# GoboLinux redefining filesystem hierarchy

The traditional Unix filesystem hierarchy is a bit complicated. As it was explained in the first section of my post on it, /opt is used for software to be contained in a single tree rather having their files spread through the system. This concept of each program gets its own directory tree is taken to extreme by GoboLinux distro. More generally it reorganizes root to a new, hopefully more logical way.

## Hierarchy

The root structure in GoboLinux is the following.

 /Data System and program resources /Mount Mount points /Programs Every program; no exceptions /System System files /Users User home directories

First of all, there’s a common misconception that descriptive directory names are for user friendliness. The actual reason is to not conflict with Unix namespace. The capitalized descriptive names originated from NeXT that also had to make its own directories coexist with Unix ones. Using the regular directory tree with different semantics can be confusing. This happens in AtheOS, where /usr behaves like /opt. The influencial Unix-derived Plan 9 also does this, or better say Unix itself did it. In Plan 9 /usr behaves like /home. This is actually similar to early Unix versions, where /usr was holding user home directories.

Having every program in /Programs means that someone can explore what is installed in their system just by doing ls /Programs. This can be thought as a database-less package management system with the directory structure itself organizing the system. As a consequence of this system, package management can take place using common Unix file tools. Specifically it’s simpler to create and share binary packages. Having this structure means that packages can be created just by compressing its directory. They can removed just by removing the directory.

Each entry in /Programs contains all files for that program, stored in a versioned subdirectory. The subdirectory mirrors /usr hierarchy of traditional systems for the specific program. The versioned tree makes it simple to maintain simultaneously multiple versions for each program.

For each file category, there is a directory under /System/Index grouping files from each application as links. Those directories are the traditional Unix ones found in /usr and specifically bin, include, lib, lib64 -> lib, libexec, sbin -> bin, and share. It can kinda be though as /usr/local.

In its initial presentation the directory was /System/Links, and the directories were Executables, Libraries, Headers, Shared and Manuals. The migration to the new hierarchy happened in version 015. The reason was issues with packaging.

Legacy applications continue to work thanks to symlink mapping of traditional paths into their GoboLinux counterparts. Those paths are hidden when listing root but application can still read and write to them. This is made possible by using GoboHide an icotls-based interface, actually a kernel extension meaning no kernel modifications are required. The gobohide is the userspace tool that talks with kernel. To show all hidden directories gobohide -l can be used.

The mapping can then be seen with

$gobohide -l / | while read dir; do ls -l$dir; done


For reference in latest (v017) version this is

 /bin -> /System/Index/bin /boot -> /System/Kernel/Boot /config -> /System/Kernel/Config /dev -> /System/Kernel/Devices /etc -> /System/Settings /lib -> /System/Index/lib /lib64 -> /System/Index/lib64 /media -> /Mount/Media /mnt -> /Mount /proc -> /System/Kernel/Status /root -> /Users/root /run -> /Data/Variable/run /sbin -> /System/Index/sbin /srv -> /Data /sys -> /System/Kernel/Objects /tmp -> /Data/Variable/tmp /var -> /Data/Variable

There’s also /usr with the following directories and files in it.

 ./bin -> /System/Index/bin ./include -> /System/Index/include ./lib -> /System/Index/lib ./lib64 -> /System/Index/lib64 ./libexec ./local -> /usr ./man -> /System/Index/share/man ./plugins ./sbin -> /System/Index/sbin ./share -> /System/Index/share ./X11R6 -> /usr

The arguments gobohide -h/-u can be used to hide and undhide a directory respectively. A useful example is mapping /home to /Users and /root to /Users/root.

# mkdir -p /Users/root
# ln -s /Users /home
# gobohide -h /home
# ln -s /Users/root /root
# gobohide -h /root


Then doing ls -l will show the same structure as that in first section, but you can do ls -l /home and cd /home just fine.

## Compile

The design of /Data/Compile is also interesting, referred as the poor-man’s portage because of its minimalistic design. The Compile and the Recipes tree are designed around the universality of source distribution and use of common build tools. The Recipes are declarative files that describe what the compilation process is like rather imperative scripts.

The recipes files are hosted on GitHub @gobolinux/Recipes. The tree structure is similar to /Programs that is directories for every program and subdirectories for every version. The tree can be downloaded locally (doing swallow clone) for easy usage doing

git clone --depth=1 https://github.com/gobolinux/Recipes /Data/Compile/Recipes


That said this isn’t required for software installation. Compile will download a recipe when a compilation is requested. Doing Compile $pkg will perform a case-insensitive search for a recipe named $pkg. A particular version may be chosen instead doing Compile $pkg$vers.

Let’s see closer how recipes work. For example, the Recipe for file/5.39 (found in the directory ./File/5.39) is

TODO: Make PR to @gobolinux/Recipes

compile_version=1.9.0
url="ftp://ftp.astron.com/pub/file/file-5.39.tar.gz"
file_size=954266
file_md5=1c450306053622803a25647d88f80f25
recipe_type=configure


There’s also a Resources directory holding metadata. This directory is eventually copied to the /Programs subdirectory of the program. The files in are the following along with their contents.

BuildDependencies

LibTool


BuildInformation

Glibc 2.24
LibSeccomp 2.3.2
ZLib 1.2.3


Dependencies

ZLib 1.2.3


Description

[Name] file
[Summary] File type identification utility
[Description] File attempts to classify files depending on their contents and prints a description if a match is found.
[Homepage] https://darwinsys.com/file


Then the program can be installed with Compile file or for that version specifically with Compile file 5.39. Extra options can be passed ad hoc as flag in Compile command. This makes it a bit like build tool-agnostic make. When the package’s files and directories have been created and populated, Compile will then create the necessary links in the /System/Index.

In my opinion this model though very simple (less complexity is good) leads to some redundancy. For example the Description file will be copied unchanged between versions. Also the others files will remain mostly the same between versions with only version changes.

## Concepts in other systems

GoboLinux is influenced and draws inspiration from others systems that build a different system on top of Unix based. Examples of such systems are NeXT, BeOS, and AtheOS. That said, GoboLinux isn’t a clone of any of those systems.

NeXT was already mentioned to be the originator of the top hierarchy naming. The well-known macOS (formerly OS X) is NeXT’s ancestor and traces of that heritage are still present in it. One of those is the hierarchy. Specifically, macOS has both its own user friendly as well as standard Unix directories that are hidden in Finder (macOS file manager). The standard macOS hierarchy (sans the Unix directories) is the following.

 /Applications Installed applications /Library App-specific resources /Network Network-accessible resources /System System/Apple-provided resources /Users User home directories /Volumes Mount points

The Unix specific directories are utilized by the system’s BSD layer. Those are actual directories rather symlinks as in GoboLinux case. It can be thought as macOS splitting its filesystem to directories originating from its NeXT and BSD heritage.

Interestingly, the Compile concept of setting a build style (not sure if GoboLinux was an inspiration) is used in Void Linux which also hosts its templates on GitHub @void-linux/void-packages. For comparison the template for file in Void Linux is (own simpler version for demo; modified from original in upstream)

pkgname=file
version=5.39
build_style=gnu-configure
makedepends="zlib-devel"
short_desc="File type identification utility"