NAME¶
cryptsetup - manage plain dm-crypt and LUKS encrypted volumes
SYNOPSIS¶
cryptsetup <options> <action> <action args>
DESCRIPTION¶
cryptsetup is used to conveniently setup dm-crypt managed device-mapper
mappings. These include plain dm-crypt volumes and LUKS volumes. The
difference is that LUKS uses a metadata header and can hence offer more
features than plain dm-crypt. On the other hand, the header is visible and
vulnerable to damage.
WARNINGS¶
A lot of good information on the risks of using encrypted storage, on handling
problems and on security aspects can be found in the
Cryptsetup FAQ.
Read it. Nonetheless, some risks deserve to be mentioned here.
Backup: Storage media die. Encryption has no influence on that. Backup is
mandatory for encrypted data as well, if the data has any worth. See the
Cryptsetup FAQ for advice on how to do backup of an encrypted volume.
Character encoding: If you enter a passphrase with special symbols, the
passphrase can change depending character encoding. Keyboard settings can also
change, which can make blind input hard or impossible. For example, switching
from some ASCII 8-bit variant to UTF-8 can lead to a different binary encoding
and hence different passphrase seen by cryptsetup, even if what you see on the
terminal is exactly the same. It is therefore highly recommended to select
passphrase characters only from 7-bit ASCII, as the encoding for 7-bit ASCII
stays the same for all ASCII variants and UTF-8.
LUKS header: If the header of a LUKS volume gets damaged, all data is
permanently lost unless you have a header-backup. If a key-slot is damaged, it
can only be restored from a header-backup or if another active key-slot with
known passphrase is undamaged. Damaging the LUKS header is something people
manage to do with surprising frequency. This risk is the result of a trade-off
between security and safety, as LUKS is designed for fast and secure wiping by
just overwriting header and key-slot area.
PLAIN MODE¶
Plain dm-crypt encrypts the device sector-by-sector with a single, non-salted
hash of the passphrase. No checks are performed, no metadata is used. There is
no formatting operation. When the raw device is mapped (created), the usual
device operations can be used on the mapped device, including filesystem
creation. Mapped devices usually reside in /dev/mapper/<name>.
There are four operations:
create <name> <device>
- Creates a mapping with <name> backed by device
<device>.
<options> can be [--hash, --cipher, --verify-passphrase,
--key-file, --keyfile-offset, --key-size, --offset, --skip, --size,
--readonly, --shared, --allow-discards]
Example: 'cryptsetup create e1 /dev/sda10' maps the raw encrypted device
/dev/sda10 to the mapped (decrypted) device /dev/mapper/e1, which can then
be mounted, fsck-ed or have a filesystem created on it.
remove <name>
- Removes the existing mapping <name> and wipes the key
from kernel memory.
status <name>
- Reports the status for the mapping <name>.
resize <name>
- Resizes an active mapping <name>.
If --size (in sectors) is not specified, the size of the underlying block
device is used. Note that this does not change the raw device geometry, it
just changes how many sectors of the raw device are represented in the
mapped device.
LUKS EXTENSION¶
LUKS, the Linux Unified Key Setup, is a standard for disk encryption. It adds a
standardized header at the start of the device, a key-slot area directly
behind the header and the bulk data area behind that. The whole set is called
a 'LUKS container'. The device that a LUKS container resides on is called a
'LUKS device'. For most purposes both terms can be used interchangeably. But
note that when the LUKS header is at a nonzero offset in a device, then the
device is not a LUKS device anymore, but has a LUKS container stored in it at
an offset.
LUKS can manage multiple passphrases that can be individually revoked or changed
and that can be securely scrubbed from persistent media due to the use of
anti-forensic stripes. Passphrases are protected against brute-force and
dictionary attacks by PBKDF2, which implements hash iteration and salting in
one function.
Each passphrase, also called a
key in this document, is associated with
one of 8 key-slots. Key operations that do not specify a slot affect the first
slot that matches the supplied passphrase or the first empty slot if a new
passphrase is added.
