lvm2/man/dmsetup.8_main

.TH DMSETUP 8 "Mar 26 2025" Linux "MAINTENANCE COMMANDS"
.
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.\" Use .SY for command synopsis
.de _NSY
.  SY \\$1
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.de CMS
.  na
.  nh
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.ds CBR \&
.
.de CME
.  hy
.  ad
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.\" avoid hyphenation of these keywords
.hw dmsetup
.
.SH NAME
.
dmsetup \(em low level logical volume management
.
.SH SYNOPSIS
.
.NSY dmsetup 1
.de CMD_CLEAR
.  CMS
.  BR clear " "\c
.  IR device_name \&
.  CME
..
.CMD_CLEAR
.
.NSY dmsetup
.de CMD_CREATE
.  CMS
.  BR create " "\c
.  IR device_name " "\c
.  RB [ -n | --notable |\: --table\ \c
.  IR table |\: table_file ] " "\c
.  RB [ --readahead " [" + ]\c
.  IR sectors |\:\c
.  BR auto | none ] " "\c
.  RB [ -u | --uuid\ \c
.  IR uuid ] " "\c
.  RB [ --addnodeoncreate |\: --addnodeonresume ]
.  B \&  \" Mask '-T html' rendering bug
.  CME
..
.CMD_CREATE
.
.NSY dmsetup
.de CMD_CREATE_CONCISE
.  CMS
.  BR create \  --concise " "\c
.  RI [ concise_de\%vice_spe\%cification ] " "\c
.  B \&
.  CME
..
.CMD_CREATE_CONCISE
.
.NSY dmsetup
.de CMD_DEPS
.  CMS
.  BR deps " "\c
.  RB [ -o\ \c
.  IR options ] " "\c
.  RI [ device_name \ .\|.\|.]
.  CME
..
.CMD_DEPS
.
.NSY dmsetup
.de CMD_HELP
.  CMS
.  BR help " "\c
.  RB [ -c | -C | --columns ]
.  CME
..
.CMD_HELP
.
.NSY dmsetup
.de CMD_INFO
.  CMS
.  BR info " "\c
.  RI [ device_name \ .\|.\|.]
.  CME
..
.CMD_INFO
.
.NSY dmsetup
.de CMD_INFOLONG
.  CMS
.  BR info " "\c
.  BR -c | -C | --columns " "\c
.  RB [ --count\ \c
.  IR count ] " "\c
.  RB [ --interval\ \c
.  IR seconds ] " "\c
.  RB [ --noheadings |\: --headings\ \c
.  BR none | abbrev |\: full |\: 0 | 1 | 2 ] " "\c
.  RB [ -o\ \c
.  IR fields ] " "\c
.  RB [ -O | --sort\ \c
.  IR sort_fields ] " "\c
.  RB [ --nameprefixes ] " "\c
.  RB [ --separator\ \c
.  IR separator ] " "\c
.  RI [ device_name ]
.  CME
..
.CMD_INFOLONG
.
.NSY dmsetup
.de CMD_LOAD
.  CMS
.  BR load " "\c
.  IR device_name " "\c
.  RB [ --table\ \c
.  IR table |\: table_file ]
.  CME
..
.CMD_LOAD
.
.NSY dmsetup
.de CMD_LS
.  CMS
.  BR ls " "\c
.  RB [ --target\ \c
.  IR target_type ] " "\c
.  RB [ -o\ \c
.  IR options ] " "\c
.  RB [ --exec\ \c
.  IR command ] " "\c
.  RB [ --tree ]
.  CME
..
.CMD_LS
.
.NSY dmsetup
.de CMD_MANGLE
.  CMS
.  BR mangle " "\c
.  RI [ device_name \ .\|.\|.]
.  CME
..
.CMD_MANGLE
.
.NSY dmsetup
.de CMD_MEASURE
.  CMS
.  BR measure " "\c
.  RI [ device_name \ .\|.\|.]
.  CME
..
.CMD_MEASURE
.
.NSY dmsetup
.de CMD_MESSAGE
.  CMS
.  BR message " "\c
.  IR device_name " " sector " " message
.  CME
..
