DMSETUP(8) MAINTENANCE COMMANDS DMSETUP(8)
NAME
dmsetup — low level logical volume management
SYNOPSIS
dmsetup clear device_name
dmsetup create device_name [-u|--uuid uuid] [--addnodeoncreate|--addnodeonresume] [-n|--notable|--table
{table|table_file}] [--readahead {[+]sectors|auto|none}]
dmsetup deps [-o options] [device_name]
dmsetup help [-c|-C|--columns]
dmsetup info [device_name]
dmsetup info -c|-C|--columns [--count count] [--interval seconds] [--nameprefixes] [--noheadings] [-o fields]
[-O|--sort sort_fields] [--separator separator] [device_name]
dmsetup load device_name [--table {table|table_file}]
dmsetup ls [--target target_type] [--exec command] [--tree] [-o options]
dmsetup mangle [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 [--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 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 histori‐
cal reasons) is equivalent to dmsetup info -c --noheadings -j major -m minor.
OPTIONS
--addnodeoncreate
Ensure /dev/mapper node exists after dmsetup create.
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 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.
--noflush Do not flush outstading 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.
-r|--readonly
Set the table being loaded read-only.
-S|--select selection
Display only rows that match selection criteria. All rows are displayed with the additional "selected"
column (-o selected) showing 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 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
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 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 [-u|--uuid uuid] [--addnodeoncreate|--addnodeonresume] [-n|--notable|--table
{table|table_file}] [--readahead {[+]sectors|auto|none}]
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 informa‐
tion on the table format.
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]
info -c|-C|--columns [--count count] [--interval seconds] [--nameprefixes] [--noheadings] [-o fields]
[-O|--sort sort_fields] [--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] [--exec command] [--tree] [-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
default), blkdevname (block device name), devname (map name for device-mapper devices, equal to blkdev‐
name 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; blkdev‐
name; 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 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).
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.
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 pre‐
cise 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 [--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. Encryp‐
tion keys are suppressed in the table output for the crypt target unless the --showkeys parameter is
supplied.
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. Nor‐
mally we don't need to create cookies since dmsetup creates and destroys them for each action automati‐
cally. 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
Waits for all pending udev processing bound to given cookie value and clean up the cookie with underly‐
ing 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 [--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 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 (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 exhibits unreliable behaviour periodically. Useful
for simulating failing devices when testing.
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
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 <[email protected]>
SEE ALSO
dmstats(8), udev(7), udevadm(8)
LVM2 resource page: https://www.sourceware.org/lvm2/
Device-mapper resource page: http://sources.redhat.com/dm/
Linux Apr 06 2006 DMSETUP(8)
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