BLKID(8)                                              MAINTENANCE COMMANDS                                              BLKID(8)



NAME
       blkid - command-line utility to locate/print block device attributes

SYNOPSIS
       blkid -L label | -U uuid

       blkid [-ghlv] [-c file] [-w file] [-o format]
             [-s tag] [-t NAME=value] [device ...]

       blkid -p [-O offset] [-S size] [-o format] [-s tag]
                [-n list] [-u list] device [device ...]

       blkid -i [-o format] [-s tag] device [device ...]


DESCRIPTION
       The  blkid  program is the command-line interface to working with libblkid(3) library.  It can determine the type of con-
       tent (e.g. filesystem, swap) a block device holds, and also attributes (tokens, NAME=value pairs) from the content  meta-
       data (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 devices.

OPTIONS
       The size and offset arguments may be followed by binary (2^N) suffixes KiB, MiB, GiB, TiB,  PiB  and  EiB  (the  "iB"  is
       optional, e.g. "K" has the same meaning as "KiB") or decimal (10^N) suffixes KB, MB, GB, PB and EB.

       -c cachefile
              Read  from  cachefile  instead  of reading from the default cache file /etc/blkid/blkid.tab.  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.

       -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 could be used together with -p option.

       -l     Look up one device that matches the search parameter specified using 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 one device that uses the label (same as: -l -o device -t LABEL=<label>).  This look up method is  able  to
              reliable  use  /dev/disk/by-label udev symlinks (depends on setting in /etc/blkid.conf). Avoid to use 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 to the -o list option. For bet-
              ter portability use "-l -o device -t LABEL=<label>" and "-o list" in your scripts rather than -L option.

       -n  list
              Restrict probing functions to defined (comma separated) list of superblock types (names).  The list  can  be  pre-
              fixed 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 -u nominix /dev/sda1

              probes for all supported formats exclude minix filesystem. This option is useful with -p only.

       -o format
              Display blkid's output using the specified format.  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)

              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

              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 could be used together with -i option.

       -p     Switch to low-level superblock probing mode (bypass cache).

       -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  probing  functions  to  defined  (comma  separated)  list  of "usage" types.  Supported usage types are:
              filesystem, raid, crypto and other. The list can 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 filesystems and others (e.g. swap) formats, and

                blkid -p -u noraid /dev/sda1

              probes for all supported formats exclude RAIDs. This option is useful with -p only.

       -U  uuid
              Look up one device that uses the uuid. For more details see the -L option.

       -v     Display version number and exit.

       -w writecachefile
              Write the device cache to writecachefile instead of writing it to the default cache file /etc/blkid/blkid.tab.  If
              you don't want to save the cache to the default file, specify /dev/null.  If not specified it  will  be  the  same
              file as that given by the -c option.

       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 (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.

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

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

SEE ALSO
       libblkid(3) findfs(8) wipefs(8)



Linux                                                     February 2009                                                 BLKID(8)