x SuSE Linux 13.1-RELEASE x
x SuSE Linux 13.1-RELEASEx
CRYPTSETUP(8) Maintenance Commands CRYPTSETUP(8)
NAME
cryptsetup - manage plain dm-crypt, LUKS, and other encrypted volumes
SYNOPSIS
cryptsetup <action> [<options>] <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.
In addition, cryptsetup provides limited support for the use of
loop-AES volumes, TrueCrypt, VeraCrypt, BitLocker and FileVault2
compatible volumes, and for hardware-based encryption on OPAL capable
drives.
For more information about specific cryptsetup action see
cryptsetup-<action>(8), where <action> is the name of the cryptsetup
action.
BASIC ACTIONS
The following are valid actions for all supported device types.
OPEN
open <device> <name> --type <device_type>
Opens (creates a mapping with) <name> backed by device <device>.
See cryptsetup-open(8).
CLOSE
close <name>
Removes the existing mapping <name> and wipes the key from kernel
memory.
See cryptsetup-close(8).
STATUS
status <name>
Reports the status for the mapping <name>.
See cryptsetup-status(8).
RESIZE
resize <name>
Resizes an active mapping <name>.
See cryptsetup-resize(8).
REFRESH
refresh <name>
Refreshes parameters of active mapping <name>.
See cryptsetup-refresh(8).
REENCRYPT
reencrypt <device> or --active-name <name> [<new_name>]
Run LUKS device reencryption.
See cryptsetup-reencrypt(8).
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 (opened), the usual device operations can be used on the mapped
device, including filesystem creation. Mapped devices usually reside in
/dev/mapper/<name>.
The following are valid plain device type actions:
OPEN
open --type plain <device> <name>
create <name> <device> (OBSOLETE syntax)
Opens (creates a mapping with) <name> backed by device <device>.
See cryptsetup-open(8).
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 Password-Based Key Derivation
Function (PBKDF).
LUKS2 is a new version of header format that allows additional
extensions like different PBKDF algorithm or authenticated encryption.
You can format device with LUKS2 header if you specify --type luks2 in
luksFormat command. For activation, the format is already recognized
automatically.
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 <device> parameter can also be specified by a LUKS UUID in the
format UUID=<uuid>. Translation to real device name uses symlinks in
/dev/disk/by-uuid directory.
To specify a detached header, the --header parameter can be used in all
LUKS commands and always takes precedence over the positional <device>
parameter.
The following are valid LUKS actions:
FORMAT
luksFormat <device> [<key file>]
Initializes a LUKS partition and sets the initial passphrase (for
key-slot 0).
See cryptsetup-luksFormat(8).
OPEN
open --type luks <device> <name>
luksOpen <device> <name> (old syntax)
Opens the LUKS device <device> and sets up a mapping <name> after
successful verification of the supplied passphrase.
See cryptsetup-open(8).
SUSPEND
luksSuspend <name>
Suspends an active device (all IO operations will block and accesses to
the device will wait indefinitely) and wipes the encryption key from
kernel memory.
See cryptsetup-luksSuspend(8).
RESUME
luksResume <name>
Resumes a suspended device and reinstates the encryption key.
See cryptsetup-luksResume(8).
ADD KEY
luksAddKey <device> [<key file with new key>]
Adds a new passphrase using an existing passphrase.
See cryptsetup-luksAddKey(8).
REMOVE KEY
luksRemoveKey <device> [<key file with passphrase to be removed>]
Removes the supplied passphrase from the LUKS device.
See cryptsetup-luksRemoveKey(8).
CHANGE KEY
luksChangeKey <device> [<new key file>]
Changes an existing passphrase.
See cryptsetup-luksChangeKey(8).
CONVERT KEY
luksConvertKey <device>
Converts an existing LUKS2 keyslot to new PBKDF parameters.
See cryptsetup-luksConvertKey(8).
KILL SLOT
luksKillSlot <device> <key slot number>
Wipe the key-slot number <key slot> from the LUKS device.
