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 ...
20
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.
48
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.
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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  (but see below note about
106              udev).  Device types in order of decreasing priority are: Device
107              Mapper,  EVMS,  LVM,  MD, and finally regular block devices.  If
108              this option is not  specified,  blkid  will  print  all  of  the
109              devices that match the search parameter.
110
111              This option forces blkid to use udev when used for LABEL or UUID
112              tokens in --match-token. The goal is to provide  output  consis‐
113              tent with another utils (like mount, etc.)  on systems where the
114              same tag is used for multiple devices.
115
116       -L, --label label
117              Look up the device that uses  this  filesystem  label;  this  is
118              equal  to  --list-one --output device --match-token LABEL=label.
119              This lookup method is able to  reliably  use  /dev/disk/by-label
120              udev  symlinks  (dependent  on  a  setting  in /etc/blkid.conf).
121              Avoid using the symlinks directly; it is not reliable to use the
122              symlinks without verification.  The --label option works on sys‐
123              tems with and without udev.
124
125              Unfortunately, the original blkid(8) from e2fsprogs uses the  -L
126              option as a synonym for -o list.  For better portability, use -l
127              -o device -t LABEL=label and -o list in your scripts rather than
128              the -L option.
129
130       -n, --match-types list
131              Restrict  the  probing  functions  to the specified (comma-sepa‐
132              rated) list of superblock types (names).  The list items may  be
133              prefixed with "no" to specify the types which should be ignored.
134              For example:
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136                blkid --probe --match-types vfat,ext3,ext4 /dev/sda1
137
138              probes for vfat, ext3 and ext4 filesystems, and
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140                blkid --probe --match-types nominix /dev/sda1
141
142              probes for all supported formats except minix filesystems.  This
143              option is only useful together with --probe.
144
145       -o, --output format
146              Use  the  specified output format.  Note that the order of vari‐
147              ables and devices is not fixed.  See also option -s.  The format
148              parameter may be:
149
150              full   print all tags (the default)
151
152              value  print the value of the tags
153
154              list   print  the devices in a user-friendly format; this output
155                     format is unsupported for low-level probing  (--probe  or
156                     --info).
157
158                     This  output  format  is  DEPRECATED  in  favour  of  the
159                     lsblk(8) command.
160
161              device print the device name only; this output format is  always
162                     enabled for the --label and --uuid options
163
164              udev   print  key="value"  pairs  for  easy import into the udev
165                     environment; the keys are prefixed by ID_FS_ or  ID_PART_
166                     prefixes.   The value may be modified to be safe for udev
167                     environment; allowed is  plain  ASCII,  hex-escaping  and
168                     valid  UTF-8,  everything else (including whitespaces) is
169                     replaced with '_'. The keys with _ENC  postfix  use  hex-
170                     escaping for unsafe chars.
171
172                     The  udev output returns the ID_FS_AMBIVALENT tag if more
173                     superblocks are detected, and  ID_PART_ENTRY_*  tags  are
174                     always returned for all partitions including empty parti‐
175                     tions.
176
177                     This output format is DEPRECATED.
178
179              export print key=value pairs for easy import into  the  environ‐
180                     ment;  this  output  format is automatically enabled when
181                     I/O Limits (--info option) are requested.
182
183                     The non-printing characters are encoded by ^ and M- nota‐
184                     tion and all potentially unsafe characters are escaped.
185
186       -O, --offset offset
187              Probe  at  the  given  offset  (only useful with --probe).  This
188              option can be used together with the --info option.
189
190       -p, --probe
191              Switch to  low-level  superblock  probing  mode  (bypassing  the
192              cache).
193
194              Note  that low-level probing also returns information about par‐
195              tition table type  (PTTYPE  tag)  and  partitions  (PART_ENTRY_*
196              tags).  The tag names produced by low-level probing are based on
197              names used internally by libblkid and it may be  different  than
198              when  executed  without --probe (for example PART_ENTRY_UUID= vs
199              PARTUUID=). See also --no-part-details.
200
201       -s, --match-tag tag
202              For each (specified) device, show only the tags that match  tag.
203              It  is  possible to specify multiple --match-tag options.  If no
204              tag is specified, then all tokens are shown for all  (specified)
205              devices.  In order to just refresh the cache without showing any
206              tokens, use --match-tag none with no other options.
207
208       -S, --size size
209              Override the size of device/file (only useful with --probe).
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211       -t, --match-token NAME=value
212              Search for block devices with tokens named NAME  that  have  the
213              value  value,  and  display any devices which are found.  Common
214              values for NAME include TYPE, LABEL, and UUID.  If there are  no
215              devices specified on the command line, all block devices will be
216              searched; otherwise only the specified devices are searched.
217
218       -u, --usages list
219              Restrict the probing functions  to  the  specified  (comma-sepa‐
220              rated)  list  of  "usage"  types.   Supported  usage  types are:
221              filesystem, raid, crypto and other.  The list items may be  pre‐
222              fixed  with  "no"  to  specify  the  usage types which should be
223              ignored.  For example:
224
225                blkid --probe --usages filesystem,other /dev/sda1
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227              probes for all filesystem and other (e.g., swap) formats, and
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229                blkid --probe --usages noraid /dev/sda1
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231              probes for all supported formats except RAIDs.  This  option  is
232              only useful together with --probe.
233
234       -U, --uuid uuid
235              Look  up  the  device  that uses this filesystem uuid.  For more
236              details see the --label option.
237
238       -V, --version
239              Display version number and exit.
240

