Ubuntu Manpage: dmsetup — low level logical volume management

Provided by: dmsetup_1.02.110-1ubuntu10_amd64

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
       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 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.

--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 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 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 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 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] [--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 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 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 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.

stats command [options]
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. 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 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).

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.

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_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) 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.

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 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 <thornber@redhat.com>