lorax/docs/lorax.rst

Lorax
=====

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

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

The `lorax <https://github.com/rhinstaller/lorax>`_ tool is used to create the
`Anaconda <https://github.com/rhinstaller/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.


Quickstart
----------

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

    dnf install lorax
    setenforce 0
    lorax -p Fedora -v 23 -r 23 \
    -s http://dl.fedoraproject.org/pub/fedora/linux/releases/23/Everything/x86_64/os/ \
    -s http://dl.fedoraproject.org/pub/fedora/linux/updates/23/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/``.


How it works
------------

Lorax uses `dnf <https://github.com/rpm-software-management/dnf>`_ 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 <http://www.makotemplates.org/>`_ with the addition of custom
commands (documented in :class:`pylorax.ltmpl.LoraxTemplateRunner`). Mako
supports ``%if/%endif`` blocks as well as free-form python code inside ``<%
%>`` tags and variable substitution with ``${}``. The 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:

* :func:`append <pylorax.ltmpl.LoraxTemplateRunner.append>` to add text to a file.
* :func:`chmod <pylorax.ltmpl.LoraxTemplateRunner.chmod>` changes the file's mode.
* :func:`gconfset <pylorax.ltmpl.LoraxTemplateRunner.gconfset>` runs gconfset.
* :func:`install <pylorax.ltmpl.LoraxTemplateRunner.install>` to install a file into the installroot.
* :func:`mkdir <pylorax.ltmpl.LoraxTemplateRunner.mkdir>` makes a new directory.
* :func:`move <pylorax.ltmpl.LoraxTemplateRunner.move>` to move a file into the installroot
* :func:`replace <pylorax.ltmpl.LoraxTemplateRunner.replace>` does text substitution in a file
* :func:`remove <pylorax.ltmpl.LoraxTemplateRunner.remove>` deletes a file
* :func:`runcmd <pylorax.ltmpl.LoraxTemplateRunner.runcmd>` run arbitrary commands.
* :func:`symlink <pylorax.ltmpl.LoraxTemplateRunner.symlink>` creates a symlink
* :func:`systemctl <pylorax.ltmpl.LoraxTemplateRunner.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:

* :func:`removepkg <pylorax.ltmpl.LoraxTemplateRunner.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.
* :func:`removefrom <pylorax.ltmpl.LoraxTemplateRunner.removefrom>`
  Removes some files from a package. A file glob can be used, or the --allbut option to 
  remove everything except a select few.
* :func:`removekmod <pylorax.ltmpl.LoraxTemplateRunner.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
:func:`treeinfo <pylorax.ltmpl.LoraxTemplateRunner.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