Manual: dmsetup
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] [-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 [--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
DESCRIPTION
dmsetup manages logical devices that use the device-mapper driver. Devices are created by loading a table that spec‐
ifies 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 rea‐
sons) 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 continue until interrupted. The default in‐
terval 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 speci‐
fied but --count is not, reports will continue to repeat until interrupted. The default interval is one sec‐
ond.
--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: au‐
to (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 abbrevia‐
tions. 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|--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 "se‐
lected" 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 sup‐
ported comparison operators. As a quick help and to see full list of column names that can be used in selec‐
tion 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. cre‐
ation 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
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-separat‐
ed 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 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] [--noheadings|--headings] [-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. Option‐
ally 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 otherwise). --tree dis‐
plays 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 necessary. Any character not on the whitelist will be man‐
gled 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 man‐
gling 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 ver‐
sion 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 sec‐
onds 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 hy‐
phen 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 [--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] [--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 com‐
mands. 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 sepa‐
rate the name, uuid, minor device number, flags ('ro' or 'rw') and the table (if present). Semi-colons sepa‐
rate 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 re‐
sumed 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 de‐
fine 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 automat‐
ically 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 for‐
mat 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 sem‐
aphore. If the cookie is not given directly, the command will try to use a value defined by DM_UDEV_COOKIE en‐
vironment 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 tar‐
get (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 ta‐
ble(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 (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 in‐
formation 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:
,,,,[,+][;,,,,[,+]]
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
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)