4. Linux Directory Hierarchy: Oriented to the Software Parts

4.1. FHS Summary

So let's summarize what the FHS has to say about Linux directories:

You may think is a bad idea to break your Software (as a whole) in many pieces, instead of keeping it all under a self-contained directory. But a package system (RPM) has a database that manages it all for you in a very professional way, taking care of configuration files, directories etc. And if you spread your Software using the FHS, beyond the user friendliness, you'll bring an intuitive way to the sysadmin configure it, and work better with performance and security.

4.2. Examples Using the FHS

Now that we know where each part of our software must be installed, lets review the Universal Parts Table applied to the FHS.

4.3. Developer, Do Not Install in /opt or /usr/local !

If you are a systems administrator, this section is not for you. This is a subject for developers and packagers, to make sysadmin's life easyer.

The /opt and /usr/local directories are used by sysadmins to manualy non-packaged files (without RPM) of a software, precisely to not loose control over those files. Notice how separated this folder are from the rest of the system.

A manual installation process (without RPM, or based on simple file copy) is documented in forgoten document inside a drawer (if it was documented), and inside the head of who made installation. If he moves to another job, that installations becomes obscure to the rest of the team, and is a time bomb.

With RPM is different. RPM (or any other package system) is an installation "process" by itself. It is self-documented in his database and pre and post-install actions, which permits total control. Turns installations independent from who did it, turning installtions in a business process.

Installations based on coping files into /opt or /usr/local are far from providing the organization, system visibility and control that RPM provides. I can say /opt and /usr/local would be obsoleted when all softwares become RPMized.

It is very important to Linux evolution and popularization (especially in the desktop battlefield), that developers stop using this hell directories, and start using the FHS. After reading this section, if you still think this folders are good business, please drop me an e-mail.

Products that are entirely installed under one directory, use the self-contained approach, that has several problems:

1. Forces the user to change environment variables like $PATH and $LD_LIBRARY_PATH to use your product easily.

2. Puts files in non-standard places, complicating system integration, and future installation of extensions to your product.

3. The sysadmin probably didn't prepared disk space in these partitions, generating problems in installation time.

4. It is an accepted approach only for pure graphical application, without the command line concept. This is why it were well accepted in Windows. But...

5. ...even using this approach, you can't avoid installing or changing files in standard locations to, for instance, make your icons appear in the user desktop.

Many developers believe that the "self-contained" approach let them work with several versions of the same product, for testing purposes, or whatever. Yes, agree, with this or any good reason in the planet. But remember that a High Quality Software (or Commercial Grade Software) objective is to be practical for the final user, and not to be easy to their developers and testers. Invite yourself to visit an unexperienced user (but potential customer) and watch him installing your product.

Developer, don't be afraid of spreading your files according to FHS because RPM will keep an eye on them.

If you have a business reason to let the user work with several versions of your Product simultaneously (or any other reason), make a relocatable package, which is described in the Maximum RPM book. Be also aware about the implications of using this feature, described in the same book.

Red Hat and derivated distributions allways use the directory standard, instead of /opt or /usr/local. Read what Red Hat says about this subject, and think about it.

The Makefiles of an OpenSource Software that is portable to other UNICES must have the standard installation in /usr/local for compatibility reasons. But must also give the option, and induct the packager, to create the package using FHS specifications.