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blkid(8) [bsd man page]

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] 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 find-
       mnt(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 permis-
	      sions 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 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 probing result is ambivalent (multiple colliding filesystems are
       detected).  The low-level probing mode (-p) provides more information and extra	return	code  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  characters are encoded by ^ and M- notation by default.  Note that the
	      --output udev output format uses a different encoding which cannot be disabled.

       -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 specified with the --match-token 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 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 systems with and  with-
	      out 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-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 --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 variables and devices is not fixed.  See also option -s.  The format param-
	      eter 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 lsblk(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 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.  This output format is DEPRECATED.

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

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

       -O, --offset offset
	      Probe at the given offset (only useful with --probe).  This option 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 partition 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=).

       -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-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 --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 details see the --label option.

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

RETURN CODE
       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 code 0 is returned.  Note the option --match-tag filters output tags, but it does not affect return code.

       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 probing result was detected by low-level probing mode (-p), an exit code of 8 is returned.

CONFIGURATION FILE
       The standard location of the /etc/blkid.conf config file can be overridden 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=all enables debug output.

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)

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