BLKID(8) MAINTENANCE COMMANDS BLKID(8)

NAME blkid - command-line utility to locate/print block device attributes

SYNOPSIS blkid -L label | -U uuid

blkid [-ghlv] [-c file] [-w file] [-o format] [-s tag] [-t NAME=value] device [device ...]

blkid -p [-O offset] [-S size] [-o format] [-s tag] [-u list] device [device ...]

blkid -i [-o format] [-s tag] device [device ...]

DESCRIPTION The blkid program is the command-line interface to working with lib- blkid(3) library. It can determine the type of content (e.g. filesys- tem, swap) a block device holds, and also attributes (tokens, NAME=value pairs) from the content metadata (e.g. LABEL or UUID fields).

Note that blkid reads information directly from devices and for non- root users it returns cached unverified information. It is better to use lsblk --fs to get a user-friendly overview of filesystems and devices. lsblk(8) is also easy to use in scripts. blkid is mostly designed for system services and to test libblkid functionality.

blkid does not read information about removable devices by default.

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.

OPTIONS -c cachefile Read from cachefile instead of reading from the default cache file /etc/blkid/blkid.tab. If you want to start with a clean cache (i.e. dont report devices previously scanned but not nec- essarily available at this time), specify /dev/null.

-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 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.

-L label 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 systems 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 portabil- ity use "-l -o device -t LABEL=<label>" and "-o list" in your scripts rather than -L option.

-u list Restrict probing functions to defined (comma separated) list of "usage" types. Supported usage types are: filesystem, raid, crypto and other. The list can 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 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.

-U uuid Look up one device that uses the uuid. For more details see the -L option.

-o format Display blkids 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

export print key=value pairs for easy import into the environ- ment. This output format is automatically enabled when I/O Limits (-i option) are requested.

-O bytes 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).

-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 bytes 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.

-v Display version number and exit.

-w writecachefile Write the device cache to writecachefile instead of writing it to the default cache file /etc/blkid/blkid.tab. If you dont 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 -c option.

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 (spec- ified) 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.

AUTHOR blkid was written by Andreas Dilger for libblkid and improved by Theodore Tso and Karel Zak.

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

SEE ALSO libblkid(3) findfs(8) wipefs(8)

Linux February 2009 BLKID(8)