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BLKID(8)                     System Administration                    BLKID(8)

NAME
       blkid - locate/print block device attributes
SYNOPSIS
       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 ...

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 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
              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 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_
                     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 (-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  (bypassing  the
              cache).
              Note  that low-level probing also returns information about par-
              tition 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
              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.
RETURN CODE
       If the specified token was found, or if any tags were shown from (spec-
       ified) 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  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=0xffff enables debug output.
SEE ALSO
       libblkid(3), findfs(8), wipefs(8)
AVAILABILITY
       The  blkid  command  is part of the util-linux package and is available
       from ftp://ftp.kernel.org/pub/linux/utils/util-linux/.

util-linux                        March 2013                          BLKID(8)