3. Using RAUC¶
For using RAUC in your embedded project, you will need to build at least two versions of it:
- One for your host (build or development) system. This will allow you to create, inspect and modify bundles.
- One for your target system. This can act both as the service for handling the installation on your system, as a command line tool that allows triggering the installation and inspecting your system or obtaining bundle information.
All common embedded Linux build system recipes for RAUC will solve the task of creating appropriate binaries for you as well as caring for bundle creation and partly system configuration. If you intend to use RAUC with Yocto, use the meta-rauc layer, in case you use PTXdist, simply enable RAUC in your configuration.
Note
When using the RAUC service from your application, the D-Bus interface is preferable to using the provided command-line tool.
3.1. Creating Bundles¶
To create an update bundle on your build host, RAUC provides the bundle
sub-command:
rauc bundle --cert=<certfile> --key=<keyfile> --keyring=<keyringfile> <input-dir> <output-file>
Where <input-dir> must be a directory containing all images and scripts the
bundle should include, as well as a manifest file manifest.raucm that
describes the content of the bundle for the RAUC updater on the target:
which image to install to which slot, which scripts to execute etc.
Note that all files in <input-dir> will be included in the bundle,
not just those specified in the manifest.
<output-file> must be the path of the bundle file to create.
Instead of the certfile and keyfile arguments, PKCS#11 URLs such as
'pkcs11:token=rauc;object=autobuilder-1' can be used to avoid storing
sensitive key material as files (see PKCS#11 Support
for details).
While the --cert and --key argument are mandatory for signing and must
provide the certificate and private key that should be used for creating the
signature, the --keyring argument is optional and (if given) will be used
for verifying the trust chain validity of the signature after creation.
Note that this is very useful to prevent from signing with obsolete
certificates, etc.
3.2. Obtaining Bundle Information¶
rauc info [--output-format=<format>] <input-file>
The info command lists the basic meta data of a bundle (compatible, version,
build-id, description) and the images and hooks contained in the bundle.
You can control the output format depending on your needs. By default it will print a human readable representation of the bundle not intended for being processed programmatically. Alternatively you can obtain a shell-parsable description or a JSON representation of the bundle content.
3.3. Installing Bundles¶
To actually install an update bundle on your target hardware, RAUC provides the
install command:
rauc install <input-file>
Alternatively you can trigger a bundle installation using the D-Bus API.
3.4. Viewing the System Status¶
For debugging purposes and for scripting it is helpful to gain an overview of
the current system as RAUC sees it.
The status command allows this:
rauc status [--detailed] [--output-format=<format>]
You can choose the output style of RAUC status depending on your needs.
By default it will print a human readable representation of your system’s most
important properties. Alternatively you can obtain a shell-parsable description,
or a JSON representation of the system status.
If more information is needed such as the slots’ status add
the command line option --detailed.
3.5. React to a Successfully Booted System/Failed Boot¶
Normally, the full system update chain is not complete before being sure that the newly installed system runs without any errors. As the definition and detection of a successful operation is really system-dependent, RAUC provides commands to preserve a slot as being the preferred one to boot or to discard a slot from being bootable.
rauc status mark-good
After verifying that the currently booted system is fully operational, one wants to signal this information to the underlying bootloader implementation which then, for example, resets a boot attempt counter.
rauc status mark-bad
If the current boot failed in some kind, this command can be used to communicate that to the underlying bootloader implementation. In most cases this will disable the currently booted slot or at least switch to a different one.
Although not very useful in the field, both commands recognize an optional argument to explicitly identify the slot to act on:
rauc status mark-{good,bad} [booted | other | <SLOT_NAME>]
This is to maintain consistency with respect to rauc status mark-active
where that argument is definitively wanted, see here.
3.6. Manually Switch to a Different Slot¶
One can think of a variety of reasons to switch the preferred slot for the next boot by hand, for example:
- Recurrently test the installation of a bundle in development starting from a known state.
- Activate a slot that has been installed sometime before and whose activation has explicitly been prevented at that time using the system configuration file’s parameter activate-installed.
- Switch back to the previous slot because one really knows better™.
