blkid(8) — Linux manual page

NAME | SYNOPSIS | DESCRIPTION | OPTIONS | EXIT STATUS | CONFIGURATION FILE | ENVIRONMENT | AUTHORS | SEE ALSO | REPORTING BUGS | AVAILABILITY

BLKID(8)                  System Administration                 BLKID(8)

NAME         top

       blkid - locate/print block device attributes

SYNOPSIS         top

       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         top

       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(3) 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 exit status 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         top

       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.

       -H, --hint setting
           Set probing hint. The hints are optional way how to force
           probing functions to check for example another location. The
           currently supported is "session_offset=number" to set session
           offset on multi-session UDF.

       -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 other utils (like mount(8), 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.

EXIT STATUS         top

       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 status 0 is returned. Note
       the option --match-tag filters output tags, but it does not
       affect exit status.

       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 status of 2 is returned.

       For usage or other errors, an exit status of 4 is returned.

       If an ambivalent probing result was detected by low-level probing
       mode (-p), an exit status of 8 is returned.

CONFIGURATION FILE         top

       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.

ENVIRONMENT         top

       Setting LIBBLKID_DEBUG=all enables debug output.

AUTHORS         top

       blkid was written by Andreas Dilger for libblkid and improved by
       Theodore Ts’o and Karel Zak.

SEE ALSO         top

       libblkid(3), findfs(8), lsblk(8), wipefs(8)

REPORTING BUGS         top

       For bug reports, use the issue tracker at
       https://github.com/karelzak/util-linux/issues.

AVAILABILITY         top

       The blkid command is part of the util-linux package which can be
       downloaded from Linux Kernel Archive
       <https://www.kernel.org/pub/linux/utils/util-linux/>. This page
       is part of the util-linux (a random collection of Linux
       utilities) project. Information about the project can be found at
       ⟨https://www.kernel.org/pub/linux/utils/util-linux/⟩. If you have
       a bug report for this manual page, send it to
       util-linux@vger.kernel.org. This page was obtained from the
       project's upstream Git repository
       ⟨git://git.kernel.org/pub/scm/utils/util-linux/util-linux.git⟩ on
       2021-06-20. (At that time, the date of the most recent commit
       that was found in the repository was 2021-06-18.) If you discover
       any rendering problems in this HTML version of the page, or you
       believe there is a better or more up-to-date source for the page,
       or you have corrections or improvements to the information in
       this COLOPHON (which is not part of the original manual page),
       send a mail to man-pages@man7.org

util-linux 2.37.109-b366e69    2021-06-20                       BLKID(8)

Pages that refer to this page: ioctl_fslabel(2)open_by_handle_at(2)libblkid(3)fstab(5)blkid(8)btrfs-device(8)findfs(8)lsblk(8)wipefs(8)