1BLKID(8)                     System Administration                    BLKID(8)
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NAME

6       blkid - locate/print block device attributes
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SYNOPSIS

9       blkid  --label label | --uuid uuid
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11
12       blkid  [--no-encoding  --garbage-collect  --list-one --cache-file file]
13              [--output format] [--match-tag tag]  [--match-token  NAME=value]
14              [device ...]
15
16
17       blkid  --probe   [--offset  offset]  [--output  format]  [--size  size]
18              [--match-tag   tag]   [--match-types   list]   [--usages   list]
19              [--no-part-details] device ...
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21
22       blkid  --info [--output format] [--match-tag tag] device ...
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24

DESCRIPTION

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
32       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
36              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.
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43
44       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 partitions or unpartitioned devices  which
47       appear in /proc/partitions are shown, if they are recognized.
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49       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
53       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.
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60

OPTIONS

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
68       -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
75       -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
81       -D, --no-part-details
82              Don't print information (PART_ENTRY_* tags) from partition table
83              in low-level probing mode.
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85       -g, --garbage-collect
86              Perform a garbage collection pass on the blkid cache  to  remove
87              devices which no longer exist.
88
89       -h, --help
90              Display a usage message and exit.
91
92       -i, --info
93              Display  information  about  I/O Limits (aka I/O topology).  The
94              'export' output format is automatically  enabled.   This  option
95              can be used together with the --probe option.
96
97       -k, --list-filesystems
98              List all known filesystems and RAIDs and exit.
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100       -l, --list-one
101              Look up only one device that matches the search parameter speci‐
102              fied with the  --match-token  option.   If  there  are  multiple
103              devices  that  match  the  specified  search parameter, then the
104              device with the highest priority is returned, and/or  the  first
105              device  found  at  a  given  priority.  Device types in order of
106              decreasing priority are:  Device  Mapper,  EVMS,  LVM,  MD,  and
107              finally regular block devices.  If this option is not specified,
108              blkid will print all of the devices that match the search param‐
109              eter.
110
111       -L, --label label
112              Look  up  the  device  that  uses this filesystem label; this is
113              equal to --list-one --output device  --match-token  LABEL=label.
114              This  lookup  method  is able to reliably use /dev/disk/by-label
115              udev symlinks  (dependent  on  a  setting  in  /etc/blkid.conf).
116              Avoid using the symlinks directly; it is not reliable to use the
117              symlinks without verification.  The --label option works on sys‐
118              tems with and without udev.
119
120              Unfortunately,  the original blkid(8) from e2fsprogs uses the -L
121              option as a synonym for -o list.  For better portability, use -l
122              -o device -t LABEL=label and -o list in your scripts rather than
123              the -L option.
124
125       -n, --match-types list
126              Restrict the probing functions  to  the  specified  (comma-sepa‐
127              rated)  list of superblock types (names).  The list items may be
128              prefixed with "no" to specify the types which should be ignored.
129              For example:
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131                blkid --probe --match-types vfat,ext3,ext4 /dev/sda1
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133              probes for vfat, ext3 and ext4 filesystems, and
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135                blkid --probe --match-types nominix /dev/sda1
136
137              probes for all supported formats except minix filesystems.  This
138              option is only useful together with --probe.
139
140       -o, --output format
141              Use the specified output format.  Note that the order  of  vari‐
142              ables and devices is not fixed.  See also option -s.  The format
143              parameter may be:
144
145              full   print all tags (the default)
146
147              value  print the value of the tags
148
149              list   print the devices in a user-friendly format; this  output
150                     format  is  unsupported for low-level probing (--probe or
151                     --info).
152
153                     This  output  format  is  DEPRECATED  in  favour  of  the
154                     lsblk(8) command.
155
156              device print  the device name only; this output format is always
157                     enabled for the --label and --uuid options
158
159              udev   print key="value" pairs for easy  import  into  the  udev
160                     environment;  the keys are prefixed by ID_FS_ or ID_PART_
161                     prefixes.  The value may be modified to be safe for  udev
162                     environment;  allowed  is  plain  ASCII, hex-escaping and
163                     valid UTF-8, everything else (including  whitespaces)  is
164                     replaced  with  '_'.  The keys with _ENC postfix use hex-
165                     escaping for unsafe chars.
166
167                     The udev output returns the ID_FS_AMBIVALENT tag if  more
168                     superblocks  are  detected,  and ID_PART_ENTRY_* tags are
169                     always returned for all partitions including empty parti‐
170                     tions.
171
172                     This output format is DEPRECATED.
173
174              export print  key=value  pairs for easy import into the environ‐
175                     ment; this output format is  automatically  enabled  when
176                     I/O Limits (--info option) are requested.
177
178                     The non-printing characters are encoded by ^ and M- nota‐
179                     tion and all potentially unsafe characters are escaped.
180
181       -O, --offset offset
182              Probe at the given offset  (only  useful  with  --probe).   This
183              option can be used together with the --info option.
184
185       -p, --probe
186              Switch  to  low-level  superblock  probing  mode  (bypassing the
187              cache).
188
189              Note that low-level probing also returns information about  par‐
190              tition  table  type  (PTTYPE  tag)  and partitions (PART_ENTRY_*
191              tags). The tag names produced by low-level probing are based  on
192              names  used  internally by libblkid and it may be different than
193              when executed without --probe (for example  PART_ENTRY_UUID=  vs
194              PARTUUID=). See also --no-part-details.
195
196       -s, --match-tag tag
197              For  each (specified) device, show only the tags that match tag.
198              It is possible to specify multiple --match-tag options.   If  no
199              tag  is specified, then all tokens are shown for all (specified)
200              devices.  In order to just refresh the cache without showing any
201              tokens, use --match-tag none with no other options.
202
203       -S, --size size
204              Override the size of device/file (only useful with --probe).
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206       -t, --match-token NAME=value
207              Search  for  block  devices with tokens named NAME that have the
208              value value, and display any devices which  are  found.   Common
209              values  for NAME include TYPE, LABEL, and UUID.  If there are no
210              devices specified on the command line, all block devices will be
211              searched; otherwise only the specified devices are searched.
212
213       -u, --usages list
214              Restrict  the  probing  functions  to the specified (comma-sepa‐
215              rated) list  of  "usage"  types.   Supported  usage  types  are:
216              filesystem,  raid, crypto and other.  The list items may be pre‐
217              fixed with "no" to specify  the  usage  types  which  should  be
218              ignored.  For example:
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220                blkid --probe --usages filesystem,other /dev/sda1
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222              probes for all filesystem and other (e.g. swap) formats, and
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224                blkid --probe --usages noraid /dev/sda1
225
226              probes  for  all supported formats except RAIDs.  This option is
227              only useful together with --probe.
228
229       -U, --uuid uuid
230              Look up the device that uses this  filesystem  uuid.   For  more
231              details see the --label option.
232
233       -V, --version
234              Display version number and exit.
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RETURN CODE

