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VERITYSETUP(8) Maintenance Commands VERITYSETUP(8)
NAME
veritysetup - manage dm-verity (block level verification) volumes
SYNOPSIS
veritysetup <options> <action> <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 de-
vices using kernel crypto API.
The dm-verity devices are always read-only.
Veritysetup supports these operations:
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 op-
tion.
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 <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_de-
vice> 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]
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 new-
line.
If option --no-superblock is used, you have to use as the same options as in ini-
tial format operation.
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 new-
line.
<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 ini-
tial format operation.
close <name>
Removes existing mapping <name>.
For backward compatibility there is remove command alias for close command.
<options> can be [--deferred] or [--cancel-deferred]
status <name>
Reports status for the active verity mapping <name>.
dump <hash_device>
Reports parameters of verity device from on-disk stored superblock.
<options> can be [--hash-offset]
OPTIONS
--verbose, -v
Print more information on command execution.
--debug
Run in debug mode with full diagnostic logs. Debug output lines are always prefixed
by '#'.
--no-superblock
Create or use dm-verity without permanent on-disk superblock.
--format=number
Specifies the hash version type. Format type 0 is original Chrome OS version. For-
mat type 1 is current version.
--data-block-size=bytes
Used block size for the data device. (Note kernel supports only page-size as maxi-
mum here.)
--hash-block-size=bytes
Used block size for the hash device. (Note kernel supports only page-size as maxi-
mum here.)
--data-blocks=blocks
Size of data device used in verification. If not specified, the whole device is
used.
--hash-offset=bytes
Offset of hash area/superblock on hash_device. Value must be aligned to disk sec-
tor offset.
--salt=hex string
Salt used for format or verification. Format is a hexadecimal string.
--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.
--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 avail-
able 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.
--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.
--hash=hash
Hash algorithm for dm-verity. For default see --help option.
--version
Show the program version.
--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 de-
vice 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 encod-
ing 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).
--root-hash-file=FILE
Path to file with stored root hash in hex-encoded text.
--root-hash-signature=FILE
Path to roothash signature file used to verify the root hash (in kernel). This
feature requires Linux kernel version 5.4 or more recent.
--deferred
Defers device removal in close command until the last user closes it.
--cancel-deferred
Removes a previously configured deferred device removal in close command.
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.
REPORTING BUGS
Report bugs, including ones in the documentation, on the cryptsetup mailing list at <dm-
crypt AT saout.de> or in the 'Issues' section on LUKS website. Please attach the output of
the failed command with the --debug option added.
AUTHORS
The first implementation of veritysetup was written by Chrome OS authors.
This version is based on verification code written by Mikulas Patocka <mpatocka@red-
hat.com> and rewritten for libcryptsetup by Milan Broz <gmazyland AT gmail.com>.
COPYRIGHT
Copyright (C) 2012-2021 Red Hat, Inc.
Copyright (C) 2012-2021 Milan Broz
This is free software; see the source for copying conditions. There is NO warranty; not
even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
SEE ALSO
The project website at https://gitlab.com/cryptsetup/cryptsetup
The verity on-disk format specification available at https://gitlab.com/cryptsetup/crypt-
setup/wikis/DMVerity
veritysetup January 2021 VERITYSETUP(8)
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On Apache
Under GNU General Public License
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