1BLKID(8) System Administration BLKID(8)
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6 blkid - locate/print block device attributes
7
9 blkid --label label | --uuid uuid
10 blkid [--no-encoding --garbage-collect --list-one --cache-file file]
13 [--output format] [--match-tag tag] [--match-token NAME=value]
14 [device ...]
15 blkid --probe [--offset offset] [--output format] [--size size]
18 [--match-tag tag] [--match-types list] [--usages list] device
19 ...
20 blkid --info [--output format] [--match-tag tag] device ...
23
26 The blkid program is the command-line interface to working with the
27 libblkid(3) library. It can determine the type of content (e.g.
28 filesystem or swap) that a block device holds, and also the attributes
29 (tokens, NAME=value pairs) from the content metadata (e.g. LABEL or
30 UUID fields).
31 It is recommended to use lsblk(8) command to get information about
33 block devices, or lsblk --fs to get an overview of filesystems, or
34 findmnt(8) to search in already mounted filesystems.
35 lsblk(8) provides more information, better control on output
37 formatting, easy to use in scripts and it does not require root
38 permissions to get actual information. blkid reads information
39 directly from devices and for non-root users it returns cached
40 unverified information. blkid is mostly designed for system
41 services and to test libblkid functionality.
42 When device is specified, tokens from only this device are displayed.
45 It is possible to specify multiple device arguments on the command
46 line. If none is given, all devices which appear in /proc/partitions
47 are shown, if they are recognized.
48 blkid has two main forms of operation: either searching for a device
50 with a specific NAME=value pair, or displaying NAME=value pairs for one
51 or more specified devices.
52 For security reasons blkid silently ignores all devices where the prob‐
54 ing result is ambivalent (multiple colliding filesystems are detected).
55 The low-level probing mode (-p) provides more information and extra
56 return code in this case. It's recommended to use wipefs(8) to get a
57 detailed overview and to erase obsolete stuff (magic strings) from the
58 device.
59
62 The size and offset arguments may be followed by the multiplicative
63 suffixes like KiB (=1024), MiB (=1024*1024), and so on for GiB, TiB,
64 PiB, EiB, ZiB and YiB (the "iB" is optional, e.g. "K" has the same
65 meaning as "KiB"), or the suffixes KB (=1000), MB (=1000*1000), and so
66 on for GB, TB, PB, EB, ZB and YB.
67 -c, --cache-file cachefile
69 Read from cachefile instead of reading from the default cache
70 file (see the CONFIGURATION FILE section for more details). If
71 you want to start with a clean cache (i.e. don't report devices
72 previously scanned but not necessarily available at this time),
73 specify /dev/null.
74 -d, --no-encoding
76 Don't encode non-printing characters. The non-printing charac‐
77 ters are encoded by ^ and M- notation by default. Note that the
78 --output udev output format uses a different encoding which can‐
79 not be disabled.
80 -g, --garbage-collect
82 Perform a garbage collection pass on the blkid cache to remove
83 devices which no longer exist.
84 -h, --help
86 Display a usage message and exit.
87 -i, --info
89 Display information about I/O Limits (aka I/O topology). The
90 'export' output format is automatically enabled. This option
91 can be used together with the --probe option.
92 -k, --list-filesystems
94 List all known filesystems and RAIDs and exit.
95 -l, --list-one
97 Look up only one device that matches the search parameter speci‐
98 fied with the --match-token option. If there are multiple
99 devices that match the specified search parameter, then the
100 device with the highest priority is returned, and/or the first
101 device found at a given priority. Device types in order of
102 decreasing priority are: Device Mapper, EVMS, LVM, MD, and
103 finally regular block devices. If this option is not specified,
104 blkid will print all of the devices that match the search param‐
105 eter.
106 -L, --label label
108 Look up the device that uses this filesystem label; this is
109 equal to --list-one --output device --match-token LABEL=label.
110 This lookup method is able to reliably use /dev/disk/by-label
111 udev symlinks (dependent on a setting in /etc/blkid.conf).
112 Avoid using the symlinks directly; it is not reliable to use the
113 symlinks without verification. The --label option works on sys‐
114 tems with and without udev.
115 Unfortunately, the original blkid(8) from e2fsprogs uses the -L
117 option as a synonym for -o list. For better portability, use -l
118 -o device -t LABEL=label and -o list in your scripts rather than
119 the -L option.
120 -n, --match-types list
122 Restrict the probing functions to the specified (comma-sepa‐
123 rated) list of superblock types (names). The list items may be
124 prefixed with "no" to specify the types which should be ignored.
125 For example:
126 blkid --probe --match-types vfat,ext3,ext4 /dev/sda1
128 probes for vfat, ext3 and ext4 filesystems, and
130 blkid --probe --match-types nominix /dev/sda1
132 probes for all supported formats except minix filesystems. This
134 option is only useful together with --probe.
135 -o, --output format
137 Use the specified output format. Note that the order of vari‐
138 ables and devices is not fixed. See also option -s. The format
139 parameter may be:
140 full print all tags (the default)
142 value print the value of the tags
144 list print the devices in a user-friendly format; this output
146 format is unsupported for low-level probing (--probe or
147 --info).
