11. Reference

11.1. System Configuration File

A configuration file located in /etc/rauc/system.conf describes the number and type of available slots. It is used to validate storage locations for update images. Each board type requires its special configuration.

This file is part of the root file system.


When changing the configuration file on your running target you need to restart the RAUC service in order to let the changes take effect.

Example configuration:

compatible=FooCorp Super BarBazzer





[system] section

A user-defined compatible string that describes the target hardware as specific enough as required to prevent faulty updating systems with the wrong firmware. It will be matched against the compatible string defined in the update manifest.
The bootloader implementation RAUC should use for its slot switching mechanism. Currently supported values (and bootloaders) are barebox, grub, uboot.
Prefix of the path where bundles and slots will be mounted. Can be overwritten by the command line option --mount. Defaults to /mnt/rauc/.
Only valid when bootloader is set to grub. Specifies the path under which the GRUB environment can be accessed.
This boolean value controls if a freshly installed slot is automatically marked active with respect to the used bootloader. Its default value is true which means that this slot is going to be started the next time the system boots. If the value of this parameter is false the slot has to be activated manually in order to be booted, see section Manually Switch to a Different Slot.
If this key exists, it points to a file where slot status information should be stored (e.g. slot specific metadata, see Slot Status). This file should be located on a filesystem which is not overwritten during updates.
Only valid when bootloader is set to barebox. Overwrites the default state state to a user-defined state name. If this key not exists, the bootchooser framework searches per default for /state or /aliases/state.
Defines the maximum downloadable bundle size in bytes, and thus must be a simple integer value (without unit) greater than zero. It overwrites the compiled-in default value of 8 MiB.

[keyring] section

The keyring section refers to the trusted keyring used for signature verification.

Path to the keyring file in PEM format. Either absolute or relative to the system.conf file.
Use the bundle signing time instead of current time for certificate validation.

[casync] section

The casync section contains casync-related settings. For more information about using casync support of RAUC, refer to RAUC casync Support.

Allows to set the path to use as chunk store path for casync to a fixed one. This is useful if your chunk store is on a dedicated server and will be the same pool for each update you perform. By default, the chunk store path is derived from the location of the RAUC bundle you install.

[autoinstall] section

The auto-install feature allows to configure a path that will be checked upon RAUC service startup. If there is a bundle placed under this specific path, this bundle will be installed automatically without any further interaction.

This feature is useful for automatically updating the slot RAUC currently runs from, like for asymmetric redundancy setups where the update is always performed from a dedicated (recovery) slot.

The full path of the bundle file to check for. If file at path exists, auto-install will be triggered.

[handlers] section

Handlers allow to customize RAUC by placing scripts in the system that RAUC can call for different purposes. All parameters expect pathnames to the script to be executed. Pathnames are either absolute or relative to the system.conf file location.

RAUC passes a set of environment variables to handler scripts. See details about using handlers in Custom Handlers (Interface).


This handler will be called when RAUC starts up, right after loading the system configuration file. It is used for obtaining further information about the individual system RAUC runs on. The handler script must print the information to standard output in form of key value pairs KEY=value. The following variables are supported:

Serial number of the individual board
This handler will be called right before RAUC starts with the installation. This is after RAUC has verified and mounted the bundle, thus you can access bundle content.
This handler will be called after a successful installation. The bundle is still mounted at this moment, thus you could access data in it if required.


When using a full custom installation (see [handler] section) RAUC will not execute any system handler script.

[slot.<slot-class>.<idx>] section

Each slot is identified by a section starting with slot. followed by the slot class name, and a slot number. The <slot-class> name is used in the update manifest to target the correct set of slots. It must not contain any . (dots) as these are used as hierarchical separator.

The slot’s device path. This one is mandatory.
The type describing the slot. Currently supported <type> values are raw, nand, ubivol, ubifs, ext4, vfat. See table Slot Type for a more detailed list of these different types. Defaults to raw if none given.
Registers the slot for being handled by the bootselection interface with the <name> specified. The actual meaning of the name provided depends on the bootloader implementation used.
The parent entry is used to bind additional slots to a bootable root file system <slot>. This is used together with the bootname to identify the set of currently active slots, so that the inactive one can be selected as the update target. The parent slot is referenced using the form <slot-class>.<idx>.
Marks the slot as existing but not updatable. May be used for sanity checking or informative purpose. A readonly slot cannot be a target slot.
If set to true this will bypass the default hash comparison for this slot and force RAUC to unconditionally update it. The default value is false, which means that updating this slot will be skipped if new image’s hash matches hash of installed one. This replaces the deprecated entry ignore-checksum.
Allows to specify custom mount options that will be passed to the slots mount call as -o argument value.

