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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 ...]

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).

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

       -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 sys-
	      tems 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 pre-
	      fixed 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 unsup-
		     ported for low-level probing (-p)

	      device print the device name only, this output format is always enabled for -L  and
		     -U options

	      udev   vol_id compatible mode; usable in udev rules

       -O bytes
	      Probe at the given offset (only useful with -p).

       -p     Switch to low-level 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 dis-
	      play  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 /etc/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 iden-
       tified, 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)
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