Provided by: cryptsetup_1.4.1-2ubuntu4_i386 bug

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.

       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 passphase; the passphase 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 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=<cipher>
           Encryption algorithm (ignored for LUKS devices). See cryptsetup -c.

       size=<size>
           Encryption key size (ignored for LUKS devices). See cryptsetup -s.

       hash=<hash>
           Hash algorithm (ignored for LUKS devices). See cryptsetup -h.

       offset=<offset>
           Start offset (ignored for LUKS devices). Uses cryptsetup -o.

       skip=<skip>
           Skip sectors at the beginning (ignored for LUKS 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.

       swap
           Run mkswap on the created device.

       tmp=<tmpfs>
           Run mkfs with filesystem type <tmpfs> on the created device.
           Default is ext2.

       precheck=<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>
           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=<arguments>
           Give <arguments> as the second argument to the check script. See
           the CHECKSCRIPTS section for more information.

       tries=<num>
           The input of the passphrase is tried <num> 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).

       noearly
           The cryptsetup init scripts are invoked twice during the boot
           process - once before lvm, evms, 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 invokation 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=<path>
           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).

           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_OPTIONS
               A list of exported crypttab options

           CRYPTTAB_OPTION_<option>
               The value of the appropriate crypttab option, with value set to
               'yes' in case the option is merely a flag.

CHECKSCRIPTS

       blkid
           Checks for any known filesystem. Supports a filesystem type as
           argument via <checkargs>:

           o   no checkargs - succeeds if any valid filesystem is found on the
               device.

           o   "none" - succeeds if no valid filesystem is found on the
               device.

           o   "ext3" [or another filesystem type like xfs, swap, crypto_LUKS,
               ...] - succeeds if ext3 filesystem is found on the device.

       un_blkid
           Checks for no known filesystem. Supports a filesystem type as
           argument via <checkargs>:

           o   no checkargs - succeeds if no valid filesystem is found on the
               device.

           o   "ext3" [or another filesystem type like xfs, swap, crypto_LUKS,
               ...] - succeeds if no ext3 filesystem is found on the device.

EXAMPLES

           # Encrypted swap device
           cswap /dev/sda6 /dev/urandom cipher=aes-cbc-essiv:sha256,hash=ripemd160,size=256,swap

           # Encrypted LUKS disk with interactive password
           cdisk0 /dev/hda1 none luks

           # Encrypted ext2 disk with interactive password
           # - retry 5 times if the check fails
           cdisk1 /dev/sda2 none cipher=aes-cbc-essiv:sha256,hash=ripemd160,size=256,checkargs=ext2,tries=5

           # Encrypted disk with interactive password
           # - use a nondefault check script
           # - no retries
           cdisk2 /dev/hdc1 none cipher=aes-cbc-essiv:sha256,hash=ripemd160,size=256,check=customscript,tries=1

           # Encrypted disk with interactive password
           # - twofish as the cipher
           cdisk3 /dev/sda3 none cipher=twofish,hash=ripemd160,size=256

ENVIRONMENT

       CRYPTDISKS_ENABLE
           Set to yes to run cryptdisks initscripts at startup. Set to no to
           disable cryptdisks initscripts. Default is yes.

       CRYPTDISKS_MOUNT
           Specifies the mountpoints that are mounted before cryptdisks is
           invoked. Takes mountpoints configured in /etc/fstab as arguments.
           Separate mountpoints by space. This is useful for keys on removable
           devices, such as cdrom, usbstick, flashcard, etc. Default is unset.

       CRYPTDISKS_CHECK
           Specifies the default checkscript to be run against the target
           device, after cryptdisks has been invoked. The target device is
           passed as the first and only argument to the checkscript. Takes
           effect if the check option is given in crypttab with no value. See
           documentation for check option above for more information.

       CRYPTDISKS_PRECHECK
           Specifies the default checkscript to be run against the source
           dm-crypt device, before cryptdisks has been invoked. The source
           device is given as the first and only argument to the checkscript.
           Takes effect if the precheck option is given in crypttab with no
           value. See documentation for precheck option above for more
           information.

KNOWN UPGRADE ISSUES

       The upstream defaults for encryption cipher, hash and keysize have
       changed several times in the past, and they're expected to change again
       in future, for example if security issues arise. On LUKS devices, the
       used settings are stored in the LUKS header, and thus don't need to be
       configured in /etc/crypttab. For plain dm-crypt devices, no information
       about used cipher, hash and keysize are available at all. Therefore we
       strongly suggest to configure the cipher, hash and keysize in
       /etc/crypttab for plain dm-crypt devices, even if they match the
       current default.

SEE ALSO

       cryptsetup(8), cryptdisks_start(8), cryptdisks_stop(8)

AUTHOR

       This manual page was originally written by Bastian Kleineidam
       calvin@debian.org for the Debian distribution of cryptsetup. It has
       been further improved by Michael Gebetsroither michael.geb@gmx.at,
       Jonas Meurer jonas@freesources.org and David Hardeman
       david@hardeman.nu.