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NAME | SYNOPSIS | DESCRIPTION | KEY ACQUISITION | SUPPORTED OPTIONS | AF_UNIX KEY FILES | EXAMPLES | SEE ALSO | NOTES | COLOPHON |
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CRYPTTAB(5) crypttab CRYPTTAB(5)
crypttab - Configuration for encrypted block devices
/etc/crypttab
The /etc/crypttab file describes encrypted block devices that are
set up during system boot.
Empty lines and lines starting with the "#" character are
ignored. Each of the remaining lines describes one encrypted
block device. Fields are delimited by white space.
Each line is in the form
volume-name encrypted-device key-file options
The first two fields are mandatory, the remaining two are
optional.
Setting up encrypted block devices using this file supports four
encryption modes: LUKS, TrueCrypt, BitLocker and plain. See
cryptsetup(8) for more information about each mode. When no mode
is specified in the options field and the block device contains a
LUKS signature, it is opened as a LUKS device; otherwise, it is
assumed to be in raw dm-crypt (plain mode) format.
The four fields of /etc/crypttab are defined as follows:
1. The first field contains the name of the resulting volume
with decrypted data; its block device is set up below
/dev/mapper/.
2. The second field contains a path to the underlying block
device or file, or a specification of a block device via
"UUID=" followed by the UUID.
3. The third field specifies an absolute path to a file with the
encryption key. Optionally, the path may be followed by ":"
and an /etc/fstab style device specification (e.g. starting
with "LABEL=" or similar); in which case the path is taken
relative to the specified device's file system root. If the
field is not present or is "none" or "-", a key file named
after the volume to unlock (i.e. the first column of the
line), suffixed with .key is automatically loaded from the
/etc/cryptsetup-keys.d/ and /run/cryptsetup-keys.d/
directories, if present. Otherwise, the password has to be
manually entered during system boot. For swap encryption,
/dev/urandom may be used as key file, resulting in a
randomized key.
If the specified key file path refers to an AF_UNIX stream
socket in the file system, the key is acquired by connecting
to the socket and reading it from the connection. This allows
the implementation of a service to provide key information
dynamically, at the moment when it is needed. For details see
below.
4. The fourth field, if present, is a comma-delimited list of
options. The supported options are listed below.
Six different mechanisms for acquiring the decryption key or
passphrase unlocking the encrypted volume are supported.
Specifically:
1. Most prominently, the user may be queried interactively
during volume activation (i.e. typically at boot), asking
them to type in the necessary passphrases.
2. The (unencrypted) key may be read from a file on disk,
possibly on removable media. The third field of each line
encodes the location, for details see above.
3. The (unencrypted) key may be requested from another service,
by specifying an AF_UNIX file system socket in place of a key
file in the third field. For details see above and below.
4. The key may be acquired via a PKCS#11 compatible hardware
security token or smartcard. In this case a saved key used in
unlock process is stored on disk/removable media, acquired
via AF_UNIX, or stored in the LUKS2 JSON token metadata
header. For RSA, the saved key is an encrypted volume key.
The encrypted volume key is then decrypted by the PKCS#11
token with an RSA private key stored on it, and used to
unlock the encrypted volume. For elliptic-curve (EC)
cryptography, the saved key is the public key generated in
enrollment process. The public key is then used to derive a
shared secret with a private key stored in the PKCS#11 token.
The derived shared secret is then used to unlock the volume.
Use the pkcs11-uri= option described below to use this
mechanism.
5. Similarly, the key may be acquired via a FIDO2 compatible
hardware security token (which must implement the
"hmac-secret" extension). In this case a key generated
randomly during enrollment is stored on disk/removable media,
acquired via AF_UNIX, or stored in the LUKS2 JSON token
metadata header. The random key is hashed via a keyed hash
function (HMAC) on the FIDO2 token, using a secret key stored
on the token that never leaves it. The resulting hash value
is then used as key to unlock the encrypted volume. Use the
fido2-device= option described below to use this mechanism.
6. Similarly, the key may be acquired via a TPM2 security chip.
In this case a (during enrollment) randomly generated key —
encrypted by an asymmetric key derived from the TPM2 chip's
seed key — is stored on disk/removable media, acquired via
AF_UNIX, or stored in the LUKS2 JSON token metadata header.
Use the tpm2-device= option described below to use this
mechanism.
