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dmsetup — low level logical volume management
Contents
Commands
cleardevice_name
Destroys the table in the inactive table slot for device_name.
createdevice_name [-n|--notable|--tabletable|table_file] [--readahead [+]sectors|auto|none] [-u|--uuiduuid] [--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 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 de‐
faults 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 [-ooptions] [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 [--countcount] [--intervalseconds] [--noheadings|--headings] [-ofields]
[-O|--sortsort_fields] [--nameprefixes] [--separatorseparator] [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)uspend‐
ed, (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 col‐
umn.
ls [--targettarget_type] [-ooptions] [--execcommand] [--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 following options: devno (major and minor
pair, used by default), blkdevname (block device name), devname (map name for device-mapper de‐
vices, 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|reloaddevice_name [--tabletable|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 de‐
vice 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.
messagedevice_namesectormessage
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 de‐
ferred removal of open devices - the device will be removed when the last user closes it. The de‐
ferred removal feature is supported since version 4.27.0 of the device-mapper driver available in
upstream kernel version 3.13. (Use dmsetupversion to check this.) If an attempt to remove a de‐
vice 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 er‐
ror 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 after‐
wards. 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.
renamedevice_namenew_name
Renames a device.
renamedevice_name--setuuiduuid
Sets the uuid of a device that was created without a uuid. After a uuid has been set it cannot be
changed.
resumedevice_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.
setgeometrydevice_namecylheadsectstart
Sets the device geometry to C/H/S.
splitnamedevice_name [subsystem]
Splits given devicename into subsystem constituents. The default subsystem is LVM. LVM current‐
ly 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.
statscommand [options]
Manages IO statistics regions for devices. See dmstats(8) for more details.
status [--targettarget_type] [--noflush] [device_name...]
Outputs status information for each of the device's targets. With --target, only information re‐
lating to the specified target type any is displayed. With --noflush, the thin target (from ver‐
sion 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 [--concise] [--targettarget_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. 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 affect‐
ed 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.
udevcompletecookie
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 --ude‐vcookie 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.
udevflagscookie
Parses given cookie value and extracts any udev control flags encoded. The output is in environ‐
ment 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 un‐
derlying semaphore. If the cookie is not given directly, the command will try to use a value de‐
fined 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_tabledevice_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).
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.
Description
dmsetup manages logical devices that use the device-mapper driver. Devices are created by loading a ta‐
ble 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 dmsetupinfo-c--noheadings-jmajor-mminor.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 alterna‐
tive 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.
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
Name
dmsetup — low level logical volume management
Options
--addnodeoncreate
Ensure /dev/mapper node exists after dmsetupcreate.
--addnodeonresume
Ensure /dev/mapper node exists after dmsetupresume (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.
--countcount
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 (syn‐
onym 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.
--intervalseconds
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.
--manglenameauto|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 man‐
gling mode is one of: auto (only do the mangling if not mangled yet, do nothing if already man‐
gled, 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 char‐
acter 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|--majormajor
Specify the major number.
-m|--minorminor
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.
--headingsnone|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 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 synchronize with udev when creating, renaming or removing devices.
-o|--optionsoptions
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|--selectselection
Process only items that match selection criteria. If the command is producing report output,
adding the "selected" column (-oselected) 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 dmsetupinfo-c-Shelp command.
--tabletable
Specify a one-line table directly on the command line. See below for more information on the ta‐
ble format.
--udevcookiecookie
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|--uuiduuid
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.
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 Apr 06 2006 DMSETUP(8)
Synopsis
dmsetupcleardevice_namedmsetupcreatedevice_name [-n|--notable|--tabletable|table_file] [--readahead [+]sectors|auto|none]
[-u|--uuiduuid] [--addnodeoncreate|--addnodeonresume]
dmsetupcreate--concise [concise_device_specification]
dmsetupdeps [-ooptions] [device_name...]
dmsetuphelp [-c|-C|--columns]
dmsetupinfo [device_name...]
dmsetupinfo-c|-C|--columns [--countcount] [--intervalseconds] [--noheadings|--headings] [-ofields]
[-O|--sortsort_fields] [--nameprefixes] [--separatorseparator] [device_name]
dmsetuploaddevice_name [--tabletable|table_file]
dmsetupls [--targettarget_type] [-ooptions] [--execcommand] [--tree]
dmsetupmangle [device_name...]
dmsetupmeasure [device_name...]
dmsetupmessagedevice_namesectormessagedmsetupmknodes [device_name...]
dmsetupreloaddevice_name [--tabletable|table_file]
dmsetupremove [-f|--force] [--retry] [--deferred] device_name...
dmsetupremove_all [-f|--force] [--deferred]
dmsetuprenamedevice_namenew_namedmsetuprenamedevice_name--setuuiduuiddmsetupresumedevice_name... [--addnodeoncreate|--addnodeonresume] [--noflush] [--nolockfs]
[--readahead [+]sectors|auto|none]
dmsetupsetgeometrydevice_namecylheadsectstartdmsetupsplitnamedevice_name [subsystem]
dmsetupstatscommand [options]
dmsetupstatus [--targettarget_type] [--noflush] [device_name...]
dmsetupsuspend [--nolockfs] [--noflush] device_name...
dmsetuptable [--concise] [--targettarget_type] [--showkeys] [device_name...]
dmsetuptargetsdmsetupudevcompletecookiedmsetupudevcomplete_all [age_in_minutes]
dmsetupudevcookiedmsetupudevcreatecookiedmsetupudevflagscookiedmsetupudevreleasecookie [cookie]
dmsetupversiondmsetupwait [--noflush] device_name [event_nr]
dmsetupwipe_tabledevice_name... [-f|--force] [--noflush] [--nolockfs]
devmap_namemajorminordevmap_namemajor:minorTable Format
Each line of the table specifies a single target and is of the form:
logical_start_sectornum_sectorstarget_typetarget_args
Simple target types and target args include:
lineardestination_devicestart_sector
The traditional linear mapping.
stripednum_stripeschunk_size [destinationstart_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-de‐
vice 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.)
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