dmsetup man page on Archlinux

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       dmsetup - low level logical volume management

       dmsetup clear device_name
       dmsetup create device_name [-u uuid] [--notable|--table <table>|
	      table_file] [{--addnodeoncreate|--addnodeonresume}] [--readahead
       dmsetup deps [-o options] [device_name]
       dmsetup help [-c|-C|--columns]
       dmsetup info [device_name]
       dmsetup info -c|-C|--columns [--noheadings] [--separator separator]
	      [-o fields] [-O|--sort sort_fields] [device_name]
       dmsetup load device_name [--table <table>|table_file]
       dmsetup ls [--target target_type] [--exec command] [--tree]
	      [-o options]
       dmsetup message device_name sector message
       dmsetup mknodes [device_name]
       dmsetup mangle [device_name]
       dmsetup reload device_name [--table <table>|table_file]
       dmsetup wipe_table device_name
       dmsetup remove [-f|--force] [--retry] device_name
       dmsetup remove_all [-f|--force]
       dmsetup rename device_name new_name
       dmsetup rename device_name --setuuid uuid
       dmsetup resume device_name [{--addnodeoncreate|--addnodeonresume}]
	      [--readahead [+]<sectors>|auto|none]
       dmsetup setgeometry device_name cyl head sect start
       dmsetup splitname device_name [subsystem]
       dmsetup status [--target target_type] [--noflush] [device_name]
       dmsetup suspend [--nolockfs] [--noflush] device_name
       dmsetup table [--target target_type] [--showkeys] [device_name]
       dmsetup targets
       dmsetup udevcomplete cookie
       dmsetup udevcomplete_all [age_in_minutes]
       dmsetup udevcookies
       dmsetup udevcreatecookie
       dmsetup udevflags cookie
       dmsetup udevreleasecookie [cookie]
       dmsetup version
       dmsetup wait [--noflush] device_name [event_nr]

       devmap_name major minor
       devmap_name major:minor

       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 command as devmap_name is equivalent to
       dmsetup info -c --noheadings -j major -m minor.

	      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.

	      Outputs a summary of the commands available, optionally  includ‐
	      ing the list of report fields (synonym with help command).

	      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.

       --manglename <mangling_mode>
	      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: none (no mangling), hex (always do  the
	      mangling)	 and auto (only do the mangling if not mangled yet, do
	      nothing if already mangled, error on  mixed;  this  is  used  by
	      default).	  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.

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

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

	      Suppress the headings line when using columnar output.

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

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

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

	      Do not synchronise with udev when creating, renaming or removing

	      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 auto‐
	      matically.   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.

       --table <table>
	      Specify a one-line table directly on the command line.

       --udevcookie cookie
	      Use cookie for udev synchronisation.

	      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.

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

       create device_name  [-u	uuid]  [--notable|--table  <table>|table_file]
	      [{--addnodeoncreate|--addnodeonresume}]  [--readahead   [+]<sec‐
	      Creates  a device with the given name.  If table_file or <table>
	      is supplied, the table is loaded and made live.  Otherwise a ta‐
	      ble  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  a  device  will  appear  as
	      /dev/mapper/<device-name>.  See below for information on the ta‐
	      ble format.

       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 includ‐
	      ing the list of report fields.

       info   [device_name]
	      Outputs some brief information about the device in the form:
		      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  [--noheadings]  [--separator   separator]   [-o
	      fields] [-O|--sort sort_fields] [device_name]
	      Output you can customise.	 Fields are comma-separated and chosen
	      from the following list: name, major, minor,  attr,  open,  seg‐
	      ments,   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 dis‐
	      played: 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 stan‐
	      dard input.

       wipe_table device_name
	      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).

       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.

       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).

       remove [-f|--force] [--retry] device_name
	      Removes a device.	 It will no  longer  be	 visible  to  dmsetup.
	      Open  devices  cannot  be removed except with older kernels that
	      contain a version of device-mapper prior to 4.8.0.  In this case
	      the  device  will	 be deleted when its open_count drops to zero.
	      From version 4.8.0 onwards, if a device can't be removed because
	      an uninterruptible process is waiting for I/O to return from it,
	      adding --force will replace the table with one  that  fails  all
	      I/O,  which  might allow the process to be killed. 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.

       remove_all [-f|--force]
	      Attempts to remove all device definitions i.e. reset the driver.
	      Use with care!  From version 4.8.0 onwards, if devices can't  be
	      removed because uninterruptible processes are waiting for I/O to
	      return from them, adding --force will replace the table with one
	      that  fails all I/O, which might allow the process to be killed.
	      This also runs mknodes afterwards.

       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}] [--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.  Default
	      subsystem is LVM.

       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 sup‐
	      ports 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  [--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  dis‐
	      played.	Encryption keys are suppressed in the table output for
	      the crypt target unless the --showkeys parameter is supplied.

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

       udevcomplete cookie
	      Wake any processes that are waiting for udev  to	complete  pro‐
	      cessing 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 process‐
	      ing.  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 command.

       udevflags cookie
	      Parses given cookie value and extracts any  udev	control	 flags
	      encoded.	 The output is in environment key format that is suit‐
	      able 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 sta‐

       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

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

	      Returns  blocks  of  zeroes  on reads.  Any data written is dis‐
	      carded silently.	This  is  a  block-device  equivalent  of  the
	      /dev/zero character-device data sink described in null(4).

       More complex targets include:

	      Transparent  encryption of block devices using the kernel crypto

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

	      Creates  a  similar  mapping  to	the linear target but exhibits
	      unreliable behaviour periodically.  Useful for simulating	 fail‐
	      ing devices when testing.

	      Mirrors data across two or more devices.

	      Mediates access through multiple paths to the same device.

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

	      Supports snapshots of devices.

       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.)

       # 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

	      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

       Original version: Joe Thornber (

       Device-mapper resource page:

Linux				  Apr 06 2006			    DMSETUP(8)

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