.CMD_MESSAGE
.
.NSY dmsetup
.de CMD_MKNODES
.  CMS
.  BR mknodes " "\c
.  RI [ device_name \ .\|.\|.]
.  CME
..
.CMD_MKNODES
.
.NSY dmsetup
.de CMD_RELOAD
.  CMS
.  BR reload " "\c
.  IR device_name " "\c
.  RB [ --table\ \c
.  IR table |\: table_file ]
.  CME
..
.CMD_RELOAD
.
.NSY dmsetup
.de CMD_REMOVE
.  CMS
.  BR remove " "\c
.  RB [ -f | --force ] " "\c
.  RB [ --retry ] " "\c
.  RB [ --deferred ] " "\c
.  IR device_name \ .\|.\|.\&
.  CME
..
.CMD_REMOVE
.
.NSY dmsetup
.de CMD_REMOVE_ALL
.  CMS
.  BR remove_all " "\c
.  RB [ -f | --force ] " "\c
.  RB [ --deferred ]
.  CME
..
.CMD_REMOVE_ALL
.
.NSY dmsetup
.de CMD_RENAME
.  CMS
.  BR rename " "\c
.  IR device_name " " new_name
.  CME
..
.CMD_RENAME
.
.NSY dmsetup
.de CMD_RENAME_UUID
.  CMS
.  BR rename " "\c
.  IR device_name " "\c
.  BR --setuuid \ \c
.  IR uuid \&
.  CME
..
.CMD_RENAME_UUID
.
.NSY dmsetup
.de CMD_RESUME
.  CMS
.  BR resume " "\c
.  IR device_name \ .\|.\|.\& " "\c
.  RB [ --addnodeoncreate |\: --addnodeonresume ] " "\c
.  RB [ --noflush ] " "\c
.  RB [ --nolockfs ] " "\c
.  RB [ --readahead\ \c
.  RB [ + ]\c
.  IR sec\%tors |\:\c
.  BR auto | none ]
.  CME
..
.CMD_RESUME
.
.NSY dmsetup
.de CMD_SETGEOMETRY
.  CMS
.  BR setgeometry " "\c
.  IR device_name " " cyl " " head " " sect " " start
.  CME
..
.CMD_SETGEOMETRY
.
.NSY dmsetup
.de CMD_SPLITNAME
.  CMS
.  BR splitname " "\c
.  IR device_name " "\c
.  RI [ subsystem ]
.  CME
..
.CMD_SPLITNAME
.
.NSY dmsetup
.de CMD_STATS
.  CMS
.  BR stats " "\c
.  IR command " [" options ]
.  CME
..
.CMD_STATS
.
.NSY dmsetup
.de CMD_STATUS
.  CMS
.  BR status " "\c
.  RB [ --target\ \c
.  IR target_type ] " "\c
.  RB [ --noflush ] " "\c
.  RI [ device_name \ .\|.\|.]
.  CME
..
.CMD_STATUS
.
.NSY dmsetup
.de CMD_SUSPEND
.  CMS
.  BR suspend " "\c
.  IR device_name \ .\|.\|.\& " "\c
.  RB [ --nolockfs ] " "\c
.  RB [ --noflush ]
.  CME
..
.CMD_SUSPEND
.
.NSY dmsetup
.de CMD_TABLE
.  CMS
.  BR table " "\c
.  RB [ --concise ] " "\c
.  RB [ --target\ \c
.  IR target_type ] " "\c
.  RB [ --showkeys ] " "\c
.  RI [ device_name \ .\|.\|.]
.  B \&
.  CME
..
.CMD_TABLE
.
.NSY dmsetup
.de CMD_TARGETS
.  CMS
.  B targets
.  CME
..
.CMD_TARGETS
.
.NSY dmsetup
.de CMD_UDEVCOMPLETE
.  CMS
.  BR udevcomplete " "\c
.  IR cookie \&
.  CME
..
.CMD_UDEVCOMPLETE
.
.NSY dmsetup
.de CMD_UDEVCOMPLETE_ALL
.  CMS
.  BR udevcomplete_all " "\c
.  RI [ age_in_minutes ]
.  CME
..
