YaST development tips & tricks

Changing the root location for agents

When testing the code, it's useful to chroot the agents so SCR operations take place in a safe environment. This can be performed with the following code.

check_version = false
path = '/tmp/chroot'
descriptor = Yast::WFM.SCROpen("chroot=#{path}:scr", check_version)
raise "Error creating the chrooted scr instance" if descriptor < 0
Yast::WFM.SCRSetDefault(descriptor)

The descriptor needs to be closed afterwards running

Yast::WFM.SCRClose(descriptor)

Change YaST during installation

It's usually necessary to run the installation process with a modified version of the YaST code. Since Ruby is an interpreted language, YaST offers several alternative ways to alter the running installer.

Using driver updates

Driver updates are a mechanism that allows to modify the system before starting the installation by providing a set of rpm packages. A driver update can be triggered by the dud option in the Linuxrc command line. More information about this approach can be found in the corresponding section of the Linuxrc documentation.

When using this method with many RPM packages, it's usually convenient to use a Linuxrc control file containing insecure=1 and several dud options.

Using a YaST update medium

A simpler alternative to driver updates are the YaST update mediums. They are also triggered by the dud Linuxrc option and they also allow to modify the system before the installation, but they only affect the files located under /usr/share/YaST2. More information can be found in the corresponding section of the Update Media HOWTO.

Running a shell before the installation

It's also possible to use the startshell=1 in Linuxrc to start a bash shell with full access to the installation system before running the installer itself. In this way it's not only possible to modify any YaST file in advance but also to configure the network or any other aspect of the system. More information can be found in this Kobliha's blog post.

Add a new package to the installation system

Sometimes you need to add a new RPM to the openSUSE installation system (called inst-sys). The installation-images package, which builds the installation system, evaluates the package dependencies and automatically adds the required packages. Simply add the needed packages as a Requires dependency to the respective package and that's it.

If you need to add a completely new YaST package to the installer then add it as a dependency to the skelcd-control-<product> package. See the openSUSE example.

Note: This works since openSUSE-13.1 and SLE12, if you need to update older systems, already released product or the rescue image then you need to modify the installation-images package and then remaster the installation medium (or update the boot server, depending how you boot the system). But there are some tricky parts that are explained in depth in this Ladislav's blog post.