Manual: blkid
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.
json
Print the tags entries in JSON objects.
-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
Display 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=
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=
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=
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 .
AVAILABILITY
The blkid command is part of the util-linux package which can be downloaded from Linux Kernel Archive
.
util-linux 2.41.3 2025-12-15 BLKID(8)