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]
              [--no-part-details] 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 partitions or unpartitioned 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
       probing 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
              characters are encoded by ^ and M- notation by default.  Note
              that the --output udev output format uses a different encoding
              which cannot be disabled.

       -D, --no-part-details
              Don't print information (PART_ENTRY_* tags) from partition table
              in low-level probing mode.

       -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
              specified 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 (but see below note about
              udev).  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.

              This option forces blkid to use udev when used for LABEL or UUID
              tokens in --match-token. The goal is to provide output
              consistent with another utils (like mount, etc.)  on systems
              where the same tag is used for multiple devices.

       -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
              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, --match-types 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 --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
              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 (--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 value may be modified to be safe for udev
                     environment; allowed is plain ASCII, hex-escaping and
                     valid UTF-8, everything else (including whitespaces) is
                     replaced with '_'. The keys with _ENC postfix use hex-
                     escaping for unsafe chars.

                     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 (--info option) are requested.

                     The non-printing characters are encoded by ^ and M-
                     notation 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
              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 --probe (for example PART_ENTRY_UUID= vs
              PARTUUID=). See also --no-part-details.

       -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-
              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 --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, or it is impossible to gather any information about the
       device identifiers or device content 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
       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), 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)