148 This output format is DEPRECATED in favour of the
150 lsblk(8) command.
151 device print the device name only; this output format is always
153 enabled for the --label and --uuid options
154 udev print key="value" pairs for easy import into the udev
156 environment; the keys are prefixed by ID_FS_ or ID_PART_
157 prefixes. The value may be modified to be safe for udev
158 environment; allowed is plain ASCII, hex-escaping and
159 valid UTF-8, everything else (including whitespaces) is
160 replaced with '_'. The keys with _ENC postfix use hex-
161 escaping for unsafe chars.
162 The udev output returns the ID_FS_AMBIVALENT tag if more
164 superblocks are detected, and ID_PART_ENTRY_* tags are
165 always returned for all partitions including empty parti‐
166 tions.
167 This output format is DEPRECATED.
169 export print key=value pairs for easy import into the environ‐
171 ment; this output format is automatically enabled when
172 I/O Limits (--info option) are requested.
173 The non-printing characters are encoded by ^ and M- nota‐
175 tion and all potentially unsafe characters are escaped.
176 -O, --offset offset
178 Probe at the given offset (only useful with --probe). This
179 option can be used together with the --info option.
180 -p, --probe
182 Switch to low-level superblock probing mode (bypassing the
183 cache).
184 Note that low-level probing also returns information about par‐
186 tition table type (PTTYPE tag) and partitions (PART_ENTRY_*
187 tags). The tag names produced by low-level probing are based on
188 names used internally by libblkid and it may be different than
189 when executed without --probe (for example PART_ENTRY_UUID= vs
190 PARTUUID=).
191 -s, --match-tag tag
193 For each (specified) device, show only the tags that match tag.
194 It is possible to specify multiple --match-tag options. If no
195 tag is specified, then all tokens are shown for all (specified)
196 devices. In order to just refresh the cache without showing any
197 tokens, use --match-tag none with no other options.
198 -S, --size size
200 Override the size of device/file (only useful with --probe).
201 -t, --match-token NAME=value
203 Search for block devices with tokens named NAME that have the
204 value value, and display any devices which are found. Common
205 values for NAME include TYPE, LABEL, and UUID. If there are no
206 devices specified on the command line, all block devices will be
207 searched; otherwise only the specified devices are searched.
208 -u, --usages list
210 Restrict the probing functions to the specified (comma-sepa‐
211 rated) list of "usage" types. Supported usage types are:
212 filesystem, raid, crypto and other. The list items may be pre‐
213 fixed with "no" to specify the usage types which should be
214 ignored. For example:
215 blkid --probe --usages filesystem,other /dev/sda1
217 probes for all filesystem and other (e.g. swap) formats, and
219 blkid --probe --usages noraid /dev/sda1
221 probes for all supported formats except RAIDs. This option is
223 only useful together with --probe.
224 -U, --uuid uuid
226 Look up the device that uses this filesystem uuid. For more
227 details see the --label option.
228 -V, --version
230 Display version number and exit.
231
233 If the specified device or device addressed by specified token (option
234 --match-token) was found and it's possible to gather any information
235 about the device, an exit code 0 is returned. Note the option
236 --match-tag filters output tags, but it does not affect return code.
237 If the specified token was not found, or no (specified) devices could
239 be identified, an exit code of 2 is returned.
240 For usage or other errors, an exit code of 4 is returned.
242 If an ambivalent probing result was detected by low-level probing mode
244 (-p), an exit code of 8 is returned.
245
247 The standard location of the /etc/blkid.conf config file can be over‐
248 ridden by the environment variable BLKID_CONF. The following options
249 control the libblkid library:
250 SEND_UEVENT=<yes|not>
252 Sends uevent when /dev/disk/by-{label,uuid,partuuid,partlabel}/
253 symlink does not match with LABEL, UUID, PARTUUID or PARTLABEL
254 on the device. Default is "yes".
255 CACHE_FILE=<path>
257 Overrides the standard location of the cache file. This setting
258 can be overridden by the environment variable BLKID_FILE.
259 Default is /run/blkid/blkid.tab, or /etc/blkid.tab on systems
260 without a /run directory.
261 EVALUATE=<methods>
263 Defines LABEL and UUID evaluation method(s). Currently, the
264 libblkid library supports the "udev" and "scan" methods. More
265 than one method may be specified in a comma-separated list.
266 Default is "udev,scan". The "udev" method uses udev
267 /dev/disk/by-* symlinks and the "scan" method scans all block
268 devices from the /proc/partitions file.
269
271 blkid was written by Andreas Dilger for libblkid and improved by
272 Theodore Ts'o and Karel Zak.
273
275 Setting LIBBLKID_DEBUG=all enables debug output.
276
278 libblkid(3), findfs(8), lsblk(8), wipefs(8)
279
281 The blkid command is part of the util-linux package and is available
282 from https://www.kernel.org/pub/linux/utils/util-linux/.
283util-linux March 2013 BLKID(8)