dmsetup(8) — Linux manual page


DMSETUP(8)                MAINTENANCE COMMANDS                DMSETUP(8)

NAME         top

       dmsetup — low level logical volume management

SYNOPSIS         top

       dmsetup clear device_name
       dmsetup create device_name [-n|--notable|--table table|
                table_file] [--readahead [+]sectors|auto|none]
                [-u|--uuid uuid] [--addnodeoncreate|--addnodeonresume]
       dmsetup create --concise [concise_device_specification]
       dmsetup deps [-o options] [device_name...]
       dmsetup help [-c|-C|--columns]
       dmsetup info [device_name...]
       dmsetup info -c|-C|--columns [--count count] [--interval seconds]
                [--noheadings] [-o fields] [-O|--sort sort_fields]
                [--nameprefixes] [--separator separator] [device_name]
       dmsetup load device_name [--table table|table_file]
       dmsetup ls [--target target_type] [-o options] [--exec command]
       dmsetup mangle [device_name...]
       dmsetup measure [device_name...]
       dmsetup message device_name sector message
       dmsetup mknodes [device_name...]
       dmsetup reload device_name [--table table|table_file]
       dmsetup remove [-f|--force] [--retry] [--deferred] device_name...

       dmsetup remove_all [-f|--force] [--deferred]
       dmsetup rename device_name new_name
       dmsetup rename device_name --setuuid uuid
       dmsetup resume device_name...  [--addnodeoncreate|--addnodeonre‐
                sume] [--noflush] [--nolockfs] [--readahead
       dmsetup setgeometry device_name cyl head sect start
       dmsetup splitname device_name [subsystem]
       dmsetup stats command [options]
       dmsetup status [--target target_type] [--noflush] [de‐
       dmsetup suspend [--nolockfs] [--noflush] device_name...
       dmsetup table [--concise] [--target target_type] [--showkeys]
       dmsetup targets
       dmsetup udevcomplete cookie
       dmsetup udevcomplete_all [age_in_minutes]
       dmsetup udevcookie
       dmsetup udevcreatecookie
       dmsetup udevflags cookie
       dmsetup udevreleasecookie [cookie]
       dmsetup version
       dmsetup wait [--noflush] device_name [event_nr]
       dmsetup wipe_table device_name...  [-f|--force] [--noflush]

       devmap_name major minor
       devmap_name major:minor

DESCRIPTION         top

       dmsetup  manages  logical devices that use the device-mapper dri‐
       ver.  Devices are created by loading a  table  that  specifies  a
       target for each sector (512 bytes) in the logical device.

       The  first argument to dmsetup is a command.  The second argument
       is the logical device name or uuid.

       Invoking the dmsetup tool as devmap_name (which is  not  normally
       distributed  and  is  supported  only  for historical reasons) is
       equivalent to dmsetup info -c --noheadings -j major -m minor.

OPTIONS         top

              Ensure /dev/mapper node exists after dmsetup create.

              Ensure /dev/mapper node exists after dmsetup resume (de‐
              fault with udev).

              Perform additional checks on the operations requested and
              report potential problems.  Useful when debugging scripts.
              In some cases these checks may slow down operations no‐

              Display output in columns rather than as Field: Value

       --count count
              Specify the number of times to repeat a report. Set this
              to zero continue until interrupted.  The default interval
              is one second.

              Try harder to complete operation.

              Outputs a summary of the commands available, optionally
              including the list of report fields (synonym with help

              When returning any table information from the kernel re‐
              port on the inactive table instead of the live table.  Re‐
              quires kernel driver version 4.16.0 or above.

       --interval seconds
              Specify the interval in seconds between successive itera‐
              tions for repeating reports. If --interval is specified
              but --count is not, reports will continue to repeat until
              interrupted.  The default interval is one second.

       --manglename auto|hex|none
              Mangle any character not on a whitelist using man‐
              gling_mode when processing device-mapper device names and
              UUIDs. The names and UUIDs are mangled on input and unman‐
              gled on output where the mangling mode is one of: auto
              (only do the mangling if not mangled yet, do nothing if
              already mangled, error on mixed), hex (always do the man‐
              gling) and none (no mangling).  Default mode is auto.
              Character whitelist: 0-9, A-Z, a-z, #+-.:=@_. This
              whitelist is also supported by udev. Any character not on
              a whitelist is replaced with its hex value (two digits)
              prefixed by \x.  Mangling mode could be also set through
              DM_DEFAULT_NAME_MANGLING_MODE environment variable.

       -j|--major major
              Specify the major number.

       -m|--minor minor
              Specify the minor number.