To do so, RAUC offers the subcommand
rauc status mark-active [booted | other | <SLOT_NAME>]
where the optional argument decides which slot to (re-)activate at the expense
of the remaining slots. Choosing other switches to the next bootable slot
that is not the one that is currently booted. In a two-slot-setup this is
just… the other one. If one wants to explicitly address a known slot, one can
do so by using its slot name which has the form <slot-class>.<idx> (e.g.
rootfs.1), see this part of section
System Configuration File. Last but not least,
after switching to a different slot by mistake, before having rebooted this can
be remedied by choosing booted as the argument which is, by the way, the
default if the optional argument has been omitted.
The date and time of activation as well as the number of activations is part of
the slot’s metadata which is stored in the slot status file, see section
Slot Status.
3.7. Customizing the Update¶
RAUC provides several ways to customize the update process. Some allow adding and extending details more fine-grainedly, some allow replacing major parts of the default behavior of RAUC.
In general, there exist three major types of customization:
- configuration parameters (in rootfs config file
/etc/rauc/system.conf) - handlers (executables in rootfs)
- hooks (executables in bundle)
The first type, configuration parameters, allow controlling parameters of the update in a predefined way.
The second type, using handlers, allows extending or replacing the installation process. They are executables (most likely shell scripts) located in the root filesystem and configured in the system’s configuration file. They control static behavior of the system that should remain the same over future updates.
The last type are hooks. They are similar to handlers, except that they are contained in the update bundle. Thus they allow to flexibly extend or customize one or more updates by some special behavior. A common example would be using a per-slot post-install hook that handles configuration migration for a new software version. Hooks are especially useful to handle details of installing an update which were not considered in the previously deployed version.
In the following, configuration parameters, handlers and hooks will be explained in more detail.
3.7.1. System Configuration Parameters¶
Beside providing the basic slot layout, RAUC’s system configuration file
(system.conf) also allows you to configure parts of its runtime behavior,
such as handlers (see below), paths, etc.
For a detailed list of possible configuration options,
see System Configuration File section in the Reference chapter.
3.7.2. System-Based Customization: Handlers¶
Handlers are executables located in the target’s root file system that allow extending the installation process on system side. They must be specified in the targets System Configuration File.
For a detailed list of all environment variables exported for the handler scripts, see the Custom Handlers (Interface) section.
Pre-Install Handler
[handlers]
pre-install=/usr/lib/rauc/pre-install
RAUC will call the pre-install handler (if given) during the bundle installation process, right before calling the default or custom installation process. At this stage, the bundle is mounted, its content is accessible and the target group has been determined successfully.
If calling the handler fails or the handler returns a non-zero exit code, RAUC will abort installation with an error.
Post-Install Handler
[handlers]
post-install=/usr/lib/rauc/post-install
The post-install handler will be called right after RAUC successfully performed a system update. If any error occurred during installation, the post-install handler will not be called.
Note that a failed call of the post-install handler or a non-zero exit code will cause a notification about the error but will not change the result of the performed update anymore.
A possible usage for the post-install handler could be to trigger an automatic restart of the system.
System-Info Handler
[handlers]
system-info=/usr/lib/rauc/system-info
The system-info handler is called after loading the configuration file. This way it can collect additional variables from the system, like the system’s serial number.
The handler script must return a system serial number by echoing RAUC_SYSTEM_SERIAL=<value> to standard out.
3.7.3. Bundle-Based Customization: Hooks¶
Unlike handlers, hooks are part of the update bundle and must be specified in the bundle’s Manifest file and handled by a common executable. Hooks allow the author of a bundle to add or replace functionality for the installation of a specific bundle. This can be useful for performing additional migration steps, checking for specific previously installed bundle versions or for manually handling updates of images RAUC cannot handle natively.
To reduce the complexity and number of files in a bundle, all hooks must be handled by a single executable that is registered in the bundle’s manifest:
[hooks]
filename=hook
Each hook must be activated explicitly and leads to a call of the hook executable
with a specific argument that allows to distinguish between the different hook
types. Multiple hook types must be separated with a ;.
In the following the available hooks are listed. Depending on their purpose, some are image-specific, i.e. they will be executed for the installation of a specific image only, while some other are global.
3.7.3.1. Install Hooks¶
Install hooks operate globally on the bundle installation.
