What exactly is POSIX?
Clash Royale CLAN TAG#URR8PPP
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I see POSIX mentioned often and everywhere, and I had assumed it to be the baseline UNIX standard.. until I noticed the following excerpt on a Wikipedia page: The Open Group
The Open Group is most famous as the
certifying body for the UNIX
trademark, and its publication of
the Single UNIX Specification
technical standard, which extends
the POSIX standards and is the
official definition of a UNIX system.
If the official definition of a UNIX system is an extension of POSIX, then what exactly is POSIX? ,,, It surely seems to be a touchstone of the UNIX world, but I don't know how it fits into the overall picture.
posix standard
add a comment |Â
up vote
123
down vote
favorite
I see POSIX mentioned often and everywhere, and I had assumed it to be the baseline UNIX standard.. until I noticed the following excerpt on a Wikipedia page: The Open Group
The Open Group is most famous as the
certifying body for the UNIX
trademark, and its publication of
the Single UNIX Specification
technical standard, which extends
the POSIX standards and is the
official definition of a UNIX system.
If the official definition of a UNIX system is an extension of POSIX, then what exactly is POSIX? ,,, It surely seems to be a touchstone of the UNIX world, but I don't know how it fits into the overall picture.
posix standard
2
SUS is the official definition of UNIX since The Open Group, not the IEEE, owns the UNIX trademark. Se my answer below.
â penguin359
Apr 25 '11 at 21:32
unix.stackexchange.com/tags/posix/info
â Premraj
May 27 '15 at 4:22
stackoverflow.com/questions/1780599/â¦
â Ciro Santilli æ°çÂÂæ¹é ä¸Âå¿ å ÂÃ¥ÂÂäºÂ件 æ³Âè½®åÂÂ
Aug 7 '15 at 22:19
add a comment |Â
up vote
123
down vote
favorite
up vote
123
down vote
favorite
I see POSIX mentioned often and everywhere, and I had assumed it to be the baseline UNIX standard.. until I noticed the following excerpt on a Wikipedia page: The Open Group
The Open Group is most famous as the
certifying body for the UNIX
trademark, and its publication of
the Single UNIX Specification
technical standard, which extends
the POSIX standards and is the
official definition of a UNIX system.
If the official definition of a UNIX system is an extension of POSIX, then what exactly is POSIX? ,,, It surely seems to be a touchstone of the UNIX world, but I don't know how it fits into the overall picture.
posix standard
I see POSIX mentioned often and everywhere, and I had assumed it to be the baseline UNIX standard.. until I noticed the following excerpt on a Wikipedia page: The Open Group
The Open Group is most famous as the
certifying body for the UNIX
trademark, and its publication of
the Single UNIX Specification
technical standard, which extends
the POSIX standards and is the
official definition of a UNIX system.
If the official definition of a UNIX system is an extension of POSIX, then what exactly is POSIX? ,,, It surely seems to be a touchstone of the UNIX world, but I don't know how it fits into the overall picture.
posix standard
posix standard
asked Apr 25 '11 at 17:41
Peter.O
18.5k1791143
18.5k1791143
2
SUS is the official definition of UNIX since The Open Group, not the IEEE, owns the UNIX trademark. Se my answer below.
â penguin359
Apr 25 '11 at 21:32
unix.stackexchange.com/tags/posix/info
â Premraj
May 27 '15 at 4:22
stackoverflow.com/questions/1780599/â¦
â Ciro Santilli æ°çÂÂæ¹é ä¸Âå¿ å ÂÃ¥ÂÂäºÂ件 æ³Âè½®åÂÂ
Aug 7 '15 at 22:19
add a comment |Â
2
SUS is the official definition of UNIX since The Open Group, not the IEEE, owns the UNIX trademark. Se my answer below.
â penguin359
Apr 25 '11 at 21:32
unix.stackexchange.com/tags/posix/info
â Premraj
May 27 '15 at 4:22
stackoverflow.com/questions/1780599/â¦
â Ciro Santilli æ°çÂÂæ¹é ä¸Âå¿ å ÂÃ¥ÂÂäºÂ件 æ³Âè½®åÂÂ
Aug 7 '15 at 22:19
2
2
SUS is the official definition of UNIX since The Open Group, not the IEEE, owns the UNIX trademark. Se my answer below.
â penguin359
Apr 25 '11 at 21:32
SUS is the official definition of UNIX since The Open Group, not the IEEE, owns the UNIX trademark. Se my answer below.
â penguin359
Apr 25 '11 at 21:32
unix.stackexchange.com/tags/posix/info
â Premraj
May 27 '15 at 4:22
unix.stackexchange.com/tags/posix/info
â Premraj
May 27 '15 at 4:22
stackoverflow.com/questions/1780599/â¦
â Ciro Santilli æ°çÂÂæ¹é ä¸Âå¿ å ÂÃ¥ÂÂäºÂ件 æ³Âè½®åÂÂ
Aug 7 '15 at 22:19
stackoverflow.com/questions/1780599/â¦
â Ciro Santilli æ°çÂÂæ¹é ä¸Âå¿ å ÂÃ¥ÂÂäºÂ件 æ³Âè½®åÂÂ
Aug 7 '15 at 22:19
add a comment |Â
4 Answers
4
active
oldest
votes
up vote
112
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accepted
POSIX first was a standard in 1988 long before the Single UNIX Specification. It was one of the attempts at unifying all the various UNIX forks and UNIX-like systems. POSIX is an IEEE Standard, but as the IEEE does not own the UNIXî trademark, the standard is not UNIXî though it is based on the existing UNIX API at that time. The first standard POSIX.1 is formally known as IEEE std 1003.1-1988.[1] IEEE charged a substantial fee to obtain a copy of the standard.
The Open Group released the Single UNIX Specification (SUSv2) in 1997 based on IEEE's work of the POSIX standard. SUSv3 was released in 2001 from a joint working group between IEEE and The Open Group known as the Austin Group. SUSv3 is also known as POSIX:2001[2]. There is now also POSIX:2004 and POSIX:2008 which is the core of SUSv4. As for what UNIXî is, UNIXî is whatever the current registered trademark holder says it is. Since 1994, that is The Open Group.
Novell acquired the UNIXî systems business from AT&T/USL which is where UNIXî was born. In 1994, they sold the right to the UNIXî trademark to X/Open[3] now know as The Open Group. They then sold the UNIXî source code to SCO as UNIXWAREî.[3] UNIXî itself has forked many times[4][5] partly due to AT&T's licensing model. Purchasing UNIXî gave you the complete source of the operating system and the full tool-chain to build it. Modifications to the source can be distributed and used by anyone who owned a license to UNIXî from AT&T. The license fee was in the thousands.
BSD was a project at Berkeley which added a number of enhancements to the UNIXî operating system. BSD code was released under a much more liberal license than AT&T's source and did not require a license fee or even a requirement to be distributed with source, unlike the GPL that the GNU Project and Linux use. This has caused a good part of the BSD code to be included with various commercial UNIX forks. By around 4.3BSD, they had nearly replaced any need for the original AT&T UNIXî source code. FreeBSD/NetBSD/OpenBSD are all forks of 4.3BSD that are a complete operating system and have none of the original AT&T source code. Nor do they have right to the UNIXî trademark, but much of their code is used by commercial UNIX operating systems. The Socket API used on UNIX was developed on BSD and the Unix Fast Filesystem code was borrowed and used on various UNIX Operating Systems like Solaris with their own enhancements.
Linux was developed in 1991, but was developed from scratch unlike BSD and uses the existing GNU Project which is a clean-room implementation of much of the UNIX user-space. It implements much of POSIX for compatibility and is UNIX-like in design, but it does not have the close connection to AT&T or UNIXî that the BSDs have.
