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 ...]

       blkid -p [-O offset] [-S size] [-o format] [-s tag]
		[-n list] [-u list] device [device ...]

       blkid -i [-o format] [-s tag] 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. 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

       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.

       -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 could be used
	      together with -p option.

       -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 prior-
	      ity.  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 portability use
	      "-l -o device -t LABEL=<label>" and "-o list" in your scripts rather than -L option.

       -n  list
	      Restrict probing functions to defined (comma separated) list of superblock types (names).  The list can 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 -u nominix /dev/sda1

	      probes for all supported formats exclude minix filesystem. This option is useful with -p only.

       -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 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 could be used together with -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	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.

       -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 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)

Linux								   February 2009							  BLKID(8)