11.2. Manifest

A valid manifest file must have the file extension .raucm.

compatible=FooCorp Super BarBazzer



[update] section

A user-defined compatible string that must match the compatible string of the system the bundle should be installed on.
A free version field that can be used to provide and track version information. No checks will be performed on this version by RAUC itself, although a handler can use this information to reject updates.
A free-form description field that can be used to provide human-readable bundle information.
A build id that would typically hold the build date or some build information provided by the bundle creation environment. This can help to determine the date and origin of the built bundle.

[hooks] section

Hook script path name, relative to the bundle content.

List of hooks enabled for this bundle. See Install Hooks for more details.

Valid items are: install-check

[handler] section

Handler script path name, relative to the bundle content. Used to fully replace default update process.
Arguments to pass to the handler script, such as args=--verbose

[image.<slot-class>] section

Name of the image file (relative to bundle content). RAUC uses the file extension and the slot type to decide how to extract the image file content to the slot.
sha256 of image file. RAUC determines this value automatically when creating a bundle, thus it is not required to set this by hand.
size of image file. RAUC determines this value automatically when creating a bundle, thus it is not required to set this by hand.

List of per-slot hooks enabled for this image. See Slot Hooks for more details.

Valid items are: pre-install, install, post-install

11.3. Slot Status

There is some slot specific metadata that are of interest for RAUC, e.g. a hash value of the slot’s content (SHA-256 per default) that is matched against its counterpart of an image inside a bundle to decide if an update of the slot has to be performed or can be skipped. These slot metadata can be persisted in one of two ways: either in a slot status file stored on each slot containing a writable filesystem or in a central status file that lives on a persistent filesystem untouched by updates. The former is RAUC’s default whereas the latter mechanism is enabled by making use of the optional key statusfile in the system.conf file. Both are formatted as INI-like key/value files where the slot information is grouped in a section named [slot] for the case of a per-slot file or in sections termed with the slot name (e.g. [slot.rootfs.1]) for the central status file:

bundle.compatible=FooCorp Super BarBazzer
bundle.description=Introduction of Galactic Feature XYZ

For a description of sha256 and size keys see this part of the section Manifest. Having the slot’s content’s size allows to re-calculate the hash via head -c <size> <slot-device> | sha256sum` or `dd bs=<size> count=1 if=<slot-device> | sha256sum.

The properties bundle.compatible, bundle.version, bundle.description and bundle.build are copies of the respective manifest properties. More information can be found in this subsection of section Manifest.

RAUC also stores the point in time of installing the image to the slot in installed.timestamp as well as the number of updates so far in installed.count. Additionally RAUC tracks the point in time when a bootable slot is activated in activated.timestamp and the number of activations in activated.count, see section Manually Switch to a Different Slot. Comparing both timestamps is useful to decide if an installed slot has ever been activated or if its activation is still pending.

11.4. Command Line Tool

  rauc [OPTION...] <COMMAND>

  -c, --conf=FILENAME               config file
  --cert=PEMFILE|PKCS11-URL         cert file or PKCS#11 URL
  --key=PEMFILE|PKCS11-URL          key file or PKCS#11 URL
  --keyring=PEMFILE                 keyring file
  --intermediate=PEMFILE            intermediate CA file name
  --mount=PATH                      mount prefix
  --override-boot-slot=SLOTNAME     override auto-detection of booted slot
  --handler-args=ARGS               extra handler arguments
  -d, --debug                       enable debug output
  --version                         display version
  -h, --help

List of rauc commands:
  bundle        Create a bundle
  resign        Resign an already signed bundle
  checksum      Update a manifest with checksums (and optionally sign it)
  install       Install a bundle
  info          Show file information
  status        Show status

Environment variables:
  RAUC_PKCS11_MODULE  Library filename for PKCS#11 module (signing only)
  RAUC_PKCS11_PIN     PIN to use for accessing PKCS#11 keys (signing only)

11.5. Custom Handlers (Interface)

Interaction between RAUC and custom handler shell scripts is done using shell variables.

