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crypttab

NAME

crypttab - static information about crypted filesystems

SYNOPSIS

crypttab

<target device> <source device> <key file> <options>

DESCRIPTION

The file /etc/crypttab contains descriptive informations about encrypted volumes. Each volume is described on a separate line; columns 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 /etc/init.d/boot.crypto script sequentially iterates through crypttab entries. All four columns are mandatory, missing or excessive columns will lead to unspecified behaviour.

*

The first column, target device specifies the mapped device name. It must be a plain filename without any directories. A mapped device /dev/mapper/device name will be created by cryptsetup(8) crypting data from and onto the source device. To actually mount that device it needs to be listed in /etc/fstab.

*

The second column source device specifies the block special device that should hold the encrypted data.

*

The third column key file specifies the file to use for decrypting the encrypted data of the source device. It can also be a device name (e.g. /dev/urandom, which is useful for encrypted swap devices). Warning: luks does not support infinite streams (like /dev/urandom), it requires a fixed size key.

If the key file is the string none, the key data (i.e. a password or 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 specifies the cryptsetup options associated with the encryption process. At minimum, the field should contain the string luks or the cipher, hash and size options. Options have to be specified in the format: key=value[,key=value ...]

OPTIONS

cipher=<cipher>

Encryption algorithm. See cryptsetup -c.

size=<size>

Encryption key size. See cryptsetup -s.

hash=<hash>

Hash algorithm. See cryptsetup -h.

verify

Verify password. See cryptsetup -y.

readonly

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

luks

Use device with luks extensions.

swap

Run mkswap on the created device.

tmp

Run mkfs on the created device. The file system to use is specified in /etc/fstab. If /etc/fstab does not list the mapped device, ext2 is used as fallback.

precheck=<precheck>

Check the source device by suitable program; if the check fails the device is not created; <precheck> is a script to check the source device. The source device is given as argument to the script.

check[=<program>]

Check the content of the mapped device by a suitable program; if the check fails the device is removed. The specified program is run giving the decrypted volume (target device) as first and the value of the checkargs option as second argument. Cryptdisks searches for the given program in /lib/cryptsetup/checks/. If no program is specified, vol_id is used.

checkargs=<argument>

Pass <argument> as second argument to the check script

tries=<num>

Prompt for the passphrase at most <num> times if the entered passphrase was wrong. Defaults is 3. Only works for LUKS volumes.

timeout=<sec>

Time out interactive password prompts after <sec> seconds.

loop

Always attach a loop device before mapping the device. Normally a loop device is used automatically only for image files. Useful if the block size of the physical device does not match the block size of the contained file system. E.g. ext2 on a CD.

noauto

Causes boot.crypto to skip this record during boot

pseed=<string>

Set a string that is appended to the passphrase after hashing. Using different seeds for volumes with the same passphrase makes dictionary attacks harder. Use for compatability with loop-AES.

itercountk=<num>

Encrypts the hashed password <num> thousand times using AES-256. Use for compatability with loop-AES.

loud, ssl, gpg, keyscript

not supported. Listed here as they are supported by Debian.

CHECKSCRIPTS

TODO

EXAMPLES

Encrypted swap device

cswap /dev/sda6 /dev/random swap

Encrypted luks volume with interactive password

cdisk0 /dev/hda1 none luks

Encrypted luks volume with interactive password, use a custom check script, no retries

cdisk2 /dev/hdc1 none luks,check=customscript,checkargs=foo,tries=1

Encrypted volume with interactive password and a cryptoloop compatible twofish256 cipher

cdisk3 /dev/sda3 none cipher=twofish-cbc-plain,size=256,hash=sha512

SEE ALSO

cryptsetup(8), /etc/crypttab, fstab(8)

AUTHOR

Manual page converted to asciidoc by Michael Gebetsroither <michael.geb@gmx.at>. Originally written by Bastian Kleineidam <calvin@debian.org> for the Debian distribution of cryptsetup. Improved by Jonas Meurer <jonas@freesources.org>. Modified for SUSE Linux by Ludwig Nussel <ludwig.nussel@suse.de>. Parts of this manual were taken and adapted from the fstab(5) manual page.