.CMD_UDEVCOMPLETE_ALL
.
.NSY dmsetup
.de CMD_UDEVCOOKIES
.  CMS
.  B udevcookie
.  CME
..
.CMD_UDEVCOOKIES
.
.NSY dmsetup
.de CMD_UDEVCREATECOOKIE
.  CMS
.  B udevcreatecookie
.  CME
..
.CMD_UDEVCREATECOOKIE
.
.NSY dmsetup
.de CMD_UDEVFLAGS
.  CMS
.  BR udevflags " "\c
.  IR cookie \&
.  CME
..
.CMD_UDEVFLAGS
.
.NSY dmsetup
.de CMD_UDEVRELEASECOOKIE
.  CMS
.  BR udevreleasecookie " "\c
.  RI [ cookie ]
.  CME
..
.CMD_UDEVRELEASECOOKIE
.
.NSY dmsetup
.de CMD_VERSION
.  CMS
.  B version
.  CME
..
.CMD_VERSION
.
.NSY dmsetup
.de CMD_WAIT
.  CMS
.  BR wait " "\c
.  IR device_name " "\c
.  RB [ --noflush ] " "\c
.  RI [ event_nr ]
.  CME
..
.CMD_WAIT
.
.NSY dmsetup
.de CMD_WIPE_TABLE
.  CMS
.  BR wipe_table " "\c
.  IR device_name \ .\|.\|.\& " "\c
.  RB [ -f | --force ] " "\c
.  RB [ --noflush ] " "\c
.  RB [ --nolockfs ]
.  CME
..
.CMD_WIPE_TABLE
.
.PD
.
.P
.B devmap_name
.I major minor
.br
.
.B devmap_name
.IR major : minor
.
.ad
.hy
.
.SH 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.
.P
The first argument to dmsetup is a command.
The second argument is the logical device name or uuid.
.P
Invoking the dmsetup tool as \fBdevmap_name\fP
(which is not normally distributed and is supported
only for historical reasons) is equivalent to
.na
.BI "dmsetup info -c --noheadings -j " major " -m " minor .
.ad
.
.SH OPTIONS
.
.TP
.B --addnodeoncreate
Ensure \fI/dev/mapper\fP node exists after \fBdmsetup create\fP.
.
.TP
.B --addnodeonresume
Ensure \fI/dev/mapper\fP node exists after \fBdmsetup\ resume\fP
(default with udev).
.
.TP
.B --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.
.
.TP
.BR -c | -C | --columns
Display output in columns rather than as Field: Value lines.
.
.TP
\fB--count\fP \fIcount\fP
Specify the number of times to repeat a report.
Set this to zero to continue until interrupted.
The default interval is one second.
.
.TP
.BR -f | --force
Try harder to complete operation.
.
.TP
.BR -h | --help
Outputs a summary of the commands available, optionally including
the list of report fields (synonym with \fBhelp\fP command).
.
.TP
.B --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.
.
.TP
\fB--interval\fP \fIseconds\fP
Specify the interval in seconds between successive iterations for
repeating reports.
If \fB--interval\fP is specified but \fB--count\fP is not,
reports will continue to repeat until interrupted.
The default interval is one second.
.
.TP
.BR --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:
\fBauto\fP (only do the mangling if not mangled yet,
do nothing if already mangled, error on mixed),
\fBhex\fP (always do the mangling) and
\fBnone\fP (no mangling).
Default mode is \fB#DEFAULT_MANGLING#\fP.
Character whitelist:
.BR 0 \(en 9 ,
.BR A \(en Z ,
.BR a \(en z ,
.BR #+\-.:=@_ .
This whitelist is also supported by udev.
Any character not on a whitelist is replaced
with its hex value (two digits) prefixed by \ex.
Mangling mode could be also set through
.B DM_DEFAULT_NAME_MAN\%GLING_MODE
environment variable.
.
.TP
\fB-j\fP|\fB --major\fP \fImajor\fP
Specify the major number.
.
