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 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

       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 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, --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

                     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

       -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 --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

       -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

       -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.

       -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

       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

       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 file.

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

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
       2020-11-01.  (At that time, the date of the most recent commit that
       was found in the repository was 2020-10-21.)  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)name_to_handle_at(2)open_by_handle_at(2)libblkid(3)fstab(5)blkid(8)btrfs-device(8)findfs(8)lsblk(8)wipefs(8)