A great answer.. all (3) answers have been good, but this one was hugely informative (especially after having been prepped by the other 2); just what I needed... and thanks for the comment (below the question body) about SUS, I understand it well enough now, thanks... (and I didn't notice it was only one paragraph...It was too interesting :)
â Peter.O
Apr 26 '11 at 1:26
2
@Mikel hopefully my edit helps a little
â penguin359
Apr 26 '11 at 4:36
1
That's a fantastic answer there @penguin359!
â boehj
Apr 28 '11 at 4:02
Does anyone have a good idea of what the X stands for? If it's just a suffix to indicate a relation to Unix, shouldn't it be lower case?
â Alex W
Aug 24 '15 at 18:07
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Most important things POSIX 7 defines
C API
Greatly extends ANSI C with things like:
- more file operations:
mkdir
,dirname
,symlink
,readlink
,link
(hardlinks),poll
,sync
- process and threads:
fork
,execl
,pipe
, semaphorssem_*
, shared memory (shm_*
),kill
, scheduling parameters (nice
,sched_
),sleep
- networking
- regular expressions
- advanced memory management:
mmap
,mlock
,mprotect
,madvise
Those APIs also determine underlying system concepts on which they depend, e.g.
fork
requires a concept of a process.Many Linux system calls exist to implement a specific POSIX C API function and make Linux compliant, e.g.
sys_write
,sys_read
, ...Major Linux desktop implementation: glibc, which in many cases just provides a shallow wrapper to system calls.
- more file operations:
CLI utilities
E.g.:
cd
,ls
,echo
, ...Many utilities are direct shell front ends for a corresponding C API function, e.g.
mkdir
.Major Linux desktop implementation: GNU Coreutils for the small ones, separate GNU projects for the big ones:
sed
,grep
,awk
, ... Some CLI utilities are implemented by Bash as built-ins.Shell language
E.g.,
a=b; echo "$a"
Major Linux desktop implementation: GNU Bash.
Environment variables
E.g.:
HOME
,PATH
.Program exit status
ANSI C says
0
orEXIT_SUCCESS
for success,EXIT_FAILURE
for failure, and leaves the rest implementation defined.POSIX adds:
126
: command found but not executable.127
: command not found.> 128
: terminated by a signal.But POSIX does not seem to specify the
128 + SIGNAL_ID
rule used by Bash: Default exit code when process is terminated?
Regular expression
There are two types: BRE (Basic) and ERE (Extended). Basic is deprecated and only kept to not break APIs.
Those are implemented by C API functions, and used throughout CLI utilities, e.g.
grep
accepts BREs by default, and EREs with-E
.E.g.:
echo 'a.1' | grep -E 'a.[[:digit:]]'
Major Linux implementation: glibc implements the functions under regex.h which programs like
grep
can use as backend.Directory struture
E.g.:
/dev/null
,/tmp
The Linux FHS greatly extends POSIX.
Filenames
/
is the path separatorNUL
cannot be used.
iscwd
,..
parent- portable filenames
- use at most max 14 chars and 256 for the full path
- can only contain:
a-zA-Z0-9._-
See also: https://stackoverflow.com/questions/18550253/what-is-posix-compliance-for-filesystem
Command line utility API conventions
Not mandatory, used by POSIX, but almost nowhere else, notably not in GNU. But true, it is too restrictive, e.g. single letter flags only (e.g.
-a
), no double hyphen long versions (e.g.--all
).A few widely used conventions:
-
means stdin where a file is expected--
terminates flags, e.g.ls -- -l
to list a directory named-l
See also: https://stackoverflow.com/questions/8957222/are-there-standards-for-linux-command-line-switches-and-arguments
Who conforms to POSIX?
Many systems follow POSIX closely, but few are actually certified by the Open Group which maintains the standard. Notable certified ones include:
- OS X (Apple) X stands for both 10 and UNIX. Was the first Apple POSIX system, released circa 2001. See also: https://stackoverflow.com/questions/5785516/is-osx-a-posix-os
- AIX (IBM)
- HP-UX (HP)
- Solaris (Oracle)
Most Linux distros are very compliant, but not certified because they don't want to pay the compliance check. Inspur's K-UX and Huawei's EulerOS are two certified examples.
The official list of certified systems be found at: https://www.opengroup.org/openbrand/register/ and also at the wiki page.
Windows
Windows implemented POSIX on some of its professional distributions.
Since it was an optional feature, programmers could not rely on it for most end user applications.
Support was deprecated in Windows 8:
- https://stackoverflow.com/questions/4746043/where-does-microsoft-windows-7-posix-implementation-currently-stand
- https://superuser.com/questions/495360/does-windows-8-still-implement-posix
- Feature request: https://windows.uservoice.com/forums/265757-windows-feature-suggestions/suggestions/6573649-full-posix-support
In 2016 a new official Linux-like API called "Windows Subsystem for Linux" was announced. It includes Linux system calls, ELF running, parts of the /proc
filesystem, Bash, GCC, (TODO likely glibc?), apt-get
and more: https://channel9.msdn.com/Events/Build/2016/P488 so I believe that it will allow Windows to run much, if not all, of POSIX. However, it is focused on developers / deployment instead of end users. In particular, there were no plans to allow access to the Windows GUI.
Historical overview of the official Microsoft POSIX compatibility: http://brianreiter.org/2010/08/24/the-sad-history-of-the-microsoft-posix-subsystem/
Cygwin is a well known GPL third-party project for that "provides substantial POSIX API functionality" for Windows, but requires that you "rebuild your application from source if you want it to run on Windows". MSYS2 is a related project that seems to add more functionality on top of Cygwin.
Android
Android has its own C library (Bionic) which does not fully support POSIX as of Android O: https://stackoverflow.com/questions/27604455/is-android-posix-compatible
Bonus level
The Linux Standard Base further extends POSIX.
Use the non-frames indexes, they are much more readable and searchable: http://pubs.opengroup.org/onlinepubs/9699919799/nfindex.html
Get a full zipped version of the HTML pages for grepping: https://stackoverflow.com/questions/453993/is-there-a-listing-of-the-posix-api-functions/45832939#45832939
5
Yes a good answer as well !!!
â Jasser
Aug 29 '15 at 13:04
3
This list deserves more upvotes.
â Junaga
Oct 29 '16 at 17:56
The question was about POSIX and SUS, but this answer doesn't mention SUS at all...
â Kidburla
Oct 6 '17 at 12:16
1
@Kidburla a great opportunity to add your own answer and get some rep :-) (or edit it into mine and give me rep hehe)
â Ciro Santilli æ°çÂÂæ¹é ä¸Âå¿ å ÂÃ¥ÂÂäºÂ件 æ³Âè½®åÂÂ
Oct 6 '17 at 12:27
1
There are actually Linux distros that are Unix-certified like K-UX and Huawei EulerOS. They appear in the POSIX certified list and also on Opengroup's website
â phuclv
3 hours ago
 |Â
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15
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POSIX is the Portable Operating System standard. It describes certain utilities, APIs, and services a compliant operating system must provide to software (for example sockets, file I/O and threading) along with conventions on how these should be called from a program.
The idea is that a program written for one POSIX-Compliant OS would be easier to port to another POSIX-compliant OS than porting between non-POSIX-compliant OSes. This is why it is much easier to port an application from, say, FreeBSD to Linux than it is to port it from FreeBSD to Windows (though Windows ostensibly supports a subset of POSIX.)
add a comment |Â
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14
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POSIX is a subset of UNIX which is intended to cover various Unix-like environments for other operating systems; this originally included environments such as Eunice for VMS, Windows NT's POSIX personality, and Apollo Domain/OS. You can think of it as a standard portability API for the subset of operating system services whose behavior is in common between Unix and non-Unix. See http://standards.ieee.org/develop/wg/POSIX.html for more information.