For a detailed list of all environment variables exported for the hooks executable, see the Install Hooks Interface section.
Install-Check Hook
[hooks]
filename=hook
hooks=install-check
This hook will be executed instead of the normal compatible check in order to allow performing a custom compatibility check based on compatible and/or version information.
To indicate that a bundle should be rejected, the script must return with an exit code >= 10.
If available, RAUC will use the last line printed to standard error by the hook executable as the rejection reason message and provide it to the user:
#!/bin/sh
case "$1" in
install-check)
if [[ "$RAUC_MF_COMPATIBLE" != "$RAUC_SYSTEM_COMPATIBLE" ]]; then
echo "Compatible does not match!" 1>&2
exit 10
fi
;;
*)
exit 1
;;
esac
exit 0
3.7.3.2. Slot Hooks¶
Slot hooks are called for each slot an image will be installed to. In order to
enable them, you have to specify them in the hooks key under the respective
image section.
Note that hook slot operations will be passed to the executable with the prefix
slot-. Thus if you intend to check for the pre-install hook, you have to
check for the argument to be slot-pre-install.
For a detailed list of all environment variables exported for the hooks executable, see the Slot Hooks Interface section.
Pre-Install Hook
The pre-install hook will be called right before the update procedure for the respective slot will be started. For slot types that represent a mountable file system, the hook will be executed with having the file system mounted.
[hooks]
filename=hook
[image.rootfs]
filename=rootfs.img
size=...
sha256=...
hooks=pre-install
Post-Install Hook
The post-install hook will be called right after the update procedure for the respective slot was finished successfully. For slot types that represent a mountable file system, the hook will be executed with having the file system mounted. This allows to write some post-install information to the slot. It is also useful to copy files from the currently active system to the newly installed slot, for example to preserve application configuration data.
[hooks]
filename=hook
[image.rootfs]
filename=rootfs.img
size=...
sha256=...
hooks=post-install
An example on how to use a post-install hook:
#!/bin/sh
case "$1" in
slot-post-install)
# only rootfs needs to be handled
test "$RAUC_SLOT_CLASS" = "rootfs" || exit 0
touch "$RAUC_SLOT_MOUNT_POINT/extra-file"
;;
*)
exit 1
;;
esac
exit 0
Install Hook
The install hook will replace the entire default installation process for the target slot of the image it was specified for. Note that when having the install hook enabled, pre- and post-install hooks will not be executed. The install hook allows to fully customize the way an image is installed. This allows performing special installation methods that are not natively supported by RAUC, for example to upgrade the bootloader to a new version while also migrating configuration settings.
[hooks]
filename=hook
[image.rootfs]
filename=rootfs.img
size=...
sha256=...
hooks=install
3.7.4. Full Custom Update¶
For some special tasks (recovery, testing, migration) it might be required to completely replace the default RAUC update mechanism and to only use its infrastructure for executing an application or a script on the target side.
For this case, you may replace the entire default installation handler of rauc by a custom handler script or application.
Refer manifest [handler] section description on how to achieve this.
3.8. Using the D-Bus API¶
The RAUC D-BUS API allows seamless integration into existing or project-specific applications, incorporation with bridge services such as the rauc-hawkbit client and also the rauc CLI uses it.
The API’s service domain is de.pengutronix.rauc while the object path is
/.
3.8.1. Installing a Bundle¶
The D-Bus API’s main purpose is to trigger and monitor the installation
process via its Installer interface.
The InstallBundle method call triggers the installation of a given bundle in the
background and returns immediately.
Upon completion of the installation RAUC emits the Completed signal,
indicating either successful or failed installation.
For details on triggering the installation process, see the
The InstallBundle() Method chapter in the
reference documentation.
While the installation is in progress, constant progress information will be
emitted in form of changes to the Progress property.
3.8.2. Processing Progress Data¶
The progress property will be updated upon each change of the progress value. For details see the The “Progress” Property chapter in the reference documentation.
To monitor Progress property changes from your application, attach to the
PropertiesChanged signal and filter on the Operation properties.
Each progress step emitted is a tuple (percentage, message, nesting depth)
describing a tree of progress steps:
├"Installing" (0%)
│ ├"Determining slot states" (0%)
│ ├"Determining slot states done." (20%)
│ ├"Checking bundle" (20%)
│ │ ├"Verifying signature" (20%)
│ │ └"Verifying signature done." (40%)
│ ├"Checking bundle done." (40%)
│ ...
