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The Unix tree rethought: an introduction to GoboLinux

Hisham Muhammad, May 09 2003.

Lately, there has been lots of discussion on the current state of Linux as a desktop system, and articles pop up here and there, occasionally with very good ideas. However, none have surprised me more than this one. It was all very hyphothetical, but had pretty radical ideas on how the thought the Linux directory tree should be reorganized. This was clearly the most polemical part of the article, and raised many discussions whether something like this could actually be implemented. And that's the reason for my surprise: we had this implemented for over an year. GoboLinux is a Linux distribution based on an alternative directory tree, which has evolved from a custom LFS installation to a distro that's used and maintained by a small group of people today. It was interesting to see that there's a lot of people interested in ideas similar to ours. So, maybe it's time for us to come out of the shadows.

A bit of history

We all remember the time when talking about Linux distributions for the desktop meant arguing which has the best installer. Much has evolved since: the easy, graphical installers are here, but we're not quite there yet. Among the usual rants on "why (insert pet peeve here) is the problem", some interesting ideas come up from time to time. More interestingly, some people started to believe maybe it's time for more adventurous attempts.

Oddly, GoboLinux did not start as one of those. The whole thing started when I had to install programs at the University. As I had no write access to the standard Unix directories, I created my own directories under $HOME the way I saw fit. I upgraded the programs from source constantly, and couldn't use a package manager. My solution was the most obvious one: to place each program in its own directory, such as ~/Programs/AfterStep. Soon the environment variables (PATH, LD_LIBRARY_PATH...) got bigger and bigger, so I created centralized directories for each class of files, containing symbolic links: ~/Libraries, ~/Headers and so on. A natural evolution was to write shell scripts to handle the links, configures and Makefiles.

This system proved itself to be very convenient to use. At my home system, I started to gradually remove pre-compiled packages and recompile them with those scripts. I was moving towards a completely custom Linux system, which I jokingly called LodeLinux. When I had it about 80% complete, the Great Filesystem Crash struck. It was time to start it all over again, but this time through a different route: instead of "deconstructing" an existing distribution, me ( Hisham Muhammad) and a friend, André Detsch, spent two days building a modified Linux From Scratch system. Without much fuss, on March 20, 2002, GoboLinux was born. A month later, we presented an article at the 3rd. Workshop on Free Software called "A new proposal for the Unix directory tree".

What is it all about?

GoboLinux is definitely not "yet another Linux distro for the desktop". It is entirely based on an alternative directory structure. Every program lives in its own directory: you'll find XFree86 4.3 at /Programs/XFree86/4.3/, and ping at /Programs/Netkit-Base/0.17/bin/ping. To see what programs are installed in the system, all you need to do is ls /Programs.

For each category of files, there is a directory under /System/Links grouping files from each application as symbolic links: Executables, Libraries, Headers, Shared and Manuals. For compatibility, each "legacy" directory is a link to a corresponding category. Therefore, /bin, /sbin, /usr/bin, /usr/local/bin (and so on) are all symlinks to /System/Links/Executables. Environment variables are also simplified: export PATH=/System/Links/Executables is enough.

In short, what he have is a database-less package management system: the directory structure itself organizes the system (wasn't that its original purpose, after all?). Each program directory (for example, /Programs/KDE) holds version directories (/Programs/KDE/3.0, /Programs/KDE/3.1.1), and a version-neutral directory for settings (/Programs/KDE/Settings), to keep files that would normally be in /etc. Keeping two or more versions of a library is trivial. When most distributions switched to GCC 3 they released a new major version, mostly incompatible with previous ones. When the 006 series of GoboLinux adopted GCC 3, it was just a matter of keeping old versions of libraries alongside the new ones, while they were gradually phased out. No "compat" packages involved.

Most tasks in GoboLinux are automated by a collection of scripts. To create a GoboLinux package, just type something like CreatePackage CoreUtils. All this command does is storing CoreUtils/5.0/ and CoreUtils/Settings in a .tar.bz2 file called CoreUtils--5.0--i686.tar.bz2. A link called /Programs/CoreUtils/Current indicates which version is currently in effect. This is used by the scripts as a 'default version'. Installation of a program is handle by three scripts: PrepareProgram, which creates the /Program/ hierarchy and passes the proper options to configure. SymlinkProgram creates the links at /System/Links. A wrapper script, CompileProgram covers the common configure && make && make install case (with a number of command-line options to handle special cases).

