Automated installations in Skolelinux
using debian-installer and base-config

Skolelinux is a Debian-based Linux distribution with simple installation and preconfigured services targeted for schools. The presentation will present how the standard debian installation system is customised for this purpose.

http://www.hungry.com/~pere/mypapers/debconf-install/debconf-install.html

Skolelinux

• Based on Debian/Woody (to get security updates)
• Simple installation
• Translated to several local languages
• Includes all the software needed in primary schools
• Preconfigured services (syslog, dns, ntp, dhcp, ssh, ldap, nfs, smb, smtp, imap, ipp, http, web-proxy, ltsp and more)
• No license administration
• Admin friendly
• Scalable

The Skolelinux architecture

The skolelinux install

• Simple (two questions and the root password)
• Automatic
• Using debian-installer (d-i) and base-config (b-c)
• Complete (everything work out of the box)
• Very little skolelinux-specific code (two udebs and three config packages).
• Rewriting the config of other packages to get the services preconfigured out of the box (against policy?)

The two stages of the Debian installation

First stage (debian-installer)

• Booting from cd/floppy/net/whatever
• Installing base system
• Making HD bootable

Second stage stage (base-config)

• Booting from HD
• Installing and configuring the non-base system

The first stage (debian-installer)

• Modular
• Extendible
• Using debconf to ask questions
• Can be mostly automatic
• Very Flexible

debian-installer structure

• Selector for installer modules (udebs)
• Select language and region
• Autodetect hardware
• Locate APT source (CD, Net or floppy)
• Load the rest of the installer modules
• Partition hard-drive
• Make filesystems or swap
• Mount filesystems
• Install base system
• Install kernel
• Install boot loader
• Reboot

debian-installer hooks

• Include or exclude d-i modules
• Running script at install system boot time
• Include or excluding packages going into the HD
• Running scripts before reboot from HD
• Partitioning

The second stage (base-config)

• Executed from init on first boot
• Modular (reading /usr/lib/base-config)
• Able to adjust the order of the scripts on the fly using return codes.
• Partly using debconf for configuration decisions.

base-config structure

• Generate locale if needed
• Start terminal emulator (for non-ascii installs) if needed
• Load variables based from first stage (/root/dbootstrap_settings)
• Turn off screen saver
• Show intro screen
• Set up console keyboard
• Set up time zone
• Configure /etc/passwd, root password and local user
• Enable ppp?
• Configure APT sources
• Select packages to install
• Fetch packages
• Configure exim
• Disable ppp?
• Show "successful install" screen
• Rewrite /etc/inittab to not start base-config on next boot

base-config hooks

• Add scripts to /usr/lib/base-config/
• Update debconf database

Skolelinux specific code

First stage

• Shorter language list
• Set debconf priority limit to high to get automatic install
• Ask about profile and do automatic partitioning for this profile
• Reorder d-i module order using dependencies and menu-item value
• Install extra packages into the HD
• Pass info to second stage using /root/dbootstrap_settings and /etc/skolelinux/config

Second stage

• Set debconf frontend to non-interactive (most of the time)
• Preload debconf answers based on profile choice
• Automatically install packages for the given profiles
• Rewrite/replace config files based on profile and language
• Configure XFree86
• Restart servers (except kdm)
• Check installation
• Restart kdm

Some solved problems

• Preloading debconf answers need a dummy question template
• Packages with insufficient install configuration support get their config files rewritten using cfengine.
• Selecting packages to install using meta-packages.

Conclusion

• The current debian-installer is extendible and can do automated installation, with the hooks needed by Skolelinux.
• The current base-config is is flexible enough for Skolelinux, but could use more hooks to reduce the amount of Skolelinux specific code.

References

• Skolelinux web site
• Skolelinux developers web site
• The Skolelinux architeture description
• debian-installer web page
• Available hooks in debian-installer

Thank you very much

Questions?