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://cvs.uclinux.org/uClibc.html)
9 - Busybox: Unix utilities (http://busybox.lineo.com)
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 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 - Run ldconfig so busybox and other binaries can have access to the libraries
90 (path to)uClibc/ld.so-1/util/ldconfig -r loop/
92 - Unmount the rootfs from the mountpoint:
101 Making a SYSLINUX boot floppy
102 -----------------------------
104 The following steps will create the boot floppy.
106 Note: You will need to have the mtools package installed beforehand.
108 - Insert a floppy in the drive and format it with an MSDOS filesystem:
112 (if the system doesn't know what device 'a:' is, look at /etc/mtools.conf)
114 - Run syslinux on the floppy:
118 (the -s stands for "safe, slow, and stupid" and should work better with
119 buggy BIOSes; it can be omitted)
121 - Put on a syslinux.cfg file:
123 mcopy syslinux.cfg a:
125 (more on syslinux.cfg below)
127 - Copy the root file system you made onto the MSDOS formatted floppy
131 - Build a linux kernel and copy it onto the disk with the filename 'linux'
133 mcopy bzImage a:linux
139 The following simple syslinux.cfg file should work. You can tweak it if you
142 ----begin-syslinux.cfg---------------
144 APPEND initrd=rootfs.gz root=/dev/ram0
147 ----end-syslinux.cfg---------------
149 Some changes you could make to syslinux.cfg:
151 - This value is the number seconds it will wait before booting. You can set
152 the timeout to 0 (or omit) to boot instantly, or you can set it as high as
155 - PROMPT can be set to 0 to disable the 'boot:' prompt.
157 - you can add this line to display the contents of a file as a welcome
167 Other useful information on making a Linux bootfloppy is available at the
170 http://www.linuxdoc.org/HOWTO/Bootdisk-HOWTO/index.html
171 http://www.linux-embedded.com/howto/Embedded-Linux-Howto.html
172 http://linux-embedded.org/howto/LFS-HOWTO.html
173 http://linux-embedded.org/pmhowto.html
174 http://recycle.lbl.gov/~ldoolitt/embedded/ (Larry Doolittle's stuff)
181 The following features that we might want to add later:
183 - support for additional filesystems besides ext2, i.e. minix
184 - different libc, static vs dynamic loading
185 - maybe using an alternate bootloader