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BLKID(8)		     System Administration		      BLKID(8)

NAME
       blkid - locate/print block device attributes

SYNOPSIS
       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
       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).

       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
       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  charac‐
	      ters 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 speci‐
	      fied  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 verifi‐
	      cation.  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-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 -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 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 (-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 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 (-i option) are requested

       -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 par‐
	      tition table type	 (PTTYPE  tag)	and  partitions	 (PART_ENTRY_*
	      tags).

       -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-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
	      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
       If the specified token was found, or if any tags were shown from (spec‐
       ified) 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.

       If an ambivalent low-level probing result was detected, an exit code 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.
	      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
       blkid was written by  Andreas  Dilger  for  libblkid  and  improved  by
       Theodore Ts'o and Karel Zak.

ENVIRONMENT
       Setting LIBBLKID_DEBUG=0xffff enables debug output.

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

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

util-linux			  March 2013			      BLKID(8)
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