309 lines
9.3 KiB
Groff
309 lines
9.3 KiB
Groff
.\" Copyright 2000 Andreas Dilger (adilger@turbolinux.com)
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.\"
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.\" This man page was created for blkid from e2fsprogs-1.25.
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.\"
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.\" This file may be copied under the terms of the GNU Public License.
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.\"
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.\" Based on uuidgen, Mon Sep 17 10:42:12 2000, Andreas Dilger
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.TH BLKID 8 "March 2013" "util-linux" "System Administration"
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.SH NAME
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blkid \- locate/print block device attributes
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.SH SYNOPSIS
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.B blkid
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.BI \-L " label"
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.BI \-U " uuid"
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.B blkid
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.RB [ \-dghlv ]
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.RB [ \-c
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.IR file ]
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.RB [ \-o
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.IR format ]
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.RB [ \-s
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.IR tag ]
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.in +6
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.RB [ \-t
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.IR NAME=value ]
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.RI [ device " ...]"
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.in -6
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.B blkid
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.BR -p " [" \-O
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.IR offset ]
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.RB [ \-o
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.IR format ]
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.RB [ \-S
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.IR size ]
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.RB [ \-s
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.IR tag ]
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.in +9
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.RB [ \-n
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.IR list ]
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.RB [ \-u
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.IR list ]
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.IR device " ..."
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.in -9
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.B blkid
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.BR -i " [" \-o
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.IR format ]
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.RB [ \-s
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.IR tag ]
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.IR device " ..."
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.SH DESCRIPTION
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The
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.B blkid
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program is the command-line interface to working with the
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.BR libblkid (3)
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library. It can determine the type of content (e.g. filesystem or swap)
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that a block device holds, and also the attributes (tokens, NAME=value pairs)
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from the content metadata (e.g. LABEL or UUID fields).
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.PP
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When
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.I device
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is specified, tokens from only this device are displayed.
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It is possible to specify multiple
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.I device
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arguments on the command line.
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If none is given, all devices which appear in
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.I /proc/partitions
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are shown, if they are recognized.
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.PP
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Note that
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.B blkid
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reads information directly from devices and for non-root users
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it returns cached unverified information. It is better to use
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.B lsblk --fs
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to get a user-friendly overview of filesystems and devices.
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.BR lsblk (8)
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is also easy to use in scripts.
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.B blkid
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is mostly designed for system services and to test libblkid functionality.
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.PP
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.B blkid
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has two main forms of operation: either searching for a device with a
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specific NAME=value pair, or displaying NAME=value pairs for one or
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more specified devices.
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.SH OPTIONS
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The \fIsize\fR and \fIoffset\fR arguments may be followed by the multiplicative
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suffixes like KiB (=1024), MiB (=1024*1024), and so on for GiB, TiB, PiB, EiB, ZiB and YiB
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(the "iB" is optional, e.g. "K" has the same meaning as "KiB"), or the suffixes
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KB (=1000), MB (=1000*1000), and so on for GB, TB, PB, EB, ZB and YB.
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.TP
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.BI \-c " cachefile"
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Read from
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.I cachefile
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instead of reading from the default cache file (see the CONFIGURATION FILE section
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for more details). If you want to start with a clean cache (i.e. don't report
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devices previously scanned but not necessarily available at this time), specify
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.IR /dev/null .
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.TP
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.B \-d
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Don't encode non-printing characters. The non-printing characters are encoded
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by ^ and M- notation by default. Note that the \fB-o udev\fR output format uses
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a different encoding which cannot be disabled.
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.TP
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.B \-g
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Perform a garbage collection pass on the blkid cache to remove
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devices which no longer exist.
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.TP
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.B \-h
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Display a usage message and exit.
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.TP
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.B \-i
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Display information about I/O Limits (aka I/O topology). The 'export' output format is
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automatically enabled. This option can be used together with the \fB-p\fR option.
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.TP
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.B \-k
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List all known filesystems and RAIDs and exit.
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.TP
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.B \-l
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Look up only one device that matches the search parameter specified with the \fB-t\fR
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option. If there are multiple devices that match the specified search
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parameter, then the device with the highest priority is returned, and/or
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the first device found at a given priority. Device types in order of
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decreasing priority are: Device Mapper, EVMS, LVM, MD, and finally regular
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block devices. If this option is not specified,
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.B blkid
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will print all of the devices that match the search parameter.
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.TP
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.BI \-L " label"
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Look up the device that uses this filesystem \fIlabel\fR; this is equal to
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.BR "-l -o device -t LABEL=\fIlabel\fR" .
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This lookup method is able to reliably use /dev/disk/by-label
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udev symlinks (dependent on a setting in /etc/blkid.conf). Avoid using the
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symlinks directly; it is not reliable to use the symlinks without verification.
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The \fB-L\fR option works on systems with and without udev.
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Unfortunately, the original
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.BR blkid (8)
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from e2fsprogs uses the \fB-L\fR option as a
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synonym for \fB-o list\fR. For better portability, use \fB-l -o device
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-t LABEL=\fIlabel\fR and \fB-o list\fR in your scripts rather than the \fB-L\fR option.
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.TP
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.BI \-n " list"
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Restrict the probing functions to the specified (comma-separated) \fIlist\fR of
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superblock types (names).
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The list items may be prefixed with "no" to specify the types which should be ignored.
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For example:
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.sp
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blkid -p -n vfat,ext3,ext4 /dev/sda1
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.sp
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probes for vfat, ext3 and ext4 filesystems, and
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.sp
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blkid -p -n nominix /dev/sda1
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.sp
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probes for all supported formats except minix filesystems.
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This option is only useful together with \fB-p\fR.
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.TP
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.BI \-o " format"
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Use the specified output format. Note that the order of variables and
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devices is not fixed. See also option \fB-s\fR. The
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.I format
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parameter may be:
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.RS
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.TP
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.B full
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print all tags (the default)
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.TP
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.B value
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print the value of the tags
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.TP
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.B list
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print the devices in a user-friendly format; this output format is unsupported
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for low-level probing (\fB-p\fR or \fB-i\fR).
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This output format is \fBDEPRECATED\fR in favour of the
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.BR lsblk (8)
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command.
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.TP
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.B device
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print the device name only; this output format is always enabled for the \fB-L\fR
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and \fB-U\fR options
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.TP
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.B udev
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print key="value" pairs for easy import into the udev environment; the keys are
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prefixed by ID_FS_ or ID_PART_ prefixes
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The udev output returns the ID_FS_AMBIVALENT tag if more superblocks are detected,
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and ID_PART_ENTRY_* tags are always returned for all partitions including empty
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partitions. This output format is \fBDEPRECATED\fR.
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.TP
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.B export
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print key=value pairs for easy import into the environment; this output format
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is automatically enabled when I/O Limits (\fB-i\fR option) are requested
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.RE
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.TP
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.BI \-O " offset"
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Probe at the given \fIoffset\fR (only useful with \fB-p\fR). This option can be
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used together with the \fB-i\fR option.
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.TP
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.BI \-p
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Switch to low-level superblock probing mode (bypassing the cache).
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Note that low-level probing also returns information about partition table type
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(PTTYPE tag) and partitions (PART_ENTRY_* tags).
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.TP
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.BI \-s " tag"
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For each (specified) device, show only the tags that match
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.IR tag .
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It is possible to specify multiple
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.B \-s
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options. If no tag is specified, then all tokens are shown for all
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(specified) devices.
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In order to just refresh the cache without showing any tokens, use
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.B "-s none"
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with no other options.
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.TP
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.BI \-S " size"
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Override the size of device/file (only useful with \fB-p\fR).
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.TP
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.BI \-t " NAME" = value
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Search for block devices with tokens named
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.I NAME
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that have the value
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.IR value ,
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and display any devices which are found.
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Common values for
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.I NAME
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include
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.BR TYPE ,
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.BR LABEL ,
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and
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.BR UUID .
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If there are no devices specified on the command line, all block devices
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will be searched; otherwise only the specified devices are searched.
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.TP
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.BI \-u " list"
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Restrict the probing functions to the specified (comma-separated) \fIlist\fR of "usage" types.
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Supported usage types are: filesystem, raid, crypto and other. The list items may be
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prefixed with "no" to specify the usage types which should be ignored. For example:
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.sp
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blkid -p -u filesystem,other /dev/sda1
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.sp
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probes for all filesystem and other (e.g. swap) formats, and
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.sp
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blkid -p -u noraid /dev/sda1
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.sp
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probes for all supported formats except RAIDs.
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This option is only useful together with \fB-p\fR.
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.TP
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.BI \-U " uuid"
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Look up the device that uses this filesystem \fIuuid\fR. For more details see the \fB-L\fR option.
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.TP
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.B \-V
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Display version number and exit.
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.SH "RETURN CODE"
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If the specified token was found, or if any tags were shown from (specified)
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devices, 0 is returned.
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If the specified token was not found, or no (specified) devices could be
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identified, an exit code of 2 is returned.
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For usage or other errors, an exit code of 4 is returned.
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If an ambivalent low-level probing result was detected, an exit code of 8 is
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returned.
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.SH CONFIGURATION FILE
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The standard location of the
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.I /etc/blkid.conf
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config file can be overridden by the environment variable BLKID_CONF.
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The following options control the libblkid library:
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.TP
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.I SEND_UEVENT=<yes|not>
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Sends uevent when
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.I /dev/disk/by-{label,uuid,partuuid,partlabel}/
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symlink does not match with LABEL, UUID, PARTUUID or PARTLABEL on the device. Default is "yes".
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.TP
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.I CACHE_FILE=<path>
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Overrides the standard location of the cache file. This setting can be
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overridden by the environment variable BLKID_FILE. Default is
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.IR /run/blkid/blkid.tab ,
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or
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.I /etc/blkid.tab
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on systems without a /run directory.
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.TP
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.I EVALUATE=<methods>
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Defines LABEL and UUID evaluation method(s). Currently, the libblkid library
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supports the "udev" and "scan" methods. More than one method may be specified in
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a comma-separated list. Default is "udev,scan". The "udev" method uses udev
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.I /dev/disk/by-*
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symlinks and the "scan" method scans all block devices from the
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.I /proc/partitions
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file.
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.SH AUTHOR
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.B blkid
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was written by Andreas Dilger for libblkid and improved by Theodore Ts'o
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and Karel Zak.
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.SH ENVIRONMENT
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.IP "Setting LIBBLKID_DEBUG=0xffff enables debug output."
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.SH SEE ALSO
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.BR libblkid (3),
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.BR findfs (8),
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.BR wipefs (8)
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.SH AVAILABILITY
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The blkid command is part of the util-linux package and is available from
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ftp://ftp.kernel.org/pub/linux/utils/util-linux/.
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