I've read more about it now, and it certainly seems that Uinx was the chicken and POSIX was the egg.. but I do wonder if UNIX still rules the roost.. ie..Does POSIX have a life of its own now, and UNIX must comply to POSIX? ... btw. it seems the name POSIX was coinded by Richard Stallman ....
â Peter.O
Apr 25 '11 at 19:11
@fred.bear: Short answer: UNIX (the trade mark) must conform to POSIX; Unix (the product) was the main basis for POSIX; unices (the family of OSes) mostly conform but have more in common. See Is Linux a Unix? and Is Mac OS X, UNIX? for related discussions.
â Gilles
Apr 25 '11 at 20:34
@fred-bear Many people argue that the POSIX standard is nowadays guided by the Linux kernel development community, which (if true) IMHO is not a good thing...
â sakisk
Apr 26 '11 at 14:05
1
@faif I've never heard this and find it unlikely, can you post a reference?
â penguin359
Apr 28 '11 at 4:06
2
@Gilles The Open Group, owner of the UNIX® trademark is also in charge of the UNIX® certification and specification which they call Single UNIX Specification or SUS. POSIX is developed by the IEEE who are not in charge of UNIX®. Since 2001, they have been developed largely in sync, but it technically SUS which is now at version 4 that defined UNIX®.
â penguin359
Apr 28 '11 at 4:11
 |Â
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4 Answers
4
active
oldest
votes
4 Answers
4
active
oldest
votes
active
oldest
votes
active
oldest
votes
up vote
112
down vote
accepted
POSIX first was a standard in 1988 long before the Single UNIX Specification. It was one of the attempts at unifying all the various UNIX forks and UNIX-like systems. POSIX is an IEEE Standard, but as the IEEE does not own the UNIXî trademark, the standard is not UNIXî though it is based on the existing UNIX API at that time. The first standard POSIX.1 is formally known as IEEE std 1003.1-1988.[1] IEEE charged a substantial fee to obtain a copy of the standard.
The Open Group released the Single UNIX Specification (SUSv2) in 1997 based on IEEE's work of the POSIX standard. SUSv3 was released in 2001 from a joint working group between IEEE and The Open Group known as the Austin Group. SUSv3 is also known as POSIX:2001[2]. There is now also POSIX:2004 and POSIX:2008 which is the core of SUSv4. As for what UNIXî is, UNIXî is whatever the current registered trademark holder says it is. Since 1994, that is The Open Group.
Novell acquired the UNIXî systems business from AT&T/USL which is where UNIXî was born. In 1994, they sold the right to the UNIXî trademark to X/Open[3] now know as The Open Group. They then sold the UNIXî source code to SCO as UNIXWAREî.[3] UNIXî itself has forked many times[4][5] partly due to AT&T's licensing model. Purchasing UNIXî gave you the complete source of the operating system and the full tool-chain to build it. Modifications to the source can be distributed and used by anyone who owned a license to UNIXî from AT&T. The license fee was in the thousands.
BSD was a project at Berkeley which added a number of enhancements to the UNIXî operating system. BSD code was released under a much more liberal license than AT&T's source and did not require a license fee or even a requirement to be distributed with source, unlike the GPL that the GNU Project and Linux use. This has caused a good part of the BSD code to be included with various commercial UNIX forks. By around 4.3BSD, they had nearly replaced any need for the original AT&T UNIXî source code. FreeBSD/NetBSD/OpenBSD are all forks of 4.3BSD that are a complete operating system and have none of the original AT&T source code. Nor do they have right to the UNIXî trademark, but much of their code is used by commercial UNIX operating systems. The Socket API used on UNIX was developed on BSD and the Unix Fast Filesystem code was borrowed and used on various UNIX Operating Systems like Solaris with their own enhancements.
Linux was developed in 1991, but was developed from scratch unlike BSD and uses the existing GNU Project which is a clean-room implementation of much of the UNIX user-space. It implements much of POSIX for compatibility and is UNIX-like in design, but it does not have the close connection to AT&T or UNIXî that the BSDs have.
A great answer.. all (3) answers have been good, but this one was hugely informative (especially after having been prepped by the other 2); just what I needed... and thanks for the comment (below the question body) about SUS, I understand it well enough now, thanks... (and I didn't notice it was only one paragraph...It was too interesting :)
â Peter.O
Apr 26 '11 at 1:26
2
@Mikel hopefully my edit helps a little
â penguin359
Apr 26 '11 at 4:36
1
That's a fantastic answer there @penguin359!
â boehj
Apr 28 '11 at 4:02
Does anyone have a good idea of what the X stands for? If it's just a suffix to indicate a relation to Unix, shouldn't it be lower case?
â Alex W
Aug 24 '15 at 18:07
add a comment |Â
up vote
112
down vote
accepted
POSIX first was a standard in 1988 long before the Single UNIX Specification. It was one of the attempts at unifying all the various UNIX forks and UNIX-like systems. POSIX is an IEEE Standard, but as the IEEE does not own the UNIXî trademark, the standard is not UNIXî though it is based on the existing UNIX API at that time. The first standard POSIX.1 is formally known as IEEE std 1003.1-1988.[1] IEEE charged a substantial fee to obtain a copy of the standard.
The Open Group released the Single UNIX Specification (SUSv2) in 1997 based on IEEE's work of the POSIX standard. SUSv3 was released in 2001 from a joint working group between IEEE and The Open Group known as the Austin Group. SUSv3 is also known as POSIX:2001[2]. There is now also POSIX:2004 and POSIX:2008 which is the core of SUSv4. As for what UNIXî is, UNIXî is whatever the current registered trademark holder says it is. Since 1994, that is The Open Group.
Novell acquired the UNIXî systems business from AT&T/USL which is where UNIXî was born. In 1994, they sold the right to the UNIXî trademark to X/Open[3] now know as The Open Group. They then sold the UNIXî source code to SCO as UNIXWAREî.[3] UNIXî itself has forked many times[4][5] partly due to AT&T's licensing model. Purchasing UNIXî gave you the complete source of the operating system and the full tool-chain to build it. Modifications to the source can be distributed and used by anyone who owned a license to UNIXî from AT&T. The license fee was in the thousands.
BSD was a project at Berkeley which added a number of enhancements to the UNIXî operating system. BSD code was released under a much more liberal license than AT&T's source and did not require a license fee or even a requirement to be distributed with source, unlike the GPL that the GNU Project and Linux use. This has caused a good part of the BSD code to be included with various commercial UNIX forks. By around 4.3BSD, they had nearly replaced any need for the original AT&T UNIXî source code. FreeBSD/NetBSD/OpenBSD are all forks of 4.3BSD that are a complete operating system and have none of the original AT&T source code. Nor do they have right to the UNIXî trademark, but much of their code is used by commercial UNIX operating systems. The Socket API used on UNIX was developed on BSD and the Unix Fast Filesystem code was borrowed and used on various UNIX Operating Systems like Solaris with their own enhancements.
Linux was developed in 1991, but was developed from scratch unlike BSD and uses the existing GNU Project which is a clean-room implementation of much of the UNIX user-space. It implements much of POSIX for compatibility and is UNIX-like in design, but it does not have the close connection to AT&T or UNIXî that the BSDs have.
A great answer.. all (3) answers have been good, but this one was hugely informative (especially after having been prepped by the other 2); just what I needed... and thanks for the comment (below the question body) about SUS, I understand it well enough now, thanks... (and I didn't notice it was only one paragraph...It was too interesting :)
â Peter.O
Apr 26 '11 at 1:26
2
@Mikel hopefully my edit helps a little
â penguin359
Apr 26 '11 at 4:36
1
That's a fantastic answer there @penguin359!
