|
HTML rendering created 2025-09-06 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
|
|
NAME | SYNOPSIS | DESCRIPTION | EXAMPLES | SEE ALSO | COLOPHON |
|
|
|
VERITYTAB(5) veritytab VERITYTAB(5)
veritytab - Configuration for verity block devices
/etc/veritytab
The /etc/veritytab file describes verity 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 protected block
device. Fields are delimited by white space.
Each line is in the form
volume-name data-device hash-device roothash [options]
The first four fields are mandatory, the remaining one is
optional.
The first field contains the name of the resulting verity volume;
its block device is set up below /dev/mapper/.
The second field contains a path to the underlying block data
device, or a specification of a block device via UUID= followed by
the UUID.
The third field contains a path to the underlying block hash
device, or a specification of a block device via UUID= followed by
the UUID.
The fourth field is the roothash in hexadecimal. If this field is
specified as dash, it is attempted to read the root hash from the
udev property "ID_DISSECT_PART_ROOTHASH=" (encoded in hexadecimal)
of the data device.
The fifth field, if present, is a comma-delimited list of options.
The following options are recognized:
superblock=BOOL
Use dm-verity with or without permanent on-disk superblock.
Added in version 254.
format=NUMBER
Specifies the hash version type. Format type "0" is original
Chrome OS version. Format type "1" is modern version.
Added in version 254.
data-block-size=BYTES
Used block size for the data device. (Note kernel supports
only page-size as maximum here; Multiples of 512 bytes.)
Added in version 254.
hash-block-size=BYTES
Used block size for the hash device. (Note kernel supports
only page-size as maximum here; Multiples of 512 bytes.)
Added in version 254.
data-blocks=BLOCKS
Number of blocks of data device used in verification. If not
specified, the whole device is used.
Added in version 254.
hash-offset=BYTES
Offset of hash area/superblock on "hash-device". (Multiples of
512 bytes.)
Added in version 254.
salt=HEX
Salt used for format or verification. Format is a hexadecimal
string; 256 bytes long maximum; "-" is the special value for
empty.
Added in version 254.
uuid=UUID
Use the provided UUID instead of generating new one. The UUID
must be provided in standard UUID format, e.g.
"12345678-1234-1234-1234-123456789abc".
Added in version 254.
ignore-corruption, restart-on-corruption, panic-on-corruption
Defines what to do if a data verity 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.)
Added in version 248.
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.
Added in version 248.
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.
Added in version 248.
hash=HASH
Hash algorithm for dm-verity. This should be the name of the
algorithm, like "sha1". For default see veritysetup --help.
Added in version 254.
fec-device=PATH
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. If fec device path does not exist, it will be
created as file. Note: block sizes for data and hash devices
must match. Also, if the verity data_device is encrypted the
fec_device should be too.
Added in version 254.
fec-offset=BYTES
This is the offset, in bytes, from the start of the FEC device
to the beginning of the encoding data. (Aligned on 512 bytes.)
Added in version 254.
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).
Added in version 254.
root-hash-signature=PATH|base64:BASE64|auto
A Base64 string encoding the root hash signature prefixed by
"base64:", or an absolute path to a root hash signature file
used to verify the root hash (in kernel). If the special
string "auto" is specified, the root hash signature is
attempted to be read from the udev property
"ID_DISSECT_PART_ROOTHASH_SIG=" (in Base64 format) of the data
device. This feature requires Linux kernel version 5.4 or more
recent.
Added in version 248.
_netdev
Marks this veritysetup device as requiring network. It will be
started after the network is available, similarly to
systemd.mount(5) units marked with _netdev. The service unit
to set up this device will be ordered between
remote-fs-pre.target and remote-veritysetup.target, instead of
veritysetup-pre.target and veritysetup.target.
Hint: if this device is used for a mount point that is
specified in fstab(5), the _netdev option should also be used
for the mount point. Otherwise, a dependency loop might be
created where the mount point will be pulled in by
local-fs.target, while the service to configure the network is
usually only started after the local file system has been
mounted.
Added in version 248.
noauto
This device will not be added to veritysetup.target. This
means that it will not be automatically enabled on boot,
unless something else pulls it in. In particular, if the
device is used for a mount point, it'll be enabled
automatically during boot, unless the mount point itself is
also disabled with noauto.
Added in version 248.
nofail
This device will not be a hard dependency of
veritysetup.target. It'll still be pulled in and started, but
the system will not wait for the device to show up and be
enabled, and boot will not fail if this is unsuccessful. Note
that other units that depend on the enabled device may still
fail. In particular, if the device is used for a mount point,
the mount point itself also needs to have the nofail option,
or the boot will fail if the device is not enabled
successfully.
Added in version 248.
x-initrd.attach
Setup this verity protected block device in the initrd,
similarly to systemd.mount(5) units marked with
x-initrd.mount.
Although it is not necessary to mark the mount entry for the
root file system with x-initrd.mount, x-initrd.attach is still
recommended with the verity protected block device containing
the root file system as otherwise systemd will attempt to
detach the device during the regular system shutdown while it
is still in use. With this option the device will still be
detached but later after the root file system is unmounted.
All other verity protected block devices that contain file
systems mounted in the initrd should use this option.
Added in version 248.
At early boot and when the system manager configuration is
reloaded, this file is translated into native systemd units by
systemd-veritysetup-generator(8).
Example 1. /etc/veritytab example
Set up two verity protected block devices. One using device
blocks, another using files.
usr PARTUUID=783e45ae-7aa3-484a-beef-a80ff9c19cbb PARTUUID=21dc1dfe-4c33-8b48-98a9-918a22eb3e37 36e3f740ad502e2c25e2a23d9c7c17bf0fdad2300b7580842d4b7ec1fb0fa263 auto
data /etc/data /etc/hash a5ee4b42f70ae1f46a08a7c92c2e0a20672ad2f514792730f5d49d7606ab8fdf auto
systemd(1), [email protected](8),
systemd-veritysetup-generator(8), fstab(5), veritysetup(8)
This page is part of the systemd (systemd system and service
manager) project. Information about the project can be found at
⟨http://www.freedesktop.org/wiki/Software/systemd⟩. If you have a
bug report for this manual page, see
⟨http://www.freedesktop.org/wiki/Software/systemd/#bugreports⟩.
This page was obtained from the project's upstream Git repository
⟨https://github.com/systemd/systemd.git⟩ on 2025-08-11. (At that
time, the date of the most recent commit that was found in the
repository was 2025-08-11.) If you discover any rendering
problems in this HTML version of the page, or you believe there is
a better or more up-to-date source for the page, or you have
corrections or improvements to the information in this COLOPHON
(which is not part of the original manual page), send a mail to
[email protected]
systemd 258~rc2 VERITYTAB(5)
Pages that refer to this page: systemd.directives(7), systemd.index(7), systemd.special(7), veritysetup(8)
|
HTML rendering created 2025-09-06 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
|