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NAME | SYNOPSIS | DESCRIPTION | OPTIONS | RETURN CODE | CONFIGURATION FILE | AUTHOR | ENVIRONMENT | SEE ALSO | AVAILABILITY | COLOPHON |
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BLKID(8) System Administration BLKID(8)
blkid - locate/print block device attributes
blkid --label label | --uuid uuid
blkid [--no-encoding --garbage-collect --list-one --cache-file file]
[--output format] [--match-tag tag] [--match-token NAME=value]
[device ...]
blkid --probe [--offset offset] [--output format] [--size size]
[--match-tag tag] [--match-types list] [--usages list] device
...
blkid --info [--output format] [--match-tag tag] device ...
The blkid program is the command-line interface to working with the
libblkid(3) library. It can determine the type of content (e.g.
filesystem or swap) that a block device holds, and also the
attributes (tokens, NAME=value pairs) from the content metadata (e.g.
LABEL or UUID fields).
It is recommended to use lsblk(8) command to get information about
block devices, or lsblk --fs to get an overview of filesystems, or
findmnt(8) to search in already mounted filesystems.
lsblk(8) provides more information, better control on output
formatting, easy to use in scripts and it does not require
root permissions to get actual information. blkid reads
information directly from devices and for non-root users it
returns cached unverified information. blkid is mostly
designed for system services and to test libblkid
functionality.
When device is specified, tokens from only this device are displayed.
It is possible to specify multiple device arguments on the command
line. If none is given, all devices which appear in /proc/partitions
are shown, if they are recognized.
blkid 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.
For security reasons blkid silently ignores all devices where the
probing result is ambivalent (multiple colliding filesystems are
detected). The low-level probing mode (-p) provides more information
and extra return code in this case. It's recommended to use
wipefs(8) to get a detailed overview and to erase obsolete stuff
(magic strings) from the device.
The size and offset arguments may be followed by the multiplicative
suffixes like KiB (=1024), MiB (=1024*1024), and so on for GiB, TiB,
PiB, EiB, ZiB and YiB (the "iB" is optional, e.g. "K" has the same
meaning as "KiB"), or the suffixes KB (=1000), MB (=1000*1000), and
so on for GB, TB, PB, EB, ZB and YB.
-c, --cache-file cachefile
Read from cachefile instead of reading from the default cache
file (see the CONFIGURATION FILE section for more details).
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 /dev/null.
-d, --no-encoding
Don't encode non-printing characters. The non-printing
characters are encoded by ^ and M- notation by default. Note
that the --output udev output format uses a different encoding
which cannot be disabled.
-g, --garbage-collect
Perform a garbage collection pass on the blkid cache to remove
devices which no longer exist.
-h, --help
Display a usage message and exit.
-i, --info
Display information about I/O Limits (aka I/O topology). The
'export' output format is automatically enabled. This option
can be used together with the --probe option.
-k, --list-filesystems
List all known filesystems and RAIDs and exit.
-l, --list-one
Look up only one device that matches the search parameter
specified with the --match-token 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, blkid will print all of the devices that match the
search parameter.
-L, --label label
Look up the device that uses this filesystem label; this is
equal to --list-one --output device --match-token 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 --label option works
on systems with and without udev.
Unfortunately, the original blkid(8) from e2fsprogs uses the
-L option as a synonym for -o list. For better portability,
use -l -o device -t LABEL=label and -o list in your scripts
rather than the -L option.
-n, --match-types 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. For example:
blkid --probe --match-types vfat,ext3,ext4 /dev/sda1
probes for vfat, ext3 and ext4 filesystems, and
blkid --probe --match-types nominix /dev/sda1
probes for all supported formats except minix filesystems.
This option is only useful together with --probe.
-o, --output format
Use the specified output format. Note that the order of
variables and devices is not fixed. See also option -s. The
format parameter may be:
full print all tags (the default)
value print the value of the tags
list print the devices in a user-friendly format; this
output format is unsupported for low-level probing
(--probe or --info).
This output format is DEPRECATED in favour of the
lsblk(8) command.
device print the device name only; this output format is
always enabled for the --label and --uuid options
udev 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
partitions. This output format is DEPRECATED.
export print key=value pairs for easy import into the
environment; this output format is automatically
enabled when I/O Limits (--info option) are requested.