â boehj
Apr 28 '11 at 4:02
Does anyone have a good idea of what the X stands for? If it's just a suffix to indicate a relation to Unix, shouldn't it be lower case?
â Alex W
Aug 24 '15 at 18:07
add a comment |Â
up vote
112
down vote
accepted
up vote
112
down vote
accepted
POSIX first was a standard in 1988 long before the Single UNIX Specification. It was one of the attempts at unifying all the various UNIX forks and UNIX-like systems. POSIX is an IEEE Standard, but as the IEEE does not own the UNIXî trademark, the standard is not UNIXî though it is based on the existing UNIX API at that time. The first standard POSIX.1 is formally known as IEEE std 1003.1-1988.[1] IEEE charged a substantial fee to obtain a copy of the standard.
The Open Group released the Single UNIX Specification (SUSv2) in 1997 based on IEEE's work of the POSIX standard. SUSv3 was released in 2001 from a joint working group between IEEE and The Open Group known as the Austin Group. SUSv3 is also known as POSIX:2001[2]. There is now also POSIX:2004 and POSIX:2008 which is the core of SUSv4. As for what UNIXî is, UNIXî is whatever the current registered trademark holder says it is. Since 1994, that is The Open Group.
Novell acquired the UNIXî systems business from AT&T/USL which is where UNIXî was born. In 1994, they sold the right to the UNIXî trademark to X/Open[3] now know as The Open Group. They then sold the UNIXî source code to SCO as UNIXWAREî.[3] UNIXî itself has forked many times[4][5] partly due to AT&T's licensing model. Purchasing UNIXî gave you the complete source of the operating system and the full tool-chain to build it. Modifications to the source can be distributed and used by anyone who owned a license to UNIXî from AT&T. The license fee was in the thousands.
BSD was a project at Berkeley which added a number of enhancements to the UNIXî operating system. BSD code was released under a much more liberal license than AT&T's source and did not require a license fee or even a requirement to be distributed with source, unlike the GPL that the GNU Project and Linux use. This has caused a good part of the BSD code to be included with various commercial UNIX forks. By around 4.3BSD, they had nearly replaced any need for the original AT&T UNIXî source code. FreeBSD/NetBSD/OpenBSD are all forks of 4.3BSD that are a complete operating system and have none of the original AT&T source code. Nor do they have right to the UNIXî trademark, but much of their code is used by commercial UNIX operating systems. The Socket API used on UNIX was developed on BSD and the Unix Fast Filesystem code was borrowed and used on various UNIX Operating Systems like Solaris with their own enhancements.
Linux was developed in 1991, but was developed from scratch unlike BSD and uses the existing GNU Project which is a clean-room implementation of much of the UNIX user-space. It implements much of POSIX for compatibility and is UNIX-like in design, but it does not have the close connection to AT&T or UNIXî that the BSDs have.
POSIX first was a standard in 1988 long before the Single UNIX Specification. It was one of the attempts at unifying all the various UNIX forks and UNIX-like systems. POSIX is an IEEE Standard, but as the IEEE does not own the UNIXî trademark, the standard is not UNIXî though it is based on the existing UNIX API at that time. The first standard POSIX.1 is formally known as IEEE std 1003.1-1988.[1] IEEE charged a substantial fee to obtain a copy of the standard.
The Open Group released the Single UNIX Specification (SUSv2) in 1997 based on IEEE's work of the POSIX standard. SUSv3 was released in 2001 from a joint working group between IEEE and The Open Group known as the Austin Group. SUSv3 is also known as POSIX:2001[2]. There is now also POSIX:2004 and POSIX:2008 which is the core of SUSv4. As for what UNIXî is, UNIXî is whatever the current registered trademark holder says it is. Since 1994, that is The Open Group.
Novell acquired the UNIXî systems business from AT&T/USL which is where UNIXî was born. In 1994, they sold the right to the UNIXî trademark to X/Open[3] now know as The Open Group. They then sold the UNIXî source code to SCO as UNIXWAREî.[3] UNIXî itself has forked many times[4][5] partly due to AT&T's licensing model. Purchasing UNIXî gave you the complete source of the operating system and the full tool-chain to build it. Modifications to the source can be distributed and used by anyone who owned a license to UNIXî from AT&T. The license fee was in the thousands.
BSD was a project at Berkeley which added a number of enhancements to the UNIXî operating system. BSD code was released under a much more liberal license than AT&T's source and did not require a license fee or even a requirement to be distributed with source, unlike the GPL that the GNU Project and Linux use. This has caused a good part of the BSD code to be included with various commercial UNIX forks. By around 4.3BSD, they had nearly replaced any need for the original AT&T UNIXî source code. FreeBSD/NetBSD/OpenBSD are all forks of 4.3BSD that are a complete operating system and have none of the original AT&T source code. Nor do they have right to the UNIXî trademark, but much of their code is used by commercial UNIX operating systems. The Socket API used on UNIX was developed on BSD and the Unix Fast Filesystem code was borrowed and used on various UNIX Operating Systems like Solaris with their own enhancements.
Linux was developed in 1991, but was developed from scratch unlike BSD and uses the existing GNU Project which is a clean-room implementation of much of the UNIX user-space. It implements much of POSIX for compatibility and is UNIX-like in design, but it does not have the close connection to AT&T or UNIXî that the BSDs have.
edited Jan 20 '15 at 21:08
Faheem Mitha
22.4k1677134
22.4k1677134
answered Apr 25 '11 at 21:27
penguin359
8,45923039
8,45923039
A great answer.. all (3) answers have been good, but this one was hugely informative (especially after having been prepped by the other 2); just what I needed... and thanks for the comment (below the question body) about SUS, I understand it well enough now, thanks... (and I didn't notice it was only one paragraph...It was too interesting :)
â Peter.O
Apr 26 '11 at 1:26
2
@Mikel hopefully my edit helps a little
â penguin359
Apr 26 '11 at 4:36
1
That's a fantastic answer there @penguin359!
â boehj
Apr 28 '11 at 4:02
Does anyone have a good idea of what the X stands for? If it's just a suffix to indicate a relation to Unix, shouldn't it be lower case?
â Alex W
Aug 24 '15 at 18:07
add a comment |Â
A great answer.. all (3) answers have been good, but this one was hugely informative (especially after having been prepped by the other 2); just what I needed... and thanks for the comment (below the question body) about SUS, I understand it well enough now, thanks... (and I didn't notice it was only one paragraph...It was too interesting :)
â Peter.O
Apr 26 '11 at 1:26
2
@Mikel hopefully my edit helps a little
â penguin359
Apr 26 '11 at 4:36
1
That's a fantastic answer there @penguin359!
â boehj
Apr 28 '11 at 4:02
Does anyone have a good idea of what the X stands for? If it's just a suffix to indicate a relation to Unix, shouldn't it be lower case?
â Alex W
Aug 24 '15 at 18:07
A great answer.. all (3) answers have been good, but this one was hugely informative (especially after having been prepped by the other 2); just what I needed... and thanks for the comment (below the question body) about SUS, I understand it well enough now, thanks... (and I didn't notice it was only one paragraph...It was too interesting :)
â Peter.O
Apr 26 '11 at 1:26
A great answer.. all (3) answers have been good, but this one was hugely informative (especially after having been prepped by the other 2); just what I needed... and thanks for the comment (below the question body) about SUS, I understand it well enough now, thanks... (and I didn't notice it was only one paragraph...It was too interesting :)
â Peter.O
Apr 26 '11 at 1:26
2
2
@Mikel hopefully my edit helps a little
â penguin359
Apr 26 '11 at 4:36
@Mikel hopefully my edit helps a little
â penguin359
Apr 26 '11 at 4:36
1
1
That's a fantastic answer there @penguin359!
