blkid - locate/print block device attributes
- 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 ...
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 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.
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.
- -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, 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.
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.
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.
blkid 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 https://www.kernel.org/pub/linux/utils/util-linux/.