1 Building a Busybox Boot Floppy
2 ==============================
4 This document describes how to buid a boot floppy using the following
7 - Linux Kernel (http://www.kernel.org)
8 - uClibc: C library (http://www.uclibc.org/)
9 - Busybox: Unix utilities (http://busybox.net/)
10 - Syslinux: bootloader (http://syslinux.zytor.com)
12 It is based heavily on a paper presented by Erik Andersen at the 2001 Embedded
17 Building The Software Components
18 --------------------------------
20 Detailed instructions on how to build Busybox, uClibc, or a working Linux
21 kernel are beyond the scope of this document. The following guidelines will
24 - Stock Busybox from CVS or a tarball will work with no modifications to
25 any files. Just extract and go.
27 - Your Linux kernel must include support for initrd or else the floppy
28 won't be able to mount it's root file system.
30 If you require further information on building Busybox uClibc or Linux, please
31 refer to the web pages and documentation for those individual programs.
35 Making a Root File System
36 -------------------------
38 The following steps will create a root file system.
40 - Create an empty file that you can format as a filesystem:
42 dd if=/dev/zero of=rootfs bs=1k count=4000
44 - Set up the rootfs file we just created to be used as a loop device (may not
47 losetup /dev/loop0 rootfs
49 - Format the rootfs file with a filesystem:
51 mkfs.ext2 -F -i 2000 rootfs
53 - Mount the file on a mountpoint so we can place files in it:
56 mount -o loop rootfs loop/
58 (you will probably need to be root to do this)
60 - Copy on the C library, the dynamic linking library, and other necessary
61 libraries. For this example, we copy the following files from the uClibc
65 (chdir to uClibc directory)
66 cp -a libc.so* uClibc*.so \
67 ld.so-1/d-link/ld-linux-uclibc.so* \
68 ld.so-1/libdl/libdl.so* \
72 - Install the Busybox binary and accompanying symlinks:
74 (chdir to busybox directory)
75 make CONFIG_PREFIX=(path to)loop/ install
77 - Make device files in /dev:
79 This can be done by running the 'mkdevs.sh' script. If you want the gory
80 details, you can read the script.
82 - Make necessary files in /etc:
84 For this, just cp -a the etc/ directory onto rootfs. Again, if you want
85 all the details, you can just look at the files in the dir.
87 - Unmount the rootfs from the mountpoint:
96 Making a SYSLINUX boot floppy
97 -----------------------------
99 The following steps will create the boot floppy.
101 Note: You will need to have the mtools package installed beforehand.
103 - Insert a floppy in the drive and format it with an MSDOS filesystem:
107 (if the system doesn't know what device 'a:' is, look at /etc/mtools.conf)
109 - Run syslinux on the floppy:
113 (the -s stands for "safe, slow, and stupid" and should work better with
114 buggy BIOSes; it can be omitted)
116 - Put on a syslinux.cfg file:
118 mcopy syslinux.cfg a:
120 (more on syslinux.cfg below)
122 - Copy the root file system you made onto the MSDOS formatted floppy
126 - Build a linux kernel and copy it onto the disk with the filename 'linux'
128 mcopy bzImage a:linux
134 The following simple syslinux.cfg file should work. You can tweak it if you
137 ----begin-syslinux.cfg---------------
139 APPEND initrd=rootfs.gz root=/dev/ram0
142 ----end-syslinux.cfg---------------
144 Some changes you could make to syslinux.cfg:
146 - This value is the number seconds it will wait before booting. You can set
147 the timeout to 0 (or omit) to boot instantly, or you can set it as high as
150 - PROMPT can be set to 0 to disable the 'boot:' prompt.
152 - you can add this line to display the contents of a file as a welcome
162 Other useful information on making a Linux bootfloppy is available at the
165 http://www.linuxdoc.org/HOWTO/Bootdisk-HOWTO/index.html
166 http://www.linux-embedded.com/howto/Embedded-Linux-Howto.html
167 http://linux-embedded.org/howto/LFS-HOWTO.html
168 http://linux-embedded.org/pmhowto.html
169 http://recycle.lbl.gov/~ldoolitt/embedded/ (Larry Doolittle's stuff)
176 The following features that we might want to add later:
178 - support for additional filesystems besides ext2, i.e. minix
179 - different libc, static vs dynamic loading
180 - maybe using an alternate bootloader