              When creating a device, don't load any table.

              Add a "DM_" prefix plus the field name to the output.
              Useful with --noheadings to produce a list of field=value
              pairs that can be used to set environment variables (for
              example, in udev(7) rules).

              Suppress the headings line when using columnar output.

              Do not flush outstanding I/O when suspending a device, or
              do not commit thin-pool metadata when obtaining thin-pool

              Do not attempt to synchronize filesystem eg, when suspend‐
              ing a device.

              Tell the kernel not to supply the open reference count for
              the device.

              Do not allow udev to manage nodes for devices in device-
              mapper directory.

              Do not synchronise with udev when creating, renaming or
              removing devices.

       -o|--options options
              Specify which fields to display.

       --readahead [+]sectors|auto|none
              Specify read ahead size in units of sectors.  The default
              value is auto which allows the kernel to choose a suitable
              value automatically.  The + prefix lets you specify a min‐
              imum value which will not be used if it is smaller than
              the value chosen by the kernel.  The value none is equiva‐
              lent to specifying zero.

              Set the table being loaded read-only.

       -S|--select selection
              Process only items that match selection criteria.  If the
              command is producing report output, adding the "selected"
              column (-o selected) displays all rows and shows 1 if the
              row matches the selection and 0 otherwise. The selection
              criteria are defined by specifying column names and their
              valid values while making use of supported comparison op‐
              erators. As a quick help and to see full list of column
              names that can be used in selection and the set of sup‐
              ported selection operators, check the output of dmset‐
              up info -c -S help command.

       --table table
              Specify a one-line table directly on the command line.
              See below for more information on the table format.

       --udevcookie cookie
              Use cookie for udev synchronisation.  Note: Same cookie
              should be used for same type of operations i.e. creation
              of multiple different devices. It's not adviced to combine
              different operations on the single device.

       -u|--uuid uuid
              Specify the uuid.

              Answer yes to all prompts automatically.

       -v|--verbose [-v|--verbose]
              Produce additional output.

              If udev synchronisation is enabled, verify that udev oper‐
              ations get performed correctly and try to fix up the de‐
              vice nodes afterwards if not.

              Display the library and kernel driver version.

COMMANDS         top

       clear device_name
              Destroys the table in the inactive table slot for de‐

       create device_name [-n|--notable|--table table|table_file]
              [--readahead [+]sectors|auto|none] [-u|--uuid uuid]
              Creates a device with the given name.   If  table  or  ta‐
              ble_file  is  supplied, the table is loaded and made live.
              Otherwise a table is read from standard input unless --no‐
              table is used.  The optional uuid can be used in place  of
              device_name in subsequent dmsetup commands.  If successful
              the  device  will  appear in table and for live device the
              node /dev/mapper/device_name is created.   See  below  for
              more information on the table format.

       create --concise [concise_device_specification]
              Creates one or more devices from a concise device specifi‐
              cation.   Each  device  is  specified by a comma-separated
              list: name, uuid, minor number, flags, comma-separated ta‐
              ble lines.  Flags defaults to read-write (rw)  or  may  be
              read-only (ro).  Uuid, minor number and flags are optional
              so  those  fields  may  be  empty.  A semi-colon separates
              specifications of different devices.  Use a  backslash  to
              escape the following character, for example a comma or se‐
              mi-colon  in  a name or table. See also CONCISE FORMAT be‐

       deps [-o options] [device_name...]
              Outputs a list of devices referenced by the live table for
              the specified device. Device names on output can  be  cus‐
              tomised by following options: devno (major and minor pair,
              used  by default), blkdevname (block device name), devname
              (map name for device-mapper devices, equal  to  blkdevname

       help [-c|-C|--columns]
              Outputs  a  summary  of the commands available, optionally
              including the list of report fields.

       info [device_name...]
              Outputs some brief information about  the  device  in  the
                      State: SUSPENDED|ACTIVE, READ-ONLY
                      Tables present: LIVE and/or INACTIVE
                      Open reference count
                      Last event sequence number (used by wait)
                      Major and minor device number
                      Number of targets in the live table

       info -c|-C|--columns [--count count] [--interval seconds]
              [--noheadings] [-o fields] [-O|--sort sort_fields]
              [--nameprefixes] [--separator separator] [device_name]
              Output  you can customise.  Fields are comma-separated and
              chosen from the following list: name, major, minor,  attr,
              open,  segments,  events,  uuid.   Attributes are: (L)ive,
              (I)nactive, (s)uspended, (r)ead-only, read-(w)rite.   Pre‐
              cede  the list with '+' to append to the default selection
              of columns instead of  replacing  it.   Precede  any  sort
              field with '-' for a reverse sort on that column.

