macOS Tahoe is certified Unix 03 [pdf]
51 comments
·September 14, 2025mrweasel
pjmlp
It is also relevant, that as proven on FOSDEM corridors full of Apple laptops, most folks only care about some sort of POSIX experience, and couldn't care less about Linux/BSD religion.
So that target audience gets a cool modern experience, without fighting with driver issues and such.
It is also the reason why Microsoft ended up bringing Project Astoria from the ashes into WSL.
UNIX has won, but not as Richard Stallman would have liked to.
ajdude
> I can't imagine many companies choosing macOS because it's a real Unix, nor would anyone really opt out of z/OS, AIX og HPUX, if they where not certified.
While Unix compliancy isn't what's keeping me on macOS, the Unix tools it has under the hood still is. I've opted to use it over Linux because I still get everything that I need from a "Unix like" standpoint while having some serious enterprise level support and compatibility with work software that's often only available for windows or Mac.
If Apple stopped caring about being Unix compliant, I wouldn't be surprised to see the tools and infrastructure that make it Unix (and useful to me) slowly be removed. Then I'd stop using it.
mdasen
I'd say that you care about it being UNIX-like, not UNIX®. You don't care that Linux isn't UNIX. You don't care that GNU versions of things like ed and awk are slightly off-spec.
In some ways, Apple's adherence to UNIX specifications probably makes macOS less useful for you. For example, I wish that grep on macOS was closer to GNU grep. When I look up commands online, I often find answers based on the GNU implementations. Those often work on macOS, but sometimes don't (or have subtly different behavior) because macOS is adhering to the UNIX specification rather than to what those utilities do on the vast majority of systems out there.
I don't think Apple would be removing UNIX-like tools from macOS even without certification. They know how valuable it is that most developers use their systems. Even Microsoft went so far as to implement the Windows Subsystem for Linux for developers. At this point, I think that UNIX certification makes macOS less compatible with the tools and help out there which generally targets Linux. Usually the differences are small, but they certainly can be meaningful.
mechanicum
> because macOS is adhering to the UNIX specification
Isn’t it rather that Darwin was based on BSD 4.4? I’d imagine GPL 3.0 is a bigger impediment to them ever migrating to GNU tools than any desire to be UNIX certified.
Avamander
Built-in grep is thankfully not as odd as the builtin find is. Might be the first one I replace on my systems.
cesaref
brew install grep?
zitterbewegung
While macOS only really gets Unix certified they design of the flavor of unix from FreeBSD. Homebrew is also the best port system and package manager I have ever used because it requires no thinking. I actually dislike using Linux because now I have to learn the replacement from ifconfig, the creation of launchd IMHO is way better than init.d and systemd, and the command line diskutil and other additions still feel like its more Unix like while Linux feels like its moving toward its own thing. Before I was using macOS I was using OpenBSD as my daily driver since high school. I still don't understand though why Ubuntu has the ability to break /boot because there isn't enough space to add another kernel to there...
StopDisinfo910
Considering the core utils have even been ported to Windows, I don’t really see what you would lose.
The Unix don’t really share much between each other apart from the small core.
qmr
> I still get everything that I need from a "Unix like" standpoint
Everything except a package manager!
zitterbewegung
Majority of people use homebrew. There is also macports.
mickael-kerjean
There are some infuriating issues though, I have wiped out a couple files on OSX using sed with the -i option to replace a text within a file only to realised OSX would wipe it out instead ....
mdasen
That explains why they got it UNIX certified back then, but couldn't they stop advertising macOS as UNIX and stop getting it certified? They even changed the name from Mac OS X to macOS since then.
crazygringo
That's my question too, why continue to bother? Apple doesn't even have any separate "Server" OS anymore. I can't find anything mentioning UNIX on any apple.com marketing pages.