For the latter five mechanisms the source for the key material
used for unlocking the volume is primarily configured in the
third field of each /etc/crypttab line, but may also configured
in /etc/cryptsetup-keys.d/ and /run/cryptsetup-keys.d/ (see
above) or in the LUKS2 JSON token header (in case of the latter
three). Use the systemd-cryptenroll(1) tool to enroll PKCS#11,
FIDO2 and TPM2 devices in LUKS2 volumes.
The following options may be used in the fourth field of each
line:
cipher=
Specifies the cipher to use. See cryptsetup(8) for possible
values and the default value of this option. A cipher with
unpredictable IV values, such as "aes-cbc-essiv:sha256", is
recommended. Embedded commas in the cipher specification need
to be escaped by preceding them with a backslash, see example
below.
Added in version 186.
discard
Allow discard requests to be passed through the encrypted
block device. This improves performance on SSD storage but
has security implications.
Added in version 207.
hash=
Specifies the hash to use for password hashing. See
cryptsetup(8) for possible values and the default value of
this option.
Added in version 186.
header=
Use a detached (separated) metadata device or file where the
header containing the master key(s) is stored. This option is
only relevant for LUKS and TrueCrypt/VeraCrypt devices. See
cryptsetup(8) for possible values and the default value of
this option.
Optionally, the path may be followed by ":" and an /etc/fstab
device specification (e.g. starting with "UUID=" or similar);
in which case, the path is relative to the device file system
root. The device gets mounted automatically for LUKS device
activation duration only.
Added in version 219.
keyfile-offset=
Specifies the number of bytes to skip at the start of the key
file. See cryptsetup(8) for possible values and the default
value of this option.
Added in version 187.
keyfile-size=
Specifies the maximum number of bytes to read from the key
file. See cryptsetup(8) for possible values and the default
value of this option. This option is ignored in plain
encryption mode, as the key file size is then given by the
key size.
Added in version 188.
keyfile-erase
If enabled, the specified key file is erased after the volume
is activated or when activation fails. This is in particular
useful when the key file is only acquired transiently before
activation (e.g. via a file in /run/, generated by a service
running before activation), and shall be removed after use.
Defaults to off.
Added in version 246.
key-slot=
Specifies the key slot to compare the passphrase or key
against. If the key slot does not match the given passphrase
or key, but another would, the setup of the device will fail
regardless. This option implies luks. See cryptsetup(8) for
possible values. The default is to try all key slots in
sequential order.
Added in version 209.
keyfile-timeout=
Specifies the timeout for the device on which the key file
resides or the device used as the key file, and falls back to
a password if it could not be accessed. See
systemd-cryptsetup-generator(8) for key files on external
devices.
Added in version 243.
luks
Force LUKS mode. When this mode is used, the following
options are ignored since they are provided by the LUKS
header on the device: cipher=, hash=, size=.
Added in version 186.
bitlk
Decrypt BitLocker drive. Encryption parameters are deduced by
cryptsetup from BitLocker header.
Added in version 246.
_netdev
Marks this cryptsetup device as requiring network. It will be
started after the network is available, similarly to
systemd.mount(5) units marked with _netdev. The service unit
to set up this device will be ordered between
remote-fs-pre.target and remote-cryptsetup.target, instead of
cryptsetup-pre.target and cryptsetup.target.
Hint: if this device is used for a mount point that is
specified in fstab(5), the _netdev option should also be used
for the mount point. Otherwise, a dependency loop might be
created where the mount point will be pulled in by
local-fs.target, while the service to configure the network
is usually only started after the local file system has been
mounted.
Added in version 235.
noauto
This device will not be added to cryptsetup.target. This
means that it will not be automatically unlocked on boot,
unless something else pulls it in. In particular, if the
device is used for a mount point, it'll be unlocked
automatically during boot, unless the mount point itself is
also disabled with noauto.
Added in version 186.
nofail
This device will not be a hard dependency of
cryptsetup.target. It'll still be pulled in and started, but
the system will not wait for the device to show up and be
unlocked, and boot will not fail if this is unsuccessful.
Note that other units that depend on the unlocked device may
still fail. In particular, if the device is used for a mount
point, the mount point itself also needs to have the nofail
option, or the boot will fail if the device is not unlocked
successfully. If a keyfile and/or a header are specified, the
dependencies on their respective directories will also not be
fatal, so that umounting said directories will not cause the
generated cryptset unit to be deactivated.
