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 [-u|--uuid uuid]
                [--addnodeoncreate|--addnodeonresume] [-n|--notable|--table
                table|table_file] [--readahead [+]sectors|auto|none]
       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]
                [--nameprefixes] [--noheadings] [-o fields] [-O|--sort
                sort_fields] [--separator separator] [device_name]
       dmsetup load device_name [--table table|table_file]
       dmsetup ls [--target target_type] [--exec command] [--tree] [-o
       dmsetup mangle [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|--addnodeonresume]
                [--noflush] [--nolockfs] [--readahead [+]sectors|auto|none]
       dmsetup setgeometry device_name cyl head sect start
       dmsetup splitname device_name [subsystem]
       dmsetup stats command [options]
       dmsetup status [--target target_type] [--noflush] [device_name...]
       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 driver.
       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 (default
              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 noticeably.

              Display output in columns rather than as Field: Value lines.

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

              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 report on
              the inactive table instead of the live table.  Requires kernel
              driver version 4.16.0 or above.

       --interval seconds
              Specify the interval in seconds between successive iterations
              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 mangling_mode
              when processing device-mapper device names and UUIDs. The
              names and UUIDs are mangled on input and unmangled 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 mangling) 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).

       --noheadings Suppress the headings line when using columnar output.

       --noflush Do not flush outstading I/O when suspending a device, or do
              not commit thin-pool metadata when obtaining thin-pool status.

              Do not attempt to synchronize filesystem eg, when suspending a

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

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

              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 minimum
              value which will not be used if it is smaller than the value
              chosen by the kernel.  The value none is equivalent 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 operators. As a quick
              help and to see full list of column names that can be used in
              selection and the set of supported selection operators, check
              the output of dmsetup 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.

              Specify the uuid.

              Answer yes to all prompts automatically.

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

              If udev synchronisation is enabled, verify that udev
              operations get performed correctly and try to fix up the
              device 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 device_name.

       create device_name [-u|--uuid uuid]
              [--addnodeoncreate|--addnodeonresume] [-n|--notable|--table
              table|table_file] [--readahead [+]sectors|auto|none]
              Creates  a device with the given name.  If table or table_file
              is supplied, the table is loaded and made live.   Otherwise  a
              table  is  read  from standard input unless --notable 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
              specification.   Each device is specified by a comma-separated
              list: name, uuid, minor number, flags,  comma-separated  table
              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 semi-colon in a name or
              table. See also CONCISE FORMAT below.

       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 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).

       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 form:
                      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]
              [--nameprefixes] [--noheadings] [-o fields] [-O|--sort
              sort_fields] [--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.   Precede
              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] [--exec command] [--tree] [-o options]
              List  device names.  Optionally only list devices that have at
              least one target of the specified type.  Optionally execute  a
              command  for  each device.  The device name is appended 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,

       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  characters
              (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  kernel  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).

       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  currently  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  dmsetup.
              Open  devices  cannot  be  removed,  but  adding  --force will
              replace the table with one that  fails  all  I/O.   --deferred
              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.   --deferred
              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 [+]sectors|auto|none]
              Un-suspends a device.  If an inactive table has  been  loaded,
              it  becomes  live.   Postponed  I/O  then  gets  re-queued for

       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,  Logical
              Volume and any internal Layer with a hyphen as separator.  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 using  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  targets.
              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 statistics.

       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 specified.  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 remain 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 suppressed in the
              table  output  for  crypt  and  integrity  targets  unless the
              --showkeys  parameter  is  supplied.  Kernel  key   references
              prefixed  with  :  are  not  affected by the parameter 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 FORMAT 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 minutes.
              Any process waiting on a cookie will be resumed immediately.

              List all existing cookies. Cookies are system-wide  semaphores
              with keys prefixed by two predefined bytes (0x0D4D).

              Creates   a  new  cookie  to  synchronize  actions  with  udev
              processing.  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  generate  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 environment 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 system-wide semaphore that
              needs to be cleaned up explicitly by calling udevreleasecookie

       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_position>  = '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  cookie
              value  and  clean  up the cookie with underlying semaphore. If
              the cookie is not given directly, the command will try to  use
              a value defined by DM_UDEV_COOKIE environment 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  release  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 form:

       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 null(4).

       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

       flakey Creates a similar mapping to the linear target but exhibits
              unreliable behaviour periodically.  Useful for simulating
              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, md.

              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 formats
       and status lines, please read the files in the Documentation/device-
       mapper directory in the kernel source tree.  (Your distribution might
       include a copy of this information in the documentation 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 assigns
              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

              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 tarball fetched from
       ⟨⟩ on 2020-08-13.  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

Linux                            Apr 06 2006                      DMSETUP(8)

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