xenial (8) blkid.8.gz

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 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 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 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.

                     The non-printing characters are encoded by ^ and M- notation  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 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 different 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 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-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  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), wipefs(8), lsblk(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/.