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 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 prob-
ing result is ambivalent (multiple colliding filesystems are detected).
The low-level probing mode (-p) provides more information and extra re-
turn code in this case. It's recommended to use wipefs(8) to get a de-
tailed 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 charac-
ters are encoded by ^ and M- notation by default. Note that the
--output udev output format uses a different encoding which can-
not 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, --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 speci-
fied with the --match-token option. If there are multiple de-
vices 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). De-
vice types in order of decreasing priority are: Device Mapper,
EVMS, LVM, MD, and finally regular block devices. If this op-
tion 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 consis-
tent with another utils (like mount, 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 sys-
tems 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-sepa-
rated) 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 vari-
ables 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 ls-
blk(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 en-
vironment; 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-es-
caping 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 parti-
tions.
This output format is DEPRECATED.
export print key=value pairs for easy import into the environ-
ment; this output format is automatically enabled when
I/O Limits (--info option) are requested.
The non-printing characters are encoded by ^ and M- nota-
tion and all potentially unsafe characters are escaped.
-O, --offset offset
Probe at the given offset (only useful with --probe). This op-
tion 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 par-
tition 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-sepa-
rated) list of "usage" types. Supported usage types are:
filesystem, raid, crypto and other. The list items may be pre-
fixed with "no" to specify the usage types which should be ig-
nored. 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 de-
tails see the --label option.
-V, --version
Display version number and exit.
RETURN CODE
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, or it is impossible to gather any information about the
device identifiers or device content 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.
CONFIGURATION FILE
The standard location of the /etc/blkid.conf config file can be over-
ridden 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. De-
fault 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. De-
fault 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.
AUTHOR
blkid was written by Andreas Dilger for libblkid and improved by
Theodore Ts'o and Karel Zak.
ENVIRONMENT
Setting LIBBLKID_DEBUG=all enables debug output.
SEE ALSO
libblkid(3), findfs(8), lsblk(8), wipefs(8)
AVAILABILITY
The blkid command is part of the util-linux package and is available
from https://www.kernel.org/pub/linux/utils/util-linux/.
util-linux March 2013 BLKID(8)