dmsetup <root
DMSETUP(8)                             MAINTENANCE COMMANDS                            DMSETUP(8)

NAME
       dmsetup — low level logical volume management

SYNOPSIS
       dmsetup clear device_name
       dmsetup create device_name [-u|--uuid uuid] [--addnodeoncreate|--addnodeonresume]
                [-n|--notable|--table {table|table_file}] [--readahead {[+]sectors|auto|none}]
       dmsetup deps [-o options] [device_name]
       dmsetup help [-c|-C|--columns]
       dmsetup info [device_name]
       dmsetup info -c|-C|--columns [--count count] [--interval seconds] [--nameprefixes]
                [--noheadings] [-o fields] [-O|--sort sort_fields] [--separator separator]
                [device_name]
       dmsetup load device_name [--table {table|table_file}]
       dmsetup ls [--target target_type] [--exec command] [--tree] [-o options]
       dmsetup mangle [device_name]
       dmsetup message device_name sector message
       dmsetup mknodes [device_name]
       dmsetup reload device_name [--table {table|table_file}]
       dmsetup remove [-f|--force] [--retry] [--deferred] device_name
       dmsetup remove_all [-f|--force] [--deferred]
       dmsetup rename device_name new_name
       dmsetup rename device_name --setuuid uuid
       dmsetup resume device_name [--addnodeoncreate|--addnodeonresume] [--noflush] [--nolockfs]
                [--readahead {[+]sectors|auto|none}]
       dmsetup setgeometry device_name cyl head sect start
       dmsetup splitname device_name [subsystem]
       dmsetup stats command [options]
       dmsetup status [--target target_type] [--noflush] [device_name]
       dmsetup suspend [--nolockfs] [--noflush] device_name
       dmsetup table [--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 sup‐
       ported      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 prob‐
              lems.  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
              interrupted.  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
              instead of the live table.  Requires kernel driver version 4.16.0 or above.

       --interval seconds
              Specify the  interval  in  seconds  between  successive  iterations  for  repeating
              reports.  If  --interval  is specified but --count is not, reports will continue to
              repeat until interrupted.  The default interval is one second.

       --manglename {auto|hex|none}
              Mangle any character not on a whitelist using mangling_mode when processing device-
              mapper  device names and UUIDs. The names and UUIDs are mangled on input and unman‐
              gled 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 outstading 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 cho‐
              sen by the kernel.  The value none is equivalent to specifying zero.

       -r|--readonly
              Set the table being loaded read-only.

       -S|--select selection
              Display  only  rows  that match selection criteria. All rows are displayed with the
              additional "selected" column (-o selected) showing 1 if the row matches the  selec‐
              tion 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 informa‐
              tion 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
              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  cor‐
              rectly 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 [-u|--uuid uuid] [--addnodeoncreate|--addnodeonresume]
              [-n|--notable|--table {table|table_file}] [--readahead {[+]sectors|auto|none}]
              Creates a device with the given name.  If table or table_file is supplied, the  ta‐
              ble  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 subse‐
              quent 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.

       deps [-o options] [device_name]
              Outputs  a  list  of devices referenced by the live table for the specified device.
              Device names on output can be customised by following  options:  devno  (major  and
              minor pair, used by default), blkdevname (block device name), devname (map name for
              device-mapper devices, equal to blkdevname otherwise).

       help [-c|-C|--columns]
              Outputs a summary of the commands  available,  optionally  including  the  list  of
              report fields.

       info [device_name]
              Outputs some brief information about the device in the form:
                      State: SUSPENDED|ACTIVE, READ-ONLY
                      Tables present: LIVE and/or INACTIVE
                      Open reference count
                      Last event sequence number (used by wait)
                      Major and minor device number
                      Number of targets in the live table
                      UUID

       info -c|-C|--columns [--count count] [--interval seconds] [--nameprefixes] [--noheadings]
              [-o fields] [-O|--sort sort_fields] [--separator separator] [device_name]
              Output you can customise.  Fields are comma-separated and chosen from the following
              list:  name,  major,  minor,  attr,  open, segments, events, uuid.  Attributes are:
              (L)ive, (I)nactive, (s)uspended, (r)ead-only, read-(w)rite.  Precede the list  with
              '+' to append to the default selection of columns instead of replacing it.  Precede
              any sort field with '-' for a reverse sort on that column.

