1 .\" Copyright 2000 Andreas Dilger (adilger@turbolinux.com)
3 .\" This file may be copied under the terms of the GNU Public License.
4 .TH BLKID 8 "March 2013" "util-linux" "System Administration"
6 blkid \- locate/print block device attributes
14 .RB [ \-\-no\-encoding
15 .B \-\-garbage\-collect \-\-list\-one \-\-cache\-file
21 .RB [ \-\-match\-token
26 .BR \-\-probe " [" \-\-offset
34 .RB [ \-\-match\-types
38 .RB [ \-\-no\-part\-details ]
42 .BR \-\-info " [" \-\-output
51 program is the command-line interface to working with the
53 library. It can determine the type of content (e.g. filesystem or swap)
54 that a block device holds, and also the attributes (tokens, NAME=value pairs)
55 from the content metadata (e.g. LABEL or UUID fields).
57 .B It is recommended to use
59 .B command to get information about block devices, or lsblk --fs to get an overview of filesystems, or
61 .B to search in already mounted filesystems.
65 provides more information, better control on output formatting, easy to use in
66 scripts and it does not require root permissions to get actual information.
68 reads information directly from devices and for non-root users
69 it returns cached unverified information.
71 is mostly designed for system services and to test libblkid functionality.
77 is specified, tokens from only this device are displayed.
78 It is possible to specify multiple
80 arguments on the command line.
81 If none is given, all partitions or unpartitioned devices which appear in
83 are shown, if they are recognized.
86 has two main forms of operation: either searching for a device with a
87 specific NAME=value pair, or displaying NAME=value pairs for one or
88 more specified devices.
92 silently ignores all devices where the probing result is ambivalent (multiple
93 colliding filesystems are detected). The low-level probing mode (\fB-p\fR)
94 provides more information and extra return code in this case.
95 It's recommended to use
97 to get a detailed overview and to erase obsolete stuff (magic strings) from the device.
100 The \fIsize\fR and \fIoffset\fR arguments may be followed by the multiplicative
101 suffixes like KiB (=1024), MiB (=1024*1024), and so on for GiB, TiB, PiB, EiB, ZiB and YiB
102 (the "iB" is optional, e.g. "K" has the same meaning as "KiB"), or the suffixes
103 KB (=1000), MB (=1000*1000), and so on for GB, TB, PB, EB, ZB and YB.
105 \fB\-c\fR, \fB\-\-cache\-file\fR \fIcachefile\fR
108 instead of reading from the default cache file (see the CONFIGURATION FILE section
109 for more details). If you want to start with a clean cache (i.e. don't report
110 devices previously scanned but not necessarily available at this time), specify
113 \fB\-d\fR, \fB\-\-no\-encoding\fR
114 Don't encode non-printing characters. The non-printing characters are encoded
115 by ^ and M- notation by default. Note that the \fB\-\-output udev\fR output format uses
116 a different encoding which cannot be disabled.
118 \fB\-D\fR, \fB\-\-no\-part\-details\fR
119 Don't print information (PART_ENTRY_* tags) from partition table in low-level probing mode.
121 \fB\-g\fR, \fB\-\-garbage\-collect\fR
122 Perform a garbage collection pass on the blkid cache to remove
123 devices which no longer exist.
125 \fB\-h\fR, \fB\-\-help\fR
126 Display a usage message and exit.
128 \fB\-i\fR, \fB\-\-info\fR
129 Display information about I/O Limits (aka I/O topology). The 'export' output format is
130 automatically enabled. This option can be used together with the \fB\-\-probe\fR option.
132 \fB\-k\fR, \fB\-\-list\-filesystems\fR
133 List all known filesystems and RAIDs and exit.
135 \fB\-l\fR, \fB\-\-list\-one\fR
136 Look up only one device that matches the search parameter specified with the \fB\-\-match\-token\fR
137 option. If there are multiple devices that match the specified search
138 parameter, then the device with the highest priority is returned, and/or
139 the first device found at a given priority. Device types in order of
140 decreasing priority are: Device Mapper, EVMS, LVM, MD, and finally regular
141 block devices. If this option is not specified,
143 will print all of the devices that match the search parameter.
145 \fB\-L\fR, \fB\-\-label\fR \fIlabel\fR
146 Look up the device that uses this filesystem \fIlabel\fR; this is equal to
147 .BR "--list-one --output device --match-token LABEL=\fIlabel\fR" .
148 This lookup method is able to reliably use /dev/disk/by-label
149 udev symlinks (dependent on a setting in /etc/blkid.conf). Avoid using the
150 symlinks directly; it is not reliable to use the symlinks without verification.
151 The \fB-\-label\fR option works on systems with and without udev.
153 Unfortunately, the original
155 from e2fsprogs uses the \fB-L\fR option as a
156 synonym for \fB-o list\fR. For better portability, use \fB-l -o device
157 -t LABEL=\fIlabel\fR and \fB-o list\fR in your scripts rather than the \fB-L\fR option.
159 \fB\-n\fR, \fB\-\-match\-types\fR \fIlist\fR
160 Restrict the probing functions to the specified (comma-separated) \fIlist\fR of
161 superblock types (names).
162 The list items may be prefixed with "no" to specify the types which should be ignored.
165 blkid --probe --match-types vfat,ext3,ext4 /dev/sda1
167 probes for vfat, ext3 and ext4 filesystems, and
169 blkid --probe --match-types nominix /dev/sda1
171 probes for all supported formats except minix filesystems.