Alternative boot scripts

Since we felt like we were "starting from scratch" and we really wanted to make a system where everything just made sense for us, we also took the time to rethink the boot scripts. I felt the two historical models (System V and BSD) were overkill for our common desktop-machine setup. GoboLinux uses a simpler system: two scripts, Init and Done, do most of the job. Additional scripts, such as Multi and Single, take care of the runlevels. These files are simply sequences of commands, prepended by the word Exec and a message string. Here's an excerpt of Init:

Exec "Setting clock..." SetClock
Exec "Loading keymap..." loadkeys "$KeymapLayout"
Exec "Bringing up the loopback interface..." ifconfig lo

More elaborate tasks such as SetClock are defined as shell functions in a Tasks file (these tasks can also be called from the command-line using the RunTask script). Configurable settings are defined as environment variables in the Options file. The wrapper function Exec allows for a nifty additional feature: boot themes. The boot sequence can look Slackware-like (with the standard error/output messages), RedHat-like (with lots of OK's), or GoboLinux-like (the latter uses a modified version of the Linux Progress Patch).

The "legacy" tree

Unfortunately, not all programs have the flexibility to be installed anywhere. Occasionally, hardcoded paths creep in even in programs that belong to userland, and should, at least theoretically, allow themselves to be installed inside, say, a user's home directory.

As much as I'd like to see this done in the long term, patching all applications is not an option. For this reason, GoboLinux keeps, as stated earlier, a legacy tree where all usual Unix paths are mapped to GoboLinux equivalents, so, if a Makefile looks for /usr/X11R6/include/X11/Xaw3d/XawInit.h, it will find it, although it is at /Programs/Xaw3d/1.5/include/X11/Xaw3d/XawInit.h, where it belongs. When two applications have a directory entry with the same name, the GoboLinux scripts recursively expand them. Both XFree86 and Xaw3d have X11 under include. A directory /System/Links/Headers/X11 is created automatically, holding links from both X11 directories.

Another interesting feature is that the GoboLinux scripts execute make install using a special user id that only has write permissions inside the program's source directories and the program's entry under /Programs. This way, files can't "escape" from the GoboLinux hierarchy and slip directory into the legacy tree.

The GoboLinux directory structure brings a fresh, clean look the Linux system, but the presence of the legacy tree, while necessary, takes some of this beauty away. Mac OS X uses a "dirty trick" to cover up its Unix nature: the Finder won't show the Unix directories, but you can see them from the command line. In Linux we have many different ways for looking at the filesystem (shells, file managers, browsers...), so we had to go deeper to have a cleanly-looking system. GoboHide is a (obviously optional) kernel patch plus userland application written by Lucas Correia Villa Real and Felipe Damásio that effectively implements "hidden files" on Linux (way beyond dot-files, which are implemented on UI-level just like Finder does).

Here's what ls / looks like on GoboLinux:

Depot  Mount     System
Files  Programs  Users

Related work

As you read this, you have probably found many familiar concepts (not to mention directory names). GoboLinux has clearly found inspiration in other operating systems, like Mac OS X, BeOS and AtheOS, but I think that the notion that they build "something different" using an existing Unix base (be it using a Unix kernel as in OS X or using GNU tools as in AtheOS) was the most important influence of all. Right now there are several other projects, in various stages of development, that use the Linux Kernel as a foundation and feature alternative directory trees. Interestingly, most of them are clones or heavily inspired by a specific proprietary operating system: ROX OS intends to be a RiscOS-like system, LinuxSTEP is a project based on GNUstep aiming for a NeXT-like system, and BlueEyedOS aims for a source-level-compatible BeOS clone.

GoboLinux, on the other hand, is not a clone of anything else. It uses standard Linux desktop software. We believe that the well-organized directory structure makes it a good testbed for new ideas -- possibilities are wide open.

Where are we now?

GoboLinux has evolved immensely during the last year. At gobolinux.org you can find an ISO image of our latest release, 006. It's a bootable "live CD" running GoboLinux in a chrooted read-only filesystem, so you can walk around the directory structure and have a peek on how GoboLinux feels like. The CD also features the usual installer scripts and extra packages. There's no flashy graphical installer yet, but I think the ease-of-use of the installation reflects the overal ease-of-use of the system as a whole (unlike it happens on many distributions).

Despite of the very small userbase (we have never really announced it anywhere yet), the project has progressed quickly and has been fully usable for quite a while right now (most GoboLinux developers use it as their only operating system, and a few others do so, too).