man > DMSETUP

DMSETUP(8)                              MAINTENANCE COMMANDS                              DMSETUP(8)

NAME
       dmsetup — low level logical volume management

SYNOPSIS

       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] [--tree]
       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] [device_name...]
       dmsetup suspend [--nolockfs] [--noflush] device_name...
       dmsetup table [--concise] [--target target_type] [--showkeys] [device_name...]
       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] [--nolockfs]

       devmap_name major minor
       devmap_name major:minor

DESCRIPTION
       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
       --addnodeoncreate
              Ensure /dev/mapper node exists after dmsetup create.

       --addnodeonresume
              Ensure /dev/mapper node exists after dmsetup resume (default with udev).

       --checks
              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.

       -c|-C|--columns
              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 inter‐
              rupted.  The default interval is one second.

       -f|--force
              Try harder to complete operation.

       -h|--help
              Outputs a summary of the commands available, optionally including the list  of  report
              fields (synonym with help command).

       --inactive
              When  returning any table information from the kernel report on the inactive table in‐
              stead 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.

       -n|--notable
              When creating a device, don't load any table.

       --nameprefixes
              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  outstanding  I/O  when suspending a device, or do not commit thin-pool
              metadata when obtaining thin-pool status.

       --nolockfs
              Do not attempt to synchronize filesystem eg, when suspending a device.

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

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

       --noudevsync
              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.

       -r|--readonly
              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  compari‐
              son  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  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.

       -y|--yes
              Answer yes to all prompts automatically.

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

       --verifyudev
              If udev synchronisation is enabled, verify that udev operations get performed correct‐
              ly and try to fix up the device nodes afterwards if not.

       --version
              Display the library and kernel driver version.

COMMANDS


       clear device_name
              Destroys the table in the inactive table slot for device_name.

       create device_name [-n|--notable|--table table|table_file] [--readahead [+]sectors|auto|none]
              [-u|--uuid uuid] [--addnodeoncreate|--addnodeonresume]
              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 --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 specification.  Each device is spec‐
              ified  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  charac‐
              ter, for example a comma or semi-colon in a name or table. See also CONCISE FORMAT be‐
              low.

       deps [-o options] [device_name...]
              Outputs  a  list of devices referenced by the live table for the specified device. De‐
              vice 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
                      UUID


       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  ap‐
              pend  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 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:  de‐
              vice/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 con‐
              taining 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 ker‐
              nel does not allow changing the UUID of active devices. Any incorrect  UUIDs  are  re‐
              ported  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  nec‐
              essary.

       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.  --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 be‐
              cause 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 mkn‐
              odes 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.  Post‐
              poned 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 no‐
              tice in any future release, so we recommend you always decode using the  current  ver‐
              sion 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 in‐
              formation 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 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 remain unflushed.

       table [--concise] [--target target_type] [--showkeys] [device_name...]
              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 com‐
              mas, semi-colons or backslashes.  See CONCISE FORMAT below.

       targets
              Displays the names and versions of the currently-loaded targets.

       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.

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

       udevcreatecookie
              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 de‐
              stroys 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  vari‐
              able 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 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_position> = '1' otherwise.  Subsystem udev flags don't have symbolic
              names assigned and these ones are always reported as DM_SUBSYSTEM_UDEV_FLAG<flag_posi‐
              tion> = '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.

       version
              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
       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
                      etc.

       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 testing.

       flakey Creates a similar mapping to the linear target but exhibits unreliable behaviour peri‐
              odically.  Useful for simulating failing devices when testing.

       mirror Mirrors data across two or more devices.

       multipath
              Mediates access through multiple paths to the same device.

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

       snapshot
              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
       # 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
       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:
              <name>,<uuid>,<minor>,<flags>,<table>[,<table>+][;<dev_name>,<uuid>,
              <minor>,<flags>,<table>[,<table>+]]

       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 (default)

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

EXAMPLES
       # 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

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

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

       DM_DEFAULT_NAME_MANGLING_MODE
              A default mangling mode. Defaults to "auto" and it is an alternative to  using  --man‐
              glename option.

AUTHORS
       Original version: Joe Thornber <thornber AT redhat.com>

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

       LVM2 resource page: https://www.sourceware.org/lvm2
       Device-mapper resource page: http://sources.redhat.com/dm

Linux                                        Apr 06 2006                                  DMSETUP(8)