AUTHOR: Csaba Henk DATE: 2003-10-27 LICENSE: The MIT License SYNOPSIS: Making an uClibc-based bootfloppy PRIMARY URI: http://www.math-inst.hu/~ekho/lowlife/ DESCRIPTION: This hints shows how to create a cutting-edge bootfloppy from scratch, based on uClibc, a lightweight C library. PREREQUISITES: This hint should be useable on any not too aged Linux installation with a non-broken toolchain. It was tested on a (by and large) LFS-4.0 system. The sudo utility is advised to have. ATTACHMENTS: http://www.linuxfromscratch.org/hints/downloads/attachments/uclibc-bootfloppy/busybox-0.60.5-Config.h http://www.linuxfromscratch.org/hints/downloads/attachments/uclibc-bootfloppy/linux-2.4.22-.config http://www.linuxfromscratch.org/hints/downloads/attachments/uclibc-bootfloppy/mkbootdisk http://www.linuxfromscratch.org/patches/downloads/devfsd/devfsd-1.3.25-uclibc-1.patch HINT: Contents -------- Preface Introduction What do we need? The concept Setting up the development environment Compiling the linux kernel Installing uClibc on the development platform Creating the root filesystem Installing uClibc for the bootdisk Installing busybox Installing gpm Other programs Creating the bootdisk Bugs and weirdnesses, todo Preface ------- * This hint is co-developed with the svnc-thinclient hint in the framework of the lowlife project, http://www.math-inst.hu/~ekho/lowlife/ This file belongs to lowlife-0.5.1. * For the most recent version check out http://www.math-inst.hu/~ekho/lowlife/uclibc-bootfloppy.txt * Comments, ideas, critics, flames are welcome. * (If you are an LFS user, you can skip this.) Although this document is formally an LFS hint, you can see use of it without knowing what LFS is (I tried to write it keeping this possibility in mind). Anyway, I recommend you to check out what LFS is. If you are not familiar with compiling source code in unix/linux environment, then there is no use of going on without checking out what LFS is. Consult the following docs first: http://www.linuxfromscratch.org/lfs/whatislfs.html http://www.linuxfromscratch.org/faq/ http://www.linuxfromscratch.org/hints/downloads/files/essential_prereading.txt http://www.linuxfromscratch.org/lfs/view/stable/preface/prerequisites.html Introduction ------------ When you are to put together a Linux bootfloppy, you need to decide what implementation of the standard C libraries will you use. One possibility is using the C library implementation which is common on Linux based systems: glibc. It's advantage is that you have it at hand: to make a glibc-based bootfloppy, the only thing you have to do is to is to copy the necessary libs to the filesystem you will put on the floppy. This is way chosen by the rescue floppy described in the BLFS-book: http://linuxfromscratch.org/blfs/view/test/postlfs/bootdisk.html However, glibc is far from being lightweight, and eats up much of the rather limited space you have when working with a floppy. So you might like seek for an alternative which suits much better to the capabilities of the floppy environment. Here we will create a bootfloppy based on the uClibc C library, which is just made for such purposes. The bootfloppy will be cutting edge: uses uClibc and Busybox which are actively developed projects for the embedded platform. Moreover, I used a kernel from the 2.4.* branch (but feel free to use other kernel releases). It is a good question to ask whether this is useful: many floppy distros use older kernels for reducing resource usage. I can say the following: on the one hand, I can afford using a recent kernel as my bootfloppy merrily runs on my 486 with 8M RAM; on the other hand, from the moment I began to use this up-to-date stuff, the problems with handling the terminal buffer and plip timeouts vanished. So unless you are really tight in resources, I think using a recent kernel is a good idea. We will also use some kind of development environment, just to stay on the safe side. This hint has a continuation: there we will describe how to install the svga vncviewer on the bootfloppy, which then becomes capable of turning a machine to an X terminal. (Check out the svnc-thinclient hint: http://www.linuxfromscratch.org/hints/downloads/files/svnc-thinclient.txt http://www.math-inst.hu/~ekho/lowlife/svnc-thinclient.txt ) Additional info and downloadable bootdisk image with svnc can be found at the lowlife homepage (or at its mirror): http://www.math-inst.hu/~ekho/lowlife/ http://www.personal.ceu.hu/students/01/Csaba_Henk/lowlife/ In this hint the assumption of using an x86 PC (both for making and booting the floppy) and gcc is set. You may try to port it to another architecture / compiler. Doing it on another architecture should not be hard. Doing it with another