# veritytab

## NAME



           veritytab - Configuration for verity block devices
    


## SYNOPSIS



           /etc/veritytab
    


## DESCRIPTION



           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).
    


## EXAMPLES



           **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
    


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