cryptsetup <options> <action> <action args>
cryptsetup is used to conveniently setup dm-crypt managed device-mapper
For basic (plain) dm-crypt mappings, 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, --key-size, --offset, --skip, --size, --readonly,
removes an existing mapping <name>.
reports the status for the mapping <name>.
resizes an active mapping <name>.
If --size (in sectors) is not specified, the size of the under-
lying block device is used.
LUKS, Linux Unified Key Setup, is a standard for hard disk encryption.
It standardizes a partition header as well as the format of the bulk
data. LUKS can manage multiple passwords that can be individually
revoked and effectively scrubbed from persistent media, and that are
protected against dictionary attacks with PBKDF2.
Each password, usually called a key in this document, is associated
with a slot, of which there are typically 8. Key operations that do
not specify a slot affect the first slot matching the supplied key.
These are valid LUKS actions:
luksFormat <device> [<key file>]
initializes a LUKS partition and sets the initial key, either
via prompting or via <key file>.
<options> can be [--cipher, --verify-passphrase, --key-size,
identical to remove.
suspends active device (all IO operations are frozen) and wipes
encryption key from kernel. Kernel version 2.6.19 or later is
After that operation you have to use luksResume to reinstate
encryption key (and resume device) or luksClose to remove mapped
WARNING: never try to suspend device where is the cryptsetup
<options> can be [--header].
Resumes suspended device and reinstates encryption key. You will
need provide passphrase identical to luksOpen command (using
prompting or key file).
<options> can be [--key-file, --keyfile-size, --header]
luksAddKey <device> [<new key file>]
add a new key file/passphrase. An existing passphrase or key
file (via --key-file) must be supplied. The key file with the
new material is supplied as a positional argument.
<options> can be [--key-file, --keyfile-size, --new-keyfile-
luksRemoveKey <device> [<key file>]
remove supplied key or key file from LUKS device in the manner
luksChangeKey <device> [<new key file>]
change existing key file or passphrase. An existing passphrase
or key file (via --key-file) must be supplied. The key file
with the new material is supplied as a positional argument.
If no key slot is specified (and there is still free key slot on
device) new slot is allocated before the old is purged.
If --key-slot option is specified (or there is no free slot)
command will overwrite existing slot.
<options> can be [--key-file, --keyfile-size].
print UUID, if <device> has a LUKS header.
set new UUID if --uuid option is specified.
returns true, if <device> is a LUKS partition. Otherwise, false.
dumps the header information of a LUKS partition.
If --dump-master-key option is used, the volume (master) key is
dumped instead of keyslot info.
Because this information can be used to access encrypted device
without passphrase knowledge (even without LUKS header) use this
option very carefully.
Dump with volume key (either printed or stored to file) should
be always stored encrypted and on safe place.
LUKS passphrase or key file is required for volume key dump.
<options> can be [--dump-master-key, --key-file, --keyfile-
luksHeaderBackup <device> --header-backup-file <file>
Stores binary backup of LUKS header and keyslot areas.
WARNING: Please note that with this backup file (and old
passphrase knowledge) you can decrypt data even if old
passphrase was wiped from real device.
Also note that anti-forensic splitter is not used during manipu-
lation with backup file.
luksHeaderRestore <device> --header-backup-file <file>
Restores binary backup of LUKS header and keyslot areas from
WARNING: All the keyslot areas are overwritten, only active
keyslots form backup file are available after issuing this com-
This command allows restoring header if device do not contain
LUKS header or if the master key size and data offset in LUKS
header on device match the backup file.
N.B. If key file is in GPG encrypted format, you have to use
--key-file=- and decrypt it before use. gpg --decrypt <keyfile>
| cryptsetup loopaesOpen --key-file=- <device> <name>
Use --key-file to specify proper key length, default compiled-in
parameters are visible in --help output.
Use --offset to specify device offset. Note the units need to be
specified in 512 bytes sectors.
Use --skip to specify IV offset. If original device used offset
and not used it in IV sector calculations, you have to explic-
itly use --skip 0 in addition to offset parameter.