compiler depends on how much does uClibc support that compiler. If you copy command from this hint to your shell, be careful that line-terminating backslashes (\) keep their position (no whitespace characters should follow them). A possible solution is open this hint in the Vim GUI, and copy'n'paste from there. What do we need? ---------------- We will need the following programs; in general, most recent stable versions are recommended. Those programs where I have a certain important comment on the version are marked with (!) and you can find the comment at the beginning of the respective install instructons. * Addons for the development platform: sudo (optional) ftp://ftp.sudo.ws/pub/sudo/ * Programs for the bootfloppy: linux-2.4.* (!) http://www.kernel.org uClibc http://www.uclibc.org/downloads/ busybox-0.60.5 (!) http://www.busybox.net/downloads/ gpm (optional) ftp://arcana.linux.it/pub/gpm The concept ----------- In LFS, bootstrapping a linux system goes in the following fashion: one first installs kernel headers, then builds a toolchain against these headers, finally builds a kernel using the shiny new toolchain. We don't need to produce a new toolchain: we will use the one of the host distro (to which we'll refer as "development environment") (though when making the userspace of our tiny linux system, we will access that toolchain via the uClibc wrappers). This lets us to proceed in a much simpler way: first we compile the kernel, then build uClibc using the headers of this kernel, finally build the userspace against uClibc. We will use optimization for size (we'll pass the -Os flag to gcc). In general you can delete sources after compilation if there is no specific reasons to keep them. In those cases when you should *not* delete the source I'll tell about it explicitly. Setting up the development environment -------------------------------------- We definitely need some kind of development environment to protect us from mucking up our system; eg., if we are in the file system which we will put on the floppy, it is very easy to mistake usr with /usr, and without such a protection, you can imagine that this mistake can have serious consequences... We will create a non-privileged user named bootdisk for doing the job. First choose a home directory for bootdisk and store this value in $BDISKHOME. Then type: groupadd bootdisk && useradd -g bootdisk -s /bin/bash -d $BDISKHOME bootdisk && mkdir -p $BDISKHOME && cat > $BDISKHOME/.bash_profile << "EOF" export CFLAGS=-Os export PATH=/usr/i386-linux-uclibc/bin/:$PATH:$HOME/bin export CC=i386-uclibc-gcc EOF Of course, you may specify more cflags, like -march=i486. The above setting of the $PATH variable assumes that the usual directories to be contained in the path are already set in /etc/profile. So the idea is that we will work as user bootdisk; however, there are some tasks during the bootdisk creation which require a privileged user -- namely, mounting ext2 files and raw-copying to a floppy. We can do two things about this problem: 1) Ignore it, and execute these tasks as root. 2) Make a script named mkbootdisk for doing this tasks. This script must be executable only by root (mode 744). With the help of the sudo utility we let the bootdisk user to use this script as well. That is, we put it to $BDISKHOME/bin and then type: echo " bootdisk ALL = NOPASSWD: $BDISKHOME/bin/mkbootdisk" >> /etc/sudoers A realization of mkbootdisk can be found as an attachment of this hint at http://www.linuxfromscratch.org/hints/downloads/attachments/uclibc-bootfloppy/ or at http://www.math-inst.hu/~ekho/lowlife/mkbootdisk or in the current directory if you read this hint as a file of the lowlife tarball avaliable at http://www.math-inst.hu/~ekho/lowlife Typing "mkbootdisk -h" will print a brief information on usage. We have the desired environment. We go on compiling the programs. Become user bootdisk: su - bootdisk In the rest of the hint we will act as user bootdisk, with the following exceptions: * as uClibc will be installed systemwise, you should install it as root; * if you don't use a mkbootdisk script, then the appropriate actions are to be done as root; * doing a chroot test of your filesystem for the floppy is possible only as root. This means that if you use a mkbootdisk script, then those steps of creating the bootfloppy which shouldn't affect your development platform, *can't* affect the development platform (provided your mkbootdisk script doesn't do anything weird, which I think is fulfilled by the one written by me). Some of the commands below assume that the actual source archive is decompressed in $HOME (which is the same as the prior $BDISKHOME). Software installation instructions always start at the point when the source tarball is already decompressed and you entered the source directory (unless we explicitely claim to act differently). Compiling the linux kernel -------------------------- At the moment the latest stable release of the linux kernel belong to the 2.4.