4 is returned.
If the ambivalent low-level probing result was detected, an exit code of 8 is
was written by Andreas Dilger for libblkid and improved by Theodore Ts'o
and Karel Zak.
The blkid command is part of the util-linux package and is available from
- RETURN CODE
- SEE ALSO
This document was created by
using the manual pages.
Time: 05:24:23 GMT, January 17, 2018