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NAME | SYNOPSIS | DESCRIPTION | OPTIONS | COMMANDS | TABLE FORMAT | EXAMPLES | CONCISE FORMAT | EXAMPLES | ENVIRONMENT VARIABLES | AUTHORS | SEE ALSO | COLOPHON |
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DMSETUP(8) MAINTENANCE COMMANDS DMSETUP(8)
dmsetup — low level logical volume management
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|--addnodeonre‐
sume] [--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
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.
--addnodeoncreate
Ensure /dev/mapper node exists after dmsetup create.
--addnodeonresume
Ensure /dev/mapper node exists after dmsetup resume (de‐
fault 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 notice‐
ably.
-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 in‐
cluding the list of report fields (synonym with help com‐
mand).
--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 itera‐
tions for repeating reports. If --interval is specified but
--count is not, reports will continue to repeat until in‐
terrupted. 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 out‐
put 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 en‐
vironment 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. Use‐
ful 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 suspend‐
ing 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 re‐
moving 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 mini‐
mum 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 comparison oper‐
ators. As a quick help and to see full list of column names
that can be used in selection and the set of supported se‐
lection operators, check the output of dmsetup in‐
fo -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 opera‐
tions get performed correctly and try to fix up the device
nodes afterwards if not.
--version
Display the library and kernel driver version.
clear device_name
Destroys the table in the inactive table slot for de‐
vice_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 ta‐
ble_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 specifi‐
cation. Each device is specified 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 spec‐
ifications 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 cus‐
tomised 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 in‐
cluding 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. Pre‐
cede 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 exe‐
cute a command for each device. The device name is append‐
ed 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), de‐
vname (map name for device-mapper devices, equal to blkdev‐
name otherwise). --tree displays dependencies between de‐
vices as a tree. It accepts a comma-separate list of op‐
tions. 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 char‐
acters (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 in‐
correct UUIDs are reported only and they must be manually
corrected by deactivating the device first and then reacti‐
vating it with proper mangling mode used (see also --man‐
glename).
measure [device_name...]
Show the data that device_name would report to the IMA sub‐
system if a measurement was triggered at the current time.
This is for debugging and does not actually trigger a mea‐
surement.
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 cor‐
rect. 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 re‐
place 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 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 re‐
place 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, Logi‐
cal Volume and any internal Layer with a hyphen as separa‐
tor. 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 tar‐
gets. 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 statis‐
tics.
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 un‐
flushed.
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 sep‐
arate devices. Backslashes escape any commas, 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 min‐
utes. Any process waiting on a cookie will be resumed im‐
mediately.
udevcookie
List all existing cookies. Cookies are system-wide sema‐
phores with keys prefixed by two predefined bytes (0x0D4D).
udevcreatecookie
Creates a new cookie to synchronize actions with udev pro‐
cessing. 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 gener‐
ate 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. Al‐
ternatively, 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 un‐
til 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_ = '1', DM_UDEV_FLAG
= '1' otherwise. Subsystem udev flags don't have symbolic
names assigned and these ones are always reported as
DM_SUBSYSTEM_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).
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 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/de‐
vice-mapper directory in the kernel source tree. (Your distribu‐
tion 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
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 as‐
signs 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 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
ENVIRONMENT VARIABLES top
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 --ude‐
vcookie option.
DM_DEFAULT_NAME_MANGLING_MODE
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: ⟨https://www.sourceware.org/lvm2⟩
Device-mapper resource page: ⟨http://sources.redhat.com/dm⟩
COLOPHON top
This page is part of the lvm2 (Logical Volume Manager 2) project.
Information about the project can be found at
⟨http://www.sourceware.org/lvm2/⟩. If you have a bug report for
this manual page, see ⟨https://github.com/lvmteam/lvm2/issues⟩.
This page was obtained from the project's upstream Git repository
⟨git://sourceware.org/git/lvm2.git⟩ on 2025-02-02. (At that time,
the date of the most recent commit that was found in the
repository was 2025-01-31.) 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
[email protected]
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)
HTML rendering created 2025-02-02
by Michael Kerrisk,
author of
The Linux Programming Interface.
For details of in-depth
Linux/UNIX system programming training courses
that I teach, look here.
Hosting by jambit GmbH.