I guess it's just, might as well keep it going, as an option for future marketing if ever needed. Maybe it helps the salespeople in some enterprise deals? I mean, if it doesn't really cost anything to keep it.
kstrauser
My (wholly unsupported) guess is that there are government or megacorp bids somewhere for Unix systems for employees, and this checks that box. The buyer could update their requirements, but why do that when you can just make your vendor jump through the hoop?
jeremiemyhren
I think it’s a quiet but deliberate strategy to keep macOS the spiritual successor to NeXTSTEP. While many of Jobs principles are under pressure at current day Apple, his ghost lives on.
monkeyelite
This also doesn’t explain anything? Is getting Unix certified a jobs principle or a requirement to be a “spiritual successor”?
randall
there’s no downside as far as i’m aware.
mdasen
There isn't much downside, but it probably involves a small amount of money (paid for the certification) and it means spending time making sure that everything remains 100% within spec. There's lots of little edge cases where BSDs differ from the spec and it means that Apple needs to take care not to drift from the spec.
bawolff
Presumably certification costs money (?)
hopelite
Famous last words
cramcgrab
You forgot solarius, well, so did oracle.
alberth
There’s an interesting story from the lead engineer to make OS X originally compliant:
> I was asked if I could lead a team to do #1. I said “Yes, under the condition that I could use the compliance project as a hammer to force other parts of the organization to make changes in their own code base, and that I could play it rather loose with commit rules regarding what it said in the bugs database for a given code change, and what the given code change actually did, in addition to what it said in the bugs database”.
…
> We were promised 1/10th of the $200 million, or $20 million in stock, on completion. $10 million to me, $5 million to Ed, and $5 million to Karen Crippes, who was looking for a home in Mac OS X development, I knew was an amazing engineer, and who could be roped into being technical liaison and periodically kicking off the tests and complaining to Ed and I about things not passing.
—-
Source: https://www.quora.com/What-goes-into-making-an-OS-to-be-Unix...
HN discussion: https://news.ycombinator.com/item?id=29984016
sgerenser
And if you read further in the comments, he never got the stock. The executive who promised it to him “took it for himself.”
Jcampuzano2
And left his wife for an HR person, can't forget that. Lol sounds like a shitshow all around when it comes to execs but wouldn't be surprised.
Guess it shows that when it comes to compensation promises always get it in writing.
nicce
Further below:
> Also, the tech lead has to fix anything no one else fixes, or no one else can fix, because they are the DRI (Directly Responsible Individual).
How many tech lead/project manager can say that they are capable for this in these days? It feels like based on my observations that other skills are taking priority on management/lead side.
0xFEE1DEAD
Thank you for sharing, what an interesting read.
homebrewer
Two general-purpose Linux distributions used to pay for Unix certification, although they don't do it anymore since hardly anyone is interested in it these days.
https://www.opengroup.org/openbrand/register/brand3617.htm
https://www.opengroup.org/openbrand/register/brand3622.htm
Save these links for the next time someone moans that Linux "is not a real Unix".
mdasen
It's not just about paying for certification. You also have to replace a lot of things like ed, awk, grep, etc. with versions that are compatible with the UNIX specification. GNU utilities didn't target 100% UNIX compatibility and they have differences that mean that a command that works on UNIX might not work (or might not work the same) on a Linux distro using GNU utilities. glibc has slight differences from the spec too.
In order to get a Linux distro certified, you'd have to make changes which would make it less compatible with all the other Linux distros out there.
The reason why RedHat doesn't pay for UNIX certification is that their distros wouldn't be compliant. The reason why they don't make their distros compliant is that their customers would vastly prefer that RedHat use "standard Linux" tools than replace them with UNIX-compliant ones. Customers don't want a Linux distro that's subtly different/incompatible compared to what everyone expects in a Linux system. They'd rather it be not-UNIX.
Yes, you can modify a Linux distro to be UNIX. However, most Linux systems are not real UNIX - and you wouldn't want it to be real UNIX.
joao
Reminded of the origin story of making Mac OS X Unix certified: https://www.quora.com/What-goes-into-making-an-OS-to-be-Unix...
null
EE84M3i
Thanks for the link, that's a good read.
enricozb
I recently learned that macOS has a (by default) case insensitive filesystem. How does this line up with the certification?
irusensei
Think of it: it's a Unix system. Literally. A unix system with the usability that your grandma can use. It supports both commercial and open source applications. The year of the linux desktop folks have been trying this for decades.
