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HTML rendering created 2025-09-06 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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NAME | SYNOPSIS | DESCRIPTION | OPTIONS | REPORTING BUGS | SEE ALSO | CRYPTSETUP |
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CRYPTSETUP...SCHANGEKEY(8) Maintenance CommandsCRYPTSETUP...SCHANGEKEY(8)
cryptsetup-luksChangeKey - change an existing passphrase
cryptsetup luksChangeKey [<options>] <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 the positional
argument.
If a keyslot is specified (via --key-slot), the passphrase for
that keyslot must be given, and the new passphrase will overwrite
the specified keyslot. If no keyslot is specified and there is
still a free keyslot, then the new passphrase will be put into a
free keyslot before the keyslot containing the old passphrase is
purged. If there is no free keyslot, then the keyslot with the old
passphrase is overwritten directly.
WARNING: If a keyslot is overwritten, a media failure during this
operation can cause the overwrite to fail after the old passphrase
has been wiped, making the LUKS container inaccessible. LUKS2
mitigates that by never overwriting the existing keyslot area as
long as there’s a free space in the keyslots area at least for one
more LUKS2 keyslot.
If you need to use both luksChangeKey and reencrypt (e.g., to
recover from a key leak), you need to use them in that order to
avoid leaking the new volume key.
Some parameters are effective only if used with the LUKS2 format
that supports per-keyslot parameters. For LUKS1, the PBKDF type
and hash algorithm are always the same for all keyslots.
<options> can be [--key-file, --keyfile-offset, --keyfile-size,
--new-keyfile-offset, --iter-time, --pbkdf,
--pbkdf-force-iterations, --pbkdf-memory, --pbkdf-parallel,
--new-keyfile-size, --key-slot, --force-password, --hash,
--header, --disable-locks, --type, --keyslot-cipher,
--keyslot-key-size, --timeout, --verify-passphrase].
--batch-mode, -q
Suppresses all confirmation questions. Use with care!
If the --verify-passphrase option is not specified, this
option also switches off the passphrase verification.
--debug or --debug-json
Run in debug mode with full diagnostic logs. Debug output
lines are always prefixed by #.
If --debug-json is used, additional LUKS2 JSON data structures
are printed.
--disable-locks
Disable lock protection for metadata on disk. This option is
valid only for LUKS2 and is ignored for other formats.
WARNING: Do not use this option unless you run cryptsetup in a
restricted environment where locking is impossible to perform
(where /run directory cannot be used).
--force-password
Do not use password quality checking for new LUKS passwords.
This option is ignored if cryptsetup is built without password
quality checking support.
For more info about password quality check, see the manual
page for pwquality.conf(5) and passwdqc.conf(5).
--hash, -h <hash-spec>
The specified hash is used for PBKDF2 and the AF splitter.
--header <device or file storing the LUKS header>
Use a detached (separated) metadata device or file where the
LUKS header is stored. This option allows one to store the
ciphertext and LUKS header on different devices.
For commands that change the LUKS header (e.g., luksAddKey),
specify the device or file with the LUKS header directly as
the LUKS device.
--help, -?
Show help text and default parameters.
--iter-time, -i <number of milliseconds>
The number of milliseconds to spend with PBKDF passphrase
processing. Specifying 0 as a parameter selects the
compiled-in default.
--key-file, -d file
Read the passphrase from the file.
If the name given is "-", then the passphrase will be read
from stdin. In this case, reading will not stop at newline
characters.
The passphrase supplied via --key-file is always the
passphrase for the existing keyslot requested by the command.
If you want to set a new passphrase via a key file, you have
to use a positional argument.
See section NOTES ON PASSPHRASE PROCESSING in cryptsetup(8)
for more information.
--keyfile-offset value
Skip value bytes at the beginning of the key file.
--keyfile-size, -l value
Read a maximum of value bytes from the key file. The 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.
--key-slot, -S <0-N>
For LUKS operations that add key material, this option allows
you to specify which keyslot is selected for the new key.
The maximum number of keyslots depends on the LUKS version.
LUKS1 can have up to 8 keyslots. LUKS2 can have up to 32
keyslots based on keyslot area size and key size, but a valid
keyslot ID can always be between 0 and 31 for LUKS2.
--keyslot-cipher <cipher-spec>
This option can be used to set specific cipher encryption for
the LUKS2 keyslot area.
--keyslot-key-size <bits>
This option can be used to set a specific key size for the
LUKS2 keyslot area.
--new-keyfile-offset value
Skip value bytes at the start when adding a new passphrase
from the key file.
--new-keyfile-size value
Read a maximum of value bytes when adding a new passphrase
from the key file. The 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.
--pbkdf <PBKDF spec>
Set Password-Based Key Derivation Function (PBKDF) algorithm
for LUKS keyslot. The PBKDF can be: pbkdf2 (for PBKDF2
according to RFC2898), argon2i for Argon2i or argon2id for
Argon2id (see Argon2
<https://www.cryptolux.org/index.php/Argon2> for more info).
For LUKS1, only PBKDF2 is accepted (no need to use this
option). The default PBKDF for LUKS2 is set during compilation
time and is available in the cryptsetup --help output.
A PBKDF is used for increasing the dictionary and brute-force
attack cost for keyslot passwords. The parameters can be time,
memory and parallel cost.
For PBKDF2, only the time cost (number of iterations) applies.
