crypttab

systemd
Documentation Miloslav Trmac mitr@redhat.com
Documentation Lennart Poettering lennart@poettering.net
crypttab 5
crypttab Configuration for encrypted block devices

`/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.

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 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.

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 `/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:

`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.

`size=`

  Specifies the key size in bits; 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 keyfile; see cryptsetup 8 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.

`keyfile-offset=`

  Specifies the number of bytes to skip at the start of the keyfile; see cryptsetup 8 for possible values and the default value of this option.

`hash=`

  Specifies the hash to use for password hashing; see cryptsetup 8 for possible values and the default value of this option.

`tries=`

  Specifies the maximum number of times the user is queried for a password.

`verify`

  If the encryption password is read from console, it has to be entered twice (to prevent typos).

`read-only`
`readonly`

  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.

`luks`

  Force LUKS mode.

`plain`

  Force plain encryption mode.

`timeout=`

  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).

`noauto`

  This device will not be automatically unlocked on boot.

`nofail`

  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.

`swap`

  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 mkswap 8.

  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.

`tmp`

  The encrypted block device will be prepared for using it as `/tmp` partition: it will be formatted using mke2fs 8.

  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.

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

/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

## See Also

systemd 1, systemd-cryptsetup@.service 8, systemd-cryptsetup-generator 8, cryptsetup 8, mkswap 8, mke2fs 8