VERITYSETUP(8)

NAME
veritysetup - manage dm-verity (block level verification) volumes

SYNOPSIS

veritysetup <action> [<options>] <action args>

DESCRIPTION

Veritysetup is used to configure dm-verity managed device-mapper mappings.

Device-mapper verity target provides read-only transparent integrity checking of block devices using kernel crypto API.

The dm-verity devices are always read-only.

BASIC ACTIONS

Veritysetup supports these operations:

  FORMAT

format <data_device> <hash_device>

Calculates and permanently stores hash verification data for data_device. Hash area can be located on the same device after data if specified by --hash-offset option.

Note you need to provide root hash string for device verification or activation. Root hash must be trusted.

The data or hash device argument can be block device or file image. If hash device path doesn’t exist, it will be created as file.

<options> can be [--hash, --no-superblock, --format, --data-block-size, --hash-block-size, --data-blocks, --hash-offset, --salt, --uuid, --root-hash-file].

If option --root-hash-file is used, the root hash is stored in hex-encoded text format in <path>.

  OPEN

open <data_device> <name> <hash_device> <root_hash>
open <data_device> <name> <hash_device> --root-hash-file <path>
create <name> <data_device> <hash_device> <root_hash> (OBSOLETE syntax)

Creates a mapping with <name> backed by device <data_device> and using <hash_device> for in-kernel verification.

The <root_hash> is a hexadecimal string.

<options> can be [--hash-offset, --no-superblock, --ignore-corruption or --restart-on-corruption, --panic-on-corruption, --ignore-zero-blocks, --check-at-most-once, --root-hash-signature, --root-hash-file, --use-tasklets, --shared].

If option --root-hash-file is used, the root hash is read from <path> instead of from the command line parameter. Expects hex-encoded text, without terminating newline.

If option --no-superblock is used, you have to use as the same options as in initial format operation.

  VERIFY

verify <data_device> <hash_device> <root_hash>
verify <data_device> <hash_device> --root-hash-file <path>

Verifies data on data_device with use of hash blocks stored on hash_device.

This command performs userspace verification, no kernel device is created.

The <root_hash> is a hexadecimal string.

If option --root-hash-file is used, the root hash is read from <path> instead of from the command line parameter. Expects hex-encoded text, without terminating newline.

<options> can be [--hash-offset, --no-superblock, --root-hash-file].

If option --no-superblock is used, you have to use as the same options as in initial format operation.

  CLOSE

close <name>
remove <name> (OBSOLETE syntax)

Removes existing mapping <name>.

<options> can be [--deferred] or [--cancel-deferred].

  STATUS

status <name>

Reports status for the active verity mapping <name>.

  DUMP

dump <hash_device>

Reports parameters of verity device from on-disk stored superblock.

<options> can be [--hash-offset].

OPTIONS

--batch-mode, -q
    Do not ask for confirmation.

--cancel-deferred
    Removes a previously configured deferred device removal in close command.

--check-at-most-once
    Instruct kernel to verify blocks only the first time they are read from the data device, rather than every time.

    WARNING: It provides a reduced level of security because only offline tampering of the data device’s content will be detected, not online tampering. This option is available since Linux kernel version 4.17.

--data-blocks=blocks
    Size of data device used in verification. If not specified, the whole device is used.

--data-block-size=bytes
    Used block size for the data device. (Note kernel supports only page-size as maximum here.)

--debug
    Run in debug mode with full diagnostic logs. Debug output lines are always prefixed by #.

--deferred
    Defers device removal in close command until the last user closes it.

--error-as-corruption
    Handle device I/O errors the same as data corruption. This option must be combined with --restart-on-corruption or --panic-on-corruption.

--fec-device=fec_device
    Use forward error correction (FEC) to recover from corruption if hash verification fails. Use encoding data from the specified device.

    The fec device argument can be block device or file image. For format, if fec device path doesn’t exist, it will be created as file.

    Block sizes for data and hash devices must match. Also, if the verity data_device is encrypted the fec_device should be too.

    FEC calculation covers data, hash area, and optional foreign metadata stored on the same device with the hash tree (additional space after hash area). Size of this optional additional area protected by FEC is calculated from image sizes, so you must be sure that you use the same images for activation.

    If the hash device is in a separate image, metadata covers the whole rest of the image after the hash area.

    If hash and FEC device is in the image, metadata ends on the FEC area offset.

