CRYPTTAB(5) crypttab CRYPTTAB(5)
NAME
crypttab - Configuration for encrypted block devices
SYNOPSIS
/etc/crypttab
DESCRIPTION
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 on the line are delimited by white space. The first two fields are mandatory,
the remaining two are optional.
Setting up encrypted block devices using this file supports three encryption modes: LUKS, TrueCrypt 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 first field contains the name of the resulting encrypted block device; the device is set up within
/dev/mapper/.
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.
The third field specifies the encryption password. If the field is not present or the password is set to
"none" or "-", the password has to be manually entered during system boot. Otherwise, the field is interpreted
as a absolute path to a file containing the encryption password. For swap encryption, /dev/urandom or the
hardware device /dev/hw_random can be used as the password file; using /dev/random may prevent boot completion
if the system does not have enough entropy to generate a truly random encryption key.
The fourth field, if present, is a comma-delimited list of options. The following options are recognized:
discard
Allow discard requests to be passed through the encrypted block device. This improves performance on SSD
storage but has security implications.
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.
hash=
Specifies the hash to use for password hashing. See cryptsetup(8) for possible values and the default
value of this option.
header=
Use a detached (separated) metadata device or file where the LUKS header is stored. This option is only
relevant for LUKS devices. See cryptsetup(8) for possible values and the default value of this option.
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.
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.
nofail
The system will not wait for the device to show up and be unlocked at boot, and not fail the boot if it
does not show up.
plain
Force plain encryption mode.
read-only, readonly
Set up the encrypted block device in read-only mode.
size=
Specifies the key size in bits. See cryptsetup(8) for possible values and the default value of this
option.
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.
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.
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.
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.
tcrypt-system
Use TrueCrypt in system encryption mode. This option implies tcrypt.
timeout=
Specifies the timeout for querying for a password. If no unit is specified, seconds is used. Supported
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.
verify
If the encryption password is read from console, it has to be entered twice to prevent typos.
At early boot and when the system manager configuration is reloaded, this file is translated into native
systemd units by systemd-cryptsetup-generator(8).
EXAMPLE
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.
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
SEE ALSO
systemd(1), [email protected](8), systemd-cryptsetup-generator(8), cryptsetup(8), mkswap(8),
mke2fs(8)
systemd 219 CRYPTTAB(5)
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