Lorax

Authors:Brian C. Lane <bcl@redhat.com>

“I am the Lorax. I speak for the trees [and images].”

The lorax tool is used to create the Anaconda installer boot.iso as well as the basic release tree, and .treeinfo metadata file. Its dependencies are fairly light-weight because it needs to be able to run in a mock chroot environment. It is best to run lorax from the same release as is being targeted because the templates may have release specific logic in them. eg. Use the rawhide version to build the boot.iso for rawhide, along with the rawhide repositories.

lorax cmdline arguments

See the output from lorax --help for the commandline arguments.

Quickstart

Run this as root to create a boot.iso in ./results/:

yum install lorax
setenforce 0
lorax -p RHEL -v 7 -r 7 \
-s http://mirror.centos.org/centos-7/7/os/x86_64/ \
-s http://mirror.centos.org/centos-7/7/updates/x86_64/ \
./results/
setenforce 1

You can add your own repos with -s and packages with higher NVRs will override the ones in the distribution repositories.

Under ./results/ will be the release tree files: .discinfo, .treeinfo, everything that goes onto the boot.iso, the pxeboot directory, and the boot.iso under ./images/.

Running inside of mock

If you are using lorax with mock v1.3.4 or later you will need to pass --old-chroot to mock. Mock now defaults to using systemd-nspawn which cannot create the needed loop device nodes. Passing --old-chroot will use the old system where /dev/loop* is setup for you.

How it works

Lorax uses yum to install packages into a temporary directory, sets up configuration files, it then removes unneeded files to save space, and creates a squashfs filesystem of the files. The iso is then built using a generic initramfs and the kernel from the selected repositories.

To drive these processes Lorax uses a custom template system, based on Mako templates with the addition of custom commands (documented in pylorax.ltmpl.LoraxTemplateRunner). Mako supports %if/%endif blocks as well as free-form python code inside <% %> tags and variable substitution with ${}. The default templates are shipped with lorax in /usr/share/lorax/ and use the .tmpl extension.

runtime-install.tmpl

The runtime-install.tmpl template lists packages to be installed using the installpkg command. This template is fairly simple, installing common packages and architecture specific packages. It must end with the run_pkg_transaction command which tells dnf to download and install the packages.

runtime-postinstall.tmpl

The runtime-postinstall.tmpl template is where the system configuration happens. The installer environment is similar to a normal running system, but needs some special handling. Configuration files are setup, systemd is told to start the anaconda.target instead of a default system target, and a number of unneeded services are disabled, some of which can interfere with the installation. A number of template commands are used here:

• append to add text to a file.
• chmod changes the file’s mode.
• gconfset runs gconfset.
• install to install a file into the installroot.
• mkdir makes a new directory.
• move to move a file into the installroot
• replace does text substitution in a file
• remove deletes a file
• runcmd run arbitrary commands.
• symlink creates a symlink
• systemctl runs systemctl in the installroot

runtime-cleanup.tmpl

The runtime-cleanup.tmpl template is used to remove files that aren’t strictly needed by the installation environment. In addition to the remove template command it uses:

• removepkg remove all of a specific package’s contents. A package may be pulled in as a dependency, but not really used. eg. sound support.
• removefrom Removes some files from a package. A file glob can be used, or the –allbut option to remove everything except a select few.
• removekmod Removes kernel modules

The squashfs filesystem

After runtime-*.tmpl templates have finished their work lorax creates an empty ext4 filesystem, copies the remaining files to it, and makes a squashfs filesystem of it. This file is the / of the boot.iso’s installer environment and is what is in the LiveOS/squashfs.img file on the iso.

iso creation

The iso creation is handled by another set of templates. The one used depends on the architecture that the iso is being created for. They are also stored in /usr/share/lorax/ and are named after the arch, like x86.tmpl and aarch64.tmpl. They handle creation of the tree, copying configuration template files, configuration variable substitution, treeinfo metadata (via the treeinfo template command). Kernel and initrd are copied from the installroot to their final locations and then mkisofs is run to create the boot.iso

Custom Templates

The default set of templates and configuration files are shipped in the /usr/share/lorax/ directory. You can make a copy of them and place them into another directory and then select the new template directory by passing --sharedir to lorax.