dmsetup
low level logical volume management
SYNOPSIS
dmsetup
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dmsetup
- 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 outstanding 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 synchronize 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
-
Process only items that match selection criteria. If the command is producing report output, adding the "selected" column (-o selected) displays all rows and shows 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 synchronization. Note: Same cookie should be used for same type of operations i.e. creation of multiple different devices. It's not advised to combine different operations on the single device.
- -u|--uuid uuid
-
Specify the uuid.
- -y|--yes
-
Answer yes to all prompts automatically.
- -v|--verbose [-v|--verbose]
-
Produce additional output.
- --verifyudev
-
If udev synchronization 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
Destroys the table in the inactive table slot for device_name.
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.
Creates one or more devices from a concise device specification. Each
device is specified by a comma-separated list: name, uuid, minor number,
flags, comma-separated table lines. Flags defaults to read-write (rw) or
may be read-only (ro). Uuid, minor number and flags are optional so
those fields may be empty. A semi-colon separates specifications of
different devices. Use a backslash to escape the following character,
for example a comma or semi-colon in a name or table. See also CONCISE
FORMAT below.
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).
Outputs a summary of the commands available, optionally including the
list of report fields.
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
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.
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|
Loads table or table_file into the inactive table slot for
device_name. If neither is supplied, reads a table from standard
input.
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).
Show the data that device_name would report to the IMA
subsystem if a measurement was triggered at the current time. This
is for debugging and does not actually trigger a measurement.
Send message to target. If sector not needed use 0.
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.
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.
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.
Renames a device.
Sets the uuid of a device that was created without a uuid. After a uuid
has been set it cannot be changed.
Un-suspends a device. If an inactive table has been loaded, it becomes
live. Postponed I/O then gets re-queued for processing.
Sets the device geometry to C/H/S.
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.
Manages IO statistics regions for devices. See
dmstats(8) for more details.
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.
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.
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. Real encryption keys are
suppressed in the table output for crypt and integrity targets unless
the --showkeys parameter is supplied. Kernel
key references prefixed with : are not
affected by the parameter and get displayed always (crypt target
only). With --concise, the output is presented
concisely on a single line. Commas then separate the name, uuid,
minor device number, flags ('ro' or 'rw') and the table (if present).
Semi-colons separate devices. Backslashes escape any commas, semi-colons
or backslashes. See CONCISE FORMAT below.
Displays the names and versions of the currently-loaded targets.
Wake any processes that are waiting for udev to complete processing the
specified cookie.
Remove all cookies older than the specified number of minutes. Any
process waiting on a cookie will be resumed immediately.
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.
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.
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.
Outputs version information.
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.
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
CONCISE FORMAT
A concise representation of one of more devices.
- A comma separates the fields of each device.
- A semi-colon separates devices.
- The representation of a device takes the form:
<name>,<uuid>,<minor>,<flags>,<table>[,<table>+][;<name>,<uuid>,<minor>,<flags>,<table>[,<table>+]]
- The fields are:
- name
-
The name of the device.
- uuid
-
The UUID of the device (or empty).
- minor
-
The minor number of the device. If empty, the kernel assigns a suitable minor number.
- flags
-
Supported flags are:
ro Sets the table being loaded for the device
read-only
rw Sets the table being loaded for the device
read-write (default)
- table
-
One line of the table. See TABLE FORMAT above.
EXAMPLES
# A simple linear read-only device
- test-linear-small,,,ro,0 2097152 linear /dev/loop0 0,2097152 2097152 linear /dev/loop1 0
# Two linear devices
- test-linear-small,,,,0 2097152 linear /dev/loop0 0;test-linear-large,,,,0 2097152 linear /dev/loop1 0, 2097152 2097152 linear /dev/loop2 0
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>
SEE ALSO
dmstats(8), udev(7), udevadm(8) LVM2 resource page: Device-mapper resource page: