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 dis- tributed and is supported only for historical reasons) 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 interval is one second.

-f|--force Try harder to complete operation.

-h|--help Outputs a summary of the commands available, optionally includ- ing 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 man- gled 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 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, dont 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.

--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 auto- matically. 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 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 opera- tions 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 information 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] Outputs a summary of the commands available, optionally includ- ing 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] [--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, seg- ments, 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 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|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 stan- dard 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.

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 hyphen as separator. Any hyphens within the names are doubled to escape them. The precise encod- ing 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.

stats command [options] Outputs status information for each of the devices 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 sup- ports 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 dis- played. Encryption 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 pro- cessing 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 process- ing. The output is a cookie value. Normally we dont 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 --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 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.

udevflags cookie Parses given cookie value and extracts any udev control flags encoded. The output is in environment key format that is suit- able 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 underlying 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) doesnt 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 devices 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 dis- carded 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 dynam- ically 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 kernels 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.)

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 alter- native to using --manglename option.

AUTHORS Original version: Joe Thornber <>

SEE ALSO dmstats(8), udev(7), udevadm(8)

LVM2 resource page: Device-mapper resource page:

Linux Apr 06 2006 DMSETUP(8)