blkid(8) — Linux manual page


BLKID(8)                  System Administration                 BLKID(8)

NAME         top

       blkid - locate/print block device attributes

SYNOPSIS         top

       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         top

       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

              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

       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.

OPTIONS         top

       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

       -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, --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
              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, 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

                     The non-printing characters are encoded by ^ and M-
                     notation and all potentially unsafe characters are

       -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

              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

       -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

       -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,

                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.

       -V, --version
              Display version number and exit.

EXIT STATUS         top

       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:

              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".

              Overrides the standard location of the cache file.  This
              setting can be overridden by the environment variable
              BLKID_FILE.  Default is /run/blkid/, or
              /etc/ on systems without a /run directory.

              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

ENVIRONMENT         top

       Setting LIBBLKID_DEBUG=all enables debug output.

AUTHORS         top

       blkid was written by Andreas Dilger for libblkid and improved by
       Theodore Ts'o and Karel Zak.

SEE ALSO         top

       libblkid(3), findfs(8), lsblk(8), wipefs(8)

AVAILABILITY         top

       The blkid command is part of the util-linux package and is
       available from

COLOPHON         top

       This page is part of the util-linux (a random collection of Linux
       utilities) project.  Information about the project can be found
       at ⟨⟩.  If you
       have a bug report for this manual page, send it to  This page was obtained from the
       project's upstream Git repository
       ⟨git://⟩ on
       2021-03-21.  (At that time, the date of the most recent commit
       that was found in the repository was 2021-03-19.)  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

util-linux                     March 2013                       BLKID(8)

Pages that refer to this page: ioctl_fslabel(2)open_by_handle_at(2)libblkid(3)fstab(5)blkid(8)btrfs-device(8)findfs(8)lsblk(8)wipefs(8)