.TP
\fB-m\fP|\fB--minor\fP \fIminor\fP
Specify the minor number.
.
.TP
.BR -n | --notable
When creating a device, don't load any table.
.
.TP
.B --nameprefixes
Add a "DM_" prefix plus the field name to the output.
Useful with \fB--noheadings\fP to produce a list of field=value
pairs that can be used to set environment variables
(for example, in
.BR udev (7)
rules).
.
.TP
.B --noheadings
Suppress the headings line when using columnar output.
.
.TP
.BR --headings " " none |\: abbrev | full |\: 0 | 1 | 2
Type of headings line to use for columnar output.
.br
\fBnone\fP or \fB0\fP \(en No headings.
.br
\fBabbrev\fP or \fB1\fP \(en Column name abbreviations.
.br
\fBfull\fP or \fB2\fP \(en Full column names.
.
.TP
.B --noflush
Do not flush outstanding I/O when suspending a device, or do not
commit thin-pool metadata when obtaining thin-pool status.
.
.TP
.B --nolockfs
Do not attempt to synchronize filesystem, e.g., when suspending a device.
.
.TP
.B --noopencount
Tell the kernel not to supply the open reference count for the device.
.
.TP
.B --noudevrules
Do not allow udev to manage nodes for devices in device-mapper directory.
.
.TP
.B --noudevsync
Do not synchronize with udev when creating, renaming or removing devices.
.
.TP
\fB-o\fP|\fB--options\fP \fIoptions\fP
Specify which fields to display.
.
.TP
\fB--readahead\fP [\fB+\fP]\fIsectors\fP|\:\fBauto\fP|\:\fBnone\fP
Specify read ahead size in units of sectors.
The default value is \fBauto\fP which allows the kernel to choose
a suitable value automatically.
The \fB+\fP 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 \fBnone\fP is equivalent to specifying zero.
.
.TP
.BR -r | --readonly
Set the table being loaded read-only.
.
.TP
\fB-S\fP|\fB--select\fP \fIselection\fP
Process only items that match \fIselection\fP criteria.
If the command is producing report output,
adding the "selected" column (\fB-o selected\fP) displays all rows
and shows 1 if the row matches the \fIselection\fP 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
.na
.nh
.B dmsetup info -c -S help
.hy
.ad
command.
.
.TP
\fB--table\fP \fItable\fP
Specify a one-line table directly on the command line.
See below for more information on the table format.
.
.TP
\fB--udevcookie\fP \fIcookie\fP
Use cookie for udev synchronization.
.br
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.
.
.TP
\fB-u\fP|\fB--uuid\fP \fIuuid\fP
Specify the \fIuuid\fP.
.
.TP
.BR -y | --yes
Answer yes to all prompts automatically.
.
.TP
.BR -v | --verbose " [" -v |\: --verbose ]
Produce additional output.
.
.TP
.B --verifyudev
If udev synchronization is enabled, verify that udev operations get performed
correctly and try to fix up the device nodes afterwards if not.
.
.TP
.B --version
Display the library and kernel driver version.
.
.SH COMMANDS
.ds CBR .br
.
.NTP
.CMD_CLEAR
Destroys the table in the inactive table slot for device_name.
.
.NTP
.CMD_CREATE
Creates a device with the given name.
If \fItable\fP or \fItable_file\fP is supplied,
the table is loaded and made live.
Otherwise a table is read from standard input unless \fB--notable\fP is used.
The optional \fIuuid\fP can be used in place of
device_name in subsequent dmsetup commands.
If successful the device will appear in table and for the live
device the node
.na
.I /dev/mapper/device_name
is created.
See below for more information on the table format.
.ad
.
.NTP
.CMD_CREATE_CONCISE
Creates one or more devices from a concise device specification.
Each device is specified by a comma-separated list:
.IR name ", " uuid ", " "minor number" ", " flags ,
.IR "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
.B CONCISE FORMAT
below.
.
.NTP
.CMD_DEPS
Outputs a list of devices referenced by the live table for the specified
device. Device names on output can be customised by the following options:
\fBdevno\fP (major and minor pair, used by default),
\fBblkdevname\fP (block device name),
\fBdevname\fP (map name for device-mapper devices, equal to blkdevname otherwise).