       ls [--target target_type] [-o options] [--exec command] [--tree]
              List device names.  Optionally only list devices that have
              at least one target of the specified type.  Optionally ex‐
              ecute  a  command for each device.  The device name is ap‐
              pended to the supplied command.  Device  names  on  output
              can  be  customised by following options: devno (major and
              minor pair, used by  default),  blkdevname  (block  device
              name),  devname (map name for device-mapper devices, equal
              to blkdevname otherwise).   --tree  displays  dependencies
              between  devices  as  a tree.  It accepts a comma-separate
              list of options.  Some specify the  information  displayed
              against  each  node:  device/nodevice; blkdevname; active,
              open, rw, uuid.  Others specify how the tree is displayed:
              ascii, utf, vt100; compact, inverted, notrunc.

       load|reload device_name [--table table|table_file]
              Loads table or table_file into the inactive table slot for
              device_name.  If neither is supplied, reads a  table  from
              standard input.

       mangle [device_name...]
              Ensure  existing  device-mapper device_name and UUID is in
              the correct mangled form containing only whitelisted char‐
              acters (supported by udev) and do a rename  if  necessary.
              Any  character  not on the whitelist will be mangled based
              on the --manglename setting. Automatic rename  works  only
              for device names and not for device UUIDs because the ker‐
              nel  does  not  allow changing the UUID of active devices.
              Any incorrect UUIDs are reported only  and  they  must  be
              manually  corrected  by  deactivating the device first and
              then reactivating it with proper mangling mode  used  (see
              also --manglename).

       measure [device_name...]
              Show  the  data  that  device_name would report to the IMA
              subsystem if a measurement was triggered  at  the  current
              time.  This is for debugging and does not actually trigger
              a measurement.

       message device_name sector message
              Send message to target. If sector not needed use 0.

       mknodes [device_name...]
              Ensure  that  the  node  in /dev/mapper for device_name is
              correct.  If no device_name is supplied, ensure  that  all
              nodes in /dev/mapper correspond to mapped devices current‐
              ly  loaded  by  the  device-mapper  kernel driver, adding,
              changing or removing nodes as necessary.

       remove [-f|--force] [--retry] [--deferred] device_name...
              Removes a device.  It will no longer be visible to  dmset‐
              up.   Open  devices  cannot be removed, but adding --force
              will replace the table with one that fails all I/O.  --de‐
              ferred will enable deferred removal of open devices -  the
              device  will  be removed when the last user closes it. The
              deferred removal feature is supported since version 4.27.0
              of the device-mapper driver available in  upstream  kernel
              version 3.13.  (Use dmsetup version to check this.)  If an
              attempt  to  remove  a  device  fails,  perhaps  because a
              process run from a quick udev rule temporarily opened  the
              device,  the --retry option will cause the operation to be
              retried for a few seconds before failing.  Do NOT  combine
              --force  and  --udevcookie,  as  udev may start to process
              udev rules in the middle of error target  replacement  and
              result in nondeterministic result.

       remove_all [-f|--force] [--deferred]
              Attempts  to  remove all device definitions i.e. reset the
              driver.  This also  runs  mknodes  afterwards.   Use  with
              care!   Open devices cannot be removed, but adding --force
              will replace the table with one that fails all I/O.  --de‐
              ferred will enable deferred removal of open devices -  the
              device  will be removed when the last user closes it.  The
              deferred removal feature is supported since version 4.27.0
              of the device-mapper driver available in  upstream  kernel
              version 3.13.

       rename device_name new_name
              Renames a device.

       rename device_name --setuuid uuid
              Sets the uuid of a device that was created without a uuid.
              After a uuid has been set it cannot be changed.

       resume device_name...  [--addnodeoncreate|--addnodeonresume]
              [--noflush] [--nolockfs] [--readahead
              Un-suspends  a  device.   If  an  inactive  table has been
              loaded, it becomes live.   Postponed  I/O  then  gets  re-
              queued for processing.

       setgeometry device_name cyl head sect start
              Sets the device geometry to C/H/S.

       splitname device_name [subsystem]
              Splits given device name into subsystem constituents.  The
              default  subsystem is LVM.  LVM currently generates device
              names by concatenating the names of the Volume Group, Log‐
              ical Volume and any internal Layer with a hyphen as  sepa‐
              rator.  Any hyphens within the names are doubled to escape
              them.  The precise encoding might change without notice in
              any  future release, so we recommend you always decode us‐
              ing the current version of this command.