Added in version 186.
offset=
Start offset in the backend device, in 512-byte sectors. This
option is only relevant for plain devices.
Added in version 220.
plain
Force plain encryption mode.
Added in version 186.
read-only, readonly
Set up the encrypted block device in read-only mode.
Added in version 186.
same-cpu-crypt
Perform encryption using the same CPU that IO was submitted
on. The default is to use an unbound workqueue so that
encryption work is automatically balanced between available
CPUs.
This requires kernel 4.0 or newer.
Added in version 242.
submit-from-crypt-cpus
Disable offloading writes to a separate thread after
encryption. There are some situations where offloading write
requests from the encryption threads to a dedicated thread
degrades performance significantly. The default is to offload
write requests to a dedicated thread because it benefits the
CFQ scheduler to have writes submitted using the same
context.
This requires kernel 4.0 or newer.
Added in version 242.
no-read-workqueue
Bypass dm-crypt internal workqueue and process read requests
synchronously. The default is to queue these requests and
process them asynchronously.
This requires kernel 5.9 or newer.
Added in version 248.
no-write-workqueue
Bypass dm-crypt internal workqueue and process write requests
synchronously. The default is to queue these requests and
process them asynchronously.
This requires kernel 5.9 or newer.
Added in version 248.
skip=
How many 512-byte sectors of the encrypted data to skip at
the beginning. This is different from the offset= option with
respect to the sector numbers used in initialization vector
(IV) calculation. Using offset= will shift the IV calculation
by the same negative amount. Hence, if offset=n is given,
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 being n.
This option is only relevant for plain devices.
Added in version 220.
size=
Specifies the key size in bits. See cryptsetup(8) for
possible values and the default value of this option.
Added in version 186.
sector-size=
Specifies the sector size in bytes. See cryptsetup(8) for
possible values and the default value of this option.
Added in version 240.
swap
The encrypted block device will be used as a swap device, and
will be formatted accordingly after setting up the encrypted
block device, with mkswap(8). This option implies plain.
WARNING: Using the swap option will destroy the contents of
the named partition during every boot, so make sure the
underlying block device is specified correctly.
Added in version 186.
tcrypt
Use TrueCrypt encryption mode. When this mode is used, the
following options are ignored since they are provided by the
TrueCrypt header on the device or do not apply: cipher=,
hash=, keyfile-offset=, keyfile-size=, size=.
When this mode is used, the passphrase is read from the key
file given in the third field. Only the first line of this
file is read, excluding the new line character.
Note that the TrueCrypt format uses both passphrase and key
files to derive a password for the volume. Therefore, the
passphrase and all key files need to be provided. Use
tcrypt-keyfile= to provide the absolute path to all key
files. When using an empty passphrase in combination with one
or more key files, use "/dev/null" as the password file in
the third field.
Added in version 206.
tcrypt-hidden
Use the hidden TrueCrypt volume. This option implies tcrypt.
This will map the hidden volume that is inside of the volume
provided in the second field. Please note that there is no
protection for the hidden volume if the outer volume is
mounted instead. See cryptsetup(8) for more information on
this limitation.
Added in version 206.
tcrypt-keyfile=
Specifies the absolute path to a key file to use for a
TrueCrypt volume. This implies tcrypt and can be used more
than once to provide several key files.
See the entry for tcrypt on the behavior of the passphrase
and key files when using TrueCrypt encryption mode.
Added in version 206.
tcrypt-system
Use TrueCrypt in system encryption mode. This option implies
tcrypt.
Added in version 206.
tcrypt-veracrypt
Check for a VeraCrypt volume. VeraCrypt is a fork of
TrueCrypt that is mostly compatible, but uses different,
stronger key derivation algorithms that cannot be detected
without this flag. Enabling this option could substantially
slow down unlocking, because VeraCrypt's key derivation takes
much longer than TrueCrypt's. This option implies tcrypt.
Added in version 232.
veracrypt-pim=
Specifies a custom Personal Iteration Multiplier (PIM) value,
which can range from 0..2147468 for standard veracrypt
volumes and 0..65535 for veracrypt system volumes. A value of
0 will imply the VeraCrypt default. This option is only
effective when tcrypt-veracrypt is set.