* branch, but 2.6.0-test* releases are already out. This situaton might change any time by the release of linux-2.6.0. The following instructions regard to the 2.4.* releases; if you want to try linux-2.6.*, not only the kernel compilation instructions but the whole bootdisk creation procedure is to be revised (eg., you can't boot a 2.6.* kernel without a boot loader). After linux-2.6.0 will be out I might consider to upgrade this hint to that version. We will compile a network-aware kernel optimized to size. I don't give a complete reference, I just highlight some crucial points.If you need not network-awareness, you may omit TCP/IP netowrking and network drivers; but even in this case it is strongly recommended to include "Unix domain sockets". In the kernel source tree type: sed -e 's%-O2%-Os%g' -e '/^CFLAGS_KERNEL/s%\(^.*$\)%\1 -Os%' Makefile > \ Makefile.tmp && mv Makefile.tmp Makefile The above commands set optimization for size in the Makefile. Edit the Makefile if you want further optimizations. Now you should configure the kernel with "make menuconfig". Choose carefully the value in the "Processor type and features ---> Processor family" menupoint. When choosing options, it is advised to include only those features you really need. Some important ones: Networking options ---> <*> Unix domain sockets [*] TCP/IP networking In the "Network device support --->" menupoint choose those network drivers you intend to use. If you want to use plip, choose it as a module, and also set: Parallel port support ---> <*> Parallel port support PC-style hardware This is advised because of the following: as I experienced, if no option is given, the kernel initializes the parallel port (PC-style) IRQ-less! At boot time we won't have the possibility to pass options to the kernel, as we won't use a boot loader or initrd. Thus we can set the appropriate IRQ value only if we load the parallel port driver as module. Also, to gain more control over the NIC drivers, consider building them as modules. In this hint we use the devfs facility, so choose File systems ---> [*] /dev file system support [*] Automatically mount at boot (See a more detailed description in the devfs hint: http://www.linuxfromscratch.org/hints/downloads/files/devfs+kernel_modules.txt ). And don't forget to include support for the mouse type you will use with the bootfloppy (if you will use any). OK, one more remark. Here I don't digress on how to use initrd, but you may have some reason for doing that. In this case with some kernels (eg., with linux-2.4.22) you might encounter with booting problems, which can be cured by the appropriate kernel patch. For info on initrd and the patch you can consult the "Creating a Custom Boot Disk" chapter of the BLFS-book, referenced in the Introduction. Now compile the kernel with the make dep && make bzImage && make modules commands. Then type mkdir $HOME/rfloppy/lib/modules and copy the NIC driver modules from the drivers/net directory to $HOME/rfloppy/lib/modules, and also the other modules you built. Eg., if you use plip, you will need the drivers/parport/parport_pc.o module. Do not delete the kernel source. If you have troubles with configuring the kernel properly, my .config file might be of your help: http://www.linuxfromscratch.org/hints/downloads/attachments/uclibc-bootfloppy/ http://www.math-inst.hu/~ekho/lowlife/linux-2.4.22/.config Installing uClibc on the development platform --------------------------------------------- Usually we will optimize to size; in case of uClibc it's done automatically. We install uClibc systemwise, thus the commands of this installation are to be executed as root. In the uClibc source tree type make menuconfig uClibc now has a configuration interface similar to that of the linux kernel. Apply the following settings: Target Architecture Features and Options ---> ($BDISKHOME/) Linux kernel header location Library Installation Options ---> (/lib) Shared library loader path This was enough for uClibc-0.9.19; in case of uClibc-0.9.21 we also need the following: General Library Settings ---> [ ] Support gprof profiling String and Stdio Support ---> [*] Support sys_siglist[] (bsd-compat) [Explanation: with profiling support set, uClibc wasn't willing to build for me. The sys_siglist[] support will be needed by busybox which encorporates some BSD code by having ash as its shell.] (Other uClibc versions may have their own gotchas.) Apart from this, the default