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HTML rendering created 2024-06-26 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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NAME | SYNOPSIS | DESCRIPTION | OPTIONS | EXIT STATUS | CONFIGURATION FILE | ENVIRONMENT | AUTHORS | SEE ALSO | REPORTING BUGS | AVAILABILITY |
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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]
[--no-part-details] 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(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.
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
Print version 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 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.
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.
Setting LIBBLKID_DEBUG=all enables debug output.
blkid was written by Andreas Dilger for libblkid and improved by
Theodore Ts’o and Karel Zak.
libblkid(3), findfs(8), lsblk(8), wipefs(8)
For bug reports, use the issue tracker at
https://github.com/util-linux/util-linux/issues.
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/>. 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
2024-06-14. (At that time, the date of the most recent commit
that was found in the repository was 2024-06-10.) 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 2.41.devel-537-e... 2024-06-13 BLKID(8)
Pages that refer to this page: FS_IOC_SETFSLABEL(2const), 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 2024-06-26 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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