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 ] [ −S size ] [ −o format ] [ −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 attributes (tokens, NAME=value pairs) from the content metadata (e.g. LABEL or UUID fields).

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 binary (2^N) suffixes KiB, MiB, GiB, TiB, PiB and EiB (the "iB" is optional, e.g. "K" has the same meaning as "KiB") or decimal (10^N) suffixes KB, MB, GB, PB and EB.

−c cachefile

Read from cachefile instead of reading from the default cache file (see 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 −o udev output format uses a diffrent encoding and this encoding 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 I/O Limits (aka I/O topology) information. The 'export' output format is automatically enabled. This option can be used together with the −p option.

−l

Look up only one device that matches the search parameter specified with −t.

−k

List all known filesystems and RAIDs and exit.

−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 label (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 use the −L option as a synonym for the −o list option. 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

Display blkid's output using the specified format. 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)

device

print the device name only; this output format is always enabled for −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.

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

−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 (bypass cache).

Note that low-level probing also returns information about partition table type (PTTYPE tag) and partitions (PART_ENTRY_* tags).

−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

Overwrite device/file size (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 uuid. For more details see the −L option.

−v

Display version number and exit.

device

Display tokens from only the specified device. It is possible to give multiple device options on the command line. If none is given, all devices which appear in /proc/partitions are shown, if they are recognized.

RETURN CODE

If the specified token was found, or if any tags were shown from (specified) devices, 0 is returned.

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 the 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}/ symlink does not match with LABEL or UUID 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 /run direcotry

EVALUATE=<methods>

Defines LABEL and UUID evaluation method(s). Currently, the libblkid library supports "udev" and "scan" methods. More than one methods 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.

AVAILABILITY

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

SEE ALSO

libblkid(3) findfs(8) wipefs(8)


  Copyright 2000 Andreas Dilger (adilgerturbolinux.com)

This man page was created for blkid from e2fsprogs-1.25.

This file may be copied under the terms of the GNU Public License.

Based on uuidgen, Mon Sep 17 10:42:12 2000, Andreas Dilger