In the Emdebian vision someone wishing to build a GNU / Linux based device would:
- Port the linux kernel to their hardware (including writing any specific device drivers).
Select the prebuilt emdebian packages needed to support their application.
- Package their application as Debian package(s) using Debian and Emdebian tools.
- Build a root filesystem using Emdebian tools from the steps above.
Emdebian is involved in steps 2,3,4 above (there are far too many embedded device hardware variations to make prebuilt kernels practical).
Thus EmDebian is a binary distribution for embedded devices (whereas most of the other contenders in this space are source distributions [of course being Debian and open source the source code is still available if required].
What emdebian does
In short, what EmDebian does is wrap around the regular debian package building tools to provide a more fine grained control over package selection, size, dependencies and content to enable creation of very small and efficient debian packages for use on naturally resource limited embedded targets.
We adapt Debian tools so you can build/cross-compile Debian packages or adapted packages with info on how to cross-build and build smaller packages.
We currently have two separate distributions - a post-processed binary-compatible distribution called Emdebian Grip for intermediate installations and a much smaller, much more involved cross-built distribution called Emdebian Crush. Each distribution can be further optimised for systems that would benefit from a static configuration by removing the maintainer scripts - this flavour is called Emdebian Baked.
Emdebian is experimenting with different approaches to cross-building and small-system-friendly packages in order to produce sustainable and robust long-term solutions. For cross-building there are two main approaches: Scratchbox (pkg), which allows cross-builds to appear to be native to the apps being built, and dpkg-cross (pkg) which allows conventional cross-builds to occur in a Debian-compatible way using emdebian-tools (pkg).
For package meta-data making packages more suitable for shrinking, two approaches are currently being investigated. The STAG approach uses a $(DEBIAN_DIR) directory to overlay changed info from the /debian directory, and is used by STAGE. The udeb approach of Debian-installer gives a tighter integration with Debian, with embedded packages having changed names so they can exist in the debian package namespace. Both mechanisms have pros and cons which are discussed in EmdebianMetaData.
New packages can be added to Grip using the emdebian-grip-server package. Adding new packages or new architectures to Crush is currently stalled until the EmdebianCodeAudit can be completed in order to resolve issues around packages with modified functionality.
Crush 2.0 is currently stalled due to build system problems - see EmdebianCrush for details of why, how this could be fixed and current experiments. If things stay as they are, there will be no release of Crush 2.0 (based on Debian 6.0 "squeeze"), instead development will target Crush 3.0 (based on Debian 7.0 - wheezy), reliant upon delivery of an implementation of Multiarch with sufficient support for cross-building.
Grip development is continuing. Grip 2.0 has been released alongside Debian 6.0 "squeeze" on six architectures (armel, mips, mipsel, i386, amd64, powerpc) and with some 2,000 packages. Work is ongoing alongside Debian for Emdebian Grip 3.0 based on Debian GNU/Linux 7.0 Wheezy.
Baked is as ready as it can be - Baked is primarily a do-it-yourself distribution but some starter packages are available.
Integration with Debian
There are various stages to integrating Emdebian into Debian, the process starts with Emdebian Grip - the binary compatible flavour.
August 17th 2006: The server has moved to a new machine in Europe instead of the US.
Frequently Asked Questions (FAQ)
Quick Start Guide
EmdebianTracker - quick notes about issues that need a fix within the Emdebian packages (issues unrelated to cross building). e.g. a postinst script that calls a binary that is not available or with an unknown option, conflicts between packages that only show up when Essential is ignored, extra dependencies needed when Essential is ignored, etc.)
EmdebianCodeAudit - coordinating a complete audit of all patches required for Emdebian Crush 1.0 to support the implementation of the patches within the relevant Debian packages.
Wiki pages in continuous devel
Domotics - Debian in X10 and other domotic standards.
EmdebianPackagingGuidelines is a document explaining to package maintainers the sorts of things they should be aware of in their packaging to make their packages 'Embedded-friendly'. This includes cross-building and small-system-building.
Embedded Debian Packaging Infrastructure explains how the Emdebian repositories are organised, where the repositories are located and how to setup your system for emdebian uploads.
Emdebian packaging rules details how emdebian packages should be built and organised.
