| VERITYTAB(5) | veritytab | VERITYTAB(5) |
.SH "NAME" veritytab - Configuration for verity block devices
.SH "SYNOPSIS"
.PP /etc/veritytab
.SH "DESCRIPTION"
.PP The /etc/veritytab file describes verity protected block devices that are
set up during system boot.
.PP 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.
.PP 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.
.PP The first field contains the name of the resulting verity volume; its
block device is set up below /dev/mapper/.
.PP 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.
.PP 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.
.PP 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.
.PP The fifth field, if present, is a comma-delimited list of options. The
following options are recognized:
.PP superblock=BOOL
Use dm-verity with or without permanent on-disk superblock.
Added in version 254.
.RE
.PP 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.
.RE
.PP 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.
.RE
.PP 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.
.RE
.PP data-blocks=BLOCKS
Number of blocks of data device used in verification. If not specified, the
whole device is used.
Added in version 254.
.RE
.PP hash-offset=BYTES
Offset of hash area/superblock on hash-device. (Multiples of 512 bytes.)
Added in version 254.
.RE
.PP 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.
.RE
.PP 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.
.RE
.PP 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.
.RE
.PP ignore-zero-blocks
Instruct kernel to not verify blocks that are expected to contain zeroes and
always directly return zeroes instead.
.if n .sp
Warning
Use this option only in very specific cases. This option is available since
Linux kernel version 4.5.
.sp .5v
Added in version 248.
.RE
.PP check-at-most-once
Instruct kernel to verify blocks only the first time they are read from the
data device, rather than every time.
.if n .sp
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.
.sp .5v
Added in version 248.
.RE
.PP 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.
.RE
.PP 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.
.RE
.PP 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.
.RE
.PP 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.
.RE
.PP
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.
.RE
.PP _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.
.RE
.PP 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.
.RE
.PP 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.
.RE
.PP 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.
.RE
.PP tpm2-measure-nvpcr=
Takes a boolean argument, or an NvPCR name as argument. May be used to enable
automatic measurement of the volume name and Verity root hash, as well as
the serials and issuers of the certificates used to generate the provided
signatures (if any) will be measured. Passing false disables the mechanism.
Passing true enables measurement into the verity NvPCR. If any other string
is specified this selects the NvPCR to measure into by name.
Added in version 260.
.RE
.PP At early boot and when the system manager configuration is reloaded, this
file is translated into native systemd units by
systemd-veritysetup-generator(8).
.SH "EXAMPLES"
.PP Example 1. /etc/veritytab example
.PP 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
.SH "SEE ALSO"
.PP systemd(1), systemd-veritysetup@.service(8),
systemd-veritysetup-generator(8), fstab(5),
veritysetup(8)
| systemd 262.2 |