configuration is quite suitable, probably you need not change anything (especially you need not use full math support). However, taking a look at the options never hurts; eg., you may consider fine-tuning the target processor type. After you exit, make && make install Further on we assume that you installed uClibc into /usr/i386-linux-uclibc/ (the default installation location). Creating the root filesystem ---------------------------- We will put the files of the root filesysem of the floppy to a directory named rfloppy. Firstly we create the directory and a basic tree of subdirectories which vaguley resembles the FHS idea: cd && mkdir -p rfloppy/{dev,proc,etc/init.d,sbin,bin,lib,mnt,usr,var/log} && cat > rfloppy/etc/init.d/rcS << "EOF" && #!/bin/sh mount proc /proc -t proc EOF The etc/init.d/rcS file will be the startup script for the floppy. Put there what you want to be done in the beginnig -- eg., syslogd, klogd, loading modules, starting gpm, etc. A very minimal etc directory is used in this setup. Enriching it (with files like passwd, group, fstab, modules.conf, and so on) is up to you -- this minimalist solution works anyway. Installing uClibc for the bootdisk ---------------------------------- We copy the necessary libraries of uClibc to the bootdisk. cp -a /usr/i386-linux-uclibc/lib/{ld-uClibc*,libc.so.0,libuClibc-*} \ ~/rfloppy/lib Installing busybox ------------------ At the moment busybox has two branches: the development branch (1.00-pre* releases) and the stable branch (0.60.* releases), but this situation might change any time by busybox-1.00 being released. The following instructions regard to the 0.60.* versions. The 1.00-pre* versions differ greatly (encorporate much more utilities, eg.), so if you go experimenting with them, these instructions probably need to be changed. When the now-devel branch get stable (1.00 comes out), this document will probably be upgraded to that version of busybox. Before making it, adjust the Config.h file according to your needs. To make busybox work with devfs, be sure that the #define BB_FEATURE_DEVFS line is uncommented (not prefixed with "//"); and it is advised to enable standard Unix utilities, moreover if you want to use network with the floppy, consider uncommenting: #define BB_IFCONFIG #define BB_TELNET #define BB_TFTP #define BB_FEATURE_IFCONFIG_STATUS Then install it with make CROSS=i386-uclibc- && make PREFIX=$HOME/rfloppy install If you have troubles with configuring busybox properly, my Config.h file might be of your help: http://www.linuxfromscratch.org/hints/downloads/attachments/uclibc-bootfloppy/ http://www.math-inst.hu/~ekho/lowlife/busybox-0.60.5/Config.h Installing gpm -------------- Having mouse at the console is not necessary, but very comfortable for a bootfloppy as well. If you want it, install gpm by running the following commands: ./configure && LDFLAGS="-lm" make && strip src/gpm && mkdir -p $HOME/rfloppy/{usr/sbin,var/run} && cp src/gpm $HOME/rfloppy/usr/sbin && cp -a /usr/i386-linux-uclibc/lib/{libm-*,libm.so.0} ~/rfloppy/lib [The /var/run directory is needed for gpm at runtime.] Other programs -------------- Now if there is anything more you want to have on the floppy, compile it and put it to the appropriate place under $HOME/rfloppy. A list of some possible extensions: * devfsd ( http://ftp.kernel.org/pub/linux/daemons/devfsd/ ) is not necessary for the bootfloppy, devfs work fine without it. So install it only if you know what you are doing. However, it needs to be hacked to get it compiled against uClibc. There is a patch for devfsd at: http://www.linuxfromscratch.org/patches/downloads/devfsd/devfsd-1.3.25-uclibc.patch or at http://www.math-inst.hu/~ekho/lowlife/patches/devfsd-1.3.25-uclibc.patch (or in the patches directory if you read this hint as a file of the lowlife tarball) and you can find some explanation on it at http://www.math-inst.hu/~ekho/lowlife/ Note that devfsd depends on the libdl.so.0 library of uClibc (which is a symlink to libdl-0.9.*.so). You have to put these to the /lib of your filesystem. * The svnc-thinclient hint tells you how to compile and install svgalib and the svga vncviewer to the floppy, giving the bootfloppy the capabilities of an X terminal. The (functionality of the) following utilities are already encorporated in the development versions of busybox. * You can put tinylogin ( http://tinylogin.busybox.net/ ) to the floppy if you want a correct login system on it (with the configuration described in this hint you just get a prompt after booting). * You can put utelnetd ( http://www.pengutronix.de/software/utelnetd_en.html ) to the floppy if you want to access it remotely. However, don't forget that communication is not encrypted