The non-printing characters are encoded by ^ and M-
notation and all potentially unsafe characters are
escaped.
-O, --offset offset
Probe at the given offset (only useful with --probe). This
option can be used together with the --info option.
-p, --probe
Switch to low-level superblock probing mode (bypassing the
cache).
Note that low-level probing also returns information about
partition table type (PTTYPE tag) and partitions (PART_ENTRY_*
tags). The tag names produced by low-level probing are based
on names used internally by libblkid and it may be different
than when executed without --probe (for example
PART_ENTRY_UUID= vs PARTUUID=).
-s, --match-tag tag
For each (specified) device, show only the tags that match
tag. It is possible to specify multiple --match-tag options.
If no tag is specified, then all tokens are shown for all
(specified) devices. In order to just refresh the cache
without showing any tokens, use --match-tag none with no other
options.
-S, --size size
Override the size of device/file (only useful with --probe).
-t, --match-token NAME=value
Search for block devices with tokens named NAME that have the
value value, and display any devices which are found. Common
values for NAME include TYPE, LABEL, and UUID. If there are
no devices specified on the command line, all block devices
will be searched; otherwise only the specified devices are
searched.
-u, --usages 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 --probe --usages filesystem,other /dev/sda1
probes for all filesystem and other (e.g. swap) formats, and
blkid --probe --usages noraid /dev/sda1
probes for all supported formats except RAIDs. This option is
only useful together with --probe.
-U, --uuid uuid
Look up the device that uses this filesystem uuid. For more
details see the --label option.
-V, --version
Display version number and exit.
If the specified device or device addressed by specified token
(option --match-token) was found and it's possible to gather any
information about the device, an exit code 0 is returned. Note the
option --match-tag filters output tags, but it does not affect return
code.
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 an ambivalent probing result was detected by low-level probing
mode (-p), an exit code of 8 is returned.
The standard location of the /etc/blkid.conf config file can be
overridden by the environment variable BLKID_CONF. The following
options control the libblkid library:
SEND_UEVENT=<yes|not>
Sends uevent when
/dev/disk/by-{label,uuid,partuuid,partlabel}/ symlink does not
match with LABEL, UUID, PARTUUID or PARTLABEL on the device.
Default is "yes".
CACHE_FILE=<path>
Overrides the standard location of the cache file. This
setting can be overridden by the environment variable
BLKID_FILE. Default is /run/blkid/blkid.tab, or
/etc/blkid.tab on systems without a /run directory.
EVALUATE=<methods>
Defines LABEL and UUID evaluation method(s). Currently, the
libblkid library supports the "udev" and "scan" methods. More
than one method may be specified in a comma-separated list.
Default is "udev,scan". The "udev" method uses udev
/dev/disk/by-* symlinks and the "scan" method scans all block
devices from the /proc/partitions file.
blkid was written by Andreas Dilger for libblkid and improved by
Theodore Ts'o and Karel Zak.
Setting LIBBLKID_DEBUG=all enables debug output.
libblkid(3), findfs(8), lsblk(8), wipefs(8)
The blkid command is part of the util-linux package and is available
from https://www.kernel.org/pub/linux/utils/util-linux/.
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
bug report for this manual page, send it to
util-linux@vger.kernel.org. This page was obtained from the
project's upstream Git repository
⟨git://git.kernel.org/pub/scm/utils/util-linux/util-linux.git⟩ on
2018-02-02. (At that time, the date of the most recent commit that
was found in the repository was 2018-02-01.) If you discover any
rendering problems in this HTML version of the page, or you believe
there is a better or more up-to-date source for the page, or you have
corrections or improvements to the information in this COLOPHON
(which is not part of the original manual page), send a mail to
man-pages@man7.org
util-linux March 2013 BLKID(8)
Pages that refer to this page: open_by_handle_at(2), libblkid(3), fstab(5), blkid(8), btrfs-device(8), findfs(8), lsblk(8), wipefs(8)
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HTML rendering created 2018-02-02 by Michael Kerrisk, author of The Linux Programming Interface, maintainer of the Linux man-pages project. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH.
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