1CRYPTTAB(5) crypttab CRYPTTAB(5)
2
6 crypttab - Configuration for encrypted block devices
7
9 /etc/crypttab
10
12 The /etc/crypttab file describes encrypted block devices that are set
13 up during system boot.
14 Empty lines and lines starting with the "#" character are ignored. Each
16 of the remaining lines describes one encrypted block device. Fields are
17 delimited by white space.
18 Each line is in the form
20 name encrypted-device password options
22 The first two fields are mandatory, the remaining two are optional.
24 Setting up encrypted block devices using this file supports three
26 encryption modes: LUKS, TrueCrypt and plain. See cryptsetup(8) for more
27 information about each mode. When no mode is specified in the options
28 field and the block device contains a LUKS signature, it is opened as a
29 LUKS device; otherwise, it is assumed to be in raw dm-crypt (plain
30 mode) format.
31 The first field contains the name of the resulting encrypted block
33 device; the device is set up within /dev/mapper/.
34 The second field contains a path to the underlying block device or
36 file, or a specification of a block device via "UUID=" followed by the
37 UUID.
38 The third field specifies the encryption password. If the field is not
40 present or the password is set to "none" or "-", the password has to be
41 manually entered during system boot. Otherwise, the field is
42 interpreted as an absolute path to a file containing the encryption
43 password. For swap encryption, /dev/urandom or the hardware device
44 /dev/hw_random can be used as the password file; using /dev/random may
45 prevent boot completion if the system does not have enough entropy to
46 generate a truly random encryption key.
47 The fourth field, if present, is a comma-delimited list of options. The
49 following options are recognized:
50 cipher=
52 Specifies the cipher to use. See cryptsetup(8) for possible values
53 and the default value of this option. A cipher with unpredictable
54 IV values, such as "aes-cbc-essiv:sha256", is recommended.
55 discard
57 Allow discard requests to be passed through the encrypted block
58 device. This improves performance on SSD storage but has security
59 implications.
60 hash=
62 Specifies the hash to use for password hashing. See cryptsetup(8)
63 for possible values and the default value of this option.
64 header=
66 Use a detached (separated) metadata device or file where the LUKS
67 header is stored. This option is only relevant for LUKS devices.
68 See cryptsetup(8) for possible values and the default value of this
69 option.
70 keyfile-offset=
72 Specifies the number of bytes to skip at the start of the key file.
73 See cryptsetup(8) for possible values and the default value of this
74 option.
75 keyfile-size=
77 Specifies the maximum number of bytes to read from the key file.
78 See cryptsetup(8) for possible values and the default value of this
79 option. This option is ignored in plain encryption mode, as the key
80 file size is then given by the key size.
81 key-slot=
83 Specifies the key slot to compare the passphrase or key against. If
84 the key slot does not match the given passphrase or key, but
85 another would, the setup of the device will fail regardless. This
86 option implies luks. See cryptsetup(8) for possible values. The
87 default is to try all key slots in sequential order.
88 luks
90 Force LUKS mode. When this mode is used, the following options are
91 ignored since they are provided by the LUKS header on the device:
92 cipher=, hash=, size=.
93 _netdev
95 Marks this cryptsetup device as requiring network. It will be
96 started after the network is available, similarly to
97 systemd.mount(5) units marked with _netdev. The service unit to set
98 up this device will be ordered between remote-fs-pre.target and
99 remote-cryptsetup.target, instead of cryptsetup-pre.target and
100 cryptsetup.target.
101 Hint: if this device is used for a mount point that is specified in
103 fstab(5), the _netdev option should also be used for the mount
104 point. Otherwise, a dependency loop might be created where the
105 mount point will be pulled in by local-fs.target, while the service
106 to configure the network is usually only started after the local
107 file system has been mounted.
108 noauto
110 This device will not be added to cryptsetup.target. This means that
111 it will not be automatically unlocked on boot, unless something
112 else pulls it in. In particular, if the device is used for a mount
113 point, it'll be unlocked automatically during boot, unless the
114 mount point itself is also disabled with noauto.
115 nofail
117 This device will not be a hard dependency of cryptsetup.target.
118 It'll be still pulled in and started, but the system will not wait
119 for the device to show up and be unlocked, and boot will not fail
120 if this is unsuccessful. Note that other units that depend on the
121 unlocked device may still fail. In particular, if the device is
122 used for a mount point, the mount point itself is also needs to
123 have noauto option, or the boot will fail if the device is not
124 unlocked successfully.
125 offset=
127 Start offset in the backend device, in 512-byte sectors. This
128 option is only relevant for plain devices.