Note that VeraCrypt enforces a minimal allowed PIM value
depending on the password strength and the hash algorithm
used for key derivation, however veracrypt-pim= is not
checked against these bounds. See Veracrypt Personal
Iterations Multiplier[1] documentation for more information.
Added in version 254.
timeout=
Specifies the timeout for querying for a password. If no unit
is specified, seconds is used. Supported units are s, ms, us,
min, h, d. A timeout of 0 waits indefinitely (which is the
default).
Added in version 186.
tmp=
The encrypted block device will be prepared for using it as
/tmp/; it will be formatted using mkfs(8). Takes a file
system type as argument, such as "ext4", "xfs" or "btrfs". If
no argument is specified defaults to "ext4". This option
implies plain.
WARNING: Using the tmp option will destroy the contents of
the named partition during every boot, so make sure the
underlying block device is specified correctly.
Added in version 186.
tries=
Specifies the maximum number of times the user is queried for
a password. The default is 3. If set to 0, the user is
queried for a password indefinitely.
Added in version 186.
headless=
Takes a boolean argument, defaults to false. If true, never
query interactively for the password/PIN. Useful for headless
systems.
Added in version 249.
verify
If the encryption password is read from console, it has to be
entered twice to prevent typos.
Added in version 186.
password-echo=yes|no|masked
Controls whether to echo passwords or security token PINs
that are read from console. Takes a boolean or the special
string "masked". The default is password-echo=masked.
If enabled, the typed characters are echoed literally. If
disabled, the typed characters are not echoed in any form,
the user will not get feedback on their input. If set to
"masked", an asterisk ("*") is echoed for each character
typed. Regardless of which mode is chosen, if the user hits
the tabulator key ("↹") at any time, or the backspace key
("⌫") before any other data has been entered, then echo is
turned off.
Added in version 249.
pkcs11-uri=
Takes either the special value "auto" or an RFC7512 PKCS#11
URI[2] pointing to a private key which is used to decrypt the
encrypted key specified in the third column of the line. This
is useful for unlocking encrypted volumes through PKCS#11
compatible security tokens or smartcards. See below for an
example how to set up this mechanism for unlocking a LUKS2
volume with a YubiKey security token.
If specified as "auto" the volume must be of type LUKS2 and
must carry PKCS#11 security token metadata in its LUKS2 JSON
token section. In this mode the URI and the encrypted key are
automatically read from the LUKS2 JSON token header. Use
systemd-cryptenroll(1) as a simple tool for enrolling PKCS#11
security tokens or smartcards in a way compatible with
"auto". In this mode the third column of the line should
remain empty (that is, specified as "-").
The specified URI can refer directly to a private key stored
on a token or alternatively just to a slot or token, in which
case a search for a suitable private key will be performed.
In this case if multiple suitable objects are found the token
is refused. The keyfile configured in the third column of the
line is used as is (i.e. in binary form, unprocessed). The
resulting decrypted key (for RSA) or derived shared secret
(for ECC) is then Base64 encoded before it is used to unlock
the LUKS volume.
Use systemd-cryptenroll --pkcs11-token-uri=list to list all
suitable PKCS#11 security tokens currently plugged in, along
with their URIs.
Note that many newer security tokens that may be used as
PKCS#11 security token typically also implement the newer and
simpler FIDO2 standard. Consider using fido2-device=
(described below) to enroll it via FIDO2 instead. Note that a
security token enrolled via PKCS#11 cannot be used to unlock
the volume via FIDO2, unless also enrolled via FIDO2, and
vice versa.
Added in version 245.
fido2-device=
Takes either the special value "auto" or the path to a
"hidraw" device node (e.g. /dev/hidraw1) referring to a
FIDO2 security token that implements the "hmac-secret"
extension (most current hardware security tokens do). See
below for an example how to set up this mechanism for
unlocking an encrypted volume with a FIDO2 security token.
If specified as "auto" the FIDO2 token device is
automatically discovered, as it is plugged in.
FIDO2 volume unlocking requires a client ID hash (CID) to be
configured via fido2-cid= (see below) and a key to pass to
the security token's HMAC functionality (configured in the
line's third column) to operate. If not configured and the
volume is of type LUKS2, the CID and the key are read from
LUKS2 JSON token metadata instead. Use systemd-cryptenroll(1)
as simple tool for enrolling FIDO2 security tokens,
compatible with this automatic mode, which is only available
for LUKS2 volumes.
