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|--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]
       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

              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
              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

       --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).

              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
              suspending 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
              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.

       -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
              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

       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
              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
                      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.
              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] [-o options] [--exec command] [--tree]
              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, 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
              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).

       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
              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
              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,
              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

       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

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

              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

       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
              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,

              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 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 2023-12-22.  (At that
       time, the date of the most recent commit that was found in the
       repository was 2023-12-06.)  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)