129 plain
131 Force plain encryption mode.
132 read-only, readonly
134 Set up the encrypted block device in read-only mode.
135 skip=
137 How many 512-byte sectors of the encrypted data to skip at the
138 beginning. This is different from the offset= option with respect
139 to the sector numbers used in initialization vector (IV)
140 calculation. Using offset= will shift the IV calculation by the
141 same negative amount. Hence, if offset=n is given, sector n will
142 get a sector number of 0 for the IV calculation. Using skip= causes
143 sector n to also be the first sector of the mapped device, but with
144 its number for IV generation being n.
145 This option is only relevant for plain devices.
147 size=
149 Specifies the key size in bits. See cryptsetup(8) for possible
150 values and the default value of this option.
151 sector-size=
153 Specifies the sector size in bytes. See cryptsetup(8) for possible
154 values and the default value of this option.
155 swap
157 The encrypted block device will be used as a swap device, and will
158 be formatted accordingly after setting up the encrypted block
159 device, with mkswap(8). This option implies plain.
160 WARNING: Using the swap option will destroy the contents of the
162 named partition during every boot, so make sure the underlying
163 block device is specified correctly.
164 tcrypt
166 Use TrueCrypt encryption mode. When this mode is used, the
167 following options are ignored since they are provided by the
168 TrueCrypt header on the device or do not apply: cipher=, hash=,
169 keyfile-offset=, keyfile-size=, size=.
170 When this mode is used, the passphrase is read from the key file
172 given in the third field. Only the first line of this file is read,
173 excluding the new line character.
174 Note that the TrueCrypt format uses both passphrase and key files
176 to derive a password for the volume. Therefore, the passphrase and
177 all key files need to be provided. Use tcrypt-keyfile= to provide
178 the absolute path to all key files. When using an empty passphrase
179 in combination with one or more key files, use "/dev/null" as the
180 password file in the third field.
181 tcrypt-hidden
183 Use the hidden TrueCrypt volume. This option implies tcrypt.
184 This will map the hidden volume that is inside of the volume
186 provided in the second field. Please note that there is no
187 protection for the hidden volume if the outer volume is mounted
188 instead. See cryptsetup(8) for more information on this limitation.
189 tcrypt-keyfile=
191 Specifies the absolute path to a key file to use for a TrueCrypt
192 volume. This implies tcrypt and can be used more than once to
193 provide several key files.
194 See the entry for tcrypt on the behavior of the passphrase and key
196 files when using TrueCrypt encryption mode.
197 tcrypt-system
199 Use TrueCrypt in system encryption mode. This option implies
200 tcrypt.
201 tcrypt-veracrypt
203 Check for a VeraCrypt volume. VeraCrypt is a fork of TrueCrypt that
204 is mostly compatible, but uses different, stronger key derivation
205 algorithms that cannot be detected without this flag. Enabling this
206 option could substantially slow down unlocking, because VeraCrypt's
207 key derivation takes much longer than TrueCrypt's. This option
208 implies tcrypt.
209 timeout=
211 Specifies the timeout for querying for a password. If no unit is
212 specified, seconds is used. Supported units are s, ms, us, min, h,
213 d. A timeout of 0 waits indefinitely (which is the default).
214 tmp
216 The encrypted block device will be prepared for using it as /tmp;
217 it will be formatted using mke2fs(8). This option implies plain.
218 WARNING: Using the tmp option will destroy the contents of the
220 named partition during every boot, so make sure the underlying
221 block device is specified correctly.
222 tries=
224 Specifies the maximum number of times the user is queried for a
225 password. The default is 3. If set to 0, the user is queried for a
226 password indefinitely.
227 verify
229 If the encryption password is read from console, it has to be
230 entered twice to prevent typos.
231 x-systemd.device-timeout=
233 Specifies how long systemd should wait for a device to show up
234 before giving up on the entry. The argument is a time in seconds or
235 explicitly specified units of "s", "min", "h", "ms".
236 At early boot and when the system manager configuration is reloaded,
238 this file is translated into native systemd units by systemd-
239 cryptsetup-generator(8).
240
242 Example 1. /etc/crypttab example
243 Set up four encrypted block devices. One using LUKS for normal storage,
245 another one for usage as a swap device and two TrueCrypt volumes.
246 luks UUID=2505567a-9e27-4efe-a4d5-15ad146c258b
248 swap /dev/sda7 /dev/urandom swap
249 truecrypt /dev/sda2 /etc/container_password tcrypt
250 hidden /mnt/tc_hidden /dev/null tcrypt-hidden,tcrypt-keyfile=/etc/keyfile
251
253 systemd(1), systemd-cryptsetup@.service(8), systemd-cryptsetup-
254 generator(8), fstab(5), cryptsetup(8), mkswap(8), mke2fs(8)
255systemd 241 CRYPTTAB(5)