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BLKID(8)		     System Administration		      BLKID(8)

NAME
       blkid - locate/print block device attributes

SYNOPSIS
       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
       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 functionality.

       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 prob-
       ing 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
       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  charac-
	      ters are encoded by ^ and	M- notation by default.	 Note that the
	      --output udev output format uses a different encoding which can-
	      not 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	speci-
	      fied with	the --match-token option.  If there are	 multiple  de-
	      vices 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).  De-
	      vice types in order of decreasing	priority are:  Device  Mapper,
	      EVMS,  LVM,  MD, and finally regular block devices.  If this op-
	      tion 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  consis-
	      tent  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 sys-
	      tems 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-sepa-
	      rated) 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 vari-
	      ables 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 ls-
		     blk(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 en-
		     vironment;	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-es-
		     caping 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	parti-
		     tions.

		     This output format	is DEPRECATED.

	      export print key=value pairs for easy import into	 the  environ-
		     ment;  this  output  format is automatically enabled when
		     I/O Limits	(--info	option)	are requested.

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

       -O, --offset offset
	      Probe  at	the given offset (only useful with --probe).  This op-
	      tion can be used together	with the --info	option.

       -p, --probe
	      Switch to	 low-level  superblock	probing	 mode  (bypassing  the
	      cache).

	      Note  that low-level probing also	returns	information about par-
	      tition 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 options.

       -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 searched.

       -u, --usages list
	      Restrict the probing functions  to  the  specified  (comma-sepa-
	      rated)  list  of	"usage"	 types.	  Supported  usage  types are:
	      filesystem, raid,	crypto and other.  The list items may be  pre-
	      fixed  with  "no"	to specify the usage types which should	be ig-
	      nored.  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 de-
	      tails see	the --label option.

       -V, --version
	      Display version number and exit.

EXIT STATUS
       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 status.

       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 returned.

       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.

CONFIGURATION FILE
       The standard location of	the /etc/blkid.conf config file	can  be	 over-
       ridden  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.  De-
	      fault 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.  De-
	      fault   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
       Setting LIBBLKID_DEBUG=all enables debug	output.

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

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

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

util-linux			  March	2013			      BLKID(8)

NAME | SYNOPSIS | DESCRIPTION | OPTIONS | EXIT STATUS | CONFIGURATION FILE | ENVIRONMENT | AUTHORS | SEE ALSO | AVAILABILITY

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