â boehj
Apr 28 '11 at 4:02
That's a fantastic answer there @penguin359!
â boehj
Apr 28 '11 at 4:02
Does anyone have a good idea of what the X stands for? If it's just a suffix to indicate a relation to Unix, shouldn't it be lower case?
â Alex W
Aug 24 '15 at 18:07
Does anyone have a good idea of what the X stands for? If it's just a suffix to indicate a relation to Unix, shouldn't it be lower case?
â Alex W
Aug 24 '15 at 18:07
add a comment |Â
up vote
47
down vote
Most important things POSIX 7 defines
C API
Greatly extends ANSI C with things like:
- more file operations:
mkdir
,dirname
,symlink
,readlink
,link
(hardlinks),poll
,sync
- process and threads:
fork
,execl
,pipe
, semaphorssem_*
, shared memory (shm_*
),kill
, scheduling parameters (nice
,sched_
),sleep
- networking
- regular expressions
- advanced memory management:
mmap
,mlock
,mprotect
,madvise
Those APIs also determine underlying system concepts on which they depend, e.g.
fork
requires a concept of a process.Many Linux system calls exist to implement a specific POSIX C API function and make Linux compliant, e.g.
sys_write
,sys_read
, ...Major Linux desktop implementation: glibc, which in many cases just provides a shallow wrapper to system calls.
- more file operations:
CLI utilities
E.g.:
cd
,ls
,echo
, ...Many utilities are direct shell front ends for a corresponding C API function, e.g.
mkdir
.Major Linux desktop implementation: GNU Coreutils for the small ones, separate GNU projects for the big ones:
sed
,grep
,awk
, ... Some CLI utilities are implemented by Bash as built-ins.Shell language
E.g.,
a=b; echo "$a"
Major Linux desktop implementation: GNU Bash.
Environment variables
E.g.:
HOME
,PATH
.Program exit status
ANSI C says
0
orEXIT_SUCCESS
for success,EXIT_FAILURE
for failure, and leaves the rest implementation defined.POSIX adds:
126
: command found but not executable.127
: command not found.> 128
: terminated by a signal.But POSIX does not seem to specify the
128 + SIGNAL_ID
rule used by Bash: Default exit code when process is terminated?
Regular expression
There are two types: BRE (Basic) and ERE (Extended). Basic is deprecated and only kept to not break APIs.
Those are implemented by C API functions, and used throughout CLI utilities, e.g.
grep
accepts BREs by default, and EREs with-E
.E.g.:
echo 'a.1' | grep -E 'a.[[:digit:]]'
Major Linux implementation: glibc implements the functions under regex.h which programs like
grep
can use as backend.Directory struture
E.g.:
/dev/null
,/tmp
The Linux FHS greatly extends POSIX.
Filenames
/
is the path separatorNUL
cannot be used.
iscwd
,..
parent- portable filenames
- use at most max 14 chars and 256 for the full path
- can only contain:
a-zA-Z0-9._-
See also: https://stackoverflow.com/questions/18550253/what-is-posix-compliance-for-filesystem
Command line utility API conventions
Not mandatory, used by POSIX, but almost nowhere else, notably not in GNU. But true, it is too restrictive, e.g. single letter flags only (e.g.
-a
), no double hyphen long versions (e.g.--all
).A few widely used conventions:
-
means stdin where a file is expected--
terminates flags, e.g.ls -- -l
to list a directory named-l
See also: https://stackoverflow.com/questions/8957222/are-there-standards-for-linux-command-line-switches-and-arguments
Who conforms to POSIX?
Many systems follow POSIX closely, but few are actually certified by the Open Group which maintains the standard. Notable certified ones include:
- OS X (Apple) X stands for both 10 and UNIX. Was the first Apple POSIX system, released circa 2001. See also: https://stackoverflow.com/questions/5785516/is-osx-a-posix-os
- AIX (IBM)
- HP-UX (HP)
- Solaris (Oracle)
Most Linux distros are very compliant, but not certified because they don't want to pay the compliance check. Inspur's K-UX and Huawei's EulerOS are two certified examples.
The official list of certified systems be found at: https://www.opengroup.org/openbrand/register/ and also at the wiki page.
Windows
Windows implemented POSIX on some of its professional distributions.
Since it was an optional feature, programmers could not rely on it for most end user applications.
Support was deprecated in Windows 8:
- https://stackoverflow.com/questions/4746043/where-does-microsoft-windows-7-posix-implementation-currently-stand
- https://superuser.com/questions/495360/does-windows-8-still-implement-posix
- Feature request: https://windows.uservoice.com/forums/265757-windows-feature-suggestions/suggestions/6573649-full-posix-support
In 2016 a new official Linux-like API called "Windows Subsystem for Linux" was announced. It includes Linux system calls, ELF running, parts of the /proc
filesystem, Bash, GCC, (TODO likely glibc?), apt-get
and more: https://channel9.msdn.com/Events/Build/2016/P488 so I believe that it will allow Windows to run much, if not all, of POSIX. However, it is focused on developers / deployment instead of end users. In particular, there were no plans to allow access to the Windows GUI.
Historical overview of the official Microsoft POSIX compatibility: http://brianreiter.org/2010/08/24/the-sad-history-of-the-microsoft-posix-subsystem/
Cygwin is a well known GPL third-party project for that "provides substantial POSIX API functionality" for Windows, but requires that you "rebuild your application from source if you want it to run on Windows". MSYS2 is a related project that seems to add more functionality on top of Cygwin.
Android
Android has its own C library (Bionic) which does not fully support POSIX as of Android O: https://stackoverflow.com/questions/27604455/is-android-posix-compatible
Bonus level
The Linux Standard Base further extends POSIX.
Use the non-frames indexes, they are much more readable and searchable: http://pubs.opengroup.org/onlinepubs/9699919799/nfindex.html
Get a full zipped version of the HTML pages for grepping: https://stackoverflow.com/questions/453993/is-there-a-listing-of-the-posix-api-functions/45832939#45832939
5
Yes a good answer as well !!!
â Jasser
Aug 29 '15 at 13:04
3
This list deserves more upvotes.
â Junaga
Oct 29 '16 at 17:56
The question was about POSIX and SUS, but this answer doesn't mention SUS at all...
â Kidburla
Oct 6 '17 at 12:16
1
@Kidburla a great opportunity to add your own answer and get some rep :-) (or edit it into mine and give me rep hehe)
â Ciro Santilli æ°çÂÂæ¹é ä¸Âå¿ å ÂÃ¥ÂÂäºÂ件 æ³Âè½®åÂÂ
Oct 6 '17 at 12:27
1
There are actually Linux distros that are Unix-certified like K-UX and Huawei EulerOS. They appear in the POSIX certified list and also on Opengroup's website
â phuclv
3 hours ago
 |Â
show 1 more comment
up vote
47
down vote
Most important things POSIX 7 defines
C API
Greatly extends ANSI C with things like:
- more file operations:
mkdir
,dirname
,symlink
,readlink
,link
(hardlinks),poll
,sync
- process and threads:
fork
,execl
,pipe
, semaphorssem_*
, shared memory (shm_*
),kill
, scheduling parameters (nice
,sched_
),sleep
- networking
- regular expressions
- advanced memory management:
mmap
,mlock
,mprotect
,madvise
Those APIs also determine underlying system concepts on which they depend, e.g.
fork
requires a concept of a process.Many Linux system calls exist to implement a specific POSIX C API function and make Linux compliant, e.g.
sys_write
,sys_read
, ...Major Linux desktop implementation: glibc, which in many cases just provides a shallow wrapper to system calls.