Use systemd-cryptenroll --fido2-device=list to list all
suitable FIDO2 security tokens currently plugged in, along
with their device nodes.
This option implements the following mechanism: the
configured key is hashed via they HMAC keyed hash function
the FIDO2 device implements, keyed by a secret key embedded
on the device. The resulting hash value is Base64 encoded and
used to unlock the LUKS2 volume. As it should not be possible
to extract the secret from the hardware token, it should not
be possible to retrieve the hashed key given the configured
key — without possessing the hardware token.
Note that many security tokens that implement FIDO2 also
implement PKCS#11, suitable for unlocking volumes via the
pkcs11-uri= option described above. Typically the newer,
simpler FIDO2 standard is preferable.
Added in version 248.
fido2-cid=
Takes a Base64 encoded FIDO2 client ID to use for the FIDO2
unlock operation. If specified, but fido2-device= is not,
fido2-device=auto is implied. If fido2-device= is used but
fido2-cid= is not, the volume must be of LUKS2 type, and the
CID is read from the LUKS2 JSON token header. Use
systemd-cryptenroll(1) for enrolling a FIDO2 token in the
LUKS2 header compatible with this automatic mode.
Added in version 248.
fido2-rp=
Takes a string, configuring the FIDO2 Relying Party (rp) for
the FIDO2 unlock operation. If not specified
"io.systemd.cryptsetup" is used, except if the LUKS2 JSON
token header contains a different value. It should normally
not be necessary to override this.
Added in version 248.
tpm2-device=
Takes either the special value "auto" or the path to a device
node (e.g. /dev/tpmrm0) referring to a TPM2 security chip.
See below for an example how to set up this mechanism for
unlocking an encrypted volume with a TPM2 chip.
Use tpm2-pcrs= (see below) to configure the set of TPM2 PCRs
to bind the volume unlocking to. Use systemd-cryptenroll(1)
as simple tool for enrolling TPM2 security chips in LUKS2
volumes.
If specified as "auto" the TPM2 device is automatically
discovered. Use systemd-cryptenroll --tpm2-device=list to
list all suitable TPM2 devices currently available, along
with their device nodes.
This option implements the following mechanism: when
enrolling a TPM2 device via systemd-cryptenroll on a LUKS2
volume, a randomized key unlocking the volume is generated on
the host and loaded into the TPM2 chip where it is encrypted
with an asymmetric "primary" key pair derived from the TPM2's
internal "seed" key. Neither the seed key nor the primary key
are permitted to ever leave the TPM2 chip — however, the now
encrypted randomized key may. It is saved in the LUKS2 volume
JSON token header. When unlocking the encrypted volume, the
primary key pair is generated on the TPM2 chip again (which
works as long as the chip's seed key is correctly maintained
by the TPM2 chip), which is then used to decrypt (on the TPM2
chip) the encrypted key from the LUKS2 volume JSON token
header saved there during enrollment. The resulting decrypted
key is then used to unlock the volume. When the randomized
key is encrypted the current values of the selected PCRs (see
below) are included in the operation, so that different PCR
state results in different encrypted keys and the decrypted
key can only be recovered if the same PCR state is
reproduced.
Added in version 248.
tpm2-pcrs=
Takes a "+" separated list of numeric TPM2 PCR (i.e.
"Platform Configuration Register") indexes to bind the TPM2
volume unlocking to. This option is only useful when TPM2
enrollment metadata is not available in the LUKS2 JSON token
header already, the way systemd-cryptenroll writes it there.
If not used (and no metadata in the LUKS2 JSON token header
defines it), defaults to a list of a single entry: PCR 7.
Assign an empty string to encode a policy that binds the key
to no PCRs, making the key accessible to local programs
regardless of the current PCR state.
Added in version 248.
tpm2-pin=
Takes a boolean argument, defaults to "false". Controls
whether TPM2 volume unlocking is bound to a PIN in addition
to PCRs. Similarly, this option is only useful when TPM2
enrollment metadata is not available.
Added in version 251.
tpm2-signature=
Takes an absolute path to a TPM2 PCR JSON signature file, as
produced by the systemd-measure(1) tool. This permits locking
LUKS2 volumes to any PCR values for which a valid signature
matching a public key specified at key enrollment time can be
provided. See systemd-cryptenroll(1) for details on enrolling
TPM2 PCR public keys. If this option is not specified but it
is attempted to unlock a LUKS2 volume with a signed TPM2 PCR
enrollment a suitable signature file tpm2-pcr-signature.json
is searched for in /etc/systemd/, /run/systemd/,
/usr/lib/systemd/ (in this order).
