You're misinterpreting the title. The author didn't intend "Unix" to literally mean only the official AT&T/TheOpenGroup UNIX® System to the exclusion of Linux.
The first sentence of "UNIX-like" makes that clear : >This is a catalog of things UNIX-like/POSIX-compliant operating systems can do atomically,
Further down, he then mentions some Linux specifics : >fcntl(fd, F_GETLK, &lock), fcntl(fd, F_SETLK, &lock), and fcntl(fd, F_SETLKW, &lock) . [...] There is a “mandatory locking” mode but Linux’s implementation is unreliable as it’s subject to a race condition.
I wasn't claiming that. I just thought the ggp had a useful comment about renameat2() which led to gp's "correction" which wasn't 100% accurate.
IBM z/OS UNIX also has renameat2(). It doesn't have the Linux specific flag RENAME_EXCHANGE.
https://www.ibm.com/docs/en/zos/3.1.0?topic=functions-rename...
If Kubernetes starts using renameat2(RENAME_EXCHANGE), they could very plausibly add it.
[0] https://www.ibm.com/docs/en/zos/3.2.0?topic=csd-unshare-bpx1...
Linux-specific open file description locks could be brought up in a modern version of TFA though.
> POSIX-compliant
Which, FWIW, doesn't mean Linux. AFAIK there is no Linux distro that's fully compliant, even before you worry about the specifics of whether it's certified as compliant.
I read author's use of "POSIX-compliant" as a loose and fuzzy family category rather than an exhaustive and authoritative reference on 100% strict compliance. Therefore, the author mentioning non-100%-compliant Linux is ok.
There seems to be 2 different expectations and interpretations of what the article is about.
- (1) article is attempting to be a strict intersection of all Unix-like systems that conform to official UNIX POSIX API. I didn't think this was a reasonable interpretation since we can't be sure the author actually verified/tested other POSIX-like systems such as FreeBSD, HP-UX, IBM AIX, etc.
- (2) article is a looser union of operating systems and can also include idiosyncracies of certain systems like Linux that the author is familiar with that don't apply to all other UNIX systems. I think some readers don't realize that all the author's citations to man pages point to Linux specific urls at : https://linux.die.net/man/
The ggp's (amstan) additional comment about renameat2(,,,,RENAME_EXCHANGE) is useful info and is consistent with interpretation (2).
If the author really didn't want Linux to be lumped in with "POSIX-like", it seems he would avoid linux.die.net and instead point to something more of a UNIX standard such as: https://unix.org/apis.html
[0] Intersection vs Union: https://en.wikipedia.org/wiki/Set_(mathematics)#Intersection
As in: Unix-like OR POSIX-compliant
In that light, it's probably fine to not nitpick over certifications here.
Many people write UNIX/POSIX without ever reading what it says.
Differing philosophies of how to interpret titles. Prescriptive vs Descriptive language.[0]
There can be different usages of the word "Unix":
#1: Unix is a UNIX(tm) System V descendent. More emphasis that the kernel needs to be UNIX. In this strict definition, you get the common reminder that "Linux is not a Unix!"
#2: "Unix" as a loose generic term for a family of o/s that looks/feels like Unix. This perspective includes using an o/s that has userland Unix utilities like cat/grep/awk. Sometimes deliberately styled as asterisk "*nix" or a suffix-qualifier "Unix-like" but often just written as a naked "Unix".
A Prescriptivist says the author's title is "incorrect". On the other hand, a Descriptivist looks at the whole content of the article -- notices the text has a lot of Linux specific info such as fcntl(,F_GETLEASE/F_SETLEASE), and every hyperlink to a man page url points to https://linux.die.net/man/ , etc -- and thus determines that the author is using "Unix"(#2) in the looser way that can include some Linux idiosyncrasies.
"Unix" instead of "*nix" as a generic term for Linux is not uncommon. Another example article where the authors use the so-called incorrect "Unix" in the title even though it's mostly discussing Linux CUPS instead of Solaris : https://www.evilsocket.net/2024/09/26/Attacking-UNIX-systems...