See cryptsetup-luksKillSlot(8).
ERASE
erase <device>
luksErase <device> (old syntax)
Erase all keyslots and make the LUKS container permanently
inaccessible.
See cryptsetup-erase(8).
UUID
luksUUID <device>
Print or set the UUID of a LUKS device.
See cryptsetup-luksUUID(8).
IS LUKS
isLuks <device>
Returns true, if <device> is a LUKS device, false otherwise.
See cryptsetup-isLuks(8).
DUMP
luksDump <device>
Dump the header information of a LUKS device.
See cryptsetup-luksDump(8).
HEADER BACKUP
luksHeaderBackup <device> --header-backup-file <file>
Stores a binary backup of the LUKS header and keyslot area.
See cryptsetup-luksHeaderBackup(8).
HEADER RESTORE
luksHeaderRestore <device> --header-backup-file <file>
Restores a binary backup of the LUKS header and keyslot area from the
specified file.
See cryptsetup-luksHeaderRestore(8).
TOKEN
token <add|remove|import|export> <device>
Manipulate token objects used for obtaining passphrases.
See cryptsetup-token(8).
CONVERT
convert <device> --type <format>
Converts the device between LUKS1 and LUKS2 format (if possible).
See cryptsetup-convert(8).
CONFIG
config <device>
Set permanent configuration options (store to LUKS header).
See cryptsetup-config(8).
LOOP-AES EXTENSION
cryptsetup supports mapping loop-AES encrypted partition using a
compatibility mode.
OPEN
open --type loopaes <device> <name> --key-file <keyfile>
loopaesOpen <device> <name> --key-file <keyfile> (old syntax)
Opens the loop-AES <device> and sets up a mapping <name>.
See cryptsetup-open(8).
See also section 7 of the FAQ and loop-AES
<http://loop-aes.sourceforge.net> for more information regarding
loop-AES.
TCRYPT (TRUECRYPT AND VERACRYPT COMPATIBLE) EXTENSION
cryptsetup supports mapping of TrueCrypt, tcplay or VeraCrypt encrypted
partition using a native Linux kernel API. Header formatting and TCRYPT
header change is not supported, cryptsetup never changes TCRYPT header
on-device.
TCRYPT extension requires kernel userspace crypto API to be available
(introduced in Linux kernel 2.6.38). If you are configuring kernel
yourself, enable "User-space interface for symmetric key cipher
algorithms" in "Cryptographic API" section (CRYPTO_USER_API_SKCIPHER
.config option).
Because TCRYPT header is encrypted, you have to always provide valid
passphrase and keyfiles.
Cryptsetup should recognize all header variants, except legacy cipher
chains using LRW encryption mode with 64 bits encryption block (namely
Blowfish in LRW mode is not recognized, this is limitation of kernel
crypto API).
VeraCrypt is extension of TrueCrypt header with increased iteration
count so unlocking can take quite a lot of time.
To open a VeraCrypt device with a custom Personal Iteration Multiplier
(PIM) value, use either the --veracrypt-pim=<PIM> option to directly
specify the PIM on the command- line or use --veracrypt-query-pim to be
prompted for the PIM.
The PIM value affects the number of iterations applied during key
derivation. Please refer to PIM
<https://www.veracrypt.fr/en/Personal%20Iterations%20Multiplier%20%28PIM%29.html>
for more detailed information.
If you need to disable VeraCrypt device support, use
--disable-veracrypt option.
NOTE: Activation with tcryptOpen is supported only for cipher chains
using LRW or XTS encryption modes.
The tcryptDump command should work for all recognized TCRYPT devices
and doesn't require superuser privilege.
To map system device (device with boot loader where the whole encrypted
system resides) use --tcrypt-system option. You can use partition
device as the parameter (parameter must be real partition device, not
an image in a file), then only this partition is mapped.
If you have the whole TCRYPT device as a file image and you want to map
multiple partition encrypted with system encryption, please create
loopback mapping with partitions first (losetup -P, see losetup(8) man
page for more info), and use loop partition as the device parameter.
