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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).

       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  dis‐
       playing 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 mean‐
       ing 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 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 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 specified with the -t option.  If there are
              multiple devices that match the specified search parameter, then the device with the  highest  priority
              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 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  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 (-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 partition table type (PTTYPE tag) and parti‐
              tions (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).

                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 (specified) 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 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 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.ker‐
       nel.org/pub/linux/utils/util-linux/.