Chapter 3. Kernel, Coreutils and Boot Loader

Chapter 3. Kernel, Coreutils and Boot Loader
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Abstract

This chapter describes building the Linux kernel using the GCC/uClibc toolchain described in Chapter 2, Toolchain and libraries. This toolchain is then used to build a small footprint coreutils. Finally it describes how to write the kernel and root file system to Compact Flash (CF).

This chapter is a part of the "Secure Internet Appliance for Small Office / Home Office HOWTO". It relies on environment variables listed in Section 2.1, “Environment Variables”.

3.1. Kernel - linux

I have evaluated linux kernel releases 2.6.11, 2.6.12.6 and 2.6.13.4 and found 2.6.11 the most stable for use in SISO. I recently switched to 2.6.22-4. Download and extract it using the commands below.

wget -P $DL_DIR ftp://ftp.kernel.org/pub/linux/kernel/v2.6/linux-2.6.24.tar.bz2 # was 2.6.11, 2.6.22-4, 2.6.23-9
mkdir -p $PRJ_DIR/kernel
tar -C $PRJ_DIR/kernel -xvjf $DL_DIR/linux-2.6.24.tar.bz2
cd $LINUX_DIR

Configure the kernel using the commands listed below. An example .config can be found in Example A.3, “linux-2.6.24 .config”. Enable serial communications to the console device drv → char → serial → 8250/16550 → Console. Otherwise the kernel might boot, but will lack any signs of life on the console. General Purpose I/O (GPIO) is supported by the scx200.c and scx200_gpio.c modules. ^[14]

make oldconfig
make xconfig

	Note
	The configuration uses CONFIG_UID16=y. Otherwise, busybox initialization will fail with a ": setuid" error message when it reverts the sticky bit for commands that do not need high permissions.

	Note
	For NAT, NF_NAT is needed, and depends on IP_NF_IPTABLES && NF_CONTRACK_IPV4

Start the compilation and install the modules to $ROOTFS_DIR.

make CROSS_COMPILE=$TOOLCHAIN_CROSS INSTALL_MOD_PATH=$ROOTFS_DIR \
     bzImage modules modules_install

^[14]The qt-devel package is required for make xconfig. Ensure that the package is installed (rpm -q qt-devel). Install as needed using yum install qt-devel.