The following are valid LUKS actions:
luksFormat <device> [<key file>]
- Initializes a LUKS partition and sets the initial
passphrase (for key-slot 0), either via prompting or via <key file>.
Note that if the second argument is present, then the passphrase is taken
from the file given there, without the need to use the --key-file option.
Also note that for both forms of reading the passphrase from file you can
give '-' as file name, which results in the passphrase being read from
stdin and the safety-question being skipped.
You can only call luksFormat on a LUKS device that is not mapped.
<options> can be [--cipher, --verify-passphrase, --key-size,
--key-slot, --key-file (takes precedence over optional second argument),
--keyfile-offset, --keyfile-size, --use-random | --use-urandom, --uuid,
--master-key-file].
WARNING: Doing a luksFormat on an existing LUKS container will make
all data the old container permanently irretrievable, unless you have a
header backup.
luksOpen <device> <name>
- Opens the LUKS device <device> and sets up a mapping
<name> after successful verification of the supplied passphrase. If
the passphrase is not supplied via --key-file, the command prompts for it
interactively.
The <device> parameter can be also specified by LUKS UUID in the
format UUID=<uuid>, which uses the symlinks in /dev/disk/by-uuid.
<options> can be [--key-file, --keyfile-offset,
--keyfile-size, --readonly, --allow-discards, --header, --key-slot,
--master-key-file].
luksClose <name>
- identical to remove.
luksSuspend <name>
- Suspends an active device (all IO operations will blocked
and accesses to the device will wait indefinitely) and wipes the
encryption key from kernel memory. Needs kernel 2.6.19 or later.
After this operation you have to use luksResume to reinstate the
encryption key and unblock the device or luksClose to remove the
mapped device.
WARNING: never suspend the device on which the cryptsetup binary
resides.
<options> can be [--header].
luksResume <name>
- Resumes a suspended device and reinstates the encryption
key. Prompts interactively for a passphrase if --key-file is not given.
<options> can be [--key-file, --keyfile-size, --header]
luksAddKey <device> [<key file with new key>]
- adds a new passphrase. An existing passphrase must be
supplied interactively or via --key-file. The new passphrase to be added
can be specified interactively or read from the file given as positional
argument.
<options> can be [--key-file, --keyfile-offset,
--keyfile-size, --new-keyfile-offset, --new-keyfile-size, --key-slot,
--master-key-file].
luksRemoveKey <device> [<key file with passphrase to be
removed>]
- Removes the supplied passphrase from the LUKS device. The
passphrase to be removed can be specified interactively, as positional
argument or via --key-file.
<options> can be [--key-file, --keyfile-offset,
--keyfile-size]
WARNING: If you read the passphrase from stdin (without further
argument or with '-' as argument to --key-file), batch-mode (-q) will be
implicitely switched on and no warning will be given when you remove the
last remaining passphrase from a LUKS container. Removing the last
passphrase makes the LUKS container permanently inaccessible.
luksChangeKey <device> [<new key file>]
- Changes an existing passphrase. The passphrase to be
changed must be supplied interactively or via --key-file. The new
passphrase can be supplied interactively or in a file given as positional
argument.
If a key-slot is specified (via --key-slot), the passphrase for that
key-slot must be given and the new passphrase will overwrite the specified
key-slot. If no key-slot is specified and there is still a free key-slot,
then the new passphrase will be put into a free key-slot before the
key-slot containing the old passphrase is purged. If there is no free
key-slot, then the key-slot with the old passphrase is overwritten
directly.
WARNING: If a key-slot is overwritten, a media failure during this
operation can cause the overwrite to fail after the old passphrase has
been wiped and make the LUKS container inaccessible.
<options> can be [--key-file, --keyfile-offset,
--keyfile-size, --new-keyfile-offset, --new-keyfile-size,
--key-slot].
luksKillSlot <device> <key slot number>
- Wipe the key-slot number <key slot> from the LUKS
device. A remaining passphrase must be supplied, either interactively or
via --key-file. This command can remove the last remaining key-slot, but
requires an interactive confirmation when doing so. Removing the last
passphrase makes a LUKS container permanently inaccessible.