Added in version 252.
tpm2-pcrlock=
Takes an absolute path to a TPM2 pcrlock policy file, as
produced by the systemd-pcrlock(1) tool. This permits locking
LUKS2 volumes to a local policy of allowed PCR values with
variants. See systemd-cryptenroll(1) for details on enrolling
TPM2 pcrlock policies. If this option is not specified but it
is attempted to unlock a LUKS2 volume with a TPM2 pcrlock
enrollment a suitable signature file pcrlock.json is searched
for in /run/systemd/ and /var/lib/systemd/ (in this order).
Added in version 255.
tpm2-measure-pcr=
Controls whether to measure the volume key of the encrypted
volume to a TPM2 PCR. If set to "no" (which is the default)
no PCR extension is done. If set to "yes" the volume key is
measured into PCR 15. If set to a decimal integer in the
range 0...23 the volume key is measured into the specified
PCR. The volume key is measured along with the activated
volume name and its UUID. This functionality is particularly
useful for the encrypted volume backing the root file system,
as it then allows later TPM objects to be securely bound to
the root file system and hence the specific installation.
Added in version 253.
tpm2-measure-bank=
Selects one or more TPM2 PCR banks to measure the volume key
into, as configured with tpm2-measure-pcr= above. Multiple
banks may be specified, separated by a colon character. If
not specified automatically determines available and used
banks. Expects a message digest name (e.g. "sha1", "sha256",
...) as argument, to identify the bank.
Added in version 253.
token-timeout=
Specifies how long to wait at most for configured security
devices (i.e. FIDO2, PKCS#11, TPM2) to show up. Takes a time
value in seconds (but other time units may be specified too,
see systemd.time(7) for supported formats). Defaults to 30s.
Once the specified timeout elapsed authentication via
password is attempted. Note that this timeout applies to
waiting for the security device to show up — it does not
apply to the PIN prompt for the device (should one be needed)
or similar. Pass 0 to turn off the time-out and wait forever.
Added in version 250.
try-empty-password=
Takes a boolean argument. If enabled, right before asking the
user for a password it is first attempted to unlock the
volume with an empty password. This is useful for systems
that are initialized with an encrypted volume with only an
empty password set, which shall be replaced with a suitable
password during first boot, but after activation.
Added in version 246.
x-systemd.device-timeout=
Specifies how long systemd should wait for a block device to
show up before giving up on the entry. The argument is a time
in seconds or explicitly specified units of "s", "min", "h",
"ms".
Added in version 216.
x-initrd.attach
Setup this encrypted block device in the initrd, similarly to
systemd.mount(5) units marked with x-initrd.mount.
Although it's not necessary to mark the mount entry for the
root file system with x-initrd.mount, x-initrd.attach is
still recommended with the encrypted block device containing
the root file system as otherwise systemd will attempt to
detach the device during the regular system shutdown while
it's still in use. With this option the device will still be
detached but later after the root file system is unmounted.
All other encrypted block devices that contain file systems
mounted in the initrd should use this option.
Added in version 245.
At early boot and when the system manager configuration is
reloaded, this file is translated into native systemd units by
systemd-cryptsetup-generator(8).
If the key file path (as specified in the third column of
/etc/crypttab entries, see above) refers to an AF_UNIX stream
socket in the file system, the key is acquired by connecting to
the socket and reading the key from the connection. The
connection is made from an AF_UNIX socket name in the abstract
namespace, see unix(7) for details. The source socket name is
chosen according the following format:
NUL RANDOM /cryptsetup/ VOLUME
In other words: a NUL byte (as required for abstract namespace
sockets), followed by a random string (consisting of alphanumeric
characters only), followed by the literal string "/cryptsetup/",
followed by the name of the volume to acquire they key for. For
example, for the volume "myvol":
\0d7067f78d9827418/cryptsetup/myvol
Services listening on the AF_UNIX stream socket may query the
source socket name with getpeername(2), and use this to determine
which key to send, allowing a single listening socket to serve
keys for multiple volumes. If the PKCS#11 logic is used (see
above), the socket source name is picked in similar fashion,
except that the literal string "/cryptsetup-pkcs11/" is used. And
similarly for FIDO2 ("/cryptsetup-fido2/") and TPM2
("/cryptsetup-tpm2/"). A different path component is used so that
services providing key material know that the secret key was not
requested directly, but instead an encrypted key that will be
decrypted via the PKCS#11/FIDO2/TPM2 logic to acquire the final
secret key.