How Grip relates to Crush
Building packages for Crush (for the EmdebianCodeAudit) now bases the final package on the Grip processing. i.e. the package is cross-built for Crush with limited changes and then the cross-built package is run through the Grip scripts to remove documentation, examples, handle Emdebian TDebs etc. This reduces the number of changes that need to be made in the patches for Crush, simplifying the patches and the build process. As the Audit proceeds, the patches necessary to allow the packages to be cross-built at all will be fed back to Debian via the BTS and included into the packages via maintainer uploads or, if necessary, with NMU's by Emdebian developers. The aim is to reduce the number of patches to only those necessary for the functional changes needed for Crush:
- Avoid calling perl scripts that cannot be replaced by busybox
- Avoid using perl in maintainer scripts
- Reduce long dependency chains by turning off optional build components
- Make maintainer scripts compatible with the busybox shell
This should allow many Debian packages to be cross-built without special tools and without external patches, with compliance to EmdebianPolicy being achieved after the cross-build is complete.
Multiarch and cross-compile
The goal is that both native and cross-compile behave the same, use files in the same location, use the same compiler flags and for all packages to be upgraded by the main system upgrades.
Current situation: all -*-cross debs, no multiarch
dpkg-cross creates -cross packages. No automated upgrades of -cross packages possible.
Soon: some -*-cross debs, some multiarch debs
When Multi-Arch starts to become available in the Debian archives, a version of dpkg will need to already exist which can understand how to install multiarch packages and that doesn't necessarily affect foreign arch packages. Installing a Multi-Arch 32bit package on a 64bit system is equivalent to installing a Multi-Arch armel package on an x86 system.
dpkg-cross will not convert multiarch packages, it simply ensures that the file exists to be installed alongside any remaining -cross packages.
pkg-config has a patch to support the --host option which is currently understood by the existing autoconf m4 macros.
Long term goal: no -*-cross debs, all multiarch
/usr/include + /usr/include/triplet
/lib/triplet + /usr/lib/triplet
All -cross packages are explicitly not Multi-Arch compatible - dpkg-cross cannot be expected to convert a standard package to a pseudo-Multi-Arch cross package.
Things that need doing are:
- Emdebianising more packages for Crush so that they
- cross-build correctly
- split packages where the default has too many dependencies
- Work on Emdebian policy and actual packages to:
- Speed up boot time
- Reduce dependencies
- Differentiate between install time and run-time dependencies
- Differentiate between build and target build-dependencies
- Shrink minimum rootfs sizes
Busybox-based rootfs as well as GNU-based EmdebianRootfs
- Dash instead of bash
- Remove perl from essential
- Work on Debian and emdebian packages to:
- Support changes due to above policy
- Push changes back into Debian as much as possible (e.g faster boot)
- Infrastructure Work:
- Completing auto-build mechansism that will keep emdebian cross-toolchains uptodate with debian toolchain versions
- Incorporate full 3-stage bootstrap changes from slind
- Auto-build emdebian packages, tracking debian versions and including support for developers to track packages which have build failures
- Making Emdebian systems
- Emdebianising new packages
- The infrastructure
- Developed Policy
- create configurations for various devices and document howto do it
- promote DEB_BUILD_OPTIONS=nodocs flag for not building docs
- promote DEB_BUILD_OPTIONS=notest or DEB_BUILD_OPTIONS=nocheck for skipping tests
- co-operate with i386-uclibc team and embedded arch porters
- Kill scratchbox in its current form and make a better scratchbox2
Set-up a buildd inside scratchbox
Document setting up the buildd so developers and non-developers can try it out for themselves.
Integrate ?uclibc in the story. This will definitely give some size boost toward smaller footprint to the packages.
Once we have proven that this works start pushing things into Debian proper.
- Make sure everything works with the successors of scratchbox
- Check the ARM build of Ubuntu
There are also a few ideas that may need to be investigated further to decide whether it is a good idea to make them a new TODO item. These are collected on the EmdebianWackyIdeas page.
Donations / Donors
Meetings, Conferences, Work Sessions
There are IRC meetings roughly every two weeks, for details please see Emdebian/Meetings
February 7th-8th in Brussels, Belgium Fosdem2009
September, Extremadura Work Meeting EmdebianWorkSessionExtremadura2008
June, TCL work session
February 23rd-24th in Brussels, Belgium http://fosdem.org/2008/
June 17-23rd, in Edinburgh, Scotland. DebConf7
February 24&25th, in Brussels, Belgium. Fosdem2007
October 25&26th, in London, UK. London Linux World Expo
May 14th - May 21st, in Mexico. DebConf6EmdebianStuff
April 12-16th, in Extremadura, Spain. DebianEmbeddedWorkSessionExtremadura2006
http://en.wikipedia.org/wiki/embedded_system - Embedded systems
http://en.wikipedia.org/wiki/cross-compilation - cross compiling
http://www.netrino.com/Publications/Glossary/ - Embedded systems glossary