- more file operations:
CLI utilities
E.g.:
cd
,ls
,echo
, ...Many utilities are direct shell front ends for a corresponding C API function, e.g.
mkdir
.Major Linux desktop implementation: GNU Coreutils for the small ones, separate GNU projects for the big ones:
sed
,grep
,awk
, ... Some CLI utilities are implemented by Bash as built-ins.Shell language
E.g.,
a=b; echo "$a"
Major Linux desktop implementation: GNU Bash.
Environment variables
E.g.:
HOME
,PATH
.Program exit status
ANSI C says
0
orEXIT_SUCCESS
for success,EXIT_FAILURE
for failure, and leaves the rest implementation defined.POSIX adds:
126
: command found but not executable.127
: command not found.> 128
: terminated by a signal.But POSIX does not seem to specify the
128 + SIGNAL_ID
rule used by Bash: Default exit code when process is terminated?
Regular expression
There are two types: BRE (Basic) and ERE (Extended). Basic is deprecated and only kept to not break APIs.
Those are implemented by C API functions, and used throughout CLI utilities, e.g.
grep
accepts BREs by default, and EREs with-E
.E.g.:
echo 'a.1' | grep -E 'a.[[:digit:]]'
Major Linux implementation: glibc implements the functions under regex.h which programs like
grep
can use as backend.Directory struture
E.g.:
/dev/null
,/tmp
The Linux FHS greatly extends POSIX.
Filenames
/
is the path separatorNUL
cannot be used.
iscwd
,..
parent- portable filenames
- use at most max 14 chars and 256 for the full path
- can only contain:
a-zA-Z0-9._-
See also: https://stackoverflow.com/questions/18550253/what-is-posix-compliance-for-filesystem
Command line utility API conventions
Not mandatory, used by POSIX, but almost nowhere else, notably not in GNU. But true, it is too restrictive, e.g. single letter flags only (e.g.
-a
), no double hyphen long versions (e.g.--all
).A few widely used conventions:
-
means stdin where a file is expected--
terminates flags, e.g.ls -- -l
to list a directory named-l
See also: https://stackoverflow.com/questions/8957222/are-there-standards-for-linux-command-line-switches-and-arguments
Who conforms to POSIX?
Many systems follow POSIX closely, but few are actually certified by the Open Group which maintains the standard. Notable certified ones include:
- OS X (Apple) X stands for both 10 and UNIX. Was the first Apple POSIX system, released circa 2001. See also: https://stackoverflow.com/questions/5785516/is-osx-a-posix-os
- AIX (IBM)
- HP-UX (HP)
- Solaris (Oracle)
Most Linux distros are very compliant, but not certified because they don't want to pay the compliance check. Inspur's K-UX and Huawei's EulerOS are two certified examples.
The official list of certified systems be found at: https://www.opengroup.org/openbrand/register/ and also at the wiki page.
Windows
Windows implemented POSIX on some of its professional distributions.
Since it was an optional feature, programmers could not rely on it for most end user applications.
Support was deprecated in Windows 8:
- https://stackoverflow.com/questions/4746043/where-does-microsoft-windows-7-posix-implementation-currently-stand
- https://superuser.com/questions/495360/does-windows-8-still-implement-posix
- Feature request: https://windows.uservoice.com/forums/265757-windows-feature-suggestions/suggestions/6573649-full-posix-support
In 2016 a new official Linux-like API called "Windows Subsystem for Linux" was announced. It includes Linux system calls, ELF running, parts of the /proc
filesystem, Bash, GCC, (TODO likely glibc?), apt-get
and more: https://channel9.msdn.com/Events/Build/2016/P488 so I believe that it will allow Windows to run much, if not all, of POSIX. However, it is focused on developers / deployment instead of end users. In particular, there were no plans to allow access to the Windows GUI.
Historical overview of the official Microsoft POSIX compatibility: http://brianreiter.org/2010/08/24/the-sad-history-of-the-microsoft-posix-subsystem/
Cygwin is a well known GPL third-party project for that "provides substantial POSIX API functionality" for Windows, but requires that you "rebuild your application from source if you want it to run on Windows". MSYS2 is a related project that seems to add more functionality on top of Cygwin.
Android
Android has its own C library (Bionic) which does not fully support POSIX as of Android O: https://stackoverflow.com/questions/27604455/is-android-posix-compatible
Bonus level
The Linux Standard Base further extends POSIX.
Use the non-frames indexes, they are much more readable and searchable: http://pubs.opengroup.org/onlinepubs/9699919799/nfindex.html
Get a full zipped version of the HTML pages for grepping: https://stackoverflow.com/questions/453993/is-there-a-listing-of-the-posix-api-functions/45832939#45832939
5
Yes a good answer as well !!!
â Jasser
Aug 29 '15 at 13:04
3
This list deserves more upvotes.
â Junaga
Oct 29 '16 at 17:56
The question was about POSIX and SUS, but this answer doesn't mention SUS at all...
â Kidburla
Oct 6 '17 at 12:16
1
@Kidburla a great opportunity to add your own answer and get some rep :-) (or edit it into mine and give me rep hehe)
â Ciro Santilli æ°çÂÂæ¹é ä¸Âå¿ å ÂÃ¥ÂÂäºÂ件 æ³Âè½®åÂÂ
Oct 6 '17 at 12:27
1
There are actually Linux distros that are Unix-certified like K-UX and Huawei EulerOS. They appear in the POSIX certified list and also on Opengroup's website
â phuclv
3 hours ago
 |Â
show 1 more comment
up vote
47
down vote
up vote
47
down vote
Most important things POSIX 7 defines
C API
Greatly extends ANSI C with things like:
- more file operations:
mkdir
,dirname
,symlink
,readlink
,link
(hardlinks),poll
,sync
- process and threads:
fork
,execl
,pipe
, semaphorssem_*
, shared memory (shm_*
),kill
, scheduling parameters (nice
,sched_
),sleep
- networking
- regular expressions
- advanced memory management:
mmap
,mlock
,mprotect
,madvise
Those APIs also determine underlying system concepts on which they depend, e.g.
fork
requires a concept of a process.Many Linux system calls exist to implement a specific POSIX C API function and make Linux compliant, e.g.
sys_write
,sys_read
, ...Major Linux desktop implementation: glibc, which in many cases just provides a shallow wrapper to system calls.
- more file operations:
CLI utilities
E.g.:
cd
,ls
,echo
, ...Many utilities are direct shell front ends for a corresponding C API function, e.g.
mkdir
.Major Linux desktop implementation: GNU Coreutils for the small ones, separate GNU projects for the big ones:
sed
,grep
,awk
, ... Some CLI utilities are implemented by Bash as built-ins.Shell language
E.g.,
a=b; echo "$a"
Major Linux desktop implementation: GNU Bash.
Environment variables
E.g.:
HOME
,PATH
.Program exit status
ANSI C says
0
orEXIT_SUCCESS
for success,EXIT_FAILURE
for failure, and leaves the rest implementation defined.POSIX adds:
126
: command found but not executable.127
: command not found.> 128
: terminated by a signal.But POSIX does not seem to specify the
128 + SIGNAL_ID
rule used by Bash: Default exit code when process is terminated?
Regular expression
There are two types: BRE (Basic) and ERE (Extended). Basic is deprecated and only kept to not break APIs.
Those are implemented by C API functions, and used throughout CLI utilities, e.g.
grep
accepts BREs by default, and EREs with-E
.E.g.:
echo 'a.1' | grep -E 'a.[[:digit:]]'
Major Linux implementation: glibc implements the functions under regex.h which programs like
grep
can use as backend.Directory struture
E.g.:
/dev/null
,/tmp
The Linux FHS greatly extends POSIX.