<options> can be [--key-file, --keyfile-offset,
--keyfile-size].
WARNING: If you read the passphrase from stdin (without further
argument or with '-' as argument to --key-file), batch-mode (-q) will be
implicitely switched on and no warning will be given when you remove the
last remaining passphrase from a LUKS container. Removing the last
passphrase makes the LUKS container permanently inaccessible.
luksUUID <device>
- Print the UUID of a LUKS device.
Set new UUID if --uuid option is specified.
isLuks <device>
- Returns true, if <device> is a LUKS device, false
otherwise. Use option -v to get human-readable feedback. 'Command
successful.' means the device is a LUKS device.
luksDump <device>
- Dump the header information of a LUKS device.
If the --dump-master-key option is used, the LUKS device master key is
dumped instead of the keyslot info. Beware that the master key cannot be
changed and can be used to decrypt the data stored in the LUKS container
without a passphrase and even without the LUKS header. This means that if
the master key is compromised, the whole device has to be erased to
prevent further access. Use this option carefully.
In order to dump the master key, a passphrase has to be supplied, either
interactively or via --key-file.
<options> can be [--dump-master-key, --key-file,
--keyfile-offset, --keyfile-size].
WARNING: If --dump-master-key is used with --key-file and the
argument to --key-file is '-', no validation question will be asked and no
warning given.
luksHeaderBackup <device> --header-backup-file <file>
- Stores a binary backup of the LUKS header and keyslot area.
Note: Using '-' as filename writes the header backup to a file named '-'.
WARNING: This backup file and a passphrase valid at the time of
backup allows decryption of the LUKS data area, even if the passphrase was
later changed or removed from the LUKS device. Also note that with a
header backup you lose the ability to securely wipe the LUKS device by
just overwriting the header and key-slots. You either need to securely
erase all header backups in addition or overwrite the encrypted data area
as well. The second option is less secure, as some sectors can survive,
e.g. due to defect management.
luksHeaderRestore <device> --header-backup-file <file>
- Restores a binary backup of the LUKS header and keyslot
area from the specified file.
Note: Using '-' as filename reads the header backup from a file named '-'.
WARNING: Header and keyslots will be replaced, only the passphrases
from the backup will work afterwards.
This command requires that the master key size and data offset of the LUKS
header already on the device and of the header backup match.
Alternatively, if there is no LUKS header on the device, the backup will
also be written to it.
repair <device>
- Tries to repair the LUKS device metadata if possible.
This command is useful to fix some known benign LUKS metadata header
corruptions. Only basic corruptions of unused keyslot are fixable. This
command will only change the LUKS header, not any key-slot data.
WARNING: Always create a binary backup of the original header before
calling this command.
loop-AES EXTENSION¶
cryptsetup supports mapping loop-AES encrypted partition using a compatibility
mode.
loopaesOpen <device> <name> --key-file <keyfile>
- Opens the loop-AES <device> and sets up a mapping
<name>.
If the key file is encrypted with GnuPG, then you have to use --key-file=-
and decrypt it before use, e.g. like this:
gpg --decrypt <keyfile> | cryptsetup loopaesOpen --key-file=-
<device> <name>
Use --key-file-size to specify the proper key length if needed.
Use --offset to specify device offset. Note that the units need to be
specified in number of 512 byte sectors.
Use --skip to specify the IV offset. If the original device used an
offset and but did not use it in IV sector calculations, you have to
explicitly use --skip 0 in addition to the offset parameter.
Use --hash to override the default hash function for passphrase
hashing (otherwise it is detected according to key size).
<options> can be [--key-file, --key-size, --offset, --skip,
--hash, --readonly, --allow-discards].
loopaesClose <name>
- Identical to remove.
