Section: System Administration (8)
Updated: March 2013
blkid - locate/print block device attributes
--garbage-collect --list-one --cache-file
program is the command-line interface to working with the
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
command to get information about block devices, or lsblk --fs to get an overview of filesystems, or
to search in already mounted filesystems.
provides more information, better control on output formatting, easy to use in
scripts and it does not require root permissions to get actual information.
reads information directly from devices and for non-root users
it returns cached unverified information.
is mostly designed for system services and to test libblkid functionality.
is specified, tokens from only this device are displayed.
It is possible to specify multiple
arguments on the command line.
If none is given, all partitions or unpartitioned devices which appear in
are shown, if they are recognized.
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
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
to get a detailed overview and to erase obsolete stuff (magic strings) from the device.
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
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
- -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,
will print all of the devices that match the search parameter.
This option forces
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, 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
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.
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
parameter may be:
print all tags (the default)
print the value of the tags
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
print the device name only; this output format is always enabled for the --label
and --uuid options
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
This output format is DEPRECATED.
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
It is possible to specify multiple
options. If no tag is specified, then all tokens are shown for all
In order to just refresh the cache without showing any tokens, use
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
that have the value
and display any devices which are found.
Common values for
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
- -V, --version
Display version number and exit.
If the specified device or device addressed by specified token (option
) was found and it's possible to gather any information about the
device, an exit status 0 is returned. Note the option --match-tag
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
The standard location of the
config file can be overridden by the environment variable BLKID_CONF.
The following options control the libblkid library:
Sends uevent when
symlink does not match with LABEL, UUID, PARTUUID or PARTLABEL on the device. Default is "yes".
Overrides the standard location of the cache file. This setting can be
overridden by the environment variable BLKID_FILE. Default is
on systems without a /run directory.
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
symlinks and the "scan" method scans all block devices from the
- Setting LIBBLKID_DEBUG=all enables debug output.
was written by Andreas Dilger for libblkid and improved by Theodore Ts'o
and Karel Zak.
The blkid command is part of the util-linux package and is available from