Example 1. /etc/crypttab example
Set up four encrypted block devices. One using LUKS for normal
storage, another one for usage as a swap device and two TrueCrypt
volumes. For the fourth device, the option string is interpreted
as two options "cipher=xchacha12,aes-adiantum-plain64",
"keyfile-timeout=10s".
luks UUID=2505567a-9e27-4efe-a4d5-15ad146c258b
swap /dev/sda7 /dev/urandom swap
truecrypt /dev/sda2 /etc/container_password tcrypt
hidden /mnt/tc_hidden /dev/null tcrypt-hidden,tcrypt-keyfile=/etc/keyfile
external /dev/sda3 keyfile:LABEL=keydev keyfile-timeout=10s,cipher=xchacha12\,aes-adiantum-plain64
Example 2. Yubikey-based PKCS#11 Volume Unlocking Example
The PKCS#11 logic allows hooking up any compatible security token
that is capable of storing RSA or EC cryptographic keys for
unlocking an encrypted volume. Here's an example how to set up a
Yubikey security token for this purpose on a LUKS2 volume, using
ykmap(1) from the yubikey-manager project to initialize the token
and systemd-cryptenroll(1) to add it in the LUKS2 volume:
# SPDX-License-Identifier: MIT-0
# Destroy any old key on the Yubikey (careful!)
ykman piv reset
# Generate a new private/public key pair on the device, store the public key in
# 'pubkey.pem'.
ykman piv generate-key -a RSA2048 9d pubkey.pem
# Create a self-signed certificate from this public key, and store it on the
# device. The "subject" should be an arbitrary user-chosen string to identify
# the token with.
ykman piv generate-certificate --subject "Knobelei" 9d pubkey.pem
# We don't need the public key anymore, let's remove it. Since it is not
# security sensitive we just do a regular "rm" here.
rm pubkey.pem
# Enroll the freshly initialized security token in the LUKS2 volume. Replace
# /dev/sdXn by the partition to use (e.g. /dev/sda1).
sudo systemd-cryptenroll --pkcs11-token-uri=auto /dev/sdXn
# Test: Let's run systemd-cryptsetup to test if this all worked.
sudo systemd-cryptsetup attach mytest /dev/sdXn - pkcs11-uri=auto
# If that worked, let's now add the same line persistently to /etc/crypttab,
# for the future. We don't want to use the (unstable) /dev/sdX name, so let's
# figure out a stable link:
udevadm info -q -r symlink /dev/sdXn
# Now add the line using the by-uuid symlink to /etc/crypttab:
sudo bash -c 'echo "mytest /dev/disk/by-uuid/... - pkcs11-uri=auto" >>/etc/crypttab'
# Depending on your distribution and encryption setup, you may need to manually
# regenerate your initramfs to be able to use a Yubikey / PKCS#11 token to
# unlock the partition during early boot.
# More information at https://unix.stackexchange.com/a/705809.
# On Fedora based systems:
sudo dracut --force
# On Debian based systems:
sudo update-initramfs -u
A few notes on the above:
• We use RSA2048, which is the longest key size current
Yubikeys support
• We use Yubikey key slot 9d, since that's apparently the
keyslot to use for decryption purposes, see Yubico PIV
certificate slots[3].
Example 3. FIDO2 Volume Unlocking Example
The FIDO2 logic allows using any compatible FIDO2 security token
that implements the "hmac-secret" extension for unlocking an
encrypted volume. Here's an example how to set up a FIDO2
security token for this purpose for a LUKS2 volume, using
systemd-cryptenroll(1):
# SPDX-License-Identifier: MIT-0
# Enroll the security token in the LUKS2 volume. Replace /dev/sdXn by the
# partition to use (e.g. /dev/sda1).
sudo systemd-cryptenroll --fido2-device=auto /dev/sdXn
# Test: Let's run systemd-cryptsetup to test if this worked.
sudo systemd-cryptsetup attach mytest /dev/sdXn - fido2-device=auto
# If that worked, let's now add the same line persistently to /etc/crypttab,
# for the future. We don't want to use the (unstable) /dev/sdX name, so let's
# figure out a stable link:
udevadm info -q -r symlink /dev/sdXn
# Now add the line using the by-uuid symlink to /etc/crypttab:
sudo bash -c 'echo "mytest /dev/disk/by-uuid/... - fido2-device=auto" >>/etc/crypttab'