Use --hash to override hash function for password hashing (oth-
erwise it is detected according to key size).
<options> can be [--key-file, --key-size, --offset, --skip,
--hash, --readonly, --allow-discards].
identical to remove.
For more information about loop-AES, see http://loop-aes.source-
Print more verbose messages.
Run in debug mode with full diagnostic logs.
For create and loopaesOpen action specifies hash to use for
For luksFormat action specifies hash used in LUKS key setup
scheme and volume key digest.
WARNING: setting hash other than sha1 causes LUKS device incom-
patible with older version of cryptsetup.
The hash string is passed to libgcrypt, so all hash algorithms
are supported (for luksFormat algorithm must provide at least 20
byte long hash). Default is set during compilation, compatible
values with old version of cryptsetup are "ripemd160" for create
action and "sha1" for luksFormat.
Use cryptsetup --help to show defaults.
set cipher specification string.
query for passwords twice. Useful when creating a (regular) map-
ping for the first time, or when running luksFormat.
use file as key material.
With LUKS, key material supplied in key files via -d are always
used for existing passphrases, except in luksFormat action where
-d is equivalent to positional key file argument.
If you want to set a new key via a key file, you have to use a
positional arg to luksAddKey.
If the key file is "-", stdin will be used. With the "-" key
file reading will not stop when new line character is detected.
See section NOTES ON PASSWORD PROCESSING for more information.
--keyfile-size, -l value
Limits read from key file to value bytes. Usable together with
all commands using key file.
Limits read from new key file to value bytes in luksAddKey when
adding new key file. Default is exhaustive read from key file.
Use pre-generated master key stored in file. For luksFormat it
allows LUKS header reformatting with the same master key (if all
other parameters are the same existing encrypted data remains
For luksAddKey it allows adding new passphrase with only master
For luksDump it allows LUKS header dump including volume (mas-
ter) key. Use with care (this information allows access to
device without passphrase knowledge).
See luksDump for more info.
For luksFormat it defines which kernel random number generator
will be used for long-term key (volume key).
See NOTES ON RNG for more information. Use cryptsetup --help to
show default RNG.
Can be used for create or luksFormat, all other LUKS actions
will use key-size specified by the LUKS header. Default is set
during compilation, if not changed it is 256 bits.
Use cryptsetup --help to show defaults.
force the size of the underlying device in sectors. This option
is only relevant for create and resize action.
start offset in the backend device (in 512-byte sectors). This
option is only relevant for create and loopaesOpen action.
how many sectors of the encrypted data to skip at the beginning.
This is different from the --offset options with respect to IV
calculations. Using --offset will shift the IV calculation by
the same negative amount. Hence, if --offset n, sector n will
be the first sector on the mapping with IV 0. Using --skip would
have resulted in sector n being the first sector also, but with
IV n. This option is only relevant for create and loopaesOpen
set up a read-only mapping.
create another non-overlapping mapping to one common ciphertext
device, e.g. to create hidden device inside another encrypted
device. This option is only relevant for create action. Use
--offset, --size and --skip to specify mapped area.
The number of milliseconds to spend with PBKDF2 password pro-
cessing. This option is only relevant to the LUKS operations as
luksFormat or luksAddKey. Note that 0 means default.
Do not ask for confirmation. Use with care! This option is only
relevant for luksFormat, luksAddKey, luksRemoveKey or luksKill-
The number of seconds to wait before timeout. This option is
relevant every time a password is asked, like create, luksOpen,
luksFormat or luksAddKey. It has no effect if used in conjunc-
tion with --key-file.
How often the input of the passphrase shall be retried. This
option is relevant every time a password is asked, like create,
luksOpen, luksFormat or luksAddKey. The default is 3 tries.
Use provided UUID in luksFormat command instead of generating
new one or change existing UUID in luksUUID command.
The UUID must be provided in standard UUID format (e.g.
Allow using of discards (TRIM) requests for device. This option
is only relevant for create, luksOpen or loopaesOpen.
