X-Git-Url: https://www.chiark.greenend.org.uk/ucgi/~ianmdlvl/git?p=elogind.git;a=blobdiff_plain;f=man%2Fcrypttab.xml;h=668e51dc0628ee25da1bcf5362111a7873e96ff2;hp=1063b46e06c452a8220eff57579fa691731f4af5;hb=dc968941bfc9be464e1df15afa05693dec3ec192;hpb=909f413d3c572baadf9b13e36e1e90beba42af86
diff --git a/man/crypttab.xml b/man/crypttab.xml
index 1063b46e0..668e51dc0 100644
--- a/man/crypttab.xml
+++ b/man/crypttab.xml
@@ -75,23 +75,29 @@
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 cryptsetup8
+ 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 a specification of a block
+ underlying block device or file, or a specification of a block
device via UUID= followed by the
- UUID. If the block device contains a LUKS signature,
- it is opened as a LUKS encrypted partition; otherwise
- it is assumed to be a raw dm-crypt partition.
+ UUID.
The third field specifies the encryption
password. If the field is not present or the password
- is set to none, the password has to be manually
- entered during system boot. Otherwise the field is
- interpreted as a path to a file containing the
- encryption password. For swap encryption
+ 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
@@ -104,185 +110,250 @@
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
+ Specifies the cipher to use. See
cryptsetup8
- for possible values and the default
- value of this option. A cipher with
- unpredictable IV values, such as
- aes-cbc-essiv:sha256,
- is recommended.
+ for possible values and the default value of
+ this option. A cipher with unpredictable IV
+ values, such as aes-cbc-essiv:sha256,
+ is recommended.
-
- size=
+ hash=
- Specifies the key size
- in bits; see
+ Specifies the hash to use for
+ password hashing. See
cryptsetup8
- for possible values and the default
- value of this
- option.
+ 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
+ cryptsetup8
+ for possible values and the default value of
+ this option.
+
keyfile-size=
Specifies the maximum number
- of bytes to read from the keyfile; see
+ of bytes to read from the key file. See
cryptsetup8
- for possible values and the default
- value of this option. This option is ignored
- in plain encryption mode, as the keyfile-size is then given by the key size.
+ 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.
-
- keyfile-offset=
-
- Specifies the number
- of bytes to skip at the start of
- the keyfile; see
+ 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
cryptsetup8
- for possible values and the default
- value of this option.
+ for possible values. The default is to try
+ all key slots in sequential order.
+
+ 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=.
+
- hash=
+ noauto
- Specifies the hash to
- use for password hashing; see
- cryptsetup8 for possible values and
- the default value of this
- option.
+ This device will not be
+ automatically unlocked on boot.
- tries=
+ nofail
- Specifies the maximum
- number of times the user is queried
- for a password.
+ 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.
- verify
+ plain
- If the encryption
- password is read from console, it has
- to be entered twice (to prevent
- typos).
+ Force plain encryption mode.
read-onlyreadonly
- Set up the encrypted
- block device in read-only
- mode.
+ Set up the encrypted block
+ device in read-only mode.
- allow-discards
-
- Allow discard requests
- to be passed through the encrypted
- block device. This improves
- performance on SSD storage but has
- security
- implications.
+ size=
+
+ Specifies the key size
+ in bits. See
+ cryptsetup8
+ for possible values and the default value of
+ this option.
- luks
+ swap
- Force LUKS mode.
+ The encrypted block device will
+ be used as a swap device, and will be formatted
+ accordingly after setting up the encrypted
+ block device, with
+ mkswap8.
+ 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.
- plain
-
- Force plain encryption
- mode.
+ 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.
- timeout=
+ tcrypt-hidden
+
+ Use the hidden TrueCrypt volume.
+ This option implies tcrypt.
- Specify 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).
+ 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
+ cryptsetup8
+ for more information on this limitation.
- noauto
+ tcrypt-keyfile=
- This device will not
- be automatically unlocked on
- boot.
+ 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.
- nofail
+ tcrypt-system
- The system will not
- wait for the device to show up and be
- unlocked at boot, and not fail the
- boot if it doesn't show
- up.
+ Use TrueCrypt in system
+ encryption mode. This option implies
+ tcrypt.
- swap
+ timeout=
- The encrypted block
- device will be used as a swap
- partition, and will be formatted as a
- swap partition after setting up the
- encrypted block device, with
- mkswap8.
-
- 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.
+ 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).
tmp
- The encrypted block
- device will be prepared for using it
- as /tmp
- partition: it will be formatted using
- mke2fs8.
-
- 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.
+ The encrypted block device will
+ be prepared for using it as /tmp;
+ it will be formatted using
+ mke2fs8.
+ 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.
+
+
+
+ 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
+ configuration is reloaded, this file is translated into
native systemd units
by systemd-cryptsetup-generator8.
@@ -291,12 +362,14 @@
Example
/etc/crypttab example
- Set up two encrypted block devices with
- LUKS: one normal one for storage, and another
- one for usage as swap device.
-
- luks-2505567a-9e27-4efe-a4d5-15ad146c258b UUID=2505567a-9e27-4efe-a4d5-15ad146c258b - timeout=0
-swap /dev/sda7 /dev/urandom swap
+ 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 /null tcrypt-hidden,tcrypt-keyfile=/etc/keyfile