.\" This file may be copied under the terms of the GNU Public License.
.\"
.\" Based on uuidgen, Mon Sep 17 10:42:12 2000, Andreas Dilger
-.TH BLKID 8 "February 2011" "util-linux" "System Administration"
+.TH BLKID 8 "March 2013" "util-linux" "System Administration"
.SH NAME
blkid \- locate/print block device attributes
.SH SYNOPSIS
.B blkid
-.RB \-L
-.IR label " | "
-.RB \-U
-.IR uuid
+.BI \-L " label"
+|
+.BI \-U " uuid"
.B blkid
.RB [ \-dghlv ]
.IR file ]
.RB [ \-o
.IR format ]
-.in +6
.RB [ \-s
.IR tag ]
+.in +6
.RB [ \-t
.IR NAME=value ]
-[\fIdevice\fR ...]
+.RI [ device " ...]"
.in -6
.B blkid
-.RB -p
-.RB [ \-O
+.BR -p " [" \-O
.IR offset ]
-.RB [ \-S
-.IR size ]
.RB [ \-o
.IR format ]
+.RB [ \-S
+.IR size ]
.RB [ \-s
.IR tag ]
.in +9
.IR list ]
.RB [ \-u
.IR list ]
-.IR device " ... "
+.IR device " ..."
.in -9
.B blkid
-.RB -i
-.RB [ \-o
+.BR -i " [" \-o
.IR format ]
.RB [ \-s
.IR tag ]
-.IR device " ... "
+.IR device " ..."
.SH DESCRIPTION
The
program is the command-line interface to working with the
.BR 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)
+that a block device holds, and also the attributes (tokens, NAME=value pairs)
from the content metadata (e.g. LABEL or UUID fields).
.PP
+When
+.I device
+is specified, tokens from only this device are displayed.
+It is possible to specify multiple
+.I device
+arguments on the command line.
+If none is given, all devices which appear in
+.I /proc/partitions
+are shown, if they are recognized.
+.PP
Note that
.B blkid
reads information directly from devices and for non-root users
-it returns cached unverified information. It's better to use
+it returns cached unverified information. It is better to use
.B lsblk --fs
-to get user-friendly overview about filesystems and devices.
+to get a user-friendly overview of filesystems and devices.
.BR lsblk (8)
is also easy to use in scripts.
.B blkid
more specified devices.
.SH OPTIONS
The \fIsize\fR and \fIoffset\fR arguments may be followed by the multiplicative
-suffixes 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.
+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.
.TP
.BI \-c " cachefile"
Read from
.I cachefile
-instead of reading from the default cache file (see CONFIGURATION FILE section
+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
.IR /dev/null .
.TP
.B \-d
-Don't encode non-printing characters. The non-printing characters are encoded
-by ^ and M- notation by default. Note that \fB-o udev\fR output format uses
-a different encoding and this encoding cannot be disabled.
+Don't encode non-printing characters. The non-printing characters are encoded
+by ^ and M- notation by default. Note that the \fB-o udev\fR output format uses
+a different encoding which cannot be disabled.
.TP
.B \-g
Perform a garbage collection pass on the blkid cache to remove
Display a usage message and exit.
.TP
.B \-i
-Display I/O Limits (aka I/O topology) information. The 'export' output format is
+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 \fB-p\fR option.
.TP
+.B \-k
+List all known filesystems and RAIDs and exit.
+.TP
.B \-l
-Look up only one device that matches the search parameter specified with \fB-t\fR
+Look up only one device that matches the search parameter specified with the \fB-t\fR
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
+decreasing priority are: Device Mapper, EVMS, LVM, MD, and finally regular
block devices. If this option is not specified,
.B blkid
will print all of the devices that match the search parameter.
.TP
-.B \-k
-List all known filesystems and RAIDs and exit.
-.TP
.BI \-L " label"
-Look up the device that uses this filesystem \fIlabel\fR (equal to: -l -o device -t
-LABEL=<label>). This lookup method is able to reliably use /dev/disk/by-label
+Look up the device that uses this filesystem \fIlabel\fR; this is equal to
+.BR "-l -o device -t LABEL=\fIlabel\fR" .
+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 \fB-L\fR option works on systems with and without udev.
Unfortunately, the original
.BR blkid (8)
-from e2fsprogs use the \fB-L\fR option as a
-synonym for the \fB-o list\fR option. For better portability, use \fB-l -o device
--t LABEL=<label>\fR and \fB-o list\fR in your scripts rather than the \fB-L\fR option.
