Editing Single UNIX Specification (section)

===Non-registered Unix-like systems===
Developers and vendors of [[Unix-like]] operating systems such as [[Linux]], [[FreeBSD]], and [[MINIX]] typically do not certify their distributions and do not install full POSIX utilities by default.

For Linux, [[pax (command)|pax]] command is usually not installed; furthermore, pax command packages available for Linux often lack pax file format support required by POSIX.<ref>{{cite web| url = https://bugs.launchpad.net/rpm/+bug/1329914| website = Ubuntu bug tracker| title = Bug #1329914 "No UNIX compatible pax implementation" : Bugs : RPM| date = June 13, 2014}}</ref> Sometimes, SUS compliance can be improved by installing additional packages, but very few Linux systems can be configured to be completely conformant. The [[Linux Standard Base]] was formed in 2001 as an attempt to standardize the internal structures of Linux-based systems for increased compatibility. It is based on the POSIX specifications, the Single UNIX Specification, and other open standards, and also extends them in several areas; but there are some conflicts between the LSB and the POSIX standards.<ref>{{cite ISO standard | csnumber=38825 | title=ISO/IEC TR 24715:2006 - Information technology -- Programming languages, their environments and system software interfaces -- Technical Report on the Conflicts between the ISO/IEC 9945 (POSIX) and the Linux Standard Base (ISO/IEC 23360) | access-date=October 15, 2011}}</ref><ref>{{cite web|url=https://personal.opengroup.org/~ajosey/tr20-08-2005.txt|title=Conflicts between ISO/IEC 9945 (POSIX) and the Linux Standard Base.|first=Andrew|last=Josey|type=Unapproved Draft|website=personal.opengroup.org|date=August 29, 2005}}</ref> Few [[Linux distribution]]s actually go through certification as LSB compliant.<ref>{{cite web| url=https://www.linuxbase.org/lsb-cert/productdir.php?by_lsb| title=Certified Products Product Directory| access-date=December 9, 2015| publisher=The Linux Foundation|archive-url=https://archive.today/20121220223126/https://www.linuxbase.org/lsb-cert/productdir.php?by_lsb|archive-date=December 20, 2012}}</ref>

[[Darwin (operating system)|Darwin]], the open source subset of macOS, has behavior that can be set to comply with UNIX&nbsp;03.<ref>{{Cite web|url=https://developer.apple.com/documentation/Darwin/Reference/Manpages/man5/compat.5.html|title=Mac OS X Manual Page for compat(5) - Mac OS X 10.3|date=October 23, 2005|website=developer.apple.com|archive-url=https://web.archive.org/web/20090310143649/http://developer.apple.com/documentation/Darwin/Reference/Manpages/man5/compat.5.html|archive-date=March 10, 2009|access-date=May 24, 2018}}</ref><ref>{{Cite web|url=https://developer.apple.com/legacy/library/documentation/Darwin/Reference/ManPages/man5/compat.5.html|title=compat(5) Manual Page - macOS 10.9|date=June 30, 2010|website=developer.apple.com|access-date=May 24, 2018}}</ref> Darwin uses a 4.4BSD-derived pax command,<ref>{{Cite web|url=https://developer.apple.com/documentation/Darwin/Reference/Manpages/man1/pax.1/html|title=Mac OS X Manual Page for pax(1) - Mac OS X 10.3|date=October 23, 2005|website=developer.apple.com|archive-url=https://web.archive.org/web/20090310143649/http://developer.apple.com/documentation/Darwin/Reference/Manpages/man1/pax.1.html|archive-date=March 10, 2009|access-date=November 25, 2023}}</ref> which lacks multibyte support for filenames.{{cn|date=November 2023}}

FreeBSD previously had a "C99 and POSIX Conformance Project" which aimed for compliance with a subset of the Single UNIX Specification, and documentation where there were differences.<ref>{{cite web|url=http://www.freebsd.org/projects/c99/|title=FreeBSD C99 and POSIX conformance project|publisher=FreeBSD Project|archive-url=https://web.archive.org/web/20131223025351/http://www.freebsd.org/projects/c99/|archive-date=December 23, 2013|url-status=dead}}</ref> FreeBSD pax command, derived from 4.4BSD, does not fully support pax file format.<ref>{{man|1|pax|FreeBSD}}</ref> pax and ustar in-archive format use the same with slightly different defaults (5120 block size vs 10240 block size);<ref>{{cite web|url=https://pubs.opengroup.org/onlinepubs/9699919799/|title=pax - portable archive interchange
|publisher=The Open Group}}</ref> however, FreeBSD's pax lacks the extended PAX headers used for extended character set support. FreeBSD man pages sometimes indicate deviations from POSIX and thus SUS in their STANDARDS sections.<ref>{{man|1|awk|FreeBSD}}</ref>

OpenBSD man pages sometimes indicate deviations from POSIX and thus SUS in their STANDARDS sections.<ref>{{man|1|sh|OpenBSD}}</ref><ref>{{man|1|awk|OpenBSD}}</ref>

MINIX pax command does not support pax file format<ref>{{cite web|url=https://man.minix3.org/cgi-bin/man.cgi?query=pax&apropos=0&sektion=0&manpath=Minix+3.3.0&arch=default&format=html|title=pax(1)|website=man.minix3.org}}</ref> and thereby fails POSIX.1-2001.