NAME | SYNOPSIS | DESCRIPTION | OPTIONS | RETURN CODE | CONFIGURATION FILE | AUTHOR | ENVIRONMENT | SEE ALSO | AVAILABILITY | COLOPHON

BLKID(8)                    System Administration                   BLKID(8)

NAME         top

       blkid - locate/print block device attributes

SYNOPSIS         top

       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         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 rather than blkid.  lsblk(8) provides more information,
       better control on output formatting and it does not require root
       permissions to get actual information.

       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 displaying NAME=value pairs for
       one or more specified devices.

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 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 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 verification.  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-
              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.

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

       -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 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 -p (for example PART_ENTRY_UUID= vs
              PARTUUID=).

       -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-
              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 -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         top

       If the specified device or device addressed by specified token
       (option -t) was found and it's possible to gather any information
       about the device, an exit code 0 is returned.  Note the option -s
       filters output tags, but it does not affect return code.

       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         top

       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         top

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

ENVIRONMENT         top

       Setting LIBBLKID_DEBUG=all enables debug output.

SEE ALSO         top

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

AVAILABILITY         top

       The blkid command is part of the util-linux package and is available
       from ftp://ftp.kernel.org/pub/linux/utils/util-linux/.

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 
       ⟨https://www.kernel.org/pub/linux/utils/util-linux/⟩.  If you have a
       bug report for this manual page, send it to
       util-linux@vger.kernel.org.  This page was obtained from the
       project's upstream Git repository 
       ⟨git://git.kernel.org/pub/scm/utils/util-linux/util-linux.git⟩ on
       2016-07-16.  If you discover any rendering problems in this HTML ver‐
       sion 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 man‐
       ual page), send a mail to man-pages@man7.org

util-linux                       March 2013                         BLKID(8)