blkid man page on Ubuntu

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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 lib‐
       blkid(3) library.  It can determine the type of content (e.g.  filesys‐
       tem,   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 necessar‐
	      ily 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 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  portabil‐
	      ity  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)

	      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  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 /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 (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.

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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