BLKID(8)						       System Administration							  BLKID(8)

NAME

       blkid - locate/print block device attributes

SYNOPSIS

       blkid -L label | -U uuid

       blkid [-dghlv] [-c file] [-w file] [-o format]
	     [-s tag] [-t NAME=value] [device ...]

       blkid -p [-O offset] [-S size] [-o format] [-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 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 specified devices.

OPTIONS

       The size and offset arguments may be followed by binary (2^N) suffixes KiB, MiB, GiB, TiB, PiB and EiB (the "iB" is optional, e.g. "K"  has
       the same meaning as "KiB") or decimal (10^N) suffixes KB, MB, GB, PB and EB.

       -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.

       -d     Don't encode non-printing characters. The non-printing characters are encoded by ^ and M- notation by default.  Note  that  -o  udev
	      output format uses a diffrent encoding and this encoding 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  I/O  Limits  (aka I/O topology) information.  The 'export' output format is automatically enabled.  This option can be used
	      together with the -p option.

       -l     Look up only one device that matches the search parameter specified with -t.

       -k     List all known filesystems and RAIDs and exit.

       -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 label (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 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 for the -o list option.  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-separated) 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
	      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; 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 partitions.

	      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 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 (bypass cache).

	      Note that low-level probing also returns information about partition 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 speci-
	      fied, 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
	      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.

       -u list
	      Restrict	the  probing  functions  to the specified (comma-separated) list of "usage" types.  Supported usage types are: filesystem,
	      raid, crypto and other.  The list items may 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 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 uuid.  For more details see the -L option.

       -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 at all, specify /dev/null.  If not specified, it will be the same file as that given with 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 identified, an exit code of 2 is returned.

       For usage or other errors, an exit code of 4 is returned.

       If the ambivalent low-level probing result was detected, an exit code of 8 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 package and is available from ftp://ftp.kernel.org/pub/linux/utils/util-linux/.

SEE ALSO

       libblkid(3) findfs(8) wipefs(8)

util-linux							   February 2011							  BLKID(8)