BLKID(8) System Administration BLKID(8)
NAME
blkid - locate/print block device attributes
SYNOPSIS
blkid -L label | -U uuid
blkid [-dghlv] [-c file] [-o format] [-s tag]
[-t NAME=value] [device ...]
blkid -p [-O offset] [-o format] [-S size] [-s tag]
[-n list] [-u list] device ...
blkid -i [-o format] [-s 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 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
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.
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 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 Don't encode non-printing characters. The non-printing charac-
ters are encoded by ^ and M- notation by default. Note that the
-o udev output format uses a different encoding which cannot be
disabled.
-g Perform a garbage collection pass on the blkid cache to remove
devices which no longer exist.
-h Display a usage message and exit.
-i 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 -p option.
-k List all known filesystems and RAIDs and exit.
-l Look up only one device that matches the search parameter speci-
fied with the -t 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
Look up the device that uses this filesystem label; this is
equal to -l -o device -t 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 verifi-
cation. The -L 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 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 -p -n vfat,ext3,ext4 /dev/sda1
probes for vfat, ext3 and ext4 filesystems, and
blkid -p -n nominix /dev/sda1
probes for all supported formats except minix filesystems. This
option is only useful together with -p.
-o 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 (-p or -i).
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 -L and -U 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 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 (-i option) are requested
-O offset
Probe at the given offset (only useful with -p). This option
can be used together with the -i option.
-p 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).
-s tag For each (specified) device, show only the tags that match tag.
It is possible to specify multiple -s 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 -s none with no other options.
-S size
Override the size of device/file (only useful with -p).
-t 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 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
ignored. For example:
blkid -p -u filesystem,other /dev/sda1
probes for all filesystem and other (e.g. swap) formats, and
blkid -p -u noraid /dev/sda1
probes for all supported formats except RAIDs. This option is
only useful together with -p.
-U uuid
Look up the device that uses this filesystem uuid. For more
details see the -L option.
-V Display version number and exit.
RETURN CODE
If the specified token was found, or if any tags were shown from (spec-
ified) devices, 0 is returned.
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.
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.
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.
AUTHOR
blkid was written by Andreas Dilger for libblkid and improved by
Theodore Ts'o and Karel Zak.
ENVIRONMENT
Setting LIBBLKID_DEBUG=0xffff enables debug output.
SEE ALSO
libblkid(3), findfs(8), wipefs(8)
AVAILABILITY
The blkid command is part of the util-linux package and is available
from ftp://ftp.kernel.org/pub/linux/utils/util-linux/.
util-linux March 2013 BLKID(8)
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