       ls [--target target_type] [--exec command] [--tree] [-o options]
              List device names.  Optionally only list devices that have at least one  target  of
              the specified type.  Optionally execute a command for each device.  The device name
              is appended to the supplied command.  Device names on output can be  customised  by
              following options: devno (major and minor pair, used by default), blkdevname (block
              device name), devname (map name for device-mapper devices, equal to blkdevname oth‐
              erwise).   --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  nec‐
              essary.  Any  character not on the whitelist will be mangled based on the --mangle‐
              name 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 incor‐
              rect UUIDs are reported only and they must be manually  corrected  by  deactivating
              the  device first and then reactivating it with proper mangling mode used (see also
              --manglename).

       message device_name sector message
              Send message to target. If sector not needed use 0.

       mknodes [device_name]
              Ensure that the node in /dev/mapper for device_name is correct.  If no  device_name
              is supplied, ensure that all nodes in /dev/mapper correspond to mapped devices cur‐
              rently 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 ver‐
              sion 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  nonde‐
              terministic result.

       remove_all [-f|--force] [--deferred]
              Attempts  to  remove  all device definitions i.e. reset the driver.  This also runs
              mknodes afterwards.  Use with care!  Open devices cannot  be  removed,  but  adding
              --force will replace the table with one that fails all I/O.  --deferred will enable
              deferred removal of open devices - the device will be removed when  the  last  user
              closes  it.   The deferred removal feature is supported since version 4.27.0 of the
              device-mapper driver available in upstream kernel version 3.13.

       rename device_name new_name
              Renames a device.

       rename device_name --setuuid uuid
              Sets the uuid of a device that was created without a uuid.  After a uuid  has  been
              set it cannot be changed.

       resume device_name [--addnodeoncreate|--addnodeonresume] [--noflush] [--nolockfs]
              [--readahead {[+]sectors|auto|none}]
              Un-suspends a device.  If an inactive table  has  been  loaded,  it  becomes  live.
              Postponed I/O then gets re-queued for 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.

       stats command [options]
              Outputs status information for each of the device's targets.  With  --target,  only
              information  relating  to  the  specified  target  type  any  is  displayed.   With
              --noflush, the thin target (from version  1.3.0)  doesn't  commit  any  outstanding
              changes to disk before reporting its statistics.

       suspend [--nolockfs] [--noflush] device_name
              Suspends  a device.  Any I/O that has already been mapped by the device but has not
              yet completed will be flushed.  Any further I/O to that device  will  be  postponed
              for  as  long  as  the  device is suspended.  If there's a filesystem on the device
              which supports the operation, an attempt will be  made  to  sync  it  first  unless
              --nolockfs  is  specified.   Some targets such as recent (October 2006) versions of
              multipath may support the --noflush option.  This lets outstanding I/O that has not
              yet reached the device to remain unflushed.

       table [--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 spec‐
              ified target type is displayed.  Encryption keys are suppressed in the table output
              for the crypt target unless the --showkeys parameter is supplied.

       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).

              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 explic‐
              itly 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  sema‐
              phore 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_ = '1',
              DM_UDEV_FLAG = '1' otherwise.  Subsystem udev flags don't have  sym‐
              bolic   names   assigned   and   these  ones  are  always  reported  as  DM_SUBSYS‐
              TEM_UDEV_FLAG = '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 release 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 fol‐
              lows:
                      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
              periodically.  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

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
              --manglename option.

AUTHORS
       Original version: Joe Thornber 

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)

Go-to-top  




Designed by SanjuD(@ngineerbabu)

<>