See also section 7 of the FAQ and
http://loop-aes.sourceforge.net for
more information regarding loop-AES.
OPTIONS¶
- --verbose, -v
- Print more information on command execution.
- --debug
- Run in debug mode with full diagnostic logs. Debug output
lines are always prefixed by '#'.
- --hash, -h <hash-spec>
- Specifies the passphrase hash for create and
loopaesOpen.
Specifies the hash used in the LUKS key setup scheme and volume key digest
for luksFormat.
The specified hash name is passed to the compiled-in crypto backend.
Different backends may support different hashes. For luksFormat,
the hash algorithm must provide at least 160 bits of output, which
excludes, e.g., MD5. Do not use a non-crypto hash like
"crc32" as this breaks security.
Values compatible with old version of cryptsetup are
"ripemd160" for create and "sha1"
for luksFormat.
Use cryptsetup --help to show the defaults.
- --cipher, -c <cipher-spec>
- Set the cipher specification string.
cryptsetup --help shows the compiled-in defaults. The current
default in the distributed sources is "aes-cbc-essiv:sha256" for
both plain dm-crypt and LUKS.
For XTS mode (a possible future default), use "aes-xts-plain" or
better "aes-xts-plain64" as cipher specification and optionally
set a key size of 512 bits with the -s option. Key size for XTS mode is
twice that for other modes for the same security level.
XTS mode requires kernel 2.6.24 or later and plain64 requires kernel 2.6.33
or later. More information can be found in the FAQ.
- --verify-passphrase, -y
- When interactively asking for a passphrase, ask for it
twice and complain if both inputs do not match. Advised when creating a
regular mapping for the first time, or when running luksFormat.
Ignores on input from file or stdin.
- --key-file, -d name
- Read the passphrase from file.
If the name given is "-", then the passphrase will be read from
stdin. In this case, reading will not stop at newline characters.
With LUKS, passphrases supplied via --key-file are always the existing
passphrases requested by a command, except in the case of
luksFormat where --key-file is equivalent to the positional key
file argument.
If you want to set a new passphrase via key file, you have to use a
positional argument to luksAddKey.
See section NOTES ON PASSPHRASE PROCESSING for more information.
- --keyfile-offset value
- Skip value bytes at the beginning of the key file.
Works with all commands that accepts key files.
- --keyfile-size, -l value
- Read a maximum of value bytes from the key file.
Default is to read the whole file up to the compiled-in maximum that can
be queried with --help. Supplying more data than the compiled-in maximum
aborts the operation.
This option is useful to cut trailing newlines, for example. If
--keyfile-offset is also given, the size count starts after the offset.
Works with all commands that accepts key files.
- --new-keyfile-offset value
- Skip value bytes at the start when adding a new
passphrase from key file with luksAddKey.
- --new-keyfile-size value
- Read a maximum of value bytes when adding a new
passphrase from key file with luksAddKey. Default is to read the
whole file up to the compiled-in maximum length that can be queried with
--help. Supplying more than the compiled in maximum aborts the operation.
When --new-keyfile-offset is also given, reading starts after the
offset.
- --master-key-file
- Use a master key stored in a file.
For luksFormat this allows creating a LUKS header with this specific
master key. If the master key was taken from an existing LUKS header and
all other parameters are the same, then the new header decrypts the data
encrypted with the header the master key was taken from.
For luksAddKey this allows adding a new passphrase without having to
know an exiting one.
For luksOpen this allows to open the LUKS device without giving a
passphrase.
- --dump-master-key
- For luksDump this option includes the master key in
the displayed information. Use with care, as the master key can be used to
bypass the passphrases, see also option --master-key-file.
- --use-random
- --use-urandom
- For luksFormat these options define which kernel
random number generator will be used to create the master key (which is a
long-term key).
See NOTES ON RANDOM NUMBER GENERATORS for more information. Use
cryptsetup --help to show the compiled-in default random number
generator.
