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 (but see below note about udev).
140 Device types in order of decreasing priority are: Device Mapper, EVMS, LVM, MD,
141 and finally regular block devices. If this option is not specified,
143 will print all of the devices that match the search parameter.
147 to use udev when used for LABEL or UUID tokens in \fB\-\-match\-token\fR. The
148 goal is to provide output consistent with another utils (like mount, etc.)
149 on systems where the same tag is used for multiple devices.
151 \fB\-L\fR, \fB\-\-label\fR \fIlabel\fR
152 Look up the device that uses this filesystem \fIlabel\fR; this is equal to
153 .BR "\-\-list-one \-\-output device \-\-match-token LABEL=\fIlabel\fR" .
154 This lookup method is able to reliably use /dev/disk/by-label
155 udev symlinks (dependent on a setting in /etc/blkid.conf). Avoid using the
156 symlinks directly; it is not reliable to use the symlinks without verification.
157 The \fB-\-label\fR option works on systems with and without udev.
159 Unfortunately, the original
161 from e2fsprogs uses the \fB\-L\fR option as a
162 synonym for \fB\-o list\fR. For better portability, use \fB\-l \-o device
163 \-t LABEL=\fIlabel\fR and \fB\-o list\fR in your scripts rather than the \fB\-L\fR option.
165 \fB\-n\fR, \fB\-\-match\-types\fR \fIlist\fR
166 Restrict the probing functions to the specified (comma-separated) \fIlist\fR of
167 superblock types (names).
168 The list items may be prefixed with "no" to specify the types which should be ignored.
171 blkid \-\-probe \-\-match-types vfat,ext3,ext4 /dev/sda1
173 probes for vfat, ext3 and ext4 filesystems, and
175 blkid \-\-probe \-\-match-types nominix /dev/sda1
177 probes for all supported formats except minix filesystems.
178 This option is only useful together with \fB\-\-probe\fR.
180 \fB\-o\fR, \fB\-\-output\fR \fIformat\fR
181 Use the specified output format. Note that the order of variables and
182 devices is not fixed. See also option \fB\-s\fR. The
188 print all tags (the default)
191 print the value of the tags
194 print the devices in a user-friendly format; this output format is unsupported
195 for low-level probing (\fB\-\-probe\fR or \fB\-\-info\fR).
197 This output format is \fBDEPRECATED\fR in favour of the
202 print the device name only; this output format is always enabled for the \fB\-\-label\fR
203 and \fB\-\-uuid\fR options
206 print key="value" pairs for easy import into the udev environment; the keys are
207 prefixed by ID_FS_ or ID_PART_ prefixes. The value may be modified to be
208 safe for udev environment; allowed is plain ASCII, hex-escaping and valid UTF-8,
209 everything else (including whitespaces) is replaced with '_'. The keys with
210 _ENC postfix use hex-escaping for unsafe chars.
212 The udev output returns the ID_FS_AMBIVALENT tag if more superblocks are detected,
213 and ID_PART_ENTRY_* tags are always returned for all partitions including empty
216 This output format is \fBDEPRECATED\fR.
219 print key=value pairs for easy import into the environment; this output format
220 is automatically enabled when I/O Limits (\fB\-\-info\fR option) are requested.
222 The non-printing characters are encoded by ^ and M- notation and all
223 potentially unsafe characters are escaped.
226 \fB\-O\fR, \fB\-\-offset\fR \fIoffset\fR
227 Probe at the given \fIoffset\fR (only useful with \fB\-\-probe\fR). This option can be
228 used together with the \fB\-\-info\fR option.
230 \fB\-p\fR, \fB\-\-probe\fR
231 Switch to low-level superblock probing mode (bypassing the cache).
233 Note that low-level probing also returns information about partition table type
234 (PTTYPE tag) and partitions (PART_ENTRY_* tags). The tag names produced by
235 low-level probing are based on names used internally by libblkid and it may be
236 different than when executed without \fB\-\-probe\fR (for example PART_ENTRY_UUID= vs
237 PARTUUID=). See also \fB\-\-no\-part\-details\fR.
239 \fB\-s\fR, \fB\-\-match\-tag\fR \fItag\fR
240 For each (specified) device, show only the tags that match
242 It is possible to specify multiple
244 options. If no tag is specified, then all tokens are shown for all
246 In order to just refresh the cache without showing any tokens, use
247 .B "\-\-match\-tag none"
248 with no other options.
250 \fB\-S\fR, \fB\-\-size\fR \fIsize\fR
251 Override the size of device/file (only useful with \fB\-\-probe\fR).
253 \fB\-t\fR, \fB\-\-match\-token\fR \fINAME=value\fR
254 Search for block devices with tokens named
258 and display any devices which are found.
266 If there are no devices specified on the command line, all block devices
267 will be searched; otherwise only the specified devices are searched.
269 \fB\-u\fR, \fB\-\-usages\fR \fIlist\fR
270 Restrict the probing functions to the specified (comma-separated) \fIlist\fR of "usage" types.
271 Supported usage types are: filesystem, raid, crypto and other. The list items may be
272 prefixed with "no" to specify the usage types which should be ignored. For example:
274 blkid \-\-probe \-\-usages filesystem,other /dev/sda1
276 probes for all filesystem and other (e.g., swap) formats, and
278 blkid \-\-probe \-\-usages noraid /dev/sda1
280 probes for all supported formats except RAIDs.
281 This option is only useful together with \fB\-\-probe\fR.
283 \fB\-U\fR, \fB\-\-uuid\fR \fIuuid\fR
284 Look up the device that uses this filesystem \fIuuid\fR. For more details see the
285 \fB\-\-label\fR option.
287 \fB\-V\fR, \fB\-\-version\fR
288 Display version number and exit.
290 If the specified device or device addressed by specified token (option
291 \fB\-\-match\-token\fR) was found and it's possible to gather any information about the
292 device, an exit code 0 is returned. Note the option \fB\-\-match\-tag\fR filters output
293 tags, but it does not affect return code.
295 If the specified token was not found, or no (specified) devices could be
296 identified, or it is impossible to gather any information about the device
297 identifiers or device content an exit code of 2 is returned.
299 For usage or other errors, an exit code of 4 is returned.
301 If an ambivalent probing result was detected by low-level probing mode (\fB\-p\fR), an exit code of 8 is
303 .SH CONFIGURATION FILE
304 The standard location of the
306 config file can be overridden by the environment variable BLKID_CONF.
307 The following options control the libblkid library:
309 .I SEND_UEVENT=<yes|not>
311 .I /dev/disk/by-{label,uuid,partuuid,partlabel}/
312 symlink does not match with LABEL, UUID, PARTUUID or PARTLABEL on the device. Default is "yes".
315 Overrides the standard location of the cache file. This setting can be
316 overridden by the environment variable BLKID_FILE. Default is
317 .IR /run/blkid/blkid.tab ,
320 on systems without a /run directory.
322 .I EVALUATE=<methods>
323 Defines LABEL and UUID evaluation method(s). Currently, the libblkid library
324 supports the "udev" and "scan" methods. More than one method may be specified in
325 a comma-separated list. Default is "udev,scan". The "udev" method uses udev
327 symlinks and the "scan" method scans all block devices from the
332 was written by Andreas Dilger for libblkid and improved by Theodore Ts'o
335 .IP "Setting LIBBLKID_DEBUG=all enables debug output."
342 The blkid command is part of the util-linux package and is available from
343 https://www.kernel.org/pub/linux/utils/util-linux/.