Filenames
/
is the path separatorNUL
cannot be used.
iscwd
,..
parent- portable filenames
- use at most max 14 chars and 256 for the full path
- can only contain:
a-zA-Z0-9._-
See also: https://stackoverflow.com/questions/18550253/what-is-posix-compliance-for-filesystem
Command line utility API conventions
Not mandatory, used by POSIX, but almost nowhere else, notably not in GNU. But true, it is too restrictive, e.g. single letter flags only (e.g.
-a
), no double hyphen long versions (e.g.--all
).A few widely used conventions:
-
means stdin where a file is expected--
terminates flags, e.g.ls -- -l
to list a directory named-l
See also: https://stackoverflow.com/questions/8957222/are-there-standards-for-linux-command-line-switches-and-arguments
Who conforms to POSIX?
Many systems follow POSIX closely, but few are actually certified by the Open Group which maintains the standard. Notable certified ones include:
- OS X (Apple) X stands for both 10 and UNIX. Was the first Apple POSIX system, released circa 2001. See also: https://stackoverflow.com/questions/5785516/is-osx-a-posix-os
- AIX (IBM)
- HP-UX (HP)
- Solaris (Oracle)
Most Linux distros are very compliant, but not certified because they don't want to pay the compliance check. Inspur's K-UX and Huawei's EulerOS are two certified examples.
The official list of certified systems be found at: https://www.opengroup.org/openbrand/register/ and also at the wiki page.
Windows
Windows implemented POSIX on some of its professional distributions.
Since it was an optional feature, programmers could not rely on it for most end user applications.
Support was deprecated in Windows 8:
- https://stackoverflow.com/questions/4746043/where-does-microsoft-windows-7-posix-implementation-currently-stand
- https://superuser.com/questions/495360/does-windows-8-still-implement-posix
- Feature request: https://windows.uservoice.com/forums/265757-windows-feature-suggestions/suggestions/6573649-full-posix-support
In 2016 a new official Linux-like API called "Windows Subsystem for Linux" was announced. It includes Linux system calls, ELF running, parts of the /proc
filesystem, Bash, GCC, (TODO likely glibc?), apt-get
and more: https://channel9.msdn.com/Events/Build/2016/P488 so I believe that it will allow Windows to run much, if not all, of POSIX. However, it is focused on developers / deployment instead of end users. In particular, there were no plans to allow access to the Windows GUI.
Historical overview of the official Microsoft POSIX compatibility: http://brianreiter.org/2010/08/24/the-sad-history-of-the-microsoft-posix-subsystem/
Cygwin is a well known GPL third-party project for that "provides substantial POSIX API functionality" for Windows, but requires that you "rebuild your application from source if you want it to run on Windows". MSYS2 is a related project that seems to add more functionality on top of Cygwin.
Android
Android has its own C library (Bionic) which does not fully support POSIX as of Android O: https://stackoverflow.com/questions/27604455/is-android-posix-compatible
Bonus level
The Linux Standard Base further extends POSIX.
Use the non-frames indexes, they are much more readable and searchable: http://pubs.opengroup.org/onlinepubs/9699919799/nfindex.html
Get a full zipped version of the HTML pages for grepping: https://stackoverflow.com/questions/453993/is-there-a-listing-of-the-posix-api-functions/45832939#45832939
Most important things POSIX 7 defines
C API
Greatly extends ANSI C with things like:
- more file operations:
mkdir
,dirname
,symlink
,readlink
,link
(hardlinks),poll
,sync
- process and threads:
fork
,execl
,pipe
, semaphorssem_*
, shared memory (shm_*
),kill
, scheduling parameters (nice
,sched_
),sleep
- networking
- regular expressions
- advanced memory management:
mmap
,mlock
,mprotect
,madvise
Those APIs also determine underlying system concepts on which they depend, e.g.
fork
requires a concept of a process.Many Linux system calls exist to implement a specific POSIX C API function and make Linux compliant, e.g.
sys_write
,sys_read
, ...Major Linux desktop implementation: glibc, which in many cases just provides a shallow wrapper to system calls.
- more file operations:
CLI utilities
E.g.:
cd
,ls
,echo
, ...Many utilities are direct shell front ends for a corresponding C API function, e.g.
mkdir
.Major Linux desktop implementation: GNU Coreutils for the small ones, separate GNU projects for the big ones:
sed
,grep
,awk
, ... Some CLI utilities are implemented by Bash as built-ins.Shell language
E.g.,
a=b; echo "$a"
Major Linux desktop implementation: GNU Bash.
Environment variables
E.g.:
HOME
,PATH
.Program exit status
ANSI C says
0
orEXIT_SUCCESS
for success,EXIT_FAILURE
for failure, and leaves the rest implementation defined.POSIX adds:
126
: command found but not executable.127
: command not found.> 128
: terminated by a signal.But POSIX does not seem to specify the
128 + SIGNAL_ID
rule used by Bash: Default exit code when process is terminated?
Regular expression
There are two types: BRE (Basic) and ERE (Extended). Basic is deprecated and only kept to not break APIs.
Those are implemented by C API functions, and used throughout CLI utilities, e.g.
grep
accepts BREs by default, and EREs with-E
.E.g.:
echo 'a.1' | grep -E 'a.[[:digit:]]'
Major Linux implementation: glibc implements the functions under regex.h which programs like
grep
can use as backend.Directory struture
E.g.:
/dev/null
,/tmp
The Linux FHS greatly extends POSIX.
Filenames
/
is the path separatorNUL
cannot be used.
iscwd
,..
parent- portable filenames
- use at most max 14 chars and 256 for the full path
- can only contain:
a-zA-Z0-9._-
See also: https://stackoverflow.com/questions/18550253/what-is-posix-compliance-for-filesystem
Command line utility API conventions
Not mandatory, used by POSIX, but almost nowhere else, notably not in GNU. But true, it is too restrictive, e.g. single letter flags only (e.g.
-a
), no double hyphen long versions (e.g.--all
).A few widely used conventions:
-
means stdin where a file is expected--
terminates flags, e.g.ls -- -l
to list a directory named-l
See also: https://stackoverflow.com/questions/8957222/are-there-standards-for-linux-command-line-switches-and-arguments
Who conforms to POSIX?
Many systems follow POSIX closely, but few are actually certified by the Open Group which maintains the standard. Notable certified ones include:
- OS X (Apple) X stands for both 10 and UNIX. Was the first Apple POSIX system, released circa 2001. See also: https://stackoverflow.com/questions/5785516/is-osx-a-posix-os
- AIX (IBM)
- HP-UX (HP)
- Solaris (Oracle)
Most Linux distros are very compliant, but not certified because they don't want to pay the compliance check. Inspur's K-UX and Huawei's EulerOS are two certified examples.
The official list of certified systems be found at: https://www.opengroup.org/openbrand/register/ and also at the wiki page.
Windows
Windows implemented POSIX on some of its professional distributions.
Since it was an optional feature, programmers could not rely on it for most end user applications.
Support was deprecated in Windows 8:
- https://stackoverflow.com/questions/4746043/where-does-microsoft-windows-7-posix-implementation-currently-stand
- https://superuser.com/questions/495360/does-windows-8-still-implement-posix
- Feature request: https://windows.uservoice.com/forums/265757-windows-feature-suggestions/suggestions/6573649-full-posix-support
In 2016 a new official Linux-like API called "Windows Subsystem for Linux" was announced. It includes Linux system calls, ELF running, parts of the /proc
filesystem, Bash, GCC, (TODO likely glibc?), apt-get
and more: https://channel9.msdn.com/Events/Build/2016/P488 so I believe that it will allow Windows to run much, if not all, of POSIX. However, it is focused on developers / deployment instead of end users. In particular, there were no plans to allow access to the Windows GUI.
