BLKID(8) System Administration BLKID(8)
NAME
blkid - locate/print block device attributes
SYNOPSIS
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]
[--no-part-details] device...
blkid --info [--output format] [--match-tag tag] device...
DESCRIPTION
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(3)
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 partitions or unpartitioned 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 exit status 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.
OPTIONS
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.
-D, --no-part-details
Don’t print information (PART_ENTRY_* tags) from partition table in
low-level probing mode.
-g, --garbage-collect
Perform a garbage collection pass on the blkid cache to remove
devices which no longer exist.
-H, --hint setting
Set probing hint. The hints are an optional way to force probing
functions to check, for example, another location. The currently
supported is "session_offset=number" to set session offset on
multi-session UDF.
-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 (but see below note about udev). 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.
This option forces blkid to use udev when used for LABEL or UUID
tokens in --match-token. The goal is to provide output consistent
with other utils (like mount(8), etc.) on systems where the same
tag is used for multiple devices.
-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 value may be modified to be safe for udev
environment; allowed is plain ASCII, hex-escaping and valid
UTF-8, everything else (including whitespaces) is replaced with
'_'. The keys with _ENC postfix use hex-escaping for unsafe
chars.
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=). See also --no-part-details.
-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.
-h, --help
Display help text and exit.
-V, --version
Print version and exit.
EXIT STATUS
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 status 0 is returned. Note the option
--match-tag filters output tags, but it does not affect exit status.
If the specified token was not found, or no (specified) devices could
be identified, or it is impossible to gather any information about the
device identifiers or device content an exit status of 2 is returned.
For usage or other errors, an exit status of 4 is returned.
If an ambivalent probing result was detected by low-level probing mode
(-p), an exit status of 8 is returned.
CONFIGURATION FILE
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.
ENVIRONMENT
Setting LIBBLKID_DEBUG=all enables debug output.
AUTHORS
blkid was written by Andreas Dilger for libblkid and improved by
Theodore Ts’o and Karel Zak.
SEE ALSO
libblkid(3), findfs(8), lsblk(8), wipefs(8)
REPORTING BUGS
For bug reports, use the issue tracker at
https://github.com/util-linux/util-linux/issues.
AVAILABILITY
The blkid command is part of the util-linux package which can be
downloaded from Linux Kernel Archive
<https://www.kernel.org/pub/linux/utils/util-linux/>.
util-linux 2.38.1 2022-05-11 BLKID(8)
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