Ubuntu Manpage: blkid - locate/print block device attributes

Provided by: util-linux_2.31.1-0.4ubuntu3.7_amd64

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] 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 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.

-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. 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 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 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=).

-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, 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.

AVAILABILITY

       The  blkid  command  is  part  of  the  util-linux   package   and   is   available   from
       https://www.kernel.org/pub/linux/utils/util-linux/.