172 This option is only useful together with \fB\-\-probe\fR.
174 \fB\-o\fR, \fB\-\-output\fR \fIformat\fR
175 Use the specified output format. Note that the order of variables and
176 devices is not fixed. See also option \fB-s\fR. The
182 print all tags (the default)
185 print the value of the tags
188 print the devices in a user-friendly format; this output format is unsupported
189 for low-level probing (\fB\-\-probe\fR or \fB\-\-info\fR).
191 This output format is \fBDEPRECATED\fR in favour of the
196 print the device name only; this output format is always enabled for the \fB\-\-label\fR
197 and \fB\-\-uuid\fR options
200 print key="value" pairs for easy import into the udev environment; the keys are
201 prefixed by ID_FS_ or ID_PART_ prefixes. The value may be modified to be
202 safe for udev environment; allowed is plain ASCII, hex-escaping and valid UTF-8,
203 everything else (including whitespaces) is replaced with '_'. The keys with
204 _ENC postfix use hex-escaping for unsafe chars.
206 The udev output returns the ID_FS_AMBIVALENT tag if more superblocks are detected,
207 and ID_PART_ENTRY_* tags are always returned for all partitions including empty
210 This output format is \fBDEPRECATED\fR.
213 print key=value pairs for easy import into the environment; this output format
214 is automatically enabled when I/O Limits (\fB\-\-info\fR option) are requested.
216 The non-printing characters are encoded by ^ and M- notation and all
217 potentially unsafe characters are escaped.
220 \fB\-O\fR, \fB\-\-offset\fR \fIoffset\fR
221 Probe at the given \fIoffset\fR (only useful with \fB\-\-probe\fR). This option can be
222 used together with the \fB\-\-info\fR option.
224 \fB\-p\fR, \fB\-\-probe\fR
225 Switch to low-level superblock probing mode (bypassing the cache).
227 Note that low-level probing also returns information about partition table type
228 (PTTYPE tag) and partitions (PART_ENTRY_* tags). The tag names produced by
229 low-level probing are based on names used internally by libblkid and it may be
230 different than when executed without \fB\-\-probe\fR (for example PART_ENTRY_UUID= vs
231 PARTUUID=). See also \fB\-\-no\-part\-details\fR.
233 \fB\-s\fR, \fB\-\-match\-tag\fR \fItag\fR
234 For each (specified) device, show only the tags that match
236 It is possible to specify multiple
238 options. If no tag is specified, then all tokens are shown for all
240 In order to just refresh the cache without showing any tokens, use
241 .B "\-\-match\-tag none"
242 with no other options.
244 \fB\-S\fR, \fB\-\-size\fR \fIsize\fR
245 Override the size of device/file (only useful with \fB\-\-probe\fR).
247 \fB\-t\fR, \fB\-\-match\-token\fR \fINAME=value\fR
248 Search for block devices with tokens named
252 and display any devices which are found.
260 If there are no devices specified on the command line, all block devices
261 will be searched; otherwise only the specified devices are searched.
263 \fB\-u\fR, \fB\-\-usages\fR \fIlist\fR
264 Restrict the probing functions to the specified (comma-separated) \fIlist\fR of "usage" types.
265 Supported usage types are: filesystem, raid, crypto and other. The list items may be
266 prefixed with "no" to specify the usage types which should be ignored. For example:
268 blkid --probe --usages filesystem,other /dev/sda1
270 probes for all filesystem and other (e.g. swap) formats, and
272 blkid --probe --usages noraid /dev/sda1
274 probes for all supported formats except RAIDs.
275 This option is only useful together with \fB\-\-probe\fR.
277 \fB\-U\fR, \fB\-\-uuid\fR \fIuuid\fR
278 Look up the device that uses this filesystem \fIuuid\fR. For more details see the
279 \fB\-\-label\fR option.
281 \fB\-V\fR, \fB\-\-version\fR
282 Display version number and exit.
284 If the specified device or device addressed by specified token (option
285 \fB\-\-match\-token\fR) was found and it's possible to gather any information about the
286 device, an exit code 0 is returned. Note the option \fB\-\-match\-tag\fR filters output
287 tags, but it does not affect return code.
289 If the specified token was not found, or no (specified) devices could be
290 identified, an exit code of 2 is returned.
292 For usage or other errors, an exit code of 4 is returned.
294 If an ambivalent probing result was detected by low-level probing mode (\fB\-p\fR), an exit code of 8 is
296 .SH CONFIGURATION FILE
297 The standard location of the
299 config file can be overridden by the environment variable BLKID_CONF.
300 The following options control the libblkid library:
302 .I SEND_UEVENT=<yes|not>
304 .I /dev/disk/by-{label,uuid,partuuid,partlabel}/
305 symlink does not match with LABEL, UUID, PARTUUID or PARTLABEL on the device. Default is "yes".
308 Overrides the standard location of the cache file. This setting can be
309 overridden by the environment variable BLKID_FILE. Default is
310 .IR /run/blkid/blkid.tab ,
313 on systems without a /run directory.
315 .I EVALUATE=<methods>
316 Defines LABEL and UUID evaluation method(s). Currently, the libblkid library
317 supports the "udev" and "scan" methods. More than one method may be specified in
318 a comma-separated list. Default is "udev,scan". The "udev" method uses udev
320 symlinks and the "scan" method scans all block devices from the
325 was written by Andreas Dilger for libblkid and improved by Theodore Ts'o
328 .IP "Setting LIBBLKID_DEBUG=all enables debug output."
335 The blkid command is part of the util-linux package and is available from
336 https://www.kernel.org/pub/linux/utils/util-linux/.