If you use the whole base device as a parameter, one device for the
whole system encryption is mapped. This mode is available only for
backward compatibility with older cryptsetup versions which mapped
TCRYPT system encryption using the whole device.
To use hidden header (and map hidden device, if available), use
--tcrypt-hidden option.
To explicitly use backup (secondary) header, use --tcrypt-backup
option.
NOTE: There is no protection for a hidden volume if the outer volume is
mounted. The reason is that if there were any protection, it would
require some metadata describing what to protect in the outer volume
and the hidden volume would become detectable.
OPEN
open --type tcrypt <device> <name>
tcryptOpen_ <device> <name> (old syntax)
Opens the TCRYPT (a TrueCrypt-compatible) <device> and sets up a
mapping <name>.
See cryptsetup-open(8).
DUMP
tcryptDump <device>
Dump the header information of a TCRYPT device.
See cryptsetup-tcryptDump(8).
See also TrueCrypt <https://en.wikipedia.org/wiki/TrueCrypt> and
VeraCrypt <https://en.wikipedia.org/wiki/VeraCrypt> pages for more
information.
Please note that cryptsetup does not use TrueCrypt or VeraCrypt code,
please report all problems related to this compatibility extension to
the cryptsetup project.
BITLK (WINDOWS BITLOCKER COMPATIBLE) EXTENSION
cryptsetup supports mapping of BitLocker and BitLocker to Go encrypted
partition using a native Linux kernel API. Header formatting and BITLK
header changes are not supported, cryptsetup never changes BITLK header
on-device.
BITLK extension requires kernel userspace crypto API to be available
(for details see TCRYPT section).
Cryptsetup should recognize all BITLK header variants, except legacy
header used in Windows Vista systems and partially decrypted BitLocker
devices. Activation of legacy devices encrypted in CBC mode requires at
least Linux kernel version 5.3 and for devices using Elephant diffuser
kernel 5.6.
The bitlkDump command should work for all recognized BITLK devices and
doesn't require superuser privilege.
For unlocking with the open a password or a recovery passphrase or a
startup key must be provided.
Additionally unlocking using volume key is supported. You must provide
BitLocker Full Volume Encryption Key (FVEK) using the --volume-key-file
option. The key must be decrypted and without the header (only
128/256/512 bits of key data depending on used cipher and mode).
Other unlocking methods (TPM, SmartCard) are not supported.
OPEN
open --type bitlk <device> <name>
bitlkOpen <device> <name> (old syntax)
Opens the BITLK (a BitLocker-compatible) <device> and sets up a mapping
<name>.
See cryptsetup-open(8).
DUMP
bitlkDump <device>
Dump the header information of a BITLK device.
See cryptsetup-bitlkDump(8).
Please note that cryptsetup does not use any Windows BitLocker code,
please report all problems related to this compatibility extension to
the cryptsetup project.
FVAULT2 (APPLE MACOS FILEVAULT2 COMPATIBLE) EXTENSION
cryptsetup supports the mapping of FileVault2 (FileVault2 full-disk
encryption) by Apple for the macOS operating system using a native
Linux kernel API.
NOTE: cryptsetup supports only FileVault2 based on Core Storage and
HFS+ filesystem (introduced in MacOS X 10.7 Lion). It does NOT support
the new version of FileVault based on the APFS filesystem used in
recent macOS versions.
Header formatting and FVAULT2 header changes are not supported;
cryptsetup never changes the FVAULT2 header on-device.
FVAULT2 extension requires kernel userspace crypto API to be available
(for details, see TCRYPT section) and kernel driver for HFS+ (hfsplus)
filesystem.
Cryptsetup should recognize the basic configuration for portable
drives.
The fvault2Dump command should work for all recognized FVAULT2 devices
and doesn't require superuser privilege.
For unlocking with the open, a password must be provided. Other
unlocking methods are not supported.
OPEN
open --type fvault2 <device> <name>
fvault2Open <device> <name> (old syntax)
Opens the FVAULT2 (a FileVault2-compatible) <device> (usually the
second partition on the device) and sets up a mapping <name>.
