BLKID(8)                     System Administration                    BLKID(8)

       blkid - locate/print block device attributes

       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 ...

       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 rather than blkid.  lsblk(8) provides  more  information,
       better  control  on output formatting and it does not require root per-
       missions to get actual information.

       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.

       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

       -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_

                     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.

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

       -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

              Note  that low-level probing also returns information about par-
              tition 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 -p (for example PART_ENTRY_UUID= vs PARTU-

       -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.

       If the specified device or device addressed by specified token  (option
       -t)  was  found  and  it's possible to gather any information about the
       device, an exit code 0 is returned.  Note the option -s 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 low-level probing result was detected, an exit code of
       8 is returned.

       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:

              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".

              Overrides the standard location of the cache file.  This setting
              can  be  overridden  by  the  environment  variable  BLKID_FILE.
              Default  is  /run/blkid/,  or /etc/ on systems
              without a /run directory.

              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.

       blkid  was  written  by  Andreas  Dilger  for  libblkid and improved by
       Theodore Ts'o and Karel Zak.

       Setting LIBBLKID_DEBUG=all enables debug output.

       libblkid(3), findfs(8), wipefs(8), lsblk(8),

       The blkid command is part of the util-linux package  and  is  available

util-linux                        March 2013                          BLKID(8)
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