The busybox version of the coreutils requires substantially less memory then the standard GNU coreutils. Download and extract busybox using:

wget -P $DL_DIR http://busybox.net/downloads/busybox-1.9.1.tar.bz2  # was 1.2.1, 1.7.0, 1.8.2
mkdir -p $PRJ_DIR/apps
tar -C $PRJ_DIR/apps -xvjf $DL_DIR/busybox-1.9.1.tar.bz2
cd $PRJ_DIR/apps/busybox-1.9.1
wget -P $DL_DIR http://busybox.net/downloads/fixes-1.9.1/busybox-1.9.1-lineedit.patch
patch -p1 < $DL_DIR/busybox-1.9.1-lineedit.patch

Configure the features that busybox should provide. An example .config is available in Example A.4, “busybox .config”.

Note

Version 1.2 used the .config to specify the location of the cross compiler. In 1.6 this is passed to the Makefile on the command line using CROSS_COMPILE. Failing to specify the cross compiler will cause the kernel to panic with "No init found". Closer inspection ("objdump -x busybox | grep NEEDED") should reveal that it uses the libgcc_s.so.1 and libc.so.0 dynamic libraries. Also note that version 1.2 specified the installation prefix on the command line; 1.6 does this in the .config.

make oldconfig
make menuconfig

Compilation and install are straightforward.

make CROSS_COMPILE=$TOOLCHAIN_CROSS install  # PREFIX=$ROOTFS_DIR

Create the root directory structure and devices.

cd $ROOTFS_DIR
mkdir -p bin boot dev etc sbin usr var/log var/lock tmp
mkdir -p etc/init.d etc/rc.d etc/sysconfig/network 
cd dev

sudo mknod ram0    b 1 0  # all one needs is ram0
sudo mknod ram1    b 1 1
ln -s ram0 ramdisk

sudo mknod hda     b 3 0 # compact flash
sudo mknod hda1    b 3 1
sudo mknod hda2    b 3 2
sudo mknod hda3    b 3 3
sudo mknod hda4    b 3 4

sudo mknod mem     c 1 1
sudo mknod kmem    c 1 2
sudo mknod null    c 1 3
sudo mknod port    c 1 4
sudo mknod zero    c 1 5
sudo mknod core    c 1 6
sudo mknod full    c 1 7
#sudo mknod random  c 1 8 # used by dropbear to generate keys
sudo mknod urandom c 1 9 # used by dropbear to generate keys
ln -s urandom random     # used by dropbear workaround, 1,8 was dead
sudo mknod vsys    c 1 10

sudo mknod ptyp0   c 2 0 # pseudo terminal devices for dropbear
sudo mknod ptyp1   c 2 1
sudo mknod ptyp2   c 2 2
sudo mknod ptyp3   c 2 3
sudo mknod ptyp4   c 2 4

sudo mknod ttyp0   c 3 0 # pseudo terminal devices for telnet
sudo mknod ttyp1   c 3 1
sudo mknod ttyp2   c 3 2
sudo mknod ttyp3   c 3 3
sudo mknod ttyp4   c 3 4

sudo mknod ttyS0   c 4 64 # console port
sudo mknod ttyS1   c 4 65 # used for kgdb

sudo mknod tty0    c 4 0
sudo mknod tty1    c 4 1 # not needed

sudo mknod tty     c 5 0
sudo mknod console c 5 1
sudo mknod ptmx    c 5 2 # dropbear sshd

sudo mknod watchdog  c 10 130  # watchdog in SC1100

sudo mknod ppp     c 108 0 # Point-to-Point Protocol

ln -s ../proc/self/fd/0 stdin # process i/o
ln -s ../proc/self/fd/1 stdout
ln -s ../proc/self/fd/2 stderr
ln -s ../proc/kcore     kcore

Example configuration files for busybox and the C library are:

mkdir -p $ROOTFS_DIR/etc/rc3.d
rm -rf $ROOTFS_DIR/etc/rc3.d/*

ln -sf ../init.d/watchdog   $ROOTFS_DIR/etc/rc3.d/S10watchdog
ln -sf ../init.d/gpio       $ROOTFS_DIR/etc/rc3.d/S11gpio

ln -sf ../init.d/network    $ROOTFS_DIR/etc/rc3.d/S21network
ln -sf ../init.d/syslogd    $ROOTFS_DIR/etc/rc3.d/S22syslogd
ln -sf ../init.d/firewall   $ROOTFS_DIR/etc/rc3.d/S23firewall
ln -sf ../init.d/tc         $ROOTFS_DIR/etc/rc3.d/S23tc

ln -sf ../init.d/hostapd    $ROOTFS_DIR/etc/rc3.d/S30hostapd 
ln -sf ../init.d/ntpd       $ROOTFS_DIR/etc/rc3.d/S31ntpd
ln -sf ../init.d/dnsmasq    $ROOTFS_DIR/etc/rc3.d/S32dnsmasq

ln -sf ../init.d/dropbear   $ROOTFS_DIR/etc/rc3.d/S40dropbear
ln -sf ../init.d/mini_httpd $ROOTFS_DIR/etc/rc3.d/S41mini_httpd

ln -sf ../init.d/l2tpd      $ROOTFS_DIR/etc/rc3.d/S50l2tpd
ln -sf ../init.d/racoon     $ROOTFS_DIR/etc/rc3.d/S52racoon

ln -sf ../init.d/l2tpd      $ROOTFS_DIR/etc/rc3.d/K10l2tpd
ln -sf ../init.d/racoon     $ROOTFS_DIR/etc/rc3.d/K11racoon

ln -sf ../init.d/mini_httpd $ROOTFS_DIR/etc/rc3.d/K20mini_httpd
ln -sf ../init.d/dropbear   $ROOTFS_DIR/etc/rc3.d/K21dropbear

ln -sf ../init.d/dnsmasq    $ROOTFS_DIR/etc/rc3.d/K30dnsmasq
ln -sf ../init.d/ntpd       $ROOTFS_DIR/etc/rc3.d/K31ntpd
ln -sf ../init.d/hostapd    $ROOTFS_DIR/etc/rc3.d/K32hostapd 

ln -sf ../init.d/tc         $ROOTFS_DIR/etc/rc3.d/K40tc 
ln -sf ../init.d/firewall   $ROOTFS_DIR/etc/rc3.d/K41firewall
ln -sf ../init.d/syslogd    $ROOTFS_DIR/etc/rc3.d/K42syslogd
ln -sf ../init.d/network    $ROOTFS_DIR/etc/rc3.d/K43network
ln -sf ../init.d/gpio       $ROOTFS_DIR/etc/rc3.d/K44gpio