dmsetup man page on ElementaryOS

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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
       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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