.
.NTP
.CMD_HELP
Outputs a summary of the commands available, optionally including
the list of report fields.
.
.NTP
.CMD_INFO
Outputs some brief information about the device in the form:
.RS
.RS
.na
.nh
State: SUSPENDED|\:ACTIVE, READ-ONLY
.br
Read Ahead: sectors
.br
Tables present: LIVE and/or INACTIVE
.br
Open reference count
.br
Last event sequence number (used by \fBwait\fP)
.br
Major and minor device number
.br
Number of targets in the live table
.br
UUID
.RE
.RE
.
.NTP
.CMD_INFOLONG
Output you can customise.
Fields are comma-separated and chosen from the following list:
.BR name ,
.BR major ,
.BR minor ,
.BR attr ,
.BR open ,
.BR segments ,
.BR events ,
.BR uuid .
Attributes are:
.RB ( L )ive,
.RB ( I )nactive,
.RB ( s )uspended,
.RB ( r )ead-only,
.RB read-( w )rite.
Precede the list with '\fB+\fP' to append
to the default selection of columns instead of replacing it.
Precede any sort field with '\fB-\fP' for a reverse sort on that column.
.
.NTP
.CMD_LS
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 the following options:
\fBdevno\fP (major and minor pair, used by default),
\fBblkdevname\fP (block device name),
\fBdevname\fP (map name for device-mapper devices, equal to blkdevname otherwise).
\fB--tree\fP displays dependencies between devices as a tree.
It accepts a comma-separated list of options.
Some specify the information displayed against each node:
.BR device\  /\: \ nodevice ;
.BR blkdevname ;
.BR active ,
.BR open ,
.BR rw ,
.BR uuid .
Others specify how the tree is displayed:
.BR ascii ,
.BR utf ,
.BR vt100 ;
.BR compact ,
.BR inverted ,
.BR notrunc .
.
.NTP
.CMD_RELOAD
Loads \fItable\fP or \fItable_file\fP
into the inactive table slot for device_name.
If neither is supplied, reads a table from standard input.
.
.NTP
.CMD_MANGLE
Ensure existing device-mapper \fIdevice_name\fP 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 \fB--manglename\fP 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 \fB--manglename\fP).
.
.NTP
.CMD_MEASURE
Show the data that \fIdevice_name\fP 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.
.
.NTP
.CMD_MESSAGE
Send message to target. If sector not needed use 0.
.
.NTP
.CMD_MKNODES
Ensure that the node in \fI/dev/mapper\fP for \fIdevice_name\fP is correct.
If no device_name is supplied, ensure that all nodes in \fI/dev/mapper\fP
correspond to mapped devices currently loaded by the device-mapper kernel
driver, adding, changing or removing nodes as necessary.
.
.NTP
.CMD_REMOVE
Removes a device.
It will no longer be visible to dmsetup.
Open devices cannot be removed, but adding \fB--force\fP
will replace the table with one that fails all I/O.
\fB--deferred\fP 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 \fBdmsetup version\fP 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 \fB--retry\fP option will cause the operation to be retried
for a few seconds before failing.
Do NOT combine \fB--force\fP and \fB--udevcookie\fP,
as udev may start to process udev rules in the middle of error target
replacement and result in nondeterministic result.
.
.NTP
.CMD_REMOVE_ALL
Attempts to remove all device definitions i.e.\& reset the driver.
This also runs \fBmknodes\fP afterwards.
Use with care!
Open devices cannot be removed, but adding \fB--force\fP
will replace the table with one that fails all I/O.
\fB--deferred\fP 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.
.
.NTP
.CMD_RENAME
Renames a device.
.
.NTP
.CMD_RENAME_UUID
Sets the uuid of a device that was created without a uuid.
After a uuid has been set it cannot be changed.
.
.NTP
.CMD_RESUME
Un-suspends a device.
If an inactive table has been loaded, it becomes live.
Postponed I/O then gets re-queued for processing.
.
