path: root/misc-utils/blkid.8

.\" Copyright 2000 Andreas Dilger (adilger@turbolinux.com)
.\"
.\" This man page was created for blkid from e2fsprogs-1.25.
.\"
.\" 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 2009" "Linux" "MAINTENANCE COMMANDS"
.SH NAME
blkid \- command\-line utility to locate/print block device attributes
.SH SYNOPSIS
.B blkid
.RB \-L
.IR label " | "
.RB \-U
.IR uuid

.B blkid
.RB [ \-ghlv ]
.RB [ \-c
.IR file ]
.RB [ \-w
.IR file ]
.RB [ \-o
.IR format ]
.in +6
.RB [ \-s
.IR tag ]
.RB [ \-t
.IR NAME=value ]
[\fIdevice\fR ...]
.in -6

.B blkid
.RB -p
.RB [ \-O
.IR offset ]
.RB [ \-S
.IR size ]
.RB [ \-o
.IR format ]
.RB [ \-s
.IR tag ]
.in +9
.RB [ \-n
.IR list ]
.RB [ \-u
.IR list ]
.I device
[\fIdevice\fR ...]
.in -9

.B blkid
.RB -i
.RB [ \-o
.IR format ]
.RB [ \-s
.IR tag ]
.I device
[\fIdevice\fR ...]

.SH DESCRIPTION
The
.B blkid
program is the command-line interface to working with
.BR 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 fields).
.PP
.B 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.
.SH OPTIONS
The \fIsize\fR and \fIoffset\fR 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.
.TP
.BI \-c " cachefile"
Read from
.I cachefile
instead of reading from the default cache file
.IR /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
.IR /dev/null .
.TP
.B \-g
Perform a garbage collection pass on the blkid cache to remove
devices which no longer exist.
.TP
.B \-h
Display a usage message and exit.
.TP
.B \-i
Display I/O Limits (aka I/O topology) information. The 'export' output format is
automatically enabled. This option could be used together with \fB-p\fR option.
.TP
.B \-l
Look up one device that matches the search parameter specified using
the
.B \-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,
.B blkid
will print all of the devices that match the search parameter.
.TP
.B \-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 \fB-L\fR option works on systems with and without udev.

Unfortunately, the original
.B blkid(8)
from e2fsprogs use the \fB-L\fR option as a
synonym to the \fB-o list\fR option. For better portability use "-l -o device
-t LABEL=<label>" and "-o list" in your scripts rather than -L option.
.TP
.B \-n " list "
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:
.sp
  blkid -p -n vfat,ext3,ext4 /dev/sda1
.sp
probes for vfat, ext3 and ext4 filesystems, and
.sp
  blkid -p -u nominix /dev/sda1
.sp
probes for all supported formats exclude minix filesystem. This option is
useful with
\fB-p\fR only.
.TP
.BI \-o " format"
Display
.BR blkid 's
output using the specified format.  The
.I format
parameter may be:
.RS
.TP
.B full
print all tags (the default)
.TP
.B value
print the value of the tags
.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)
.TP
.B device
print the device name only, this output format is always enabled for \fB-L\fR
and \fB-U\fR options
.TP
.B udev
print key="value" pairs for easy import into the udev environment
.TP
.B export
print key=value pairs for easy import into the environment.  This output format
is automatically enabled when I/O Limits (\fB-i\fR option) are requested. 
.RE
.TP
.BI \-O " offset"
Probe at the given offset (only useful with \fB-p\fR). This option could be
used together with \fB-i\fR option.
.TP
.BI \-p
Switch to low-level superblock probing mode (bypass cache).
.TP
.BI \-s " tag"
For each (specified) device, show only the tags that match
.IR tag .
It is possible to specify multiple
.B \-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
.B "-s none"
with no other options.
.TP
.BI \-S " size"
Overwrite device/file size (only useful with \fB-p\fR).
.TP
.BI \-t " NAME" = "value"
Search for block devices with tokens named
.I NAME
that have the value
.IR value ,
and display any devices which are found.
Common values for
.I NAME
include
.BR TYPE ,
.BR LABEL ,
and
.BR UUID .
If there are no devices specified on the command line, all block devices
will be searched; otherwise only the specified devices are searched.
.TP
.B \-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:
.sp
  blkid -p -u filesystem,other /dev/sda1
.sp
probes for all filesystems and others (e.g. swap) formats, and
.sp
  blkid -p -u noraid /dev/sda1
.sp
probes for all supported formats exclude RAIDs. This option is useful with
\fB-p\fR only.
.TP
.B \-U " uuid "
Look up one device that uses the uuid. For more details see the \fB-L\fR option.
.TP
.B \-v
Display version number and exit.
.TP
.BI \-w " writecachefile"
Write the device cache to
.I writecachefile
instead of writing it to the default cache file
.IR /etc/blkid.tab .
If you don't want to save the cache to the default file, specify
.IR /dev/null.
If not specified it will be the same file as that given by the
.B \-c
option.
.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.  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.
.SH AUTHOR
.B blkid
was written by Andreas Dilger for libblkid and improved by Theodore Ts'o
and Karel Zak.
.SH 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/.
.SH "SEE ALSO"
.BR libblkid (3)
.BR findfs (8)
.BR wipefs (8)