Ubuntu Manpage: dmsetup - low level logical volume management

Provided by: dmsetup_1.02.77-6ubuntu2_amd64

NAME

       dmsetup - low level logical volume management

SYNOPSIS

       dmsetup clear device_name
       dmsetup create device_name [-u uuid] [--notable|--table <table>|
              table_file] [{--addnodeoncreate|--addnodeonresume}] [--readahead [+]<sectors>|auto|none]
       dmsetup deps [-o options] [device_name]
       dmsetup help [-c|-C|--columns]
       dmsetup info [device_name]
       dmsetup info -c|-C|--columns [--noheadings] [--separator separator]
              [-o fields] [-O|--sort sort_fields] [device_name]
       dmsetup load device_name [--table <table>|table_file]
       dmsetup ls [--target target_type] [--exec command] [--tree] [-o options]
       dmsetup message device_name sector message
       dmsetup mknodes [device_name]
       dmsetup mangle [device_name]
       dmsetup reload device_name [--table <table>|table_file]
       dmsetup wipe_table device_name
       dmsetup remove [-f|--force] [--retry] device_name
       dmsetup remove_all [-f|--force]
       dmsetup rename device_name new_name
       dmsetup rename device_name --setuuid uuid
       dmsetup resume device_name [{--addnodeoncreate|--addnodeonresume}]
              [--readahead [+]<sectors>|auto|none]
       dmsetup setgeometry device_name cyl head sect start
       dmsetup splitname device_name [subsystem]
       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 udevcookies
       dmsetup udevcreatecookie
       dmsetup udevflags cookie
       dmsetup udevreleasecookie [cookie]
       dmsetup version
       dmsetup wait [--noflush] device_name [event_nr]

       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 command as devmap_name 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.

-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.

--manglename <mangling_mode>
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: none (no mangling), hex (always do the mangling) and auto (only do the
mangling if not mangled yet, do nothing if already mangled, error on mixed; this is used by
default). 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.

-j|--major major
Specify the major number.

-m|--minor minor
Specify the minor number.

-n|--noheadings
Suppress the headings line when using columnar output.

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

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

--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
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.

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

--udevcookie cookie
Use cookie for udev synchronisation.

-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] [--notable|--table <table>|table_file]
[{--addnodeoncreate|--addnodeonresume}] [--readahead [+]<sectors>|auto|none]
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/mapper/<device-name>. See below for 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 [--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.

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.

wipe_table device_name
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).

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.

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).

remove [-f|--force] [--retry] 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. 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.

remove_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.

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}] [--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. Default subsystem is LVM.

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. 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.

udevcookies
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.
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.

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:

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.

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.

AUTHORS

       Original version: Joe Thornber (thornber@sistina.com)