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 on
17 the line are delimited by white space. The first two fields are
18 mandatory, the remaining two are optional.
19 Setting up encrypted block devices using this file supports three
21 encryption modes: LUKS, TrueCrypt and plain. See cryptsetup(8) for more
22 information about each mode. When no mode is specified in the options
23 field and the block device contains a LUKS signature, it is opened as a
24 LUKS device; otherwise, it is assumed to be in raw dm-crypt (plain
25 mode) format.
26 The first field contains the name of the resulting encrypted block
28 device; the device is set up within /dev/mapper/.
29 The second field contains a path to the underlying block device or
31 file, or a specification of a block device via "UUID=" followed by the
32 UUID.
33 The third field specifies the encryption password. If the field is not
35 present or the password is set to "none" or "-", the password has to be
36 manually entered during system boot. Otherwise, the field is
37 interpreted as a absolute path to a file containing the encryption
38 password. For swap encryption, /dev/urandom or the hardware device
39 /dev/hw_random can be used as the password file; using /dev/random may
40 prevent boot completion if the system does not have enough entropy to
41 generate a truly random encryption key.
42 The fourth field, if present, is a comma-delimited list of options. The
44 following options are recognized:
45 discard
47 Allow discard requests to be passed through the encrypted block
48 device. This improves performance on SSD storage but has security
49 implications.
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 hash=
57 Specifies the hash to use for password hashing. See cryptsetup(8)
58 for possible values and the default value of this option.
59 header=
61 Use a detached (separated) metadata device or file where the LUKS
62 header is stored. This option is only relevant for LUKS devices.
63 See cryptsetup(8) for possible values and the default value of this
64 option.
65 keyfile-offset=
67 Specifies the number of bytes to skip at the start of the key file.
68 See cryptsetup(8) for possible values and the default value of this
69 option.
70 keyfile-size=
72 Specifies the maximum number of bytes to read from the key file.
73 See cryptsetup(8) for possible values and the default value of this
74 option. This option is ignored in plain encryption mode, as the key
75 file size is then given by the key size.
76 key-slot=
78 Specifies the key slot to compare the passphrase or key against. If
79 the key slot does not match the given passphrase or key, but
80 another would, the setup of the device will fail regardless. This
81 option implies luks. See cryptsetup(8) for possible values. The
82 default is to try all key slots in sequential order.
83 luks
85 Force LUKS mode. When this mode is used, the following options are
86 ignored since they are provided by the LUKS header on the device:
87 cipher=, hash=, size=.
88 _netdev
90 Marks this cryptsetup device as requiring network. It will be
91 started after the network is available, similarly to
92 systemd.mount(5) units marked with _netdev. The service unit to set
93 up this device will be ordered between remote-fs-pre.target and
94 remote-cryptsetup.target, instead of cryptsetup-pre.target and
95 cryptsetup.target.
96 Hint: if this device is used for a mount point that is specified in
98 fstab(5), the _netdev option should also be used for the mount
99 point. Otherwise, a dependency loop might be created where the
100 mount point will be pulled in by local-fs.target, while the service
101 to configure the network is usually only started after the local
102 file system has been mounted.
103 noauto
105 This device will not be automatically unlocked on boot.
106 nofail
108 The system will not wait for the device to show up and be unlocked
109 at boot, and not fail the boot if it does not show up.
110 plain
112 Force plain encryption mode.
113 read-only, readonly
115 Set up the encrypted block device in read-only mode.
116 size=
118 Specifies the key size in bits. See cryptsetup(8) for possible
119 values and the default value of this option.
120 swap
122 The encrypted block device will be used as a swap device, and will
123 be formatted accordingly after setting up the encrypted block
124 device, with mkswap(8). This option implies plain.
125 WARNING: Using the swap option will destroy the contents of the
127 named partition during every boot, so make sure the underlying
128 block device is specified correctly.
129 tcrypt
131 Use TrueCrypt encryption mode. When this mode is used, the
132 following options are ignored since they are provided by the
133 TrueCrypt header on the device or do not apply: cipher=, hash=,
134 keyfile-offset=, keyfile-size=, size=.
135 When this mode is used, the passphrase is read from the key file
137 given in the third field. Only the first line of this file is read,
138 excluding the new line character.
139 Note that the TrueCrypt format uses both passphrase and key files
141 to derive a password for the volume. Therefore, the passphrase and
142 all key files need to be provided. Use tcrypt-keyfile= to provide
143 the absolute path to all key files. When using an empty passphrase
144 in combination with one or more key files, use "/dev/null" as the
145 password file in the third field.
146 tcrypt-hidden
148 Use the hidden TrueCrypt volume. This option implies tcrypt.
149 This will map the hidden volume that is inside of the volume
151 provided in the second field. Please note that there is no
152 protection for the hidden volume if the outer volume is mounted
153 instead. See cryptsetup(8) for more information on this limitation.
154 tcrypt-keyfile=
156 Specifies the absolute path to a key file to use for a TrueCrypt
157 volume. This implies tcrypt and can be used more than once to
158 provide several key files.
159 See the entry for tcrypt on the behavior of the passphrase and key
161 files when using TrueCrypt encryption mode.
162 tcrypt-system
164 Use TrueCrypt in system encryption mode. This option implies
165 tcrypt.
166 timeout=
168 Specifies the timeout for querying for a password. If no unit is
169 specified, seconds is used. Supported units are s, ms, us, min, h,
170 d. A timeout of 0 waits indefinitely (which is the default).
171 x-systemd.device-timeout=
173 Specifies how long systemd should wait for a device to show up
174 before giving up on the entry. The argument is a time in seconds or
175 explicitly specified units of "s", "min", "h", "ms".
176 tmp
178 The encrypted block device will be prepared for using it as /tmp;
179 it will be formatted using mke2fs(8). This option implies plain.
180 WARNING: Using the tmp option will destroy the contents of the
182 named partition during every boot, so make sure the underlying
183 block device is specified correctly.
184 tries=
186 Specifies the maximum number of times the user is queried for a
187 password. The default is 3. If set to 0, the user is queried for a
188 password indefinitely.
189 verify
191 If the encryption password is read from console, it has to be
192 entered twice to prevent typos.
193 At early boot and when the system manager configuration is reloaded,
195 this file is translated into native systemd units by systemd-
196 cryptsetup-generator(8).
197
199 Example 1. /etc/crypttab example
200 Set up four encrypted block devices. One using LUKS for normal storage,
202 another one for usage as a swap device and two TrueCrypt volumes.
203 luks UUID=2505567a-9e27-4efe-a4d5-15ad146c258b
205 swap /dev/sda7 /dev/urandom swap
206 truecrypt /dev/sda2 /etc/container_password tcrypt
207 hidden /mnt/tc_hidden /dev/null tcrypt-hidden,tcrypt-keyfile=/etc/keyfile
208
210 systemd(1), systemd-cryptsetup@.service(8), systemd-cryptsetup-
211 generator(8), fstab(5), cryptsetup(8), mkswap(8), mke2fs(8)
212systemd 219 CRYPTTAB(5)