blkid

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
       findmnt(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
              permissions  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 prob-
       ing 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  charac-
              ters are encoded by ^ and M- notation by default.  Note that the
              --output udev output format uses a different encoding which can-
              not 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 speci-
              fied  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 param-
              eter.

       -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 sys-
              tems 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, --match-types 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 --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 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  (--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 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 (--info option) are requested.

                     The non-printing characters are encoded by ^ and M- nota-
                     tion 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 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 --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-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 --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 over-
       ridden 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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