       stats command [options]
              Manages IO statistics regions for devices.  See dmstats(8)
              for more details.

       status [--target target_type] [--noflush] [device_name...]
              Outputs status information for each of the  device's  tar‐
              gets.   With  --target,  only  information relating to the
              specified target type any is displayed.   With  --noflush,
              the  thin  target  (from version 1.3.0) doesn't commit any
              outstanding changes to disk before reporting  its  statis‐

       suspend [--nolockfs] [--noflush] device_name...
              Suspends  a  device.  Any I/O that has already been mapped
              by the device but has not yet completed will  be  flushed.
              Any  further  I/O  to that device will be postponed for as
              long as the device is suspended.  If there's a  filesystem
              on  the  device  which  supports the operation, an attempt
              will be made to sync it first unless --nolockfs is  speci‐
              fied.  Some targets such as recent (October 2006) versions
              of  multipath may support the --noflush option.  This lets
              outstanding I/O that has not yet reached the device to re‐
              main unflushed.

       table [--concise] [--target target_type] [--showkeys]
              Outputs the current table for the device in a format  that
              can  be  fed  back  in  using the create or load commands.
              With --target, only information relating to the  specified
              target  type  is displayed.  Real encryption keys are sup‐
              pressed in the table output for crypt and  integrity  tar‐
              gets  unless  the --showkeys parameter is supplied. Kernel
              key references prefixed with : are not affected by the pa‐
              rameter and get  displayed  always  (crypt  target  only).
              With  --concise,  the  output  is presented concisely on a
              single line.  Commas then separate the name,  uuid,  minor
              device  number,  flags  ('ro'  or  'rw') and the table (if
              present). Semi-colons separate devices. Backslashes escape
              any commas, semi-colons or backslashes.  See CONCISE  FOR‐
              MAT below.

              Displays  the  names  and versions of the currently-loaded

       udevcomplete cookie
              Wake any processes that are waiting for udev  to  complete
              processing the specified cookie.

       udevcomplete_all [age_in_minutes]
              Remove all cookies older than the specified number of min‐
              utes.  Any process waiting on a cookie will be resumed im‐

              List  all  existing cookies. Cookies are system-wide sema‐
              phores  with  keys  prefixed  by  two   predefined   bytes

              Creates a new cookie to synchronize actions with udev pro‐
              cessing.   The output is a cookie value. Normally we don't
              need to create cookies since dmsetup creates and  destroys
              them for each action automatically. However, we can gener‐
              ate  one  explicitly to group several actions together and
              use only one cookie instead. We can define a cookie to use
              for each relevant command by  using  --udevcookie  option.
              Alternatively,  we can export this value into the environ‐
              ment of the dmsetup process as DM_UDEV_COOKIE variable and
              it will be used automatically with all subsequent commands
              until it is unset.  Invoking this command will create sys‐
              tem-wide semaphore that needs to be cleaned up  explicitly
              by calling udevreleasecookie command.

       udevflags cookie
              Parses  given  cookie  value and extracts any udev control
              flags encoded.  The output is in  environment  key  format
              that  is  suitable  for use in udev rules. If the flag has
              its  symbolic   name   assigned   then   the   output   is
              DM_UDEV_FLAG_<flag_name>  =  '1',  DM_UDEV_FLAG<flag_posi‐
              tion> = '1' otherwise.  Subsystem udev  flags  don't  have
              symbolic names assigned and these ones are always reported
              as  DM_SUBSYSTEM_UDEV_FLAG<flag_position> = '1'. There are
              16 udev flags altogether.

       udevreleasecookie [cookie]
              Waits for all pending udev processing bound to given cook‐
              ie value and clean up the  cookie  with  underlying  sema‐
              phore.  If  the  cookie is not given directly, the command
              will try to use a value defined by DM_UDEV_COOKIE environ‐
              ment variable.

              Outputs version information.

       wait [--noflush] device_name [event_nr]
              Sleeps until the event  counter  for  device_name  exceeds
              event_nr.   Use  -v  to see the event number returned.  To
              wait until the next event is triggered, use info  to  find
              the  last  event  number.  With --noflush, the thin target
              (from  version  1.3.0)  doesn't  commit  any   outstanding
              changes to disk before reporting its statistics.

       wipe_table device_name...  [-f|--force] [--noflush] [--nolockfs]
              Wait for any I/O in-flight through the device to complete,
              then replace the table with a new table that fails any new
              I/O  sent  to  the device.  If successful, this should re‐
              lease any devices held open by the device's table(s).