Path to the system configuration file (default path is /etc/rauc/system.conf)
Bootname of the slot the system is currently booted from
Path to mounted update bundle, e.g. /mnt/rauc/bundle
Provides the path prefix that may be used for RAUC mount points
An iterator list to loop over all existing slots. Each item in the list is an integer referencing one of the slots. To get the slot parameters, you have to resolve the per-slot variables (suffixed with <N> placeholder for the respective slot number).
An iterator list similar to RAUC_SLOTS but only containing slots that were selected as target slots by the RAUC target slot selection algorithm. You may use this list for safely installing images into these slots.
The name of slot number <N>, e.g. rootfs.0
The class of slot number <N>, e.g. rootfs
The type of slot number <N>, e.g. raw
The device path of slot number <N>, e.g. /dev/sda1
The bootloader name of slot number <N>, e.g. system0
The name of slot number <N>, empty if none, otherwise name of parent slot
for i in $RAUC_TARGET_SLOTS; do

11.6. D-Bus API

RAUC provides a D-Bus API that allows other applications to easily communicate with RAUC for installing new firmware.


11.6.1. Methods

Install (IN s source);

Info (IN s bundle, s compatible, s version);

Mark (IN s state, IN s slot_identifier, s slot_name, s message);

GetSlotStatus (a(sa{sv}) slot_status_array);

11.6.2. Signals

Completed (i result);

11.6.3. Properties

Operation readable s

LastError readable s

Progress readable (isi)

Compatible readable s

Variant readable s

BootSlot readable s

11.6.4. Description

11.6.5. Method Details The Install() Method

Install (IN  s source);

Triggers the installation of a bundle. This method call is non-blocking. After completion, the “Completed” signal will be emitted.

IN s source:
Path to bundle to be installed The Info() Method

Info (IN  s bundle, s compatible, s version);

Provides bundle info.

IN s bundle:
Path to bundle information should be shown
s compatible:
Compatible of bundle
s version:
Version string of bundle The Mark() Method

Mark (IN  s state, IN  s slot_identifier, s slot_name, s message);

Keeps a slot bootable (state == “good”), makes it unbootable (state == “bad”) or explicitly activates it for the next boot (state == “active”).

IN s state:
Operation to perform (one out of “good”, “bad” or “active”)
IN s slot_identifier:
Can be “booted”, “other” or <SLOT_NAME> (e.g. “rootfs.1”)
s slot_name:
Name of the slot which has ultimately been marked
s message:
Message describing what has been done successfully (e.g. “activated slot rootfs.0”) The GetSlotStatus() Method

GetSlotStatus (a(sa{sv}) slot_status_array);

Access method to get all slots’ status.

a(sa{sv}) slot_status_array:
Array of (slotname, dict) tuples with each dictionary representing the status of the corresponding slot

11.6.6. Signal Details The “Completed” Signal

Completed (i result);

This signal is emitted when an installation completed, either successfully or with an error.

i result:
return code (0 for success)

11.6.7. Property Details The “Operation” Property

Operation  readable   s

Represents the current (global) operation RAUC performs. The “LastError” Property

LastError  readable   s

Holds the last message of the last error that occurred. The “Progress” Property

Progress  readable   (isi)

Provides installation progress information in the form

(percentage, message, nesting depth) The “Compatible” Property

Compatible  readable   s

Represents the system’s compatible. This can be used to check for usable bundels. The “Variant” Property

Variant  readable   s

Represents the system’s variant. This can be used to select parts of an bundle. The “BootSlot” Property

BootSlot  readable   s

Represents the used boot slot.

11.7. RAUC’s Basic Update Procedure

Performing an update using the default RAUC mechanism will work as follows:

  1. Startup, read system configuration
  2. Determine slot states
  3. Verify bundle signature (reject if invalid)
  4. Mount bundle (SquashFS)
  5. Parse and verify manifest
  6. Determine target install group
    1. Execute pre install handler (optional)
  7. Verify bundle compatible against system compatible (reject if not matching)
  8. Mark target slots as non-bootable for bootloader
  9. Iterate over each image specified in the manifest
    1. Determine update handler (based on image and slot type)
    2. Try to mount slot and read slot status information
      1. Skip update if new image hash matches hash of installed one
    3. Perform slot update (image copy / mkfs+tar extract / …)
    4. Try to write slot status information
  10. Mark target slots as new primary boot source for the bootloader
    1. Execute post install handler (optional)
  11. Unmount bundle
  12. Terminate successfully if no error occurred

11.8. Bootloader Interaction

RAUC comes with a generic interface for interacting with the bootloader. It handles all slots that have a bootname property set.

