integritytab - Man Page

/etc/integritytab

The /etc/integritytab file describes integrity protected block devices that are set up during system boot.

Empty lines and lines starting with the "#" character are ignored. Each of the remaining lines describes one verity integrity protected block device. Fields are delimited by white space.

Each line is in the form

volume-name block-device
    [keyfile|-] [options|-]

The first two fields are mandatory, the remaining two are optional and only required if user specified non-default options during integrity format.

The first field contains the name of the resulting integrity volume; its block device is set up below /dev/mapper/.

The second field contains a path to the underlying block device, or a specification of a block device via "UUID=" followed by the UUID, "PARTUUID=" followed by the partition UUID, "LABEL=" followed by the label, "PARTLABEL=" followed by the partition label.

The third field if present contains an absolute filename path to a key file or a "-" to specify none. When the filename is present, the "integrity-algorithm" defaults to "hmac-sha256" with the key length derived from the number of bytes in the key file. At this time the only supported integrity algorithm when using key file is hmac-sha256. The maximum size of the key file is 4096 bytes.

The fourth field, if present, is a comma-delimited list of options or a "-" to specify none. The following options are recognized:

allow-discards

Allow the use of discard (TRIM) requests for the device. This option is available since the Linux kernel version 5.7.

Added in version 250.

mode=(journal|bitmap|direct)

Enable journaled, bitmapped or direct (passthrough) mode. Journaled mode is the default when this option is not specified. It provides safety against crashes, but can be slow because all data has to be written twice. Bitmap mode is more efficient since it requires only a single write, but it is less reliable because if data corruption happens when the machine crashes, it might not be detected. Direct mode disables the journal and the bitmap. Corresponds to the "direct writes" mode documented in the dm-integrity documentation^[1]. Note that without a journal, if there is a crash, it is possible that the integrity tags and data will not match. If used, the journal-* options below will have no effect if passed.

Added in version 254.

journal-watermark=[0..100]%

Journal watermark in percent. When the journal percentage exceeds this watermark, the journal flush will be started. Setting a value of "0%" uses default value.

Added in version 250.

journal-commit-time=[0..N]

Commit time in milliseconds. When this time passes (and no explicit flush operation was issued), the journal is written. Setting a value of zero uses default value.

Added in version 250.

data-device=/dev/disk/by-...

Specify a separate block device that contains existing data. The second field specified in the integritytab for block device then will contain calculated integrity tags and journal for data-device, but not the end user data.

Added in version 250.

integrity-algorithm=[crc32c|crc32|xxhash64|sha1|sha256|hmac-sha256]

The algorithm used for integrity checking. The default is crc32c. Must match option used during format.

Added in version 250.

At early boot and when the system manager configuration is reloaded, this file is translated into native systemd units by systemd-integritysetup-generator(8).

Example 1. /etc/integritytab

Set up two integrity protected block devices.

home PARTUUID=4973d0b8-1b15-c449-96ec-94bab7f6a7b8 - journal-commit-time=10,allow-discards,journal-watermark=55%
data PARTUUID=5d4b1808-be76-774d-88af-03c4c3a41761 - allow-discards

Example 2. /etc/integritytab

Set up 1 integrity protected block device using defaults

home PARTUUID=4973d0b8-1b15-c449-96ec-94bab7f6a7b8

Example 3. /etc/integritytab

Set up 1 integrity device using existing data block device which contains user data

home PARTUUID=4973d0b8-1b15-c449-96ec-94bab7f6a7b8 - data-device=/dev/disk/by-uuid/9276d9c0-d4e3-4297-b4ff-3307cd0d092f

Example 4. /etc/integritytab

Set up 1 integrity device using a HMAC key file using defaults

home PARTUUID=4973d0b8-1b15-c449-96ec-94bab7f6a7b8 /etc/hmac.key

systemd(1), systemd-integritysetup@.service(8), systemd-integritysetup-generator(8), integritysetup(8)

1.

the dm-integrity documentation
https://docs.kernel.org/admin-guide/device-mapper/dm-integrity.html

systemd.directives(7), systemd.index(7), systemd-integritysetup@.service(8).