TABLE FORMAT         top

       Each line of the table specifies a single target and  is  of  the

       logical_start_sector num_sectors target_type target_args

       Simple target types and target args include:

       linear destination_device start_sector
              The traditional linear mapping.

       striped num_stripes chunk_size [destination start_sector]...
              Creates a striped area.
              e.g. striped 2 32 /dev/hda1 0 /dev/hdb1 0 will map the
              first chunk (16k) as follows:

                      LV chunk 1 → hda1, chunk 1
                      LV chunk 2 → hdb1, chunk 1
                      LV chunk 3 → hda1, chunk 2
                      LV chunk 4 → hdb1, chunk 2

       error  Errors any I/O that goes to this area.  Useful for testing
              or for creating devices with holes in them.

       zero   Returns blocks of zeroes on reads.  Any data written is
              discarded silently.  This is a block-device equivalent of
              the /dev/zero character-device data sink described in

       More complex targets include:

       cache  Improves performance of a block device (eg, a spindle) by
              dynamically migrating some of its data to a faster smaller
              device (eg, an SSD).

       crypt  Transparent encryption of block devices using the kernel
              crypto API.

       delay  Delays reads and/or writes to different devices.  Useful
              for testing.

       flakey Creates a similar mapping to the linear target but ex‐
              hibits unreliable behaviour periodically.  Useful for sim‐
              ulating failing devices when testing.

       mirror Mirrors data across two or more devices.

              Mediates access through multiple paths to the same device.

       raid   Offers an interface to the kernel's software raid driver,

              Supports snapshots of devices.

       thin, thin-pool
              Supports thin provisioning of devices and also provides a
              better snapshot support.

       To find out more about the various targets and their table for‐
       mats and status lines, please read the files in the Documenta‐
       tion/device-mapper directory in the kernel source tree.  (Your
       distribution might include a copy of this information in the doc‐
       umentation directory for the device-mapper package.)

EXAMPLES         top

       # A table to join two disks together
       0 1028160 linear /dev/hda 0
       1028160 3903762 linear /dev/hdb 0

       # A table to stripe across the two disks,
       # and add the spare space from
       # hdb to the back of the volume
       0 2056320 striped 2 32 /dev/hda 0 /dev/hdb 0
       2056320 2875602 linear /dev/hdb 1028160

CONCISE FORMAT         top

       A concise representation of one of more devices.

       - A comma separates the fields of each device.
       - A semi-colon separates devices.

       The representation of a device takes the form:

       The fields are:

       name   The name of the device.

       uuid   The UUID of the device (or empty).

       minor  The minor number of the device.  If empty, the kernel as‐
              signs a suitable minor number.

       flags  Supported flags are:
              ro Sets the table being loaded for the device read-only
              rw Sets the table being loaded for the device read-write

       table  One line of the table. See TABLE FORMAT above.

EXAMPLES         top

       # A simple linear read-only device
       test-linear-small,,,ro,0 2097152 linear /dev/loop0 0,2097152
       2097152 linear /dev/loop1 0
       # Two linear devices
       test-linear-small,,,,0 2097152 linear /dev/loop0 0;test-
       linear-large,,,,0 2097152 linear /dev/loop1 0, 2097152 2097152
       linear /dev/loop2 0


              The device directory name.  Defaults to "/dev" and must be
              an absolute path.

              A cookie to use for all relevant commands to synchronize
              with udev processing.  It is an alternative to using
              --udevcookie option.

              A default mangling mode. Defaults to "auto" and it is an
              alternative to using --manglename option.

AUTHORS         top

       Original version: Joe Thornber <>

SEE ALSO         top

       dmstats(8), udev(7), udevadm(8)

       LVM2 resource page: ⟨⟩
       Device-mapper resource page: ⟨

COLOPHON         top

       This page is part of the lvm2 (Logical Volume Manager 2) project.
       Information about the project can be found at 
       ⟨⟩.  If you have a bug report for
       this manual page, see ⟨⟩.
       This page was obtained from the project's upstream Git repository
       ⟨git://⟩ on 2024-06-14.  (At that
       time, the date of the most recent commit that was found in the
       repository was 2024-06-11.)  If you discover any rendering
       problems in this HTML version of the page, or you believe there
       is a better or more up-to-date source for the page, or you have
       corrections or improvements to the information in this COLOPHON
       (which is not part of the original manual page), send a mail to

Linux                          Apr 06 2006                    DMSETUP(8)

Pages that refer to this page: pmdadm(1)blkdeactivate(8)blkmapd(8)dmstats(8)fsfreeze(8)lvm(8)xfs_io(8)