WARNING: In a low-entropy situation (e.g. in an embedded system),
both selections are problematic. Using /dev/urandom can lead to weak keys.
Using /dev/random can block a long time, potentially forever, if not
enough entropy can be harvested by the kernel.
- --key-slot, -S <0-7>
- For LUKS operations that add key material, this options
allows you to specify which key slot is selected for the new key. This
option can be used for luksFormat, and luksAddKey.
In addition, for luksOpen, this option selects a specific key-slot to
compare the passphrase against. If the given passphrase would only match a
different key-slot, the operation fails.
- --key-size, -s <bits>
- Sets key size in bits. The argument has to be a multiple of
8. The possible key-sizes are limited by the cipher and mode used.
See /proc/crypto for more information. Note that key-size in /proc/crypto is
stated in bytes.
This option can be used for create or luksFormat. All other
LUKS actions will use the key-size specified in the LUKS header. Use
cryptsetup --help to show the compiled-in defaults.
- --size, -b <number of 512 byte sectors>
- Force the size of the underlying device in sectors of 512
bytes. This option is only relevant for the create and
resize actions.
- --offset, -o <number of 512 byte sectors>
- Start offset in the backend device in 512-byte sectors.
This option is only relevant for the create and loopaesOpen
actions.
- --skip, -p <number of 512 byte sectors>
- How many sectors of the encrypted data to skip at the
beginning. This option is only relevant for create and
loopaesOpen action.
This is different from the --offset options with respect to the sector
numbers used in IV calculation. Using --offset will shift the IV
calculation by the same negative amount. Hence, if --offset n,
sector n will get a sector number of 0 for the IV
calculation. Using --skip causes sector n to also be the first
sector of the mapped device, but with its number for IV generation is
n.
- --readonly, -r
- set up a read-only mapping.
- --shared
- Creates an additional mapping for one common ciphertext
device. Arbitrary mappings are supported. This option is only relevant for
the create action. Use --offset, --size and --skip to specify the
mapped area.
- --iter-time, -i <number of milliseconds>
- The number of milliseconds to spend with PBKDF2 passphrase
processing. This option is only relevant for LUKS operations that set or
change passphrases, such as luksFormat or luksAddKey.
Specifying 0 as parameter selects the compiled-in default.
- --batch-mode, -q
- Suppresses all confirmation questions. Use with care!
If the -y option is not specified, this option also switches off the
passphrase verification for luksFormat.
- --timeout, -t <number of seconds>
- The number of seconds to wait before timeout on passphrase
input via terminal. It is relevant every time a passphrase is asked, for
example for create, luksOpen, luksFormat or
luksAddKey. It has no effect if used in conjunction with
--key-file.
This option is useful when the system should not stall if the user does not
input a passphrase, e.g. during boot. The default is a value of 0 seconds,
which means to wait forever.
- --tries, -T
- How often the input of the passphrase shall be retried.
This option is relevant every time a passphrase is asked, for example for
create, luksOpen, luksFormat or luksAddKey.
The default is 3 tries.
- --align-payload <number of 512 byte
sectors>
- Align payload at a boundary of value 512-byte
sectors. This option is relevant for luksFormat.
If not specified, cryptsetup tries to use the topology info provided by
kernel for the underlying device to get optimal alignment. If not
available (or the calculated value is a multiple of the default) data is
by default aligned to a 1MiB boundary (i.e. 2048 512-byte sectors).
For a detached LUKS header this option specifies the offset on the data
device. See also the --header option.
- --uuid=UUID
- Use the provided UUID for the luksFormat
command instead of generating new one. Changes the existing UUID when used
with the luksUUID command.
The UUID must be provided in the standard UUID format, e.g.
12345678-1234-1234-1234-123456789abc.
- --allow-discards
- Allow the use of discard (TRIM) requests for device. This
option is only relevant for create, luksOpen and
loopaesOpen.
WARNING: This command can have a negative security impact because it
can make filesystem-level operations visible on the physical device. For
example, information leaking filesystem type, used space, etc. may be
extractable from the physical device if the discarded blocks can be
located later. If in doubt, do no use it.
