dmsetup - low level logical volume management


dmsetup help [-c|-C|--columns]

dmsetup create device_name [-u uuid] [--notable | --table <table> | table_file]

dmsetup remove [-f|--force] device_name

dmsetup remove_all [-f|--force]

dmsetup suspend [--nolockfs] [--noflush] device_name

dmsetup resume device_name

dmsetup load device_name [--table <table> | table_file]

dmsetup clear device_name

dmsetup reload device_name [--table <table> | table_file]

dmsetup rename device_name new_name

dmsetup message device_name sector message

dmsetup ls [--target target_type] [--exec command] [--tree [-o options]]

dmsetup info [device_name]

dmsetup info -c|-C|--columns [--noheadings] [--separator separator] [-o fields] [-O|--sort sort_fields] [device_name]

dmsetup deps [device_name]

dmsetup status [--target target_type] [device_name]

dmsetup table [--target target_type] [--showkeys] [device_name]

dmsetup wait device_name [event_nr]

dmsetup mknodes [device_name]

dmsetup udevcreatecookie

dmsetup udevreleasecookie [cookie]

dmsetup udevflags cookie

dmsetup udevcomplete cookie

dmsetup udevcomplete_all

dmsetup udevcookies

dmsetup targets

dmsetup version

dmsetup setgeometry device_name cyl head sect start

dmsetup splitname device_name [subsystem]

devmap_name major minor

devmap_name major:minor


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 command as devmap_name is equivalent to
\fBdmsetup info -c --noheadings -j major\fB -m \fIminor.


Display output in columns rather than as Field: Value lines.

Outputs a summary of the commands available, optionally including the list of report fields (synonym with help command).

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.

\fB-j|--major \fImajor
Specify the major number.

\fB-m|--minor \fIminor
Specify the minor number.

Suppress the headings line when using columnar output.

Tell the kernel not to supply the open reference count for the device.

When creating a device, don't load any table.

\fB--udevcookie \fIcookie
Use cookie for udev synchronisation.

\fB--noudevrules Do not allow udev to manage nodes for devices in device-mapper directory.

\fB--noudevsync Do not synchronise with udev when creating, renaming or removing devices.

Specify which fields to display.

Set the table being loaded read-only.

\fB--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. "None" is equivalent to specifying zero.

\fB--table <table>
Specify a one-line table directly on the command line.

Specify the uuid.

Answer yes to all prompts automatically.

\fB-v|--verbose [-v|--verbose]
Produce additional output.

Display the library and kernel driver version.


\fBcreate device_name [-u uuid] [--notable | --table <table> | table_file]
Creates a device with the given name. If table_file or <table> 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 a device will appear as /dev/device-mapper/<device-name>. See below for information on the table format.

\fBdeps [device_name]
Outputs a list of (major, minor) pairs for devices referenced by the live table for the specified device.

\fBhelp [-c|-C|--columns]
Outputs a summary of the commands available, optionally including the list of report fields.

\fBinfo [device_name]
Outputs some brief information about the device in the form:
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

\fBinfo -c|-C|--columns [--noheadings] [--separator separator] [-o fields] [-O|--sort sort_fields] [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.

\fBls [--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. --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; active, open, rw, uuid. Others specify how the tree is displayed: ascii, utf, vt100; compact, inverted, notrunc.

\fBload|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.

\fBmessage device_name sector message
Send message to target. If sector not needed use 0.

\fBmknodes [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.

\fBremove [-f|--force] device_name
Removes a device. It will no longer be visible to dmsetup. Open devices cannot be removed except with older kernels that contain a version of device-mapper prior to 4.8.0. In this case the device will be deleted when its open_count drops to zero. From version 4.8.0 onwards, if a device can't be removed because an uninterruptible process is waiting for I/O to return from it, adding --force will replace the table with one that fails all I/O, which might allow the process to be killed.

\fBremove_all [-f|--force]
Attempts to remove all device definitions i.e. reset the driver. Use with care! From version 4.8.0 onwards, if devices can't be removed because uninterruptible processes are waiting for I/O to return from them, adding --force will replace the table with one that fails all I/O, which might allow the process to be killed. This also runs mknodes afterwards.

\fBrename device_name new_name
Renames a device.

\fBresume device_name
Un-suspends a device. If an inactive table has been loaded, it becomes live. Postponed I/O then gets re-queued for processing.

\fBsetgeometry device_name cyl head sect start
Sets the device geometry to C/H/S.

\fBsplitname device_name [subsystem]
Splits given device name into subsystem constituents. Default subsystem is LVM.

\fBstatus [--target target_type] [device_name]
Outputs status information for each of the device's targets. With --target, only information relating to the specified target type is displayed.

\fBsuspend [--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.

\fBtable [--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. Encryption keys are suppressed in the table output for the crypt target unless the --showkeys parameter is supplied.

Displays the names and versions of the currently-loaded targets.

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 --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.

\fBudevreleasecookie [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.

\fBudevflags 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 ouput 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.

\fBudevcomplete cookie
Wake any processes that are waiting for udev to complete processing the specified cookie.

\fBudevcomplete_all Remove all cookies. Any process waiting on a cookie will be resumed immediately.

\fBudevcookies List all existing cookies. Cookies are system-wide semaphores with keys prefixed by two predefined bytes (0x0D4D).

Outputs version information.

\fBwait 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.


Each line of the table specifies a single target and is of the form:
logical_start_sector num_sectors target_type target_args

There are currently three simple target types available together with more complex optional ones that implement snapshots and mirrors.

\fBlinear destination_device start_sector
The traditional linear mapping.

\fBstriped 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

Errors any I/O that goes to this area. Useful for testing or for creating devices with holes in them.


# 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


        The device directory name. Defaults to "/dev" and must be an absolute path.
        A cookie to use for all relevant commands to synchronize with udev processing. It is an alternative to using --udevcookie option.


Original version: Joe Thornber ( )


Device-mapper resource page: http://sources.redhat.com/dm/