For Argon2i/id, there is also memory cost (memory required
during the process of key derivation) and parallel cost
(number of threads that run in parallel during the key
derivation.
Note that increasing memory cost also increases time, so the
final parameter values are measured by a benchmark. The
benchmark tries to find iteration time (--iter-time) with
required memory cost --pbkdf-memory. If it is not possible,
the memory cost is decreased as well. The parallel cost
--pbkdf-parallel is constant and is checked against available
CPU cores.
You can see all PBKDF parameters for a particular LUKS2
keyslot with the cryptsetup-luksDump(8) command.
If you do not want to use benchmark and want to specify all
parameters directly, use --pbkdf-force-iterations with
--pbkdf-memory and --pbkdf-parallel. This will override the
values without benchmarking. Note it can cause extremely long
unlocking time or cause out-of-memory conditions with
unconditional process termination. Use only in specific cases,
for example, if you know that the formatted device will be
used on some small embedded system.
MINIMAL AND MAXIMAL PBKDF COSTS: For PBKDF2, the minimum
iteration count is 1000 and the maximum is 4294967295 (maximum
for 32-bit unsigned integer). Memory and parallel costs are
not supported for PBKDF2. For Argon2i and Argon2id, the
minimum iteration count (CPU cost) is 4, and the maximum is
4294967295 (maximum for a 32-bit unsigned integer). Minimum
memory cost is 32 KiB and maximum is 4 GiB. If the memory cost
parameter is benchmarked (not specified by a parameter), it is
always in the range from 64 MiB to 1 GiB. Memory cost above
1GiB (up to the 4GiB maximum) can be setup only by the
--pbkdf-memory parameter. The parallel cost minimum is 1 and
maximum 4 (if enough CPU cores are available, otherwise it is
decreased by the available CPU cores).
WARNING: Increasing PBKDF computational costs above the
mentioned limits provides negligible additional security
improvement. While elevated costs significantly increase
brute-force overhead, they offer negligible protection against
dictionary attacks. The marginal cost increase for processing
an entire dictionary remains fundamentally insufficient.
The hardcoded PBKDF limits represent engineered trade-offs
between cryptographic security and operational usability. LUKS
maintains portability and must be used within a reasonable
time on resource-constrained systems.
Cryptsetup deliberately restricts maximum memory cost (4 GiB)
and parallel cost (4) parameters due to architectural
limitations (like embedded and legacy systems).
PBKDF memory cost mandates actual physical RAM allocation with
intensive write operations that must remain in physical RAM.
Any swap usage results in unacceptable performance
degradation. Memory management often overcommits allocations
beyond available physical memory, expecting most allocated
memory to remain unused. In such situations, as PBKDF always
uses all allocated memory, it frequently causes out-of-memory
failures that abort cryptsetup operations.
--pbkdf-force-iterations number
Avoid the PBKDF benchmark and set the time cost (iterations)
directly. It can be used only for a LUKS/LUKS2 device. See
--pbkdf option for more info.
--pbkdf-memory number
Set the memory cost for PBKDF (for Argon2i/id, the number
represents kilobytes). Note that it is the maximal value;
PBKDF benchmark or available physical memory can decrease it.
This option is not available for PBKDF2.
--pbkdf-parallel number
Set the parallel cost for PBKDF (number of threads, up to 4).
Note that it is the maximal value; it is decreased
automatically if the CPU online count is lower. This option is
not available for PBKDF2.
--timeout, -t seconds
The number of seconds to wait before a timeout on passphrase
input via terminal. It is relevant every time a passphrase is
asked. 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.
--type type
Specifies required device type, for more info, read the BASIC
ACTIONS section in cryptsetup(8).
--usage
Show short option help.
--verify-passphrase, -y
When interactively asking for a passphrase, ask for it twice
and complain if both inputs do not match. Ignored on input
from file or stdin.
--version, -V
Show the program version.
Report bugs at cryptsetup mailing list
<cryptsetup@lists.linux.dev> or in Issues project section
<https://gitlab.com/cryptsetup/cryptsetup/-/issues/new>.
Please attach the output of the failed command with --debug option
added.
Cryptsetup FAQ
<https://gitlab.com/cryptsetup/cryptsetup/wikis/FrequentlyAskedQuestions>
cryptsetup(8), integritysetup(8) and veritysetup(8)
Part of cryptsetup project
<https://gitlab.com/cryptsetup/cryptsetup/>. This page is part of
the Cryptsetup ((open-source disk encryption)) project.
Information about the project can be found at
⟨https://gitlab.com/cryptsetup/cryptsetup⟩. If you have a bug
report for this manual page, send it to dm-crypt@saout.de. This
page was obtained from the project's upstream Git repository
⟨https://gitlab.com/cryptsetup/cryptsetup.git⟩ on 2025-08-11. (At
that time, the date of the most recent commit that was found in
the repository was 2025-08-01.) If you discover any rendering
problems in this HTML version of the page, or you believe there is
a better or more up-to-date source for the page, or you have
corrections or improvements to the information in this COLOPHON
(which is not part of the original manual page), send a mail to
man-pages@man7.org
cryptsetup 2.8.1-git 2025-08-09 CRYPTSETUP...SCHANGEKEY(8)
Pages that refer to this page: cryptsetup(8)
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HTML rendering created 2025-09-06 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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