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|--headings none|abbrev|full|0|1|2] [-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 device_name ... [--nolockfs] [--noflush]
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 device_name [--noflush] [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 to 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 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.
--headings none|abbrev|full|0|1|2
Type of headings line to use for columnar output.
none or 0 – No headings.
abbrev or 1 – Column name abbreviations.
full or 2 – Full column names.
--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, e.g., 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 synchronize 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 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 information on the table format.
--udevcookie cookie
Use cookie for udev synchronization.
Note: Same cookie should be used for same type of operations
i.e. creation of multiple different devices. It's not advised
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 synchronization is enabled, verify that udev operations
get performed correctly 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 --notable 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 the 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 specified by a comma-separated list: name, uuid,
minor number, flags, comma-separated table 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 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 customised by
the 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
Read Ahead: sectors
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|--headings none|abbrev|full|0|1|2] [-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 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 execute a
command for each device. The device name is appended to the
supplied command. Device names on output can be customised by
the 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-separated 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.
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 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).
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 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 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
nondeterministic 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.
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 device_name ... [--nolockfs] [--noflush]
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 [--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 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 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 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
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_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.
version
Outputs version information.
wait device_name [--noflush] [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 (16 KiB) 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 (e.g., a spindle) by
dynamically migrating some of its data to a faster smaller
device (e.g., 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
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>+][;<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 --manglename option.
AUTHORS
Original version: Joe Thornber <thornber@redhat.com>
SEE ALSO
dmstats(8), udev(7), udevadm(8)
LVM2 resource page: <https://www.sourceware.org/lvm2>
Device-mapper resource page: <https://www.sourceware.org/dm>
Linux Mar 26 2025 DMSETUP(8)
dmsetup \(em low level logical volume management