What started as investigating /opt on FreeBSD


Last month I wrote a post about symlinking svnlite(1) to /opt/bin/svn on stock FreeBSD, thus allowing Ansible’s subversion module to checkout a repository in a playbook I was writing. This lead to more research into this file system structure than I expected.

Did I get this from Solaris?

This post was SPARC’d—hah—from a discussion with two other Australian BSD gentleman on The Twitters last week. This wasn’t the first awful Solaris joke I’ve made today.

Here’s Ben Woods, whom I had the pleasure of meeting at the FreeBSD miniconf last month at Linux.conf.au:

/opt/ ???? I feel dirty :)

And Jason Tubnor, whom I met at AsiaBSDCon:

Old skool Solaris admins still do

illumos icon

I now felt dirty, and was questioning whether I picked up the /opt habit from using Solaris myself. I did use SunOS briefly at when studying at UniSA, and OpenSolaris was my introduction to ZFS back in the day. I even ran the first closed-source Solaris on my HP Microserver after Oracle sank their teeth into Sun. But I’m fairly sure my usage predates these.

My justification had always been about preventing package manager collisions with my own manually installed tarballs and scripts. The standard place for these is generally /usr/local, but that’s where the BSDs put their packages by default, and macOS Homebrew puts brews. More on that later in this post.

Checking out /opt on the BSDs

This rote behaviour got me curious, so I decided to do a bit of digging and checked out the hier(7) manpage on various operating systems, starting with everyone’s favourites.

Interesting! So wherever I picked this up, it was outside the BSDs. It’s starting to look like it might have been a Solaris-ism after all.

GNU/Linux does mention it

systemd’s file-hierarchy(7) page doesn’t include /opt. But the Linux manpage does mention /opt/, and as a bonus didn’t even tell me to look in the GNU Info page instead. It also mentions another use at the start I didn’t recognise:

/etc/opt Host-specific configuration files for add-on applications installed in /opt.

/opt This directory should contain add-on packages that contain static files.

I use /opt with separate directories for each package I’m installing, so my config would be in /opt/$PACKAGE/etc not in /etc/opt. And I’d put consolidated config into /opt/src.

The manpage also mentioned the Linux Filesystem Hierarchy Standard, which sure enough describes /opt in section 3.13, last updated in 2015:

/opt is reserved for the installation of add-on application software packages. A package to be installed in /opt must locate its static files in a separate /opt/<package> or /opt/<provider> directory tree, where <package> is a name that describes the software package and <provider> is the provider’s LANANA registered name.

The Rationale section has some interesting history:

The use of /opt for add-on software is a well-established practice in the UNIX community. The System V Application Binary Interface [AT&T 1990], based on the System V Interface Definition (Third Edition), provides for an /opt structure very similar to the one defined here.

The Intel Binary Compatibility Standard v. 2 (iBCS2) also provides a similar structure for /opt.

Generally, all data required to support a package on a system must be present within /opt/<package>, including files intended to be copied into /etc/opt/<package> and /var/opt/<package> as well as reserved directories in /opt.

The minor restrictions on distributions using /opt are necessary because conflicts are possible between distribution-installed and locally-installed software, especially in the case of fixed pathnames found in some binary software.

Those possible conflicts are also another reason why I prefer running FreeBSD over other non-BSD operating systems. Keeping installed packages and the base system separate prevents whole classes of problems, and makes the system easier to maintain.

The System V Interface Definition

I was invested in researching this hierarchy, so I went to the source as described in the above Rationale section and downloaded the System V Application Binary Interface documentation from… SCO. That and Sun Microsystems break my heart. Under the File System Stricture and Contents section on page 189:

The directory /opt of the / file system is the point of access to the /opt subtree. This directory subtree contains files installed by add-on application packages. The following describes the structure of the /opt subtree:

  • /opt – The top directory of the /opt subtree.

  • /opt/pkg/bin – Executable files provided by application packages and invoked directly by users.

  • /opt/pkg – Where pkg is the abbreviated name of an add-on software package, contains all the static files installed on the system as part of that package.

Filesystem Hierarchy Standard

I wrote this post a fortnight ago, but left it in drafts so I could clean up the formatting. Since then I was reading this thread on the Gentoo forums about why Portage defaults to /usr, given it’s stated design inspiration was the FreeBSD port system that uses /usr/local. This lead to a PDF of the latest Filesystem Hierarchy Standard. Page 12 stated:

/opt is reserved for the installation of add-on application software packages. A package to be installed in /opt must locate its static files in a separate /opt/<package> or /opt/<provider> directory tree, where <package> is a name that describes the software package and <provider> is the provider’s LANANA registered name.

This to me is key, and a good place to end this post:

Distributions may install software in /opt, but must not modify or delete software installed by the local system administrator without the assent of the local system administrator.


The history for where I started using this is no less vague than when I started, but I love this kind of research. It gets me thinking what other *nix assumptions I’ve been living under over the last decade.

Am I using /opt correctly? I’d say at best, maybe.

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Ruben Schade is a technical writer and IaaS engineer in Sydney, Australia who refers to himself in the third person in bios. Wait, not BIOS… my brain should be EFI by now.

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