BLKID(8) System Administration BLKID(8)NAMEblkid - locate/print block device attributes
SYNOPSISblkid-L label | -U uuid
blkid [-dghlv] [-c file] [-o format]
[-s tag] [-t NAME=value] [device ...]
blkid-p [-O offset] [-S size] [-o format] [-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 attributes
(tokens, NAME=value pairs) from the content metadata (e.g. LABEL or
UUID fields).
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.
OPTIONS
The size and offset arguments may be followed by the multiplicative
suffixes 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, PB, EB, ZB and
YB.
-c cachefile
Read from cachefile instead of reading from the default cache
file (see CONFIGURATION FILE section for more details). If you
want to start with a clean cache (i.e. don't report devices pre‐
viously 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 -o
udev output format uses a different encoding and this encoding
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 I/O Limits (aka I/O topology) information. The 'export'
output format is automatically enabled. This option can be used
together with the -p option.
-l Look up only one device that matches the search parameter speci‐
fied with -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.
-k List all known filesystems and RAIDs and exit.
-L label
Look up the device that uses this filesystem label (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 verification.
The -L option works on systems with and without udev.
Unfortunately, the original blkid(8) from e2fsprogs use the -L
option as a synonym for the -o list option. For better porta‐
bility, 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
Display blkid's output using the specified format. Note that the
variables order and devices order is variable. See also -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 lsblk(8)
command.
device print the device name only; this output format is always
enabled for -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 (bypass 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
Overwrite device/file size (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.
device Display tokens from only the specified device. It is possible
to give multiple device options on the command line. If none is
given, all devices which appear in /proc/partitions are shown,
if they are recognized.
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 the ambivalent low-level probing result was detected, 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 /run directory
EVALUATE=<methods>
Defines LABEL and UUID evaluation method(s). Currently, the lib‐
blkid library supports "udev" and "scan" methods. More than one
methods 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.
AUTHORblkid was written by Andreas Dilger for libblkid and improved by
Theodore Ts'o and Karel Zak.
ENVIRONMENT
LIBBLKID_DEBUG=0xffff
enables debug output.
AVAILABILITY
The blkid command is part of the util-linux package and is available
from ftp://ftp.kernel.org/pub/linux/utils/util-linux/.
SEE ALSOlibblkid(3)findfs(8)wipefs(8)util-linux February 2011 BLKID(8)