.NTP
.CMD_SETGEOMETRY
Sets the device geometry to C/H/S.
.
.NTP
.CMD_SPLITNAME
Splits given \fIdevice name\fP into \fIsubsystem\fP 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.
.
.NTP
.CMD_STATS
Manages IO statistics regions for devices.
See
.BR dmstats (8)
for more details.
.
.NTP
.CMD_STATUS
Outputs status information for each of the device's targets.
With \fB--target\fP, only information relating
to the specified target type any is displayed.
With \fB--noflush\fP, the thin target (from version 1.3.0)
doesn't commit any outstanding changes to disk
before reporting its statistics.
.
.NTP
.CMD_SUSPEND
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 \fB--nolockfs\fP is specified.
Some targets such as recent (October 2006) versions of multipath may support
the \fB--noflush\fP option.  This lets outstanding I/O that has not yet
reached the device to remain unflushed.
.
.NTP
.CMD_TABLE
Outputs the current table for the device in a format that can be fed
back in using the create or load commands.
With \fB--target\fP, 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 \fB--showkeys\fP parameter is supplied. Kernel key
references prefixed with \fB:\fP are not affected by the parameter and get
displayed always (crypt target only).
With \fB--concise\fP, 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
.B CONCISE FORMAT
below.
.
.NTP
.CMD_TARGETS
Displays the names and versions of the currently-loaded targets.
.
.NTP
.CMD_UDEVCOMPLETE
Wake any processes
that are waiting for udev to complete processing the specified cookie.
.
.NTP
.CMD_UDEVCOMPLETE_ALL
Remove all cookies older than the specified number of minutes.
Any process waiting on a cookie will be resumed immediately.
.
.NTP
.CMD_UDEVCOOKIES
List all existing cookies. Cookies are system-wide semaphores with keys
prefixed by two predefined bytes (0x0D4D).
.
.NTP
.CMD_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
\fB--udevcookie\fP option.
Alternatively, we can export this value into the environment
of the dmsetup process as \fBDM_UDEV_COOKIE\fP 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.
.
.NTP
.CMD_UDEVFLAGS
Parses given \fIcookie\fP 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
.na
DM_UDEV_FLAG_\:<flag_\:name> =\ '1',
DM_UDEV_FLAG\:<flag_\:position> =\ '1'
.ad
otherwise.
Subsystem udev flags don't have symbolic names assigned and these ones are
always reported as
.na
DM_SUBSYSTEM_\:UDEV_\:FLAG\:<flag_\:position> =\ '1'.
.ad
There are 16 udev flags altogether.
.
.NTP
.CMD_UDEVRELEASECOOKIE
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 \fBDM_UDEV_COOKIE\fP
environment variable.
.
.NTP
.CMD_VERSION
Outputs version information.
.
.NTP
.CMD_WAIT
Sleeps until the event counter for device_name exceeds event_nr.
Use \fB-v\fP to see the event number returned.
To wait until the next event is triggered, use \fBinfo\fP to find
the last event number.
With \fB--noflush\fP, the thin target (from version 1.3.0) doesn't commit
any outstanding changes to disk before reporting its statistics.
.
.NTP
.CMD_WIPE_TABLE
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).
.
.SH TABLE FORMAT
.
Each line of the table specifies a single target and is of the form:
.P
.shc \\
.na
.nh
.I \%logical_start_sector\%\ num_sectors\%\ \c
.B target_type\%\ \c
.I target_args
.hy
.ad
.shc
.
.sp
Simple target types and target args include:
.
.NTP
.CMS
\fBlinear\fP \fIdestination_device start_sector\fP
.CME
The traditional linear mapping.
.
.NTP
.CMS
\fBstriped\fP \fInum_stripes chunk_size\fP \
[\fIdestination start_sector\fP]\ .\|.\|.
.CME
Creates a striped area.
.br
.na
e.g.\& striped 2 32 /dev/hda1 0 /dev/hdb1 0
will map the first chunk (16\ KiB) as follows:
.RS
.RS
LV chunk 1 \[->] hda1, chunk 1
.br
LV chunk 2 \[->] hdb1, chunk 1
.br
LV chunk 3 \[->] hda1, chunk 2
.br
LV chunk 4 \[->] hdb1, chunk 2
.br
etc.
