Oz advanced
Because Oz is a general purpose utility, it has a few configuration options that make it more useful to someone who doesn't just want the (sensible) defaults that Oz provides.
Oz supports a configuration file in the standard ini format. By default Oz will look in /etc/oz/oz.cfg for the configuration, though this can be overridden on the oz-install, oz-customize, or oz-generate-icicle command lines. The ini file that Oz expects to see looks like:
[paths] output_dir = /var/lib/libvirt/images data_dir = /var/lib/oz [libvirt] uri = qemu:///system type = kvm
The output_dir under the paths section describes where the diskimage that Oz will be stored. By default, Oz uses /var/lib/libvirt/images for these diskimages, but this configuration key allows the user to set it to any directory in the system. Because operating systems take significant amounts of space to install (depending on the operating system and configuration, up to many gigabytes), this should be a large data area.
The data_dir under the paths section describes where the work area that Oz uses is located. By default, this work area is under /var/lib/oz, but this configuration key allows the user to set it to any directory in the system. Because operating system installation disks can take significant amounts of space to store and extract, this should be a large data area. Also note that Oz caches the "pristine" installation media that it downloads in this area, so this can grow quite large (in general it is safe to delete contents of this directory, though that may slow down future guest installations when the installation media needs to be re-downloaded).
The uri under the libvirt section describes what libvirt URI Oz should use when manipulating the guests. By default, the qemu libvirt driver (which also supports KVM guests) is used. Note that this has not been tested on hypervisors other than qemu/kvm, so your mileage may vary if you change this.
The type under the libvirt section describes what type of guest Oz should use when creating libvirt guests. By default, the "kvm" type of guests is used. Note that this is intimately tied to the URI that is specified in the uri section, so changing this to a value that a particular libvirt driver doesn't understand will lead to failure.
When trying to track down a problem with Oz, it is most helpful to have verbose debugging information. All of the Oz tools (oz-install, oz-customize, and oz-generate-icicle) support the -d parameter that manipulates the debugging level. When submitting a bug report, please make sure to turn the -d level to 3 or greater to generate lots of debugging information.
This is a powerful feature of Oz, but with great power comes great responsibility. By default Oz generates a minimal operating system automated installation file, just enough to get the OS up and running. As described in the oz-architecture document, this is done to reduce the possibility of errors during the initial installation phase. However, for users who really know what they are doing and what they want, oz-install supports the -a parameter, which allows the user to specify a custom automated installation file. In order for this to succeed, the user-specified automated installation file must do the following:
- Run all installation steps without prompting
- Additional steps or packages must not fail
- Automatically shut down the installer (operating system) at the end of installation