under telnet! * One more useful program is hdparm ( http://ftp.ibiblio.org/pub/Linux/system/hardware ): if you boot with this floppy, the harddisk is probably not used, but still is a source of noise by its spinning. You can stop it with hdparm. (See its -y option.) Creating the bootdisk --------------------- Before creating the floppy, you may wish to test the proposed filesystem by chrooting to it; if so, execute as root: chroot $BDISKHOME/rfloppy /bin/sh Typing this you get the prompt of the busybox shell, and you should be able to run those utilities which do not require much I/O (ls, cat, echo,...). Proceed on again as the bootdisk user. Put a floppy to the floppy drive (if you are not sure about its integrity, you might want to run fdformat on it). If you use my mkbootdisk script, check whether the device name of the floppy drive is set correctly in the script (it is set to /dev/fd0 and no option can change it, in order to prevent the bootdisk user in being able to muck up the development platform), and whether the $MKE2FSAPP, $RDEVAPP variables in the script store the correct path to the mke2fs, rdev utilities in your system (they should if you follow standards). If everything is fine, simply run cd && sudo mkbootdisk If you don't use the mkbootdisk script, become root, store the name of your floppy device (typically /dev/fd0) in the variable $DISK. Now its time to find out how big the root filesystem of the floppy should be, and how much inodes should it have. Concerning the size, I think the size of the stuff in the rfloppy directory + 150k is enough; concerning the number of inodes, I think the number of files in rfloppy + 100 is enough. But you should know. Store the chosen filesystem size in the variable $SIZE (the number of kilobytes), and the chosen number of inodes in the variable $INODES. Then type the following: cd $BDISKHOME && # We we create and compress the root filesystem of the floppy: dd if=/dev/zero of=rootfs bs=1k count=$SIZE && yes | mke2fs -m 0 -N $INODES rootfs && mkdir -p loop && mount rootfs -o loop loop && rmdir loop/lost+found && cp -a rfloppy/* loop && chown -R 0:0 loop/* && umount loop && dd if=rootfs bs=1k | gzip -v9 > rootfs.gz Now check whether rootfs.gz and your kernel image (probably linux-2.4.*/arch/i386/boot/bzImage) fit on a floppy together (a floppy is of 1440k usually but it can be formatted to bigger sizes as well). If everything is fine, go on: # We copy the kernel to the floppy: let KERNELSIZE=`dd bs=1k of=$DISK < linux-2.4.*/arch/i386/boot/bzImage 2>&1 | sed -n '1s%\([0-9][0-9]*\).*%\1%p'`+1 && # We perform some adjustments on the kernel copied to the floppy: rdev $DISK 0,0 && rdev -R $DISK 0 && rdev -r $DISK `expr 16384 + $KERNELSIZE` && # Finally we copy the compressed filesystem to its appropriate place \ # on the floppy: dd if=rootfs.gz of=$DISK bs=1k seek=$KERNELSIZE [Explanation -- also for those who wonder how the mkbootdisk script works "yes | mke2fs -m 0 -N $INODES rootfs": This pipe construct is a common trick for answering stupid questions non-interactively. "# We copy the kernel to the floppy" : In the command after this comment we not only copy the kernel to floppy, but we also store the number of transferred kb's in the variable $KERNELSIZE. "# We perform some adjustments on the kernel copied to the floppy" : We won't have a bootloader to tell the kernel where to find its root filesystem. The commands after this comment set some specified bits in the kernel, thus hardwiring the location of the root filesystem to it: firstly, we tell the kernel to seek for the filesystem in the floppy, secondly, we tell the kernel that a ramdisk is to be made and the filesystem is to be decompressed to it, thirdly, we tell the kernel the location of the filesystem within the floppy. The number 16384 = 2^14 is used for shifting within the range of bits in the kernel devoted for describing these data. For more information consult with the Bootdisk HOWTO available at tldp.org. "# Finally we copy [...]" : In the dd command after this comment we use the seek option to copy the compressed filesystem nicely after the kernel image.] Now you have the floppy, boot & enjoy! Bugs and weirdnesses, todo -------------------------- This hint is co-developed with the svnc-thinclient hint in the framework of the lowlife project. These informations can be found in the svnc-thinclient hint. ACKNOWLEDGEMENTS: This hint is co-developed with the svnc-thinclient hint in the framework of the lowlife project. These informations can be found in the svnc-thinclient hint. CHANGELOG: This hint is co-developed with the svnc-thinclient hint in the framework of the lowlife project. These informations can be found in the svnc-thinclient hint.