Manual Reference Pages  - BLKID (8)

NAME

blkid - locate/print block device attributes

CONTENTS

Synopsis
Description
Options
Author
Availability

SYNOPSIS

blkid -L label | -U uuid

blkid [-dghlv] [-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 ...

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

DESCRIPTION

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 attributes (tokens, NAME=value pairs) from the content metadata (e.g. LABEL or UUID fields).

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.

OPTIONS

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.
-c cachefile
  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.
-d Don’t encode non-printing characters. The non-printing characters are encoded by ^ and M- notation by default. Note that -o udev output format uses a diffrent encoding and this encoding cannot be disabled.
-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 can be used together with the -p option.
-l Look up only one device that matches the search parameter specified with -t.
-k List all known filesystems and RAIDs and exit.
-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 the device that uses this label (equal to: -l -o device -t 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 -L option works on systems with and without udev.

Unfortunately, the original blkid(8) from e2fsprogs use the -L option as a synonym for the -o list option. For better portability, use -l -o device -t LABEL=<label> and -o list in your scripts rather than the -L option.

-n 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 -p -n vfat,ext3,ext4 /dev/sda1

probes for vfat, ext3 and ext4 filesystems, and

blkid -p -n nominix /dev/sda1

probes for all supported formats except minix filesystems. This option is only useful together with -p.

-o format
  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 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; the keys are prefixed by ID_FS_ or ID_PART_ prefixes

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.

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
-O offset
  Probe at the given offset (only useful with -p). This option can be used together with the -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.
-S size 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.
-u 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 -p -u filesystem,other /dev/sda1

probes for all filesystem and other (e.g. swap) formats, and

blkid -p -u noraid /dev/sda1

probes for all supported formats except RAIDs. This option is only useful together with -p.

-U uuid
  Look up the device that uses this uuid. For more details see the -L option.
-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.tab. If you don’t want to save the cache at all, specify /dev/null. If not specified, it will be the same file as that given with 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 (specified) 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.

If the ambivalent low-level probing result was detected, an exit code of 8 is returned.

AUTHOR

blkid was written by Andreas Dilger for libblkid and improved by Theodore Ts’o and Karel Zak.

AVAILABILITY

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

SEE ALSO

libblkid(3) findfs(8) wipefs(8)


util-linux BLKID (8) February 2011
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