NAME¶

dmsetup - low level logical volume management

SYNOPSIS¶

dmsetup clear device_name dmsetup create device_name [-u uuid] [--notable|--table <table>| dmsetup deps [-o options] [device_name] dmsetup help [-c|-C|--columns] dmsetup info [device_name] dmsetup info -c|-C|--columns [--noheadings] [--separator separator] 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}] dmsetup setgeometry device_name cyl head sect start dmsetup splitname device_name [subsystem] dmsetup status [--target target_type] [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 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. The names 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:

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.

 

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.

 

status

[--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.

 

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.

 

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.

 

version

 

Outputs version information.

 

wait

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.

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:

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.

raid

 

Offers an interface to the kernel's software raid driver, md.

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)

SEE ALSO¶

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