Something about Syslinux...

Syslinux is quite interesting bootloader for x86 based machines. It’s not as fancy as Grub (especially 2.0 version and up), but it’s very simple to install and supports booting kernel from, among others, fat or ext2/3/4 partition. It’s perfect for my project of making Ebox3300 based router. In this post I’ll describe the basic installation and configuration.

Preparing target

Our target will be standard µSD card. We’ll use one partition formatted as ext2. In my system the card is seen as /dev/mmcblk0. First we need to create partition on it using our favourite tool. I use fdisk (root permissions are probably needed to successfully run this command). This is sequence of commands to create one partition on the device, using whole available space and making it bootable:

fdisk /dev/mmcblk0
o
n
p
[ENTER]
[ENTER]
[ENTER]
a
w

After successfully creating new partition we must format it with, for example, mke2fs command, which is often part of package named e2fstools, e2fsprogs or something similar — it depends on our linux distribution. After creating partition, there should be /dev/mmcblk0p1 device. That’s our partition.

mke2fs /dev/mmcblk0p1

After successfull execution of this command we now have prepared target device for our bootloader.

Installing Syslinux

[Project homepage]

Sometimes there is precompiled package in our distro repositories, but it’s more fun to compile Syslinux ourselves. First we need sources from here. Newest version is fine (I’ve used 6.02). For building it we need perl, nasm assembler, and of course gcc with other standard build tools (like make etc.). We build it by running:

make bios

If we just run make it will build also the EFI version which is not needed. After, hopefully, successfull build our tool is bios/extlinux/extlinux and there is also master boot record image: bios/mbr/mbr.bin which we’ll need. The installation is described in details here. In my system, I do it that way (as root):

mount /dev/mmcblk0p1 /mnt/media
./bios/extlinux/extlinux --install /mnt/media
cat bios/mbr/mbr.bin > /dev/mmcblk0

Now we must create syslinux configuration file extlinux.conf on the target partition where we installed syslinux. It’s contents for me in Ebox3300 project are:

DEFAULT linux
LABEL linux
    SAY Now booting the kernel...
    KERNEL vmlinuz
    APPEND console=ttyS0,115200n8

For details look at the Syslinux homepage.

After copying vmlinuz image with kernel and initramfs to the target partition we will have bootable µSD card for our device.

Summary

This is quick, dirty and basic how-to concerning installing bootloader manually for our project. We may also use Grub, which is also great bootloader and can be used, of course.