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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 [device ...]

       blkid -p [-O offset] [-S size] [-o format] [-s tag]
                [-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 content (e.g. filesystem, swap) a block device holds, and also attributes (tokens,  NAME=value  pairs)  from
       the content metadata (e.g. LABEL or UUID fields).

       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 does not read information about removable devices by default.

       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 devices.

OPTIONS
       -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 multi-
              ple  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 prior-
              ity  are  Device Mapper, EVMS, LVM, MD, and finally regular block devices.  If this option is not speci-
              fied, 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 better portability use "-l -o device -t LABEL=<label>" and "-o list" in your scripts  rather
              than -L option.

       -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.

       -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 bytes
              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 bytes
              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.

       -v     Display version number and exit.

       -w writecachefile
              Write the device cache to writecachefile instead of writing it to the default cache file.

              This functionality has never been implemented and the option is no more supported on  the  recent  blkid
              versions (>= v2.21).

       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.ker-
       nel.org/pub/linux/utils/util-linux-ng/.

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



Linux                            February 2009                        BLKID(8)