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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  rather
       than  blkid.   lsblk(8) provides more information, better control on output formatting and
       it does not require root permissions 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.

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 CONFIG‐
              URATION 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 characters 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 for‐
              mat 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  specified  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  verification.   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-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 -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 variables 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 unsup‐
                     ported 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 partitions.  This output format is DEPRECATED.

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

                     The  non-printing characters are encoded by ^ and M- notation and all poten‐
                     tially 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 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 differ‐
              ent than when executed without -p (for example PART_ENTRY_UUID= vs PARTUUID=).

       -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 dis‐
              play 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-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 -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 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.

CONFIGURATION FILE
       The standard location of the /etc/blkid.conf config file can be overridden by the environ‐
       ment variable BLKID_CONF.  The following options control the libblkid library:

       SEND_UEVENT=
              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=
              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=
              Defines LABEL and UUID evaluation method(s).  Currently, the libblkid library  sup‐
              ports  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), wipefs(8), lsblk(8),

AVAILABILITY
       The  blkid  command is part of the util-linux package and is available from ftp://ftp.ker‐
       nel.org/pub/linux/utils/util-linux/.

util-linux                                  March 2013                                   BLKID(8)

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