└"Installing done." (100%)
This hierarchical structure allows applications to decide for the appropriate
granularity to display information.
Progress messages with a nesting depth of 1 are only Installing and
Installing done..
A nesting depth of 2 means more fine-grained information while larger depths
are even more detailed.
Additionally, the nesting depth information allows the application to print
tree-like views as shown above.
The percentage value always goes from 0 to 100 while the message is
always a human-readable English string.
For internationalization you may use a
gettext-based approach.
3.8.3. Examples Using busctl Command¶
Triggering an installation:
busctl call de.pengutronix.rauc / de.pengutronix.rauc.Installer InstallBundle sa{sv} "/path/to/bundle" 0
Mark a slot as good:
busctl call de.pengutronix.rauc / de.pengutronix.rauc.Installer Mark ss "good" "rootfs.0"
Mark a slot as active:
busctl call de.pengutronix.rauc / de.pengutronix.rauc.Installer Mark ss "active" "rootfs.0"
Get the Operation property containing the current operation:
busctl get-property de.pengutronix.rauc / de.pengutronix.rauc.Installer Operation
Get the Progress property containing the progress information:
busctl get-property de.pengutronix.rauc / de.pengutronix.rauc.Installer Progress
Get the LastError property, which contains the last error that occurred during an installation.
busctl get-property de.pengutronix.rauc / de.pengutronix.rauc.Installer LastError
Get the status of all slots
busctl call de.pengutronix.rauc / de.pengutronix.rauc.Installer GetSlotStatus
Get the current primary slot
busctl call de.pengutronix.rauc / de.pengutronix.rauc.Installer GetPrimary
Monitor the D-Bus interface
busctl monitor de.pengutronix.rauc
3.9. Debugging RAUC¶
When RAUC fails to start on your target during integration or later during installation of new bundles it can have a variety of causes.
This section will lead you trough the most common options you have for debugging what actually went wrong.
In each case it is quite essential to know that RAUC, if not compiled with
--disable-service runs as a service on your target that is either
controlled by your custom application or by the RAUC command line interface.
The frontend will always only show the ‘high level’ error outpt, e.g. when an installation failed:
rauc-Message: 08:27:12.083: installing /home/enrico/Code/rauc/good-bundle-hook.raucb: LastError: Failed mounting bundle: failed to run mount: Child process exited with code 1
rauc-Message: 08:27:12.083: installing /home/enrico/Code/rauc/good-bundle-hook.raucb: idle
Installing `/home/enrico/Code/rauc/good-bundle-hook.raucb` failed
In simple cases this might be sufficient for identifying the actual problem, in more complicated cases this may give a rough hint. For a more detailed look on what went wrong you need to inspect the rauc service log instead.
If you run RAUC using systemd, the log can be obtained using
journalctl -u rauc
When using SysVInit, your service script needs to configure logging itself. A common way is to dump the log e.g. /var/log/rauc.
It may also be worth starting the RAUC service via command line on a second
shell to have a live view of what is going on when you invoke e.g. rauc
install on the first shell.
3.9.1. Increasing Debug Verbosity¶
Both for the service and the command line interface it is often useful to increase the log level for narrowing down the actual error cause or gaining more information about the circumstances when the error occurs.
RAUC uses glib and the glib logging framework with the basic log domain ‘rauc’.
For simple cases, you can activate logging by passing the -d or --debug option to either the CLI:
rauc install -d bundle.raucb ..
or the service (you might need to modify your systemd or SysVInit service file).
rauc service -d
For more fine grained and advanced debugging options, use the
G_MESSAGES_DEBUG environment variable.
This allows enabling different log domains. Currently available are:
| all: | enable all log domains |
|---|---|
| rauc: | enable default RAUC log domain (same as calling with |
| rauc-subprocess: | |
enable logging of subprocess calls This will dump the entire program call invoked by RAUC and can help tracing down or reproducing issues caused by other programs invoked. |
|
Example invocation:
G_MESSAGES_DEBUG="rauc rauc-subprocess" rauc service