--fec-offset=bytes
    This is the offset, in bytes, from the start of the FEC device to the beginning of the encoding data.

--fec-roots=num
    Number of generator roots. This equals to the number of parity bytes in the encoding data. In RS(M, N) encoding, the number of roots is M-N. M is 255 and M-N is between 2 and 24 (including).

--format=number
    Specifies the hash version type. Format type 0 is original Chrome OS version. Format type 1 is current version.

--hash=hash
    Hash algorithm for dm-verity. For default see --help option.

--hash-block-size=bytes
    Used block size for the hash device. (Note kernel supports only page-size as maximum here.)

--hash-offset=bytes
    Offset of hash area/superblock on hash_device. Value must be aligned to disk sector offset.

--help, -?
    Show help text and default parameters.

--ignore-corruption, --restart-on-corruption, --panic-on-corruption
    Defines what to do if data integrity problem is detected (data corruption).

    Without these options kernel fails the IO operation with I/O error. With --ignore-corruption option the corruption is only logged. With --restart-on-corruption or --panic-on-corruption the kernel is restarted (panicked) immediately. (You have to provide way how to avoid restart loops.)

    WARNING: Use these options only for very specific cases. These options are available since Linux kernel version 4.1.

--ignore-zero-blocks
    Instruct kernel to not verify blocks that are expected to contain zeroes and always directly return zeroes instead.

    WARNING: Use this option only in very specific cases. This option is available since Linux kernel version 4.5.

--no-superblock
    Create or use dm-verity without permanent on-disk superblock.

--root-hash-file=FILE
    Path to file with stored root hash in hex-encoded text.

--root-hash-signature=FILE
    Path to root hash signature file used to verify the root hash (in kernel). This feature requires Linux kernel version 5.4 or more recent.

--salt=hex string
    Salt used for format or verification. Format is a hexadecimal string.

--shared
    Allows data device to be used in shared mode. The data device is not checked for exclusive access in-before the device activation and may be mapped in multiple verity mappings.

--usage
    Show short option help.

--use-tasklets
    Try to use kernel tasklets in dm-verity driver for performance reasons. This option is available since Linux kernel version 6.0.

--uuid=UUID
    Use the provided UUID for format command instead of generating new one.

    The UUID must be provided in standard UUID format, e.g. 12345678-1234-1234-1234-123456789abc.

--verbose, -v
    Print more information on command execution.

--version, -V
    Show the program version.

RETURN CODES

Veritysetup returns 0 on success and a non-zero value on error.

Error codes are: 1 wrong parameters, 2 no permission, 3 out of memory, 4 wrong device specified, 5 device already exists or device is busy.

EXAMPLES

veritysetup --data-blocks=256 format <data_device> <hash_device>

Calculates and stores verification data on hash_device for the first 256 blocks (of block-size). If hash_device does not exist, it is created (as file image).

veritysetup format --root-hash-file <path> <data_device> <hash_device>

Calculates and stores verification data on hash_device for the whole data_device, and store the root hash as hex-encoded text in <path>.

veritysetup --data-blocks=256 --hash-offset=1052672 format <device> <device>

Verification data (hashes) is stored on the same device as data (starting at hash-offset). Hash-offset must be greater than number of blocks in data-area.

veritysetup --data-blocks=256 --hash-offset=1052672 create test-device <device> <device> <root_hash>

Activates the verity device named test-device. Options --data-blocks and --hash-offset are the same as in the format command. The <root_hash> was calculated in format command.

veritysetup --data-blocks=256 --hash-offset=1052672 verify <data_device> <hash_device> <root_hash>

Verifies device without activation (in userspace).

veritysetup --data-blocks=256 --hash-offset=1052672 --root-hash-file <path> verify <data_device> <hash_device>

Verifies device without activation (in userspace). Root hash passed via a file rather than inline.

veritysetup --fec-device=<fec_device> --fec-roots=10 format <data_device> <hash_device>

Calculates and stores verification and encoding data for data_device.

DM-VERITY ON-DISK SPECIFICATION

The on-disk format specification is available at page.

AUTHORS

The first implementation of veritysetup was written by Chrome OS authors.

This version is based on verification code written by and rewritten for libcryptsetup by

REPORTING BUGS

Report bugs at or in

Please attach output of the failed command with --debug option added.

SEE ALSO

cryptsetup(8), integritysetup(8) and veritysetup(8)

CRYPTSETUP

Part of