BLKID(8) MAINTENANCE COMMANDS BLKID(8)
blkid - command-line utility to locate/print block device attributes
blkid -L label | -U uuid
blkid [-ghlv] [-c file] [-w file] [-o format]
[-s tag] [-t NAME=value] [device ...]
blkid -p [-O offset] [-S size] [-o format] [-s tag]
[-n list] [-u list] device [device ...]
blkid -i [-o format] [-s tag] device [device ...]
The blkid program is the command-line interface to working with libblkid(3) library. It
can determine the type of content (e.g. filesystem, swap) a block device holds, and also
attributes (tokens, NAME=value pairs) from the content metadata (e.g. LABEL or UUID
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 devices.
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.
Read from cachefile instead of reading from the default cache file /etc/blkid.tab.
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.
-g Perform a garbage collection pass on the blkid cache to remove devices which no
-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 could be used together with -p option.
-l Look up one device that matches the search parameter specified using the -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.
Look up one device that uses the label (same as: -l -o device -t LABEL=<label>).
This look up method is able to reliable use /dev/disk/by-label udev symlinks
(depends on setting in /etc/blkid.conf). Avoid to use the symlinks directly. It is
not reliable to use the symlinks without verification. The -L option works on sys-
tems with and without udev.
Unfortunately, the original blkid(8) from e2fsprogs use the -L option as a synonym
to the -o list option. For better portability use "-l -o device -t LABEL=<label>"
and "-o list" in your scripts rather than -L option.
Restrict probing functions to defined (comma separated) list of superblock types
(names). The list can 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 -u nominix /dev/sda1
probes for all supported formats exclude minix filesystem. This option is useful
with -p only.
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 unsup-
ported for low-level probing (-p or -i)
device print the device name only, this output format is always enabled for -L and
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 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.
Probe at the given offset (only useful with -p). This option could be used together
with -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.
Overwrite device/file size (only useful with -p).
Search for block devices with tokens named NAME that have the value value, and dis-
play 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.
Restrict probing functions to defined (comma separated) list of "usage" types.
Supported usage types are: filesystem, raid, crypto and other. The list can be pre-
fixed with "no" to specify the usage types which should be ignored. For example:
blkid -p -u filesystem,other /dev/sda1
probes for all filesystems and others (e.g. swap) formats, and
blkid -p -u noraid /dev/sda1
probes for all supported formats exclude RAIDs. This option is useful with -p only.
Look up one device that uses the uuid. For more details see the -L option.
-v Display version number and exit.
Write the device cache to writecachefile instead of writing it to the default cache
file /etc/blkid.tab. If you don't want to save the cache to the default file,
specify /dev/null. If not specified it will be the same file as that given by the
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.
If the specified token was found, or if any tags were shown from (specified) devices, 0 is
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.
blkid was written by Andreas Dilger for libblkid and improved by Theodore Ts'o and Karel
The blkid command is part of the util-linux package and is available from ftp://ftp.ker-
libblkid(3) findfs(8) wipefs(8)
Linux February 2009 BLKID(8)