+from e2fsprogs uses the \fB-L\fR option as a
+synonym for \fB-o list\fR. For better portability, use \fB-l -o device
+-t LABEL=\fIlabel\fR and \fB-o list\fR in your scripts rather than the \fB-L\fR option.
.TP
-.BI \-n " list "
+.BI \-n " list"
Restrict the probing functions to the specified (comma-separated) \fIlist\fR of
superblock types (names).
The list items may be prefixed with "no" to specify the types which should be ignored.
This option is only useful together with \fB-p\fR.
.TP
.BI \-o " format"
-Display
-.BR blkid 's
-output using the specified format. Note that the variables order and
-devices order is variable. See also \fB-s\fR. The
+Use the specified output format. Note that the order of variables and
+devices is not fixed. See also option \fB-s\fR. The
.I format
parameter may be:
.RS
.TP
.B list
print the devices in a user-friendly format; this output format is unsupported
-for low-level probing (\fB-p\fR or \fB-i\fR). This output format is \fBDEPRECATED\fR
-in favour of
+for low-level probing (\fB-p\fR or \fB-i\fR).
+
+This output format is \fBDEPRECATED\fR in favour of the
.BR lsblk (8)
command.
.TP
.B device
-print the device name only; this output format is always enabled for \fB-L\fR
+print the device name only; this output format is always enabled for the \fB-L\fR
and \fB-U\fR options
.TP
.B udev
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 \fBDEPRECATED\fR.
+partitions. This output format is \fBDEPRECATED\fR.
.TP
.B export
print key=value pairs for easy import into the environment; this output format
used together with the \fB-i\fR option.
.TP
.BI \-p
-Switch to low-level superblock probing mode (bypass cache).
+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).
with no other options.
.TP
.BI \-S " size"
-Overwrite device/file size (only useful with \fB-p\fR).
+Override the size of device/file (only useful with \fB-p\fR).
.TP
-.BI \-t " NAME" = "value"
+.BI \-t " NAME" = value
Search for block devices with tokens named
.I NAME
that have the value
If there are no devices specified on the command line, all block devices
will be searched; otherwise only the specified devices are searched.
.TP
-.BI \-u " list "
+.BI \-u " list"
Restrict the probing functions to the specified (comma-separated) \fIlist\fR 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:
probes for all supported formats except RAIDs.
This option is only useful together with \fB-p\fR.
.TP
-.BI \-U " uuid "
+.BI \-U " uuid"
Look up the device that uses this filesystem \fIuuid\fR. For more details see the \fB-L\fR option.
.TP
.B \-v
Display version number and exit.
-.TP
-.I device
-Display tokens from only the specified device. It is possible to
-give multiple
-.I device
-options on the command line. If none is given, all devices which
-appear in
-.I /proc/partitions
-are shown, if they are recognized.
.SH "RETURN CODE"
If the specified token was found, or if any tags were shown from (specified)
devices, 0 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
+If an ambivalent low-level probing result was detected, an exit code of 8 is
returned.
.SH CONFIGURATION FILE
The standard location of the
.I SEND_UEVENT=<yes|not>
Sends uevent when
.I /dev/disk/by-{label,uuid,partuuid,partlabel}/
-symlink does not match with LABEL, UUID, PARTUUID or PARTLABEL on the device. Default is "yes".
+symlink does not match with LABEL, UUID, PARTUUID or PARTLABEL on the device. Default is "yes".
.TP
.I CACHE_FILE=<path>
-Overrides the standard location of the cache file. This setting can be
-overridden by the environment variable BLKID_FILE. Default is
-.I /run/blkid/blkid.tab
+Overrides the standard location of the cache file. This setting can be
+overridden by the environment variable BLKID_FILE. Default is
+.IR /run/blkid/blkid.tab ,
or
.I /etc/blkid.tab
-on systems without /run directory
+on systems without a /run directory.
.TP
.I EVALUATE=<methods>
-Defines LABEL and UUID evaluation method(s). Currently, the libblkid library
-supports "udev" and "scan" methods. More than one methods may be specified in
-a comma separated list. Default is "udev,scan". The "udev" method uses udev
+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
.I /dev/disk/by-*
symlinks and the "scan" method scans all block devices from the
.I /proc/partitions
was written by Andreas Dilger for libblkid and improved by Theodore Ts'o
and Karel Zak.
.SH ENVIRONMENT
-.IP LIBBLKID_DEBUG=0xffff
-enables debug output.
+.IP "Setting LIBBLKID_DEBUG=0xffff enables debug output."
.SH AVAILABILITY
The blkid command is part of the util-linux package and is available from
ftp://ftp.kernel.org/pub/linux/utils/util-linux/.
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