And Further

We showed you how to create a boot diskette with one set of features. Now you know how to do this, you should be able to customize it to your needs. You can turn it into a full featured rescue disk, an installation disk for your brand new Linux distribution, a demonstration disk or an embedded project, such as a router or print server.

First try to add kernel module support. Modules come in very handy for devices that are seldom used or are only available on some target systems. Serial ports, network adapters and SCSI features may be candidates for compiling as modules, as well as additional file systems. In order to use modules you have to do the following:

• Reconfigure the kernel with module support enabled. Configure certain features to be compiled as modules.
• Rebuild the kernel.
• Run the additional make step make modules.
• Copy the kernel to the boot disk (and run LILO if necessary).
• Copy the modules to the root file system or a different diskette.
• Rebuild busybox with the insmod and rmmod commands enabled. Move this to the root file system as well.
• If you use a RAM disk, you should recreate a RAM disk image, compress it and rerun LILO on your boot disk . If you hadn't made a shell script to perform all these tasks, you should do by now.

One additional feature that you might try (it only exists in 2.4 kernels) is the devfs file system. Instead of a /dev directory with hundreds of useless device node you mount a pseudo file system on the /dev directory, not unlike the /proc file system. There the device nodes appear for only the devices that exist.

After module support you may want to add network support. Once you have added an Ethernet adapter to your old 386, you can connect it to your LAN and you do not need diskettes so often. With a little bit of luck, this still runs on a 4MB machine, but forget about using a RAM disk.

• Rebuild the kernel with networking enabled. Of course you have to rebuild the modules as well.
• Rebuild Busybox with network commands enabled (ifconfig, telnet, ping etc.)
• Copy all relevant files to their respective places.
• Recreate the RAM disk image and rerun LILO if appropriate.

You can add additional programs and libraries to the target system.

• Many programs need curses. The ncurses library is reported to be usable with uClibc. You must recompile it in order to achieve this. You will probably need a stripped down termcap file on your target system as well.
• With ncurses and the standard libraries of uClibc, you should really be able to compile a lot of programs that do not require X.
• Some make files try to run the programs you have just built. This can be a problem. It should be possible to copy the uClibc shared libraries to the /lib directory of the host system, as their names are different from the glibc libraries. The programs linked against glibc will still work and the uClibc programs will work too. I just haven't tried this, so don't do it on a life-critical system or if you haven't made a backup.
• Even gcc and X are reported to work with uClibc, so give them a try! A target system with uClibc as the only C library should therefore be able to run a C development environment and X. Building this is certainly not for beginners.

The RAM disk version of the boot disk runs on a 4MB machine, the version without RAM disk should run with 3MB or RAM, but nothing so far has run on a machine with just 2MB of RAM. In the good old days, people ran Linux routinely on such machines and it should still be possible with modern (if not the newest) software. Some hints:

• Do not use a RAM disk.
• Remove more features from the kernel. RAM disk support can be removed, use the disk-only driver instead of the more functional IDE driver, remove file systems such as FAT and ISO9660. If you do have a 387 in that 2MB box, get rid of math emulation.
• Use an older kernel, 2.2 or even 2.0. Note: if you use 2.0, remember to use the -O none option on mke2fs if you make a file system for the target system. Kernel 2.0 does not understand some features added by later kernels.
• Remove more functions from busybox. This should not help much as busybox will be demand loaded. Parts that are not demanded, will not be loaded. It may help to a certain degree. Features like color ls and command line editing can be removed and a more primitive shell can be utilized.
• Remove init and start /bin/sh directly at startup.
• If this lets you do do fdisk, mkswap and swapon, you can get swapping enabled on the target system. From there you should be fine.