It provides two base functions:

  1. Setting state ‘good’ or ‘bad’, reflected by API routine r_boot_set_state() and command line tool option rauc status mark <good/bad>
  2. Marking a slot ‘primary’, reflected by API routine r_boot_set_primary() and command line tool option rauc status mark-active

The default flow of how they will be called during the installation of a new bundle (on Slot ‘A’) looks as follows:

start   ->  install  ->  reboot  -> operating state  ->
        |            |                               |
   set A bad   set A primary                     set A good/bad

The aim of setting state ‘bad’ is to disable a slot in a way that the bootloader will not select it for booting anymore. As shown above this is either the case before an installation to make the update atomic from the bootloader’s perspective, or optionally after the installation and a reboot into the new system, when a service detects that the system is in an unusable state. This potentially allows falling back to a working system.

The aim of setting a slot ‘primary’ is to let the bootloader select this slot upon next reboot in case of having completed the installation successfully. An alternative to directly marking a slot primary after installation is to manually mark it primary at a later point in time, e.g. to let a complete set of devices change their software revision at the same time.

Setting the slot ‘good’ is relevant for the first boot but for all subsequent boots, too. In most cases, this interaction with the bootloader is required by the mechanism that enables fallback capability; rebooting a system one or several times without calling rauc status mark-good will let the bootloader boot an alternative system or abort boot operation (depending on configuration). Usually, bootloaders implement this fallback mechanism by some kind of counters they maintain and decrease upon each boot. In these cases marking good means resetting these counters.

A normal reboot of the system will look as follows:

operating state  ->  reboot  -> operating state  ->
                                           set A good/bad

Some bootloaders do not require explicitly setting state ‘good’ as they are able to differentiate between a POR and a watchdog reset, for example.

What the high-level functions described above actually do mainly depends on the underlying bootloader used and the capabilities it provides. Below is a short description about behavior of each bootloader interface currently implemented:

11.8.1. U-Boot

The U-Boot implementation assumes to have variables BOOT_ORDER and BOOT_x_ATTEMPTS handled by the bootloader scripting.

state bad:Sets the BOOT_x_ATTEMPTS variable of the slot to 0 and removes it from the BOOT_ORDER list
state good:Sets the BOOT_x_ATTEMPTS variable back to its default value (3).
primary:Moves the slot from its current position in the list in BOOT_ORDER to the first place and sets BOOT_x_ATTEMPTS to its initial value (3). If BOOT_ORDER was unset before, it generates a new list of all slots known to RAUC with the one to activate at the first position.

11.8.2. Barebox

The barebox implementation assumes using barebox bootchooser.

state bad:Sets both the bootstate.systemX.priority and bootstate.systemX.remaining_attempts to 0.
state good:Sets the bootstate.systemX.remaining_attempts to its default value (3).
primary:Sets bootstate.systemX.priority to 20 and all other priorities that were non-zero before to 10. It also sets bootstate.systemX.remaining_attempts to its initial value (3).

11.8.3. GRUB

state bad:Sets slot x_OK to 0 and resets x_TRY to 0.
state good:Sets slot x_OK to 1 and resets x_TRY to 0.
primary:Sets slot x_OK to 1 and resets x_TRY to 0. Sets ORDER to contain slot x as first element and all other after.

11.8.4. EFI

state bad:Removes the slot from BootOrder
state good:Prepends the slot to the BootOrder list. This behaves slightly different than the other implementations because we use BootNext for allowing setting primary with an initial fallback option. Setting state good is then used to persist this.
primary:Sets the slot as BootNext. This will make the slot being booted upon next reboot only!


EFI implementations differ in how they handle new or unbootable targets etc. It may also depend on the actual implementation if EFI variable writing is atomic or not. Thus make sure your EFI works as expected and required.