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).
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.
Note that blkid reads information directly from devices and for non-root users it returns cached unverified
information. It is better to use lsblk --fs to get a user-friendly overview of filesystems and devices.
lsblk(8) is also easy to use in scripts. blkid is mostly designed for system services and to test libblkid
functionality.
blkid has two main forms of operation: either searching for a device with a specific NAME=value pair, or dis‐
playing NAME=value pairs for one or more specified devices.
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 mean‐
ing 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 characters 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 specified with the -t option. If there are
multiple devices that match the specified search parameter, then the device with the highest priority
option.
-n 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 -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 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 (-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 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 (-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 partition table type (PTTYPE tag) and parti‐
tions (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).
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 (specified) 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 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 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.
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.ker‐
nel.org/pub/linux/utils/util-linux/.
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