Create an Artifact

Mender uses Artifacts to package the software updates for delivery to devices. As a user you manage the Artifacts with the help of the mender-artifact command. You can get it either as a pre-built executable from the downloads section or build from sources. The two basic usage scenarios of this utility reflect the two main update types Mender supports: Operating System update and Application update.

Create an Operating System update Artifact

Assuming you already have a generated filesystem image in rootfs.ext4 file, you can use the following command to generate an Artifact that contains the entire filesystem image as the payload:

mender-artifact write rootfs-image \
   -t beaglebone \
   -n release-1 \
   --software-version rootfs-v1 \
   -f rootfs.ext4 \
   -o artifact.mender

Note that the rootfs.ext4 filesystem image must be properly integrated with Mender for successful deployments. This generally means that you either generated it using the Yocto Project, or converted it from an existing Debian image.

The remaining flags specify the parameters used to match devices to deployments as follows:

• -t: specifies the compatible device types.
• -n: specifies the name of the Artifact.
• --software-version specifies the version string for the rootfs-image.
• -o: specifies the path to the output file.

Create an application update Artifact

Creating an Artifact takes a different form in the case of application updates.

For application updates, the command for mender-artifact tool will be different depending on the implementation details of the actual update module. Most of the Update Modules come with a script to simplify the Artifact creation so that the implementation details are hidden from the final user.

For example, assume that you want to copy a new authorized_keys file to the /home/${USER}/.ssh directory on your devices, where USER holds your user name.

We will use the single file Update Module to create a module-image.

First, download the script to generate the Artifact and make it executable:

curl -O https://raw.githubusercontent.com/mendersoftware/mender/3.5.3/support/modules-artifact-gen/single-file-artifact-gen
chmod +x single-file-artifact-gen

Now create the Artifact with:

./single-file-artifact-gen \
  --device-type raspberrypi4 \
  -o artifact.mender \
  -n updated-authorized_keys-1.0 \
  --software-name authorized_keys \
  --software-version 1.0 \
  --dest-dir /home/${USER}/.ssh \
  authorized_keys

Note specifically that in this case we are creating a module-image, using the single file Update Module. The Artifact created will be compatible with the raspberrypi4 device type, although you can specify more device types using multiple times --device-type if needed. The name of the Artifact is declared as updated-authorized_keys-1.0, we set the version of the software to 1.0 and indicate that it will be installed in the rootfs partition. The resulting file artifact.mender holds the Artifact.

Inspect the source code of the single file Update Module to learn about the implementation details of this module.

Server side Artifact generation

The hosted Mender Server and any on-premise server installation, can generate application update Artifacts automatically using the single file Update Module. You can test it by uploading any file to the releases page. The resulting Artifact will carry the file you have uploaded, the destination directory, the filename, and permissions, exactly as we saw above.

For more details on how to write Update Modules, visit the Create a custom Update Module section and the Update Module API specification.