EDIT: already downvoted to negatives. The Linux folks really don't like to be reminded of that.
ksec
Has there been any work for something post Unix 03?
quink
I may have mentioned on occasion, here or there, about how ludicrous it is that there appears to be no well-defined standard that user space shall have sqlite3 and git and gzip.
So, for all intents and purposes, nothing that would be relevant in any reasonable end-user way in 2025. It’s all just: here’s defaults and here’s scripts to set up your environment and here’s a dozen things to run brew with. But no standard.
Pet_Ant
Yes, there is "UNIX V7" in 2013... which apparently only IBM's AIX supports. This is ironic because the whole idea of UNIX is to create a common platform for interoperability, but only one platform actually supports. I really wonder why Apple just doesn't put a couple of FTEs on it and upgrade to V7. I'm sure it wouldn't take much. But it sort of reminds me of Java and HTML where there were standards to allow for independent implementations, but have collapsed to single implementations.
https://en.wikipedia.org/wiki/Single_UNIX_Specification#Comp...
badgersnake
Solaris did support it, I guess it was more relevant when there were multiple vendors
oldpersonintx2
[dead]
signa11
same for sequoia as well, discussed here: https://news.ycombinator.com/item?id=41698775
Keyframe
Good thing to know when I go back to 1980s with a macbook!
amiga386
OK, great.
Can I call poll(2) on a terminal device's file descriptor?
Requirement for certification: https://pubs.opengroup.org/onlinepubs/9799919799.2024edition...
> The poll() and ppoll() functions shall support regular files, terminal and pseudo-terminal devices, FIFOs, pipes, and sockets.
Apple (last time I checked): https://developer.apple.com/library/archive/documentation/Sy...
> BUGS: The poll() system call currently does not support devices.
I asked the same question of Sequoia: https://news.ycombinator.com/item?id=41822308
johnisgood
And someone said:
> It's not simply that certification costs money. It's that a lot of modern UNIX-like operating systems don't adhere to the UNIX spec. For example, the OpenBSD man pages specify the ways in which they diverge from POSIX and UNIX in the Standards section: https://man.openbsd.org/sh.1#STANDARDS, https://man.openbsd.org/awk.1#STANDARDS. Often times these are small deviations that might not matter to most people, but it means that they aren't UNIX.
Except it seems like macOS diverges, too, yet it is certified. I wonder in what other ways it diverges.
brewmarche
Note: while the link above points to a newer standard, the quote has already been present in the one for UNIX 03 it seems: < https://pubs.opengroup.org/onlinepubs/009696699/functions/po...>
mamcx
Also, the weird `fsync` behaviors is not part of it?
qhwudbebd
I came here to mention this too, but saw you'd beaten me to it. It's remarkable how bad non-free OSes are at maintaining basic infrastructure in their kernel and userspace compared to Linux and the BSDs isn't it? Basic bugs get neglected for decades in favour of rearranging the cosmetics - in this case, it's been more than 20 years since I first reported this to Apple's /dev/null service, and I'm sure I wasn't first and I'm only one of many.
veggieroll
I don't think it's that surprising that the Open Group would cut corners certifying Unix compatibility.
So for those who, like me, wonders why Apple keeps getting macOS Unix certified, it's to avoid a lawsuit. Apple misused the Unix trademark when they first launched MacOS, so to avoid legal trouble with The Open Group, Terry Lambert was put in charge of getting MacOS Unix compliant and certified: https://www.quora.com/What-goes-into-making-an-OS-to-be-Unix...
It's basically the only relevance the Unix trademark has these days. I can't imagine many companies choosing macOS because it's a real Unix, nor would anyone really opt out of z/OS, AIX og HPUX, if they where not certified.