Why Linux Is Unix-Like But Not Unix

Main ideas / concepts

• FreeBSD vs. Unix vs. Unix-like

  • The speaker references a previous discussion claiming FreeBSD removed GPL code, clarifying that FreeBSD removed it from user space, but still includes GPL code in the kernel (notably due to drivers originally from Linux).
  • The core topic becomes the distinction:
    • FreeBSD is “Unix-like” but not “Unix.”
    • A misconception is raised from comments: some people argue “BSD is Unix.” The speaker disagrees, framing Unix as a specific branded/defined category rather than any OS that resembles Unix.

• What Unix is

  • Unix is described as a multi-user, multi-tasking OS originally developed in 1969 at AT&T Bell Labs by Ken Thompson, Dennis Ritchie, and others.
  • It is characterized by technical principles like stability, security, and modular design.
  • The speaker explains that the Unix ecosystem branched into many variants quickly, leading to complexity.

• The “Unix Wars” and fragmentation

  • In the 1980s, multiple Unix systems existed (examples given include AT&T System 3, Microsoft Xenix, PC/IX).
  • Many platforms diverged and proliferated (e.g., HP-UX, SCO Xenix, SunOS, BSD), producing a “big mess” of related systems.
  • This fragmentation created a software support nightmare:
    • Developers had to decide which Unix to support.
    • Porting and compatibility across multiple Unix variants became costly and difficult.
    • A feature on one system might not exist or work similarly on another.

• POSIX as a standardization effort

  • To address fragmentation, industry agreements led to POSIX, published as IEEE 1003 in 1988.
  • POSIX is presented as a way to standardize behavior across many systems.
  • A “fun fact” is included: the name “POSIX” is attributed to Richard Stallman (originally they wanted a different name: “IEEE IX”).

• How Unix branding became controlled

  • The speaker traces how standards and portability specs evolved into broader frameworks:
    • X/Open (initially a group of European Unix vendors such as Bull, ICL, Siemens, Olivetti, Nixdorf; later Philips and Ericsson; later renamed X/Open).
    • X/Open CAE and portability guides that expanded beyond POSIX.
  • Later, an industry consortium COS forms with major Unix vendors (including SCO, Sun, HP, IBM, etc.).
  • By 1993, Novell held the Unix trademark, which later transferred to X/Open.
  • In 1994, X/Open published the SUS (Single Unix Specification), combining multiple standards including POSIX and others.
  • X/Open merged with the Open Software Foundation to become The Open Group.
  • Key consequence: because The Open Group holds Unix source/trademark control, it defines what counts as “Unix.”

• SUS versions / Unix branded versions

  • The speaker lists branded “Unix” standards/labels derived from SUS over time:
    • Unix 93, Unix 95, Unix 98, Unix 03, Unix V7
  • The speaker notes the “V7” naming change seems intentional, implying branding choices are not purely technical.

• Unix certification exists—but doesn’t matter much in practice

  • The speaker claims there is a Unix certification program run by the standards/trademark holders.
  • It is framed as expensive (expected ~$100k/year or more).
  • Examples of certified distributions/platforms are mentioned (notably enterprise/corporate Unix systems).
  • The speaker argues certification is mainly relevant for very specific B2B / legacy migration scenarios (e.g., migrating from AIX, HP/UX, etc.), not for typical users.
  • For most people using modern systems (Linux distros), knowing a system is Unix-certified “doesn’t change” day-to-day use.

• macOS as a special case

  • macOS is described as technically Unix-certified, but with major caveats:
    • For newer Unix versions (e.g., “Unix v7”), much of the list of included compatibility is said to disappear (example claim: only AIX 7 remains).
    • For older standards (e.g., Unix 03), more systems remain included.
  • The speaker claims macOS would need significant modifications to pass required certification test suites, including:
    • Disabling System Integrity Protection
    • Enabling root account
    • Enabling core file generation
    • Enabling timeout coalescing
    • Mounting APFS partitions with stricter timing options
    • Making APFS case sensitive (possibly requiring reinstall)
    • Disabling Spotlight
    • Copying specific binaries between directories (UUCP/UUNAME/UUUSTAT/UUX and UUCICO/UUXQT)
    • Setting the setuid bit on certain binaries
    • Adjusting the PATH ordering
    • Enabling UUCP service
    • Handling “mystery issues” related to four temporary waivers