See cryptsetup-open(8).
SED (SELF ENCRYPTING DRIVE) OPAL EXTENSION
cryptsetup supports using native hardware encryption on drives that
provide an OPAL interface, both nested with dm-crypt and standalone.
Passphrases, tokens and metadata are stored using the LUKS2 header
format, and are thus compatible with any software or system that uses
LUKS2 (e.g.: tokens).
WARNING: this support is new and experimental, and requires at least
kernel v6.4. Resizing devices is not supported.
--hw-opal can be specified for OPAL + dm-crypt, and --hw-opal-only can
be specified to use OPAL only, without a dm-crypt layer.
Opening, closing and enrolling tokens work in the same way as with
LUKS2 and dm-crypt. The new parameters are only necessary when
formatting, the LUKS2 metadata will ensure the right setup is performed
when opening or closing. If no subsystem is specified, it will be
automatically set to HW-OPAL so that it is immediately apparent when a
device uses OPAL.
FORMAT
luksFormat --type luks2 --hw-opal <device> [<key file>]
Additionally specify --hw-opal-only instead of --hw-opal to avoid the
dm-crypt layer. Other than the usual passphrase, an admin password will
have to be specified when formatting the first partition of the drive,
and will have to be re-supplied when formatting any other partition
until a factory reset is performed.
ERASE
erase <device>
Securely erase a partition or device. Requires admin password.
Additionally specify --hw-opal-factory-reset for a FULL factory reset
of the drive, using the drive's PSID (typically printed on the label)
instead of the admin password. WARNING: a factory reset will cause ALL
data on the device to be lost, regardless of the partition it is ran
on, if any, and regardless of any LUKS2 header backup.
MISCELLANEOUS ACTIONS
REPAIR
repair <device>
Tries to repair the device metadata if possible. Currently supported
only for LUKS device type.
See cryptsetup-repair(8).
BENCHMARK
benchmark <options>
Benchmarks ciphers and KDF (key derivation function).
See cryptsetup-benchmark(8).
PLAIN DM-CRYPT OR LUKS?
Unless you understand the cryptographic background well, use LUKS. With
plain dm-crypt there are a number of possible user errors that
massively decrease security. While LUKS cannot fix them all, it can
lessen the impact for many of them.
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 a backup of an encrypted
volume.
Character encoding: If you enter a passphrase with special symbols, the
passphrase can change depending on 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.
Previously used partitions: If a partition was previously used, it is a
very good idea to wipe filesystem signatures, data, etc. before
creating a LUKS or plain dm-crypt container on it. For a quick removal
of filesystem signatures, use wipefs(8). Take care though that this may
not remove everything. In particular, MD RAID signatures at the end of
a device may survive. It also does not remove data. For a full wipe,
overwrite the whole partition before container creation. If you do not
know how to do that, the cryptsetup FAQ describes several options.
EXAMPLES
Example 1: Create LUKS 2 container on block device /dev/sdX.
sudo cryptsetup --type luks2 luksFormat /dev/sdX
Example 2: Add an additional passphrase to key slot 5.
sudo cryptsetup luksAddKey --key-slot 5 /dev/sdX
Example 3: Create LUKS header backup and save it to file.
sudo cryptsetup luksHeaderBackup /dev/sdX --header-backup-file
/var/tmp/NameOfBackupFile
Example 4: Open LUKS container on /dev/sdX and map it to sdX_crypt.
sudo cryptsetup open /dev/sdX sdX_crypt
WARNING: The command in example 5 will erase all key slots.
Your cannot use your LUKS container afterward anymore unless you
have a backup to restore.
Example 5: Erase all key slots on /dev/sdX.
sudo cryptsetup erase /dev/sdX
Example 6: Restore LUKS header from backup file.
sudo cryptsetup luksHeaderRestore /dev/sdX --header-backup-file
/var/tmp/NameOfBackupFile
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
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 hash 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 hash 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 a binary key.
