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A Mender Artifact is a file Mender uses to deploy updates. Please see Mender Artifacts for a more detailed description.
When testing deployments, it is useful that the Artifact you are deploying is different from the one that you have installed so you can see that the update is successful. You might also want to configure certain aspects of the update after you build it, but before deploying it.
In this tutorial we will unpack a Mender Artifact,
recognized by its
.mender suffix, mount the rootfs (e.g.
.ext4) inside it,
modify it, and then create a new Mender Artifact that has these modifications
by using the
You need a standard
tar utility, like the ones that are bundled with popular
mender-artifact utility is used to create and inspect Mender Artifacts.
You can download a prebuilt mender-artifact Linux binary here.
If you need to build
mender-artifact from source, please see Compiling mender-artifact.
The Mender Artifact can be unpacked using a standard tar utility, we simply create a directory for it and unpack it. Depending on the version of the artifact used, for a BeagleBone Black Artifact, the commands and output will look like the following:
mkdir core-image-base-beaglebone && tar -C core-image-base-beaglebone -xvf core-image-base-beaglebone.mender
The output for the version 2 should look similar to the following:
You can inspect the metadata files to learn about how they work,
but it is not recommended to modify them directly as this can
be quite error-prone. We will rather use the
mender-artifact utility to make
The updates to be deployed are stored in the
data subdirectory. We
can extract the first (and currently only) file there, which is the root file system,
like the following:
cd core-image-base-beaglebone && tar zxvf data/0000.tar.gz
Once we have the file system image, a simple way to modify its contents is to loopback-mount the rootfs on your workstation and modify the configuration files you need in the mounted directory.
In this example we will modify
/etc/issue on an
ext4 file system
so you can see which rootfs image you are running just before the login prompt,
but these steps can be used for modifying any configuration file and for
several file system types.
First we make the mount directory and copy the rootfs image:
sudo mkdir /mnt/rootfs
cp core-image-base-beaglebone.ext4 core-image-base-beaglebone-modified.ext4
sudo mount -t ext4 -o loop core-image-base-beaglebone-modified.ext4 /mnt/rootfs/
Now you can modify the file system found at
/mnt/rootfs. For example,
you can change
/mnt/rootfs/etc/issue so you can detect that a deployment
changed the system. After saving your modified files, simply unmount
the rootfs again:
sudo umount /mnt/rootfs
You need to adjust the path to the rootfs image and its type depending on the machine and file system you are building for.
We would probably like to reuse some of the original Artifact metadata for the new Artifact, as for example the device types it is compatible with is the same.
To see which metadata the original Artifact contains, you can run the following command:
mender-artifact read core-image-base-beaglebone.mender
Compatible devices: '[beaglebone]'
modified: 2016-12-20 15:36:11 +0100 CET
The most important fields to note for writing a new Artifact are the Compatible devices and Name.
When working with a signed Artifact, you can verify the signature by providing the public verification key to the
-k option, e.g.
mender-artifact read core-image-base-beaglebone.mender -k public.key.
We now have the information we need to generate a new Artifact, including the metadata to use and modified rootfs.
In this example, we will keep the original Compatible devices and Name of the original Artifact, so only the rootfs modifications will be different:
mender-artifact write rootfs-image -t beaglebone -n release-1 -u core-image-base-beaglebone-modified.ext4 -o core-image-base-beaglebone-modified.mender
The Artifact name (
-n) must correspond to the name stated inside the root file system at
/etc/mender/artifact_info, so make sure to change both places if you are modifying it.
If you are building for older Mender Clients that do not support the latest version of the Artifact format, you can build an older Artifact version with the
-v option. For example, to build a version 1 Artifact, you can run
mender-artifact write rootfs-image -v 1 -t beaglebone -n release-1 -u core-image-base-beaglebone-modified.ext4 -o core-image-base-beaglebone-modified.mender. The default Artifact version is the latest one. Also see the build variable MENDER_ARTIFACT_EXTRA_ARGS.
If you would like to generate a signed Artifact, simply add the
-k option with the path to your private key. In our example above, the full command would be
mender-artifact write rootfs-image -t beaglebone -n release-1 -u core-image-base-beaglebone-modified.ext4 -o core-image-base-beaglebone-signed.mender -k private.key.
After deploying this Artifact with Mender and rebooting, your configuration changes will be in effect!
mender-artifact is only necessary if you can not use the prebuilt
mender-artifact binary for Linux.
The Golang compiler is integrated with
git, so we need
on the system. On Ubuntu this can be achieved with:
sudo apt-get install git
Since the Mender Artifact utility is written in golang, a Golang compiler needs to be installed and set up in order to build it. You can find Golang download and installation instructions at https://golang.org/dl/.
You should check the latest version, adjust the paths to your needs
and add the exports to your
.profile as described when
clicking on the download link.
This is an example of installing and setting up Golang on a Linux system:
sudo tar -C /usr/local -xzf go1.7.4.linux-amd64.tar.gz
mkdir $HOME/golang && export GOPATH=$HOME/golang && cd $HOME/golang
After these steps, verify that Golang is correctly installed:
go version go1.7.4 linux/amd64
The Mender Artifact utility is available as open source in the Mender artifact repository on GitHub.
You can download and install it with the following commands:
go get github.com/mendersoftware/mender-artifact
go get ./...
You can now run the
mender-artifact utility in
$GOPATH/bin/mender-artifact, and make sure it works
mender-artifact version 0.1
For convenience, we can also make sure the
mender-artifact utility is in PATH: