Ubuntu Manpage: blkid - locate/print block device attributes

Provided by: util-linux_2.27.1-6ubuntu3.10_amd64

NAME

       blkid - locate/print block device attributes

SYNOPSIS

       blkid -L label | -U uuid

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

       blkid -p [-O offset] [-o format] [-S size] [-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  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 rather than blkid.
       lsblk(8) provides more information, better control on output formatting and  it  does  not  require  root
       permissions to get actual information.

       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 devices which appear in /proc/partitions are
       shown, if they are recognized.

       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 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 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 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 Don't encode non-printing characters. The non-printing characters are encoded by ^ and M-
notation by default. Note that the -o udev output format uses a different encoding which 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 information about I/O Limits (aka I/O topology). The 'export' output format is
automatically enabled. This option can be used together with the -p option.

-k List all known filesystems and RAIDs and exit.

-l Look up only one device that matches the search parameter specified with 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 the device that uses this filesystem label; this is 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 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 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
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 (-p or -i).

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 -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.
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 (-i option) are requested.

The non-printing characters are encoded by ^ and M- notation and all potentially unsafe
characters are escaped.

-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 (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 -p (for example
PART_ENTRY_UUID= vs PARTUUID=).

-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
Override the size of device/file (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 filesystem uuid. For more details see the -L option.

-V Display version number and exit.

RETURN CODE

       If the specified device or device addressed by specified token (option -t) was found and it's possible to
       gather any information about the device, an exit code 0 is returned.  Note the option -s  filters  output
       tags, but it does not affect return code.

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

CONFIGURATION FILE

       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.

AUTHOR

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

ENVIRONMENT

       Setting LIBBLKID_DEBUG=all enables debug output.

AVAILABILITY

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

util-linux                                         March 2013                                           BLKID(8)