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CRYPTTAB(5)                             cryptsetup manual                             CRYPTTAB(5)

NAME
       crypttab - static information about encrypted filesystems

DESCRIPTION
       The file /etc/crypttab contains descriptive information about encrypted filesystems.
       crypttab is only read by programs (e.g. cryptdisks_start and cryptdisks_stop), and not
       written; it is the duty of the system administrator to properly create and maintain this
       file. Each filesystem is described on a separate line; fields on each line are separated
       by tabs or spaces. Lines starting with “#” are comments, empty lines are ignored. The
       order of records in crypttab is important because the init scripts sequentially iterate
       through crypttab doing their thing.

       The first field, target, describes the mapped device name. It must be a plain filename
       without any directory components. A mapped device which encrypts/decrypts data to/from the
       source device will be created at /dev/mapper/target by cryptsetup.

       The second field, source device, describes either the block special device or file that
       contains the encrypted data. Instead of giving the source device explicitly, the UUID is
       supported as well, using UUID=.

       The third field, key file, describes the file to use as a key for decrypting the data of
       the source device. Note that the entire key file will be used as the passphrase; the
       passphrase must not be followed by a newline character.

       It can also be a device name (e.g. /dev/urandom), note however that LUKS requires a
       persistent key and therefore does not support random data keys.

       If the key file is the string “none”, a passphrase will be read interactively from the
       console. In this case, the options precheck, check, checkargs and tries may be useful.

       The fourth field, options, describes the cryptsetup options associated with the encryption
       process. At minimum, the field should contain either the string luks respectively tcrypt
       or the cipher, hash and size options.

       Options are in the format: key=value [,key=value ...]. The supported options are described
       below.

       Note that all four fields are mandatory and that a missing field will lead to unspecified
       behaviour.

OPTIONS
       cipher=
           Encryption algorithm (ignored for LUKS and TCRYPT devices). See cryptsetup -c.

       size=
           Encryption key size (ignored for LUKS and TCRYPT devices). See cryptsetup -s.

       hash=
           Hash algorithm (ignored for LUKS and TCRYPT devices). See cryptsetup -h.

       offset=
           Start offset (ignored for LUKS and TCRYPT devices). Uses cryptsetup -o.

       skip=
           Skip sectors at the beginning (ignored for LUKS and TCRYPT devices). Uses cryptsetup
           -p.

       verify
           Verify password. Uses cryptsetup -y.

       readonly
           The backing device is read-only (eg: a dvd).

       discard
           Allow using of discards (TRIM) requests for device.

           WARNING: Assess the specific security risks carefully before enabling this option. For
           example, allowing discards on encrypted devices may lead to the leak of information
           about the ciphertext device (filesystem type, used space etc.) if the discarded blocks
           can be located easily on the device later.

           Kernel version 3.1 or more recent is required. For older versions is the option
           ignored.

       luks
           Use device with LUKS extensions.

       tcrypt
           Use device with TCRYPT extensions.

       swap
           Run mkswap on the created device.

       tmp=
           Run mkfs with filesystem type  on the created device. Default is ext4.

       precheck=
           Check the content of the source device by a suitable program; if the check fails, the
           device is not created. If a program is provided as an argument, it is run, giving the
           source device as argument. Cryptdisks/cryptroot searches for the given progam in
           /lib/cryptsetup/checks/ first, but full path to program is supported as well.

           Prechecks aren't invoked for LUKS devices, as these are checked with isLuks anyway.
           Default for plain dm-crypt devices is set in /etc/default/cryptdisks, or un_blkid
           otherwise. Set to /bin/true in order to disable precheck for plain dm-crypt device.

       check=
           Check the content of the target device by a suitable program; if the check fails, the
           device is removed. If a program is provided as an argument, it is run, giving the
           decrypted volume (target device) as first argument, and the value of the checkargs
           option as second argument. Cryptdisks/cryptroot searches for the given program in
           /lib/cryptsetup/checks/ first, but full path to program is supported as well.

           Default is set in /etc/default/cryptdisks (blkid).

       checkargs=
           Give  as the second argument to the check script. See the CHECKSCRIPTS
           section for more information.

       tries=
           The input of the passphrase is tried  times in case of failure. If you want to
           disable retries, pass “tries=1”. Default is 3. Setting “tries=0” will ask for the
           passphrase until a correct one has been submitted (infinitive retries).

       initramfs
           The initramfs hook processes the root device, any resume devices and any devices with
           the initramfs option set. These devices are processed within the initramfs stage of
           boot. As an example, that allows the use of remote unlocking using dropbear.

       noearly
           The cryptsetup init scripts are invoked twice during the boot process - once before
           lvm, raid, etc. are started and once again after that. Sometimes you need to start
           your encrypted disks in a special order. With this option the device is ignored during
           the first invocation of the cryptsetup init scripts.

       noauto
           Entirely ignore the device at the boot process. It's still possible to map the device
           manually using cryptdisks_start.

       loud
           Be loud. Print warnings if a device does not exist. This option overwrites the option
           quiet.

       quiet
           Be quiet. Don't print warnings if a device does not exist. This option overwrites the
           option loud.

       keyscript=
           The executable at the indicated path is executed with the key file from the third
           field of the crypttab as its only argument and the output is used as the key. This
           also works with encrypted root filesystems via initramfs if the executable is
           self-contained (i.e. an executable which does not rely on any external program which
           is not present in the initramfs environment).

           LIMITATIONS: All binaries and files on which the keyscript depends must be available
           at the time of execution. Special care needs to be taken for encrypted filesystems
           like /usr or /var. As an example, unlocking encrypted /usr must not depend on binaries
           from /usr/(s)bin.

           All fields of the appropriate crypttab entry are available to the keyscript as
           exported environment variables:

           CRYPTTAB_NAME
               The target name

           CRYPTTAB_SOURCE
               The source device

           CRYPTTAB_KEY
               The key file

           CRYPTTAB_TRIED
               Number of previous tries since start of cryptdisks (counts until maximum number of
               tries is reached).

           CRYPTTAB_OPTIONS
               A list of exported crypttab options

           CRYPTTAB_OPTION_

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