A kernel version of 3.1 or later is needed. For earlier kernels this option
is ignored.
- --header <device or file storing the LUKS
header>
- Use a detached (separated) metadata device or file where
the LUKS header is stored. This options allows to store ciphertext and
LUKS header on different devices.
This option is only relevant for LUKS devices and can be used with the
luksFormat, luksOpen, luksSuspend, luksResume,
status and resize commands.
For luksFormat with a file name as argument to --header, it has to
exist and be large enough to contain the LUKS header. See the cryptsetup
FAQ for header size calculation.
For other commands that change the LUKS header (e.g. luksAddKey),
specify the device or file with the LUKS header directly as the LUKS
device.
If used with luksFormat, the --align-payload option is taken as
absolute sector alignment on ciphertext device and can be zero.
WARNING: There is no check whether the ciphertext device specified
actually belongs to the header given. In fact you can specify an arbitrary
device as the ciphertext device for luksOpen with the --header
option. Use with care.
- --version
- Show the program version.
RETURN CODES¶
Cryptsetup returns 0 on success and a non-zero value on error.
Error codes are: 1 wrong parameters, 2 no permission (bad passphrase), 3 out of
memory, 4 wrong device specified, 5 device already exists or device is busy.
NOTES ON PASSPHRASE PROCESSING FOR PLAIN MODE¶
Note that no iterated hashing or salting is done in plain mode. If hashing is
done, it is a single direct hash. This means that low-entropy passphrases are
easy to attack in plain mode.
From a terminal: The passphrase is read until the first newline, i.e.
'\n'. The input without the newline character is processed with the default
hash or the hash specified with --hash. The has result will be truncated to
the key size of the used cipher, or the size specified with -s.
From stdin: Reading will continue until a newline (or until the maximum
input size is reached), with the trailing newline stripped. The maximum input
size is defined by the same compiled-in default as for the maximum key file
size and can be overwritten using --keyfile-size option.
The data read will be hashed with the default hash or the hash specified with
--hash. The has result will be truncated to the key size of the used cipher,
or the size specified with -s.
Note that if --key-file=- is used for reading the key from stdin, trailing
newlines are not stripped from the input.
If "plain" is used as argument to --hash, the input data will not be
hashed. Instead, it will be zero padded (if shorter than the key size) or
truncated (if longer than the key size) and used directly as the binary key.
This is useful for directly specifying a binary key. No warning will be given
if the amount of data read from stdin is less than the key size.
From a key file: It will be truncated to the key size of the used cipher
or the size given by -s and directly used as binary key. if the key file is
shorter than the key, cryptsetup will quit with an error.
NOTES ON PASSPHRASE PROCESSING FOR LUKS¶
LUKS uses PBKDF2 to protect against dictionary attacks and to give some
protection to low-entropy passphrases (see RFC 2898 and the cryptsetup FAQ).
From a terminal: The passphrase is read until the first newline and then
processed by PBKDF2 without the newline character.
From stdin: LUKS will read passphrases from stdin up to the first newline
character or the compiled-in maximum key file length. If --keyfile-size is
given, it is ignored.
From key file: The complete keyfile is read up to the compiled-in maximum
size. Newline characters do not terminate the input. The --keyfile-size option
can be used to limit what is read.
Passphrase processing: Whenever a passphrase is added to a LUKS header
(luksAddKey, luksFormat), the user may specify how much the time the
passphrase processing should consume. The time is used to determine the
iteration count for PBKDF2 and higher times will offer better protection for
low-entropy passphrases, but luksOpen will take longer to complete. For
passphrases that have entropy higher than the used key length, higher
iteration times will not increase security.
The default setting of one second is sufficient for most practical cases. The
only exception is a low-entropy passphrase used on a slow device.