• The concluding argument

  • The speaker’s thesis:
    • FreeBSD is Unix-like, not Unix because Unix is ultimately a trademarked/standardized branded category.
    • Paying for certification is portrayed as pointless because:
      • Users generally don’t choose software based on “Unix certification”
      • There’s no practical incentive to be “Unix” rather than “Unix-like”
  • The speaker ends with the refrain: “FreeBSD is Unix-like, not Unix.”

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Methodology / instructions mentioned (detailed bullets)

A) What “Unix certification” (as described) would require on macOS to pass test suites

The speaker provides a checklist-like set of steps/conditions (presented as prerequisites for macOS to behave as Unix per the certification tests):

• Disable: System Integrity Protection (SIP)
• Enable: the root account
• Enable: core file generation
• Enable: timeout coalescing
• APFS partition handling
  • Mount APFS partitions with the stricter time option
  • Ensure APFS is formatted case sensitive (since default APFS is case-insensitive; may require reinstall)
• Disable: Spotlight
• Binary relocation/copying
  • Copy binaries:
    • UUCP, UUNAME, UUUSTAT, UUX from usr/bin → usr/local/bin
  • Copy binaries:
    • UUCICO, UUXQT from usr/sbin → usr/local/bin
• Permissions changes
  • Set the setuid bit on all these UU* binaries mentioned above
• PATH configuration
  • Ensure /usr/local/bin is added to the PATH before /usr/bin and /usr/sbin
• Service enablement
  • Enable the UUCP service
• Temporary waivers
  • Address additional required issues tied to four temporary waivers (the speaker implies there are specific minor interoperability/portability issues that must be resolved within the waiver process)

B) Conceptual “support nightmare” problem described (not an instruction, but a practical dilemma)

• Decide which Unix variant to support (e.g., System 3 vs System V vs Xenix vs BSD variants vs HP-UX vs AIX vs SunOS, etc.)
• Deal with client migration risk:
  • If clients switch Unix variants, software porting or rework is needed
• Optionally:
  • Build a “minimal viable” version that works across many systems
• React to feature divergence:
  • If one system has a standout feature, other versions may lack it, complicating compatibility

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Speakers / sources featured (as mentioned)

• Ken Thompson (co-developer of Unix)
• Dennis Ritchie (co-developer of Unix)
• Richard Stallman (mentioned as associated with the naming “POSIX”)
• The Open Group (described as controlling the Unix definition via trademark/source control and certification)
• AT&T Bell Labs (institution where Unix originated)
• IEEE 1003 / POSIX (standard referenced)
• X/Open (organization referenced in the development of SUS/standards and trademark transfer)
• Open Software Foundation (merged with X/Open to become The Open Group)
• Novell (held Unix trademark in 1993)
• COS consortium / “Common Open Software Environment” (referenced as a Unix industry consortium)

Companies specifically referenced as Unix vendors / members

• Bull
• ICL
• Siemens
• Olivetti
• Nixdorf (noted as operating under the name “Bison” at the time)
• Philips
• Ericsson
• Santa Cruz Operation (SCO)
• Unix System Laboratories
• Univel
• Sun Microsystems
• Hewlett-Packard (HP)
• IBM
• SCO (again, in COS context)

Systems/products referenced

• FreeBSD, NetBSD
• Linux distros: Fedora, Ubuntu, Arch (and “Hannah Montana Linux” as a humorous placeholder)
• EulerOS (Huawei)
• InspurKUX (Inspur)
• IBM z/OS, IBM AIX, IBM Unixware, HP-UX

• macOS, including “macOS 15.0” (as referenced in the checklist-like description)

• Steve Jobs (referenced via an old talk; implied as a source of claims about Apple’s Unix involvement)