RETURN CODE

242       If the specified device or device addressed by specified token  (option
243       --match-token)  was  found  and it's possible to gather any information
244       about the device,  an  exit  code  0  is  returned.   Note  the  option
245       --match-tag filters output tags, but it does not affect return code.
246
247       If  the  specified token was not found, or no (specified) devices could
248       be identified, or it is impossible to gather any information about  the
249       device identifiers or device content an exit code of 2 is returned.
250
251       For usage or other errors, an exit code of 4 is returned.
252
253       If  an ambivalent probing result was detected by low-level probing mode
254       (-p), an exit code of 8 is returned.
255

CONFIGURATION FILE

257       The standard location of the /etc/blkid.conf config file can  be  over‐
258       ridden  by  the environment variable BLKID_CONF.  The following options
259       control the libblkid library:
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261       SEND_UEVENT=<yes|not>
262              Sends uevent when  /dev/disk/by-{label,uuid,partuuid,partlabel}/
263              symlink  does  not match with LABEL, UUID, PARTUUID or PARTLABEL
264              on the device.  Default is "yes".
265
266       CACHE_FILE=<path>
267              Overrides the standard location of the cache file.  This setting
268              can  be  overridden  by  the  environment  variable  BLKID_FILE.
269              Default is /run/blkid/blkid.tab, or  /etc/blkid.tab  on  systems
270              without a /run directory.
271
272       EVALUATE=<methods>
273              Defines  LABEL  and  UUID  evaluation method(s).  Currently, the
274              libblkid library supports the "udev" and "scan"  methods.   More
275              than  one  method  may  be  specified in a comma-separated list.
276              Default  is  "udev,scan".    The   "udev"   method   uses   udev
277              /dev/disk/by-*  symlinks  and  the "scan" method scans all block
278              devices from the /proc/partitions file.
279

AUTHOR

281       blkid was written by  Andreas  Dilger  for  libblkid  and  improved  by
282       Theodore Ts'o and Karel Zak.
283

ENVIRONMENT

285       Setting LIBBLKID_DEBUG=all enables debug output.
286

SEE ALSO

288       libblkid(3), findfs(8), lsblk(8), wipefs(8)
289

AVAILABILITY

291       The  blkid  command  is part of the util-linux package and is available
292       from https://www.kernel.org/pub/linux/utils/util-linux/.
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296util-linux                        March 2013                          BLKID(8)
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