INCOHERENT BEHAVIOR FOR INVALID PASSPHRASES/KEYS¶
LUKS checks for a valid passphrase when an encrypted partition is unlocked. The
behavior of plain dm-crypt is different. It will always decrypt with the
passphrase given. If the given passphrase is wrong, the device mapped by plain
dm-crypt will essentially still contain encrypted data and will be unreadable.
NOTES ON SUPPORTED CIPHERS, MODES, HASHES AND KEY SIZES¶
The available combinations of ciphers, modes, hashes and key sizes depend on
kernel support. See /proc/crypto for a list of available options. You might
need to load additional kernel crypto modules in order to get more options.
For the --hash option, if the crypto backend is libgcrypt, then all algorithms
supported by the gcrypt library are available. For other crypto backends some
algorithms may be missing.
NOTES ON PASSPHRASES¶
Mathematics can't be bribed. Make sure you keep your passphrases safe. There are
a few nice tricks for constructing a fallback, when suddenly out of the blue,
your brain refuses to cooperate. These fallbacks need LUKS, as it's only
possible with LUKS to have multiple passphrases. Still, if your attacker model
does not prevent it, storing your passphrase in a sealed envelope somewhere
may be a good idea as well.
NOTES ON RANDOM NUMBER GENERATORS¶
Random Number Generators (RNG) used in cryptsetup are always the kernel RNGs
without any modifications or additions to data stream produced.
There are two types of randomness cryptsetup/LUKS needs. One type (which always
uses /dev/urandom) is used for salts, the AF splitter and for wiping deleted
keyslots.
The second type is used for the volume (master) key. You can switch between
using /dev/random and /dev/urandom here, see
--use-random and
--use-urandom options. Using /dev/random on a system without enough
entropy sources can cause
luksFormat to block until the requested
amount of random data is gathered. In a low-entropy situation (embedded
system), this can take a very long time and potentially forever. At the same
time, using /dev/urandom in a low-entropy situation will produce low-quality
keys. This is a serious problem, but solving it is out of scope for a mere
man-page. See
urandom(4) for more information.
NOTES ON LOOPBACK DEVICE USE¶
Cryptsetup is usually used directly on a block device (disk partition or LVM
volume). However, if the device argument is a file, cryptsetup tries to
allocate a loopback device and map it into this file. This mode requires Linux
kernel 2.6.25 or more recent which supports the loop autoclear flag (loop
device is cleared on last close automatically). Of course, you can always map
a file to a loop-device manually. See the cryptsetup FAQ for an example.
When device mapping is active, you can see the loop backing file in the status
command output. Also see
losetup(8).
DEPRECATED ACTIONS¶
The
reload action is no longer supported. Please use
dmsetup(8) if
you need to directly manipulate with the device mapping table.
The
luksDelKey was replaced with
luksKillSlot.
REPORTING BUGS¶
Report bugs, including ones in the documentation, on the cryptsetup mailing list
at <dm-crypt@saout.de> or in the 'Issues' section on LUKS website.
Please attach the output of the failed command with the --debug option added.
AUTHORS¶
cryptsetup originally written by Christophe Saout <christophe@saout.de>
The LUKS extensions and original man page were written by Clemens Fruhwirth
<clemens@endorphin.org>.
Man page extensions by Milan Broz <gmazyland@gmail.com>.
Man page rewrite and extension by Arno Wagner <arno@wagner.name>.
COPYRIGHT¶
Copyright © 2004 Christophe Saout
Copyright © 2004-2006 Clemens Fruhwirth
Copyright © 2009-2011 Red Hat, Inc.
Copyright © 2012 Arno Wagner
This is free software; see the source for copying conditions. There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
SEE ALSO¶
The LUKS website at
http://code.google.com/p/cryptsetup/
The cryptsetup FAQ, contained in the distribution package and online at
http://code.google.com/p/cryptsetup/wiki/FrequentlyAskedQuestions
The cryptsetup mailing list and list archive, see FAQ entry 1.6.
The LUKS on-disk format specification available at
http://code.google.com/p/cryptsetup/wiki/Specification