WARNING: Assess the specific security risks carefully before
enabling this option. For example, allowing discards on
encrypted devices may lead to the leak of information about the
ciphertext device (filesystem type, used space etc.) if the
discarded blocks can be located easily on the device later.
Kernel version 3.1 or more recent is required. For older ver-
sions is the option ignored.
Set detached (separated) metadata device or file with LUKS
This options allows separation of ciphertext device and on-disk
This option is only relevant for LUKS devices and can be used in
luksFormat, luksOpen, luksSuspend, luksResume and resize com-
If used with luksFormat the --align-payload option is taken as
absolute sector alignment on ciphertext device and can be zero.
For other commands with separated metadata device you have to
always specify path to metadata device (not to the ciphertext
WARNING: There is no possible check that specified ciphertext
device is correct if on-disk header is detached. Use with care.
Show the version.
Crypsetup returns 0 on success or non-zero 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 PASSWORD PROCESSING FOR PLAIN MODE
From a terminal: Password processing is new-line sensitive, meaning the
reading will stop after encountering \n. It will process the read
If "plain" is used as an argument to the hash option, the input data
will not be hashed. Instead, it will be zero padded (if shorter than
the keysize) or truncated (if longer than the keysize) and used
directly as the key. No warning will be given if the amount of data
read from stdin is less than the keysize.
From a key file: It will be cropped to the size given by -s. If there
is insufficient key material in the key file, cryptsetup will quit with
If --key-file=- is used for reading the key from stdin, no trailing
newline is stripped from the input. Without that option, cryptsetup
strips trailing newlines from stdin input.
NOTES ON PASSWORD PROCESSING FOR LUKS
LUKS uses PBKDF2 to protect against dictionary attacks (see RFC 2898).
LUKS will always do an exhaustive password reading. Hence, password
can not be read from /dev/random, /dev/zero or any other stream that
does not terminate. To prevent exhausting of system memory, cryptsetup
limits maximum key file size. Compiled-in default is displayed in
--help output. You can limit reads from key file using --key-size
option, this option takes precedence over compiled-in default.
For any password creation action (luksAddKey, or luksFormat), the user
may specify how much the time the password processing should consume.
Increasing the time will lead to a more secure password, but also will
take luksOpen longer to complete. The default setting of one second is
sufficient for good security.
INCOHERENT BEHAVIOUR FOR INVALID PASSWORDS/KEYS
LUKS checks for a valid password or key when an encrypted partition is
unlocked. Thus the luksOpen action fails with invalid password or key,
contrary to the plain dm-crypt create action.
Please also be sure that you are using the same keyboard and language
setting as during device format.
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 --hash option all algorithms supported by gcrypt library are avail-
NOTES ON PASSWORDS
Mathematics can't be bribed. Make sure you keep your passwords safe.
There are a few nice tricks for constructing a fallback, when suddenly
out of (or after being) blue, your brain refuses to cooperate. These
fallbacks are possible with LUKS, as it's only possible with LUKS to
have multiple passwords.
urandom options. Using /dev/random on system without enough entropy
sources can cause luksFormat to block until the requested amount of
random data is gathered. See urandom(4) for more information.
NOTES ON LOOPBACK DEVICE USE
Cryptsetup is usually used directly over block device (like disk parti-
tion or LVM volume). However if the device argument is file, crypt-
setup tries to allocate loopback device and map it into this file. This
mode requires Linux kernel 2.6.25 or more recent which supports loop
autoclear flag (loop device is cleared on last close automatically).
When device mapping is active, you can see loop backing file in status
command output. Also see losetup(8).
cryptsetup is written by Christophe Saout <firstname.lastname@example.org>
LUKS extensions, and man page by Clemens Fruhwirth <clemens@endor-
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.
Report bugs to <email@example.com> or Issues section on LUKS website.
Please attach output of failed command with added --debug option.
Copyright (C) 2004 Christophe Saout
Copyright (C) 2004-2006 Clemens Fruhwirth
Copyright (C) 2009-2011 Red Hat, Inc.
This is free software; see the source for copying conditions. There is
NO warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR
LUKS website, http://code.google.com/p/cryptsetup/
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All Rights Reserved.