How to setup a cross-builder (to build linaro-nano)


  • Configure your machine to use updated tools from PPA
  • Create build chroot containing tools
  • Configure the build
  • Run the build
  • Create the image

Setting up for building

There are two ways you can do this.

1) Make a cross-build chroot to do your work in.

2) You can do everything in your main machine if it's already natty. (In which case see the section below 'Using a local setup' instead of 'Creating build Chroot'.) However I don't recommend this if you ever build anything else there, and it's not what I've tested. The main reason is that the rootfs used for building will fill up with a lot of build-dependencies.

Creating Build Chroot

You need multistrap 2.6.3ubuntu6 for a smooth experience (you'll have to update the config files otherwise)

So add the tools PPA (with add-apt-repository):

sudo apt-add-repository ppa:linaro-foundations/cross-build-tools

Or manually:

deb natty main

preferably to /etc/apt/source.list.d/crosstoolsPPA.list

Then do

sudo apt-get install multistrap

to get 2.6.3ubuntu6

Now you can do

sudo multistrap -f /usr/share/multistrap/xbuilder.conf -d chroots/natty-build

Which should make a new local-architecture chroot, install the cross-tools into it, and set up apt sources.

You can do this by hand using debootstrap and then installing the sources, packages and config you need, but this is a lot easier.

In order to use the chroot you have made conveniently it is best to use schroot, which manages your chroot and makes your home dir and system mounts/services available.

apt-get install schroot

if you don't have it already then add a config like this to your /etc/schroot/schroot.conf

description=Ubuntu Natty (11.04)

Changing USER to be your username.

Change into the chroot using

schroot -c natty-build

Configure the build

All you need to do is make a file which is a list of the packages you want building. Ideally it's a list of source packages, but a list of binary packages will work too (but if you list several binaries from the same source package then that package will get built more than once). The format is one package per line and the file is called buildlist. A sample buildlist for linaro-nano is in the xbuilder package, so:

cp /usr/share/xbuilder/examples/buildlist-nano-pruned buildlist

The pruning there is because it lists binary packages, but has had the duplicates weeded out to avoid unnecessary builds.

To build a single package just make buildlist one line with the package name on.

To avoid the build stalling at password prompts generated by sudo, increase the timeout to several hours in the sudo config:

In /etc/sudoers Change the line

Defaults        env_reset


Defaults        env_reset, timestamp_timeout=600

600 is 10 hours, which is enough for almost all builds to complete.

Run the Build

Update apt cache:

sudo apt-get update

And simply set the cross-builder running:


It runs through the packages in buildlist one by one, downloading sources to build/xdeb and putting build logs in logs/xdeb, running xdeb in only-explicit mode (i.e building against the archive).

xbuilder can be set to use pdebuild-cross instead of xdeb (by editing /usr/bin/xbuilder-simple) if preferred, but that's not been tested on this version.

Not all packages in the PPA will successfully cross-build right now. 81 out of 117 binaries should build successfully (2011-09-28). See LinaroNanoStatus or for full current nano/ALIP status

Create the Image

Once the build is complete you can generate a bootable image by running multistrap with the linaro-nano config. This can equally be done inside or outside the natty-build chroot, but you already have the package installed outside, so easiest to do it there, so exit the chroot if you haven't already.

cp /usr/share/multistrap/linaro-nano.conf linao-nano.conf

You'll need to change the config to point at your local .deb collection so the [nano] section should look something like this

source=file:///home/USER/PATH-TO-BUILDLIST-DIR/build/xdeb/ ./
packages=apt apt-utils base-files base-passwd bsdutils console-setup coreutils dash debianutils debconf diffutils dpkg e2fsprogs findutils gnupg ifupdown initramfs-tools initscripts ipr$

touch /home/USER/PATH-TO-BUILDLIST-DIR/build/xdeb/Sources
multistrap --no-auth -f linaro-nano.conf

Currently this will fail because not all packages are available.

Adding an http source to fill in the gaps should allow a test image to be generated (not yet tested).


Manual Details

If you have trouble with any of the above stages then you'll need more details about how it works to fix things. This section provides such details.

Installing the PPA key

If the linaro-foundation-keyring package is not doing the trick for you then:

Run this command to install the key
sudo apt-key adv --recv-keys --keyserver 099F4315

should enabled authenticated downloads from the PPA.

Creating a Crossbuilder Chroot

You need a basic natty image, as provided by debootstrap/cdebootstrap/multistrap etc with these extra packages:

From the Cross-tools-PPA:xdeb dpkg-cross xbuilder

From the normal repo: g++-arm-linux-gnueabi libc-dev-armel-cross linux-libc-dev-armel-cross dpkg-dev build-essential fakeroot binutils-multiarch ubuntu-keyring gnupg realpath

Configuring the chroot for building

You need somewhere to get armel packages from for crossing: deb [arch=armel] natty main universe


Platform/DevPlatform/CrossCompile/CrossBuildNano (last modified 2011-10-11 14:10:02)