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Learning with Linux From Scratch

May 19, 2004

This article was contributed by Ladislav Bodnar

In the midst of all the excitement surrounding the release of Fedora Core 2 this week, some of the smaller projects that announced new versions at about the same time might have escaped attention. One of them was Linux From Scratch 5.1.

As the popularity of Linux increases, many people ask: "Is there a fast and fun way to learn the ins and outs of the Linux operating system? Are there any entertaining alternatives to conventional training courses and books?" For many, the answer might very well be Linux From Scratch (LFS), a book that provides step-by-step instructions to build a complete Linux operating system from source code available for download on the Internet.

Linux From Scratch is a mature project. Its beginnings date back to December 1999 when version 1.0 was released. In it, the book's author Gerard Beekmans explains the purpose of the new "distribution":

I started this document about 6 months ago. I tried a few Linux distributions and came to the conclusion that there wasn't a distribution I totally liked. Every distribution has its own advantages and disadvantages, but I was never satisfied with what I had (although Debian comes very close to what I want), so I decided to explore the possibility of building my own Linux distribution using nothing but source code of programs. As I found out there's quite a bit of work involved, but it's also a lot of fun and you really learn a lot by doing it, since you need to configure every single aspect of the system. This forces you to read a lot of manuals on how to configure various software. It also gives you total control over your system (well, that's the idea). You know exactly what software is installed, how it is configured and where all the configuration files reside.

Yes, Linux From Scratch is primarily about learning. Although the final product can indeed be used as a distribution in its own right, the road that one has to walk in order to get to the destination is too tedious to turn it a regular routine. Installing Linux From Scratch is even harder than installing Gentoo: there is no Portage to do the hard work and all compiling has to be done with the classic UNIX tools of configure, make and make install. But this is where the educational value of Linux From Scratch manifests itself. The process is possibly the most practical way to learn about every detail regarding file structures, processor optimizations, configuration files, security matters and thousands of other issues. How much would you pay for a commercial Linux training course? Linux From Scratch is a great resource which will not only teach you the very basics of Linux, it will do so in a most entertaining way, all for free.

If you decide to embark on this experience, consider these prerequisites:

Make sure that you have an existing Linux installation on your hard disk. Any recent distribution will do, as long as it is complete with a GCC compiler and relevant development tools.
Download the LFS packages. All the required LFS packages can be downloaded from LFS mirrors, either individually, or as one complete tarball. Alternative methods using P2P networks or a wget script are also available.
Download the LFS book. The LFS book contains around 200 pages and can be downloaded in HTML or PDF formats.

Although trying to absorb 200 highly technical pages split into 9 chapters might sound like a lot of hard work, the truth is that a great deal of the book consists of reference information, such as package descriptions and listings of program files and their dependencies. The preface and the first chapter can be skimmed over - they contain little beside a foreword, acknowledgment, conventions, changelog and other general information. Chapter 2 explains how to create a new partition, format it with an ext2 file system and mount it. Chapter 3 lists packages needed to build LFS, while chapter 4 details the final preparations before the actual build, inclusive of setting up the build environment.

The real meat of the book starts in Chapter 5, which contains instructions about compiling and installing a minimal Linux system. At this stage, all compilation is done with tools "borrowed" from the host environment, but with static linking to system libraries to gain "independence" from the host system. This will ensure that the newly compiled tools still work in a subsequent, "chroot-ed" stage. The compile process starts with GNU Binutils and continues with GCC, Linux header files, Glibc, Tcl, several essential GNU utilities, and Perl. After installing Glibc, both Binutils and GCC have to be recompiled for the second time to link them against the new Glibc. The compiling of most packages will only take a minute or two, with the exception of Glibc and GCC, which will take a lot longer. However, the time it takes to compile the packages can be utilized for reading the relevant sections in the book, which provide detailed information about such interesting matters as the purpose of the many available GCC compiler flags and other related topics.

Chapter 6 starts with mounting the proc and devpts file systems, followed by a chroot into the newly compiled base LFS partition. The next step is to create a standard UNIX directory structure. If you are fairly new to the world of Linux, this is a great chapter to learn about file permissions, passwords, users and groups, log files, and also about creating devices in the /dev directory. Next comes a detailed explanation on compiling Glibc, including notes on locales, how to configure the dynamic loader, and a list of commands provided by Glibc. A very useful chapter indeed! In order to enable dynamic linking to system libraries, all applications compiled in the previous chapter need to be recompiled here for the second time (or, in the case of Binutils and GCC, for the third time). The remaining system packages will also be compiled in this chapter. Interestingly, beside GCC 3.3.3, the book also recommends installing GCC 2.95.3, which will be used exclusively for compiling the Linux kernel; the well-tested older compiler is said to be more suitable for building a rock-solid kernel than any of the new GCC 3.x series.

The full Linux kernel is finally compiled in chapter 8. However, to get there, one still needs to go through the short, but important chapter 7 - another invaluable section of the book providing all the necessary bootscripts and filled with information about setting up the system clock, the syslog daemon, and networking. The kernel compilation chapter does not deal with kernel configuration issues; it merely provides instructions to compile a default kernel, with a suggested alternative of copying an existing kernel configuration file from a known working system. The very final step of the book is to configure the Grub boot loader (previous versions of LFS used lilo, but version 5.1 switched to Grub) to make the newly compiled Linux system bootable.

Completing all the steps in the book will probably kill a whole weekend, but besides the freshly acquired knowledge and experience, the brand new Linux system on your hard disk is very bare-bones and not particularly useful. So how can you make it useful? By moving on to the next book - the 413-page Beyond Linux From Scratch (BLFS). This is a priceless resource with detailed instruction on how to compile many common applications, including essential utilities, server packages (Apache, MySQL, Samba...), desktop environments (XFree86 + KDE, GNOME, XFce...), OpenOffice.org, multimedia and printing packages, and many other open source applications. At this stage, you'll probably start craving a binary Linux distribution, one that can be installed and is ready to use in 20 minutes. But even if you don't plan on further package compiling, the BLFS book is a great reference for those moments when you do need to compile applications, with many tricks, workarounds and guidelines.

Linux From Scratch is a wonderful project. It should become a compulsory reading material for all Linux training courses, and something that every Linux enthusiast should complete at least once. This would also create another interesting side effect: people who tend to be quick in expressing dissatisfaction on the distributions' mailing lists and forums would probably show a lot more respect for the developers. Installing a ready-made distribution is a trivial task. Building up a set of 4 CDs containing a stable, secure and reliable operating system, plus thousands of applications, is most definitely not.

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