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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] [de‐
vice_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 dri‐
ver. 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 no‐
ticeably.
-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
including the list of report fields (synonym with help
command).
--inactive
When returning any table information from the kernel re‐
port on the inactive table instead of the live table. Re‐
quires 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
interrupted. The default interval is one second.
--manglename auto|hex|none
Mangle any character not on a whitelist using man‐
gling_mode when processing device-mapper device names and
UUIDs. The names and UUIDs are mangled on input and unman‐
gled 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 man‐
gling) 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.
--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
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 min‐
imum value which will not be used if it is smaller than
the value chosen by the kernel. The value none is equiva‐
lent 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 op‐
erators. As a quick help and to see full list of column
names that can be used in selection and the set of sup‐
ported selection operators, check the output of dmset‐
up 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 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 oper‐
ations get performed correctly and try to fix up the de‐
vice 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
specifications of different devices. Use a backslash to
escape the following character, for example a comma or se‐
mi-colon in a name or table. See also CONCISE FORMAT be‐
low.
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
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] [-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 ex‐
ecute a command for each device. The device name is ap‐
pended 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 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 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 ker‐
nel 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 current‐
ly 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 dmset‐
up. Open devices cannot be removed, but adding --force
will replace the table with one that fails all I/O. --de‐
ferred 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. --de‐
ferred 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, Log‐
ical Volume and any internal Layer with a hyphen as sepa‐
rator. 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 us‐
ing 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 speci‐
fied. 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 re‐
main 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 sup‐
pressed in the table output for crypt and integrity tar‐
gets unless the --showkeys parameter is supplied. Kernel
key references prefixed with : are not affected by the pa‐
rameter 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 FOR‐
MAT 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.
Alternatively, we can export this value into the environ‐
ment 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 sys‐
tem-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_posi‐
tion> = '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 cook‐
ie value and clean up the cookie with underlying sema‐
phore. If the cookie is not given directly, the command
will try to use a value defined by DM_UDEV_COOKIE environ‐
ment 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 re‐
lease 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 ex‐
hibits unreliable behaviour periodically. Useful for sim‐
ulating 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 for‐
mats and status lines, please read the files in the Documenta‐
tion/device-mapper directory in the kernel source tree. (Your
distribution might include a copy of this information in the doc‐
umentation 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:
<name>,<uuid>,<minor>,<flags>,<table>[,<table>+]
[;<dev_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 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.
# 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
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.
Original version: Joe Thornber <[email protected]>
dmstats(8), udev(7), udevadm(8)
LVM2 resource page: ⟨https://www.sourceware.org/lvm2⟩
Device-mapper resource page: ⟨http://sources.redhat.com/dm⟩
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 2024-06-14. (At that
time, the date of the most recent commit that was found in the
repository was 2024-06-11.) 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)
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