# Depending on your distribution and encryption setup, you may need to manually
# regenerate your initramfs to be able to use a FIDO2 device to unlock the
# partition during early boot.
# More information at https://unix.stackexchange.com/a/705809.
# On Fedora based systems:
sudo dracut --force
# On Debian based systems:
sudo update-initramfs -u
Example 4. TPM2 Volume Unlocking Example
The TPM2 logic allows using any TPM2 chip supported by the Linux
kernel for unlocking an encrypted volume. Here's an example how
to set up a TPM2 chip for this purpose for a LUKS2 volume, using
systemd-cryptenroll(1):
# SPDX-License-Identifier: MIT-0
# Enroll the TPM2 security chip in the LUKS2 volume, and bind it to PCR 7
# only. Replace /dev/sdXn by the partition to use (e.g. /dev/sda1).
sudo systemd-cryptenroll --tpm2-device=auto --tpm2-pcrs=7 /dev/sdXn
# Test: Let's run systemd-cryptsetup to test if this worked.
sudo systemd-cryptsetup attach mytest /dev/sdXn - tpm2-device=auto
# If that worked, let's now add the same line persistently to /etc/crypttab,
# for the future. We don't want to use the (unstable) /dev/sdX name, so let's
# figure out a stable link:
udevadm info -q -r symlink /dev/sdXn
# Now add the line using the by-uuid symlink to /etc/crypttab:
sudo bash -c 'echo "mytest /dev/disk/by-uuid/... - tpm2-device=auto" >>/etc/crypttab'
# And now let's check that automatic unlocking works:
sudo systemd-cryptsetup detach mytest
sudo systemctl daemon-reload
sudo systemctl start cryptsetup.target
systemctl is-active systemd-cryptsetup@mytest.service
# Once we have the device which will be unlocked automatically, we can use it.
# Usually we would create a file system and add it to /etc/fstab:
sudo mkfs.ext4 /dev/mapper/mytest
# This prints a 'Filesystem UUID', which we can use as a stable name:
sudo bash -c 'echo "/dev/disk/by-uuid/... /var/mytest ext4 defaults,x-systemd.mkdir 0 2" >>/etc/fstab'
# And now let's check that the mounting works:
sudo systemctl daemon-reload
sudo systemctl start /var/mytest
systemctl status /var/mytest
# Depending on your distribution and encryption setup, you may need to manually
# regenerate your initramfs to be able to use a TPM2 security chip to unlock
# the partition during early boot.
# More information at https://unix.stackexchange.com/a/705809.
# On Fedora based systems:
sudo dracut --force
# On Debian based systems:
sudo update-initramfs -u
systemd(1), systemd-cryptsetup@.service(8),
systemd-cryptsetup-generator(8), systemd-cryptenroll(1),
fstab(5), cryptsetup(8), mkswap(8), mke2fs(8)
1. Veracrypt Personal Iterations Multiplier
https://www.veracrypt.fr/en/Personal%20Iterations%20Multiplier%20%28PIM%29.html
2. RFC7512 PKCS#11 URI
https://tools.ietf.org/html/rfc7512
3. Yubico PIV certificate slots
https://developers.yubico.com/PIV/Introduction/Certificate_slots.html
This page is part of the systemd (systemd system and service
manager) project. Information about the project can be found at
⟨http://www.freedesktop.org/wiki/Software/systemd⟩. If you have
a bug report for this manual page, see
⟨http://www.freedesktop.org/wiki/Software/systemd/#bugreports⟩.
This page was obtained from the project's upstream Git repository
⟨https://github.com/systemd/systemd.git⟩ on 2023-12-22. (At that
time, the date of the most recent commit that was found in the
repository was 2023-12-22.) 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
systemd 255 CRYPTTAB(5)
Pages that refer to this page: systemd-cryptenroll(1), systemd-system.conf(5), systemd.directives(7), systemd.index(7), systemd-cryptsetup(8), systemd-cryptsetup-generator(8)
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