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
cachefileRead 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−encodingDon'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−detailsDon't print information (PART_ENTRY_* tags) from partition table in low-level probing mode.
−g, −−garbage−collectPerform a garbage collection pass on the blkid cache to remove devices which no longer exist.
−h, −−helpDisplay a usage message and exit.
−i, −−infoDisplay 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−filesystemsList all known filesystems and RAIDs and exit.
−l, −−list−oneLook 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 labelLook up the device that uses this filesystem
label; this is
equal to −−list−one
−−output device
−−match−token 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−−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
listRestrict 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 formatUse 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
listprint the devices in a user-friendly format; this output format is unsupported for low-level probing (
−−probeor−−info).This output format is
DEPRECATEDin favour of the lsblk(8) command.deviceprint the device name only; this output format is always enabled for the
−−labeland−−uuidoptions- 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 (
−−infooption) are requested.The non-printing characters are encoded by ^ and M- notation and all potentially unsafe characters are escaped.
−O, −−offset offsetProbe at the given offset (only useful with
−−probe). This
option can be used together with the −−info option.
−p, −−probeSwitch 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 tagFor 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 sizeOverride the size of device/file (only useful with
−−probe).
−t, −−match−token
NAME=valueSearch 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 listRestrict 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 uuidLook up the device that uses this filesystem
uuid. For more
details see the −−label option.
−V, −−versionDisplay 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.