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/.

util-linux                                         March 2013                                           BLKID(8)