237       If  the specified device or device addressed by specified token (option
238       --match-token) was found and it's possible to  gather  any  information
239       about  the  device,  an  exit  code  0  is  returned.   Note the option
240       --match-tag filters output tags, but it does not affect return code.
241
242       If the specified token was not found, or no (specified)  devices  could
243       be  identified, or it is impossible to gather any information about the
244       device identifiers or device content an exit code of 2 is returned.
245
246       For usage or other errors, an exit code of 4 is returned.
247
248       If an ambivalent probing result was detected by low-level probing  mode
249       (-p), an exit code of 8 is returned.
250

CONFIGURATION FILE

252       The  standard  location of the /etc/blkid.conf config file can be over‐
253       ridden by the environment variable BLKID_CONF.  The  following  options
254       control the libblkid library:
255
256       SEND_UEVENT=<yes|not>
257              Sends  uevent when /dev/disk/by-{label,uuid,partuuid,partlabel}/
258              symlink does not match with LABEL, UUID, PARTUUID  or  PARTLABEL
259              on the device.  Default is "yes".
260
261       CACHE_FILE=<path>
262              Overrides the standard location of the cache file.  This setting
263              can  be  overridden  by  the  environment  variable  BLKID_FILE.
264              Default  is  /run/blkid/blkid.tab,  or /etc/blkid.tab on systems
265              without a /run directory.
266
267       EVALUATE=<methods>
268              Defines LABEL and UUID  evaluation  method(s).   Currently,  the
269              libblkid  library  supports the "udev" and "scan" methods.  More
270              than one method may be  specified  in  a  comma-separated  list.
271              Default   is   "udev,scan".    The   "udev"   method  uses  udev
272              /dev/disk/by-* symlinks and the "scan" method  scans  all  block
273              devices from the /proc/partitions file.
274

AUTHOR

276       blkid  was  written  by  Andreas  Dilger  for  libblkid and improved by
277       Theodore Ts'o and Karel Zak.
278

ENVIRONMENT

280       Setting LIBBLKID_DEBUG=all enables debug output.
281

SEE ALSO

283       libblkid(3), findfs(8), lsblk(8), wipefs(8)
284

AVAILABILITY

286       The blkid command is part of the util-linux package  and  is  available
287       from https://www.kernel.org/pub/linux/utils/util-linux/.
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291util-linux                        March 2013                          BLKID(8)
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