dmsetup — low level logical volume management
create device_name [-u|--uuid uuid]
create --concise [concise_device_specification]
deps [-o options] [device_name...]
info -c|-C|--columns [--count count]
[--interval seconds] [--nameprefixes]
[--noheadings] [-o fields] [-O|--sort
sort_fields] [--separator separator]
load device_name [--table
ls [--target target_type] [--exec command]
[--tree] [-o options]
message device_name sector message
reload device_name [--table
remove [-f|--force] [--retry] [--deferred]
remove_all [-f|--force] [--deferred]
rename device_name new_name
rename device_name --setuuid uuid
setgeometry device_name cyl head sect
splitname device_name [subsystem]
stats command [options]
status [--target target_type] [--noflush]
suspend [--nolockfs] [--noflush]
table [--concise] [--target target_type]
wait [--noflush] device_name [event_nr]
wipe_table device_name... [-f|--force]
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
node exists after dmsetup create
node exists after dmsetup resume
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.
Specify the number of times to repeat a report. Set this to zero continue until
interrupted. The default interval is one second.
Try harder to complete operation.
Outputs a summary of the commands available, optionally including the list of
report fields (synonym with help
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
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
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
do the mangling if not mangled yet, do nothing if already mangled, error on
(always do the mangling) and none
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
Specify the major number.
Specify the minor number.
When creating a device, don't load any table.
Add a "DM_" prefix plus the field name to the output. Useful with
to produce a list of field=value pairs that can be used to
set environment variables (for example, in udev
Suppress the headings line when using columnar output.
Do not flush outstading I/O when suspending a device, or do not commit
thin-pool metadata when obtaining thin-pool status.
Do not attempt to synchronize filesystem eg, when suspending a device.
Tell the kernel not to supply the open reference count for the device.
Do not allow udev to manage nodes for devices in device-mapper directory.
Do not synchronise with udev when creating, renaming or removing devices.
Specify which fields to display.
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
equivalent to specifying zero.
Set the table being loaded read-only.
Process only items that match selection
criteria. If the command is
producing report output, adding the "selected" column ( -o
) displays all rows and shows 1 if the row matches the
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
Specify a one-line table directly on the command line. See below for more
information on the table format.
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.
Specify the uuid
Answer yes to all prompts automatically.
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.
Destroys the table in the inactive table slot for device_name.
Creates a device with the given name. If table
supplied, the table is loaded and made live. Otherwise a table is read from
standard input unless --notable
is used. The optional uuid
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
is created. See below for more information on
the table format.
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.
Outputs a list of devices referenced by the live table for the specified device.
Device names on output can be customised by following options
(major and minor pair, used by default), blkdevname
device name), devname
(map name for device-mapper devices, equal to
Outputs a summary of the commands available, optionally including the list of
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
] [-o fields
] [--separator separator
Output you can customise. Fields are comma-separated and chosen from the
following list: name
. Attributes are:
)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.
] [--exec command
] [-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
(block device name), devname
(map name for
device-mapper devices, equal to blkdevname otherwise). --tree
dependencies between devices as a tree. It accepts a comma-separate list of
. Some specify the information displayed against each node:
. Others specify how the tree is displayed:
into the inactive table slot for
device_name. If neither is supplied, reads a table from standard input.
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
device_name sector message
Send message to target. If sector not needed use 0.
Ensure that the node in /dev/mapper
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.
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
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
, as udev may
start to process udev rules in the middle of error target replacement and
result in nondeterministic result.
Attempts to remove all device definitions i.e. reset the driver. This also runs
afterwards. Use with care! Open devices cannot be removed, but
will replace the table with one that fails all I/O.
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.
Renames a device.
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.
Un-suspends a device. If an inactive table has been loaded, it becomes live.
Postponed I/O then gets re-queued for processing.
device_name cyl head sect start
Sets the device geometry to C/H/S.
Splits given device name
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.
Manages IO statistics regions for devices. See dmstats
(8) for more
Outputs status information for each of the device's targets. With
, 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.
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
This lets outstanding I/O that has not yet reached the device to remain
] [--target target_type
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 the crypt target unless the
parameter is supplied. Kernel key references prefixed with
are not affected by the parameter and get displayed always. With
, 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.
Displays the names and versions of the currently-loaded targets.
Wake any processes that are waiting for udev to complete processing the
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 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
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.
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.
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
Outputs version information.
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,
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.
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
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
- Creates a striped area.
e.g. striped 2 32 /dev/hda1 0 /dev/hdb1 0 will map the first chunk (16k) as
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
discarded silently. This is a block-device equivalent of the
/dev/zero character-device data sink described in
More complex targets include:
- Improves performance of a block device (eg, a spindle) by
dynamically migrating some of its data to a faster smaller device (eg, an
- Transparent encryption of block devices using the kernel
- 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 failing devices
- Mirrors data across two or more devices.
- Mediates access through multiple paths to the same
- Offers an interface to the kernel's software raid driver,
- 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.)
# 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:
- The name of the device.
- The UUID of the device (or empty).
- The minor number of the device. If empty, the kernel
assigns a suitable minor number.
- 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
- One line of the table. See TABLE FORMAT above.
# A simple linear read-only device
test-linear-small,,,ro,0 2097152 linear /dev/loop0 0, 2097152 2097152 linear
# 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
- 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
- A default mangling mode. Defaults to
"auto" and it is an alternative to using
Original version: Joe Thornber <firstname.lastname@example.org>
LVM2 resource page: https://www.sourceware.org/lvm2/
Device-mapper resource page: http://sources.redhat.com/dm/