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Building an Emdebian (Embedded Debian) root filesystem for GuruPlug/armel

Many of the distros are dropping support for ARMv5 and when you do find one, today's 'minimal' root filesystem is typically a couple hundred of megabytes.

Emdebian (Embedded Debian) has the advantage that not only still supporting ARMv5, but it has a multistrap tool that gives the ability to customise the root filesystem on the host and only include the packages you need.

Debian is now my choice for a root filesystem on the GuruPlug.

Prerequisites

Install the following prerequisites

apt-get install multistrap
apt-get install qemu
apt-get install qemu-user-static
apt-get install binfmt-support
apt-get install dpkg-cross

Building your Debian rootfs

To build your root filesystem, create a multistrap configuration file called GuruPlugRootFS.conf and add the following:

[General]
arch=armel
directory=guruplug-rootfs
cleanup=true
noauth=true
unpack=true
debootstrap=Emdebian Net Utils
aptsources=Emdebian 

[Emdebian]
packages=apt
source=http://www.emdebian.org/grip
keyring=emdebian-archive-keyring
suite=wheezy-grip

[Net]
#Basic packages to enable the networking
packages=netbase net-tools ethtool udev iproute iputils-ping iptables ifupdown isc-dhcp-client ssh 
source=http://www.emdebian.org/grip

[Utils]
#General purpose utilities
packages=locales adduser nano less wget vim rsyslog dialog
source=http://www.emdebian.org/grip

Save and run the multistrap tool:

# multistrap -f GuruPlugRootFS.conf

Now configure the Emdebian packages with the QEMU emulator. This will configure various packages, set your shell and time zone.

# cp /usr/bin/qemu-arm-static guruplug-rootfs/usr/bin
# LC_ALL=C LANGUAGE=C LANG=C chroot guruplug-rootfs dpkg --configure -a

Root Password

Set your root password:

# sudo chroot guruplug-rootfs passwd

Other Miscellaneous Configurations

Set your hostname:

# echo guruplug >> guruplug-rootfs/etc/hostname

Initialise your fstab:

# echo proc /proc proc defaults 0 0 >> guruplug-rootfs/etc/fstab

Set-up Terminal on Serial Console

If you desire to have a terminal available on the serial/console port, you will need to edit /etc/inittab and modify/uncomment:

# Example how to put a getty on a serial line (for a terminal)
#
#T0:23:respawn:/sbin/getty -L ttyS0 9600 vt100
#T1:23:respawn:/sbin/getty -L ttyS1 9600 vt100

I use

T0:23:respawn:/sbin/getty -L ttyS0 115200 vt100

UBI/MTD Utilities

If you are planning on making an UBI filesystem it may be advantageous to add your UBI MTD utilities at this stage. We have instructions to build them here, or you can use some with prepared earlier:

wget http://wiki.beyondlogic.org/prebuilt/mtdutils-1.5.0-arm-linux-gnueabi.tar.bz2
tar -xjf mtdutils-1.5.0-arm-linux-gnueabi.tar.bz2 -C guruplug-rootfs

Kernel Modules

Your root filesystem needs to be populated with any kernel modules corresponding to the Linux kernel version you are using.

Jump to the folder containing your kernel and execute:

# make ARCH=arm CROSS_COMPILE=arm-linux-gnueabi- modules
# make ARCH=arm CROSS_COMPILE=arm-linux-gnueabi- INSTALL_MOD_PATH=<path of your guruplug-rootfs> modules_install