WARNING: The --hash argument is being ignored. The --hash option is
usable only for stdin input in plain mode.
If the key file is shorter than the key, cryptsetup will quit with an
error. 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.
Passphrase processing for LUKS
LUKS uses PBKDF to protect against dictionary attacks and to give some
protection to low-entropy passphrases (see 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 open 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 or two seconds is sufficient for most
practical cases. The only exception is a low-entropy passphrase used on
a device with a slow CPU, as this will result in a low iteration count.
On a slow device, it may be advisable to increase the iteration time
using the --iter-time option in order to obtain a higher iteration
count. This does slow down all later luksOpen operations accordingly.
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.
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 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.
Authenticated disk encryption (EXPERIMENTAL)
Since Linux kernel version 4.12 dm-crypt supports authenticated disk
encryption.
Normal disk encryption modes are length-preserving (plaintext sector is
of the same size as a ciphertext sector) and can provide only
confidentiality protection, but not cryptographically sound data
integrity protection.
Authenticated modes require additional space per-sector for
authentication tag and use Authenticated Encryption with Additional
Data (AEAD) algorithms.
If you configure LUKS2 device with data integrity protection, there
will be an underlying dm-integrity device, which provides additional
per-sector metadata space and also provide data journal protection to
ensure atomicity of data and metadata update. Because there must be
additional space for metadata and journal, the available space for the
device will be smaller than for length-preserving modes.
The dm-crypt device then resides on top of such a dm-integrity device.
All activation and deactivation of this device stack is performed by
cryptsetup, there is no difference in using luksOpen for integrity
protected devices. If you want to format LUKS2 device with data
integrity protection, use --integrity option (see
cryptsetup-luksFormat(8)).
Albeit Linux kernel 5.7 added TRIM support for standalone dm-integrity
devices, cryptsetup(8) can't offer support for discards (TRIM) in
authenticated encryption mode, because the underlying dm-crypt kernel
module does not support this functionality when dm-integrity is used as
auth tag space allocator (see --allow-discards in
cryptsetup-luksFormat(8)).
Some integrity modes requires two independent keys (key for encryption
and for authentication). Both these keys are stored in one LUKS
keyslot.
WARNING: All support for authenticated modes is experimental and there
are only some modes available for now. Note that there are a very few
authenticated encryption algorithms that are suitable for disk
encryption. You also cannot use CRC32 or any other non-cryptographic
checksums (other than the special integrity mode "none"). If for some
reason you want to have integrity control without using authentication
mode, then you should separately configure dm-integrity independently
of LUKS2.
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 the 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).
LUKS2 header locking
The LUKS2 on-disk metadata is updated in several steps and to achieve
proper atomic update, there is a locking mechanism. For an image in
file, code uses flock(2) system call. For a block device, lock is
performed over a special file stored in a locking directory (by default
/run/cryptsetup). The locking directory should be created with the
proper security context by the distribution during the boot-up phase.
Only LUKS2 uses locks, other formats do not use this mechanism.
LUKS on-disk format specification
For LUKS on-disk metadata specification see LUKS1
<https://gitlab.com/cryptsetup/cryptsetup/wikis/Specification> and
LUKS2 <https://gitlab.com/cryptsetup/LUKS2-docs>.
AUTHORS
Cryptsetup is originally written by Jana Saout <jana@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>.
REPORTING BUGS
Report bugs at cryptsetup mailing list <cryptsetup@lists.linux.dev> or
in Issues project section
<https://gitlab.com/cryptsetup/cryptsetup/-/issues/new>.
Please attach output of the failed command with --debug option added.
SEE ALSO
Cryptsetup FAQ
<https://gitlab.com/cryptsetup/cryptsetup/wikis/FrequentlyAskedQuestions>
cryptsetup(8), integritysetup(8) and veritysetup(8)
CRYPTSETUP
Part of cryptsetup project <https://gitlab.com/cryptsetup/cryptsetup/>.
cryptsetup 2.7.0 2024-08-30 CRYPTSETUP(8)
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