.RE
.RE
.na
.
.TP
.B error
Errors any I/O that goes to this area.  Useful for testing or
for creating devices with holes in them.
.
.TP
.B zero
Returns blocks of zeroes on reads.
Any data written is discarded silently.
This is a block-device equivalent of the \fI/dev/zero\fP
character-device data sink described in \fBnull\fP(4).
.P
More complex targets include:
.
.TP
.B cache
Improves performance of a block device (e.g., a spindle) by dynamically
migrating some of its data to a faster smaller device (e.g., an SSD).
.
.TP
.B crypt
Transparent encryption of block devices using the kernel crypto API.
.
.TP
.B delay
Delays reads and/or writes to different devices.
Useful for testing.
.
.TP
.B flakey
Creates a similar mapping to the linear target
but exhibits unreliable behaviour periodically.
Useful for simulating failing devices when testing.
.
.TP
.B mirror
Mirrors data across two or more devices.
.
.TP
.B multipath
Mediates access through multiple paths to the same device.
.
.TP
.B raid
Offers an interface to the kernel's software raid driver, md.
.
.TP
.B snapshot
Supports snapshots of devices.
.
.TP
.BR thin ", " thin-pool
Supports thin provisioning of devices and also provides
a better snapshot support.
.P
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.)
.
.SH EXAMPLES
.
.EX
# A table to join two disks together
0 1028160 linear /dev/hda 0
1028160 3903762 linear /dev/hdb 0
.sp
# 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
.EE
.
.SH CONCISE FORMAT
.
A concise representation of one of more devices:
.
.PD 0
.
.IP \(bu 2
A comma separates the fields of each device.
.
.IP \(bu
A semi-colon separates devices.
.
.PD
.
.P
The representation of a device takes the form:
.RS
.shc \\
.na
.nh
.RI \%< name >,< uuid >,\%< minor >,< flags >,\%< table >\%\c
.RI [,< table >+]\%\c
.RI [;< name >,< uuid >,\%< minor >,< flags >,\%< table >\%\c
.RI [,< table >+]]
.hy
.ad
.shc
.RE
.
.P
The fields are:
.
.TP
.I name
The name of the device.
.
.TP
.I uuid
The UUID of the device (or empty).
.
.TP
.I minor
The minor number of the device.
If empty, the kernel assigns a suitable minor number.
.
.TP
.I flags
Supported flags are:
.
.PD 0
.RS
.
.TP 4
.B ro
Sets the table being loaded for the device read-only
.
.TP
.B rw
Sets the table being loaded for the device read-write (default)
.RE
.PD
.
.TP
.I table
One line of the table. See TABLE FORMAT above.
.
.SH EXAMPLES
.
.EX
# A simple linear read-only device
test-linear-small,,,ro,\\
\ 0 2097152 linear /dev/loop0\ 0,\\
\ 2097152 2097152 linear /dev/loop1 0
.sp
# 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
.EE
.
.SH ENVIRONMENT VARIABLES
.
.TP
.B DM_DEV_DIR
The device directory name.
Defaults to "\fI/dev\fP" and must be an absolute path.
.
.TP
.B DM_UDEV_COOKIE
A cookie to use for all relevant commands to synchronize with udev processing.
It is an alternative to using \fB--udevcookie\fP option.
.
.TP
.B DM_DEFAULT_NAME_MANGLING_MODE
A default mangling mode.
Defaults to "\fB#DEFAULT_MANGLING#\fP"
and it is an alternative to using \fB--manglename\fP option.
.
.SH AUTHORS
.
.na
.nh
Original version:
.MT thornber@redhat.com
Joe Thornber
.ME
.
.SH SEE ALSO
.
.na
.nh
.BR dmstats (8),
.BR udev (7),
.BR udevadm (8)
.P
.UR https://\:www.sourceware.org/lvm2
LVM2 resource page:
.UE
.br
.UR https://\:www.sourceware.org/dm
Device-mapper resource page:
.UE