Historical overview of the official Microsoft POSIX compatibility: http://brianreiter.org/2010/08/24/the-sad-history-of-the-microsoft-posix-subsystem/
Cygwin is a well known GPL third-party project for that "provides substantial POSIX API functionality" for Windows, but requires that you "rebuild your application from source if you want it to run on Windows". MSYS2 is a related project that seems to add more functionality on top of Cygwin.
Android
Android has its own C library (Bionic) which does not fully support POSIX as of Android O: https://stackoverflow.com/questions/27604455/is-android-posix-compatible
Bonus level
The Linux Standard Base further extends POSIX.
Use the non-frames indexes, they are much more readable and searchable: http://pubs.opengroup.org/onlinepubs/9699919799/nfindex.html
Get a full zipped version of the HTML pages for grepping: https://stackoverflow.com/questions/453993/is-there-a-listing-of-the-posix-api-functions/45832939#45832939
edited 8 mins ago
answered Aug 7 '15 at 22:12
Ciro Santilli æ°çÂÂæ¹é ä¸Âå¿ å ÂÃ¥ÂÂäºÂ件 æ³Âè½®åÂÂ
4,52123938
4,52123938
5
Yes a good answer as well !!!
â Jasser
Aug 29 '15 at 13:04
3
This list deserves more upvotes.
â Junaga
Oct 29 '16 at 17:56
The question was about POSIX and SUS, but this answer doesn't mention SUS at all...
â Kidburla
Oct 6 '17 at 12:16
1
@Kidburla a great opportunity to add your own answer and get some rep :-) (or edit it into mine and give me rep hehe)
â Ciro Santilli æ°çÂÂæ¹é ä¸Âå¿ å ÂÃ¥ÂÂäºÂ件 æ³Âè½®åÂÂ
Oct 6 '17 at 12:27
1
There are actually Linux distros that are Unix-certified like K-UX and Huawei EulerOS. They appear in the POSIX certified list and also on Opengroup's website
â phuclv
3 hours ago
 |Â
show 1 more comment
5
Yes a good answer as well !!!
â Jasser
Aug 29 '15 at 13:04
3
This list deserves more upvotes.
â Junaga
Oct 29 '16 at 17:56
The question was about POSIX and SUS, but this answer doesn't mention SUS at all...
â Kidburla
Oct 6 '17 at 12:16
1
@Kidburla a great opportunity to add your own answer and get some rep :-) (or edit it into mine and give me rep hehe)
â Ciro Santilli æ°çÂÂæ¹é ä¸Âå¿ å ÂÃ¥ÂÂäºÂ件 æ³Âè½®åÂÂ
Oct 6 '17 at 12:27
1
There are actually Linux distros that are Unix-certified like K-UX and Huawei EulerOS. They appear in the POSIX certified list and also on Opengroup's website
â phuclv
3 hours ago
5
5
Yes a good answer as well !!!
â Jasser
Aug 29 '15 at 13:04
Yes a good answer as well !!!
â Jasser
Aug 29 '15 at 13:04
3
3
This list deserves more upvotes.
â Junaga
Oct 29 '16 at 17:56
This list deserves more upvotes.
â Junaga
Oct 29 '16 at 17:56
The question was about POSIX and SUS, but this answer doesn't mention SUS at all...
â Kidburla
Oct 6 '17 at 12:16
The question was about POSIX and SUS, but this answer doesn't mention SUS at all...
â Kidburla
Oct 6 '17 at 12:16
1
1
@Kidburla a great opportunity to add your own answer and get some rep :-) (or edit it into mine and give me rep hehe)
â Ciro Santilli æ°çÂÂæ¹é ä¸Âå¿ å ÂÃ¥ÂÂäºÂ件 æ³Âè½®åÂÂ
Oct 6 '17 at 12:27
@Kidburla a great opportunity to add your own answer and get some rep :-) (or edit it into mine and give me rep hehe)
â Ciro Santilli æ°çÂÂæ¹é ä¸Âå¿ å ÂÃ¥ÂÂäºÂ件 æ³Âè½®åÂÂ
Oct 6 '17 at 12:27
1
1
There are actually Linux distros that are Unix-certified like K-UX and Huawei EulerOS. They appear in the POSIX certified list and also on Opengroup's website
â phuclv
3 hours ago
There are actually Linux distros that are Unix-certified like K-UX and Huawei EulerOS. They appear in the POSIX certified list and also on Opengroup's website
â phuclv
3 hours ago
 |Â
show 1 more comment
up vote
15
down vote
POSIX is the Portable Operating System standard. It describes certain utilities, APIs, and services a compliant operating system must provide to software (for example sockets, file I/O and threading) along with conventions on how these should be called from a program.
The idea is that a program written for one POSIX-Compliant OS would be easier to port to another POSIX-compliant OS than porting between non-POSIX-compliant OSes. This is why it is much easier to port an application from, say, FreeBSD to Linux than it is to port it from FreeBSD to Windows (though Windows ostensibly supports a subset of POSIX.)
add a comment |Â
up vote
15
down vote
POSIX is the Portable Operating System standard. It describes certain utilities, APIs, and services a compliant operating system must provide to software (for example sockets, file I/O and threading) along with conventions on how these should be called from a program.
The idea is that a program written for one POSIX-Compliant OS would be easier to port to another POSIX-compliant OS than porting between non-POSIX-compliant OSes. This is why it is much easier to port an application from, say, FreeBSD to Linux than it is to port it from FreeBSD to Windows (though Windows ostensibly supports a subset of POSIX.)
add a comment |Â
up vote
15
down vote
up vote
15
down vote
POSIX is the Portable Operating System standard. It describes certain utilities, APIs, and services a compliant operating system must provide to software (for example sockets, file I/O and threading) along with conventions on how these should be called from a program.
The idea is that a program written for one POSIX-Compliant OS would be easier to port to another POSIX-compliant OS than porting between non-POSIX-compliant OSes. This is why it is much easier to port an application from, say, FreeBSD to Linux than it is to port it from FreeBSD to Windows (though Windows ostensibly supports a subset of POSIX.)
POSIX is the Portable Operating System standard. It describes certain utilities, APIs, and services a compliant operating system must provide to software (for example sockets, file I/O and threading) along with conventions on how these should be called from a program.
The idea is that a program written for one POSIX-Compliant OS would be easier to port to another POSIX-compliant OS than porting between non-POSIX-compliant OSes. This is why it is much easier to port an application from, say, FreeBSD to Linux than it is to port it from FreeBSD to Windows (though Windows ostensibly supports a subset of POSIX.)
answered Apr 25 '11 at 18:03
Andrew Lambert
1,79511116
1,79511116
add a comment |Â
add a comment |Â
up vote
14
down vote
POSIX is a subset of UNIX which is intended to cover various Unix-like environments for other operating systems; this originally included environments such as Eunice for VMS, Windows NT's POSIX personality, and Apollo Domain/OS. You can think of it as a standard portability API for the subset of operating system services whose behavior is in common between Unix and non-Unix. See http://standards.ieee.org/develop/wg/POSIX.html for more information.
I've read more about it now, and it certainly seems that Uinx was the chicken and POSIX was the egg.. but I do wonder if UNIX still rules the roost.. ie..Does POSIX have a life of its own now, and UNIX must comply to POSIX? ... btw. it seems the name POSIX was coinded by Richard Stallman ....
â Peter.O
Apr 25 '11 at 19:11
@fred.bear: Short answer: UNIX (the trade mark) must conform to POSIX; Unix (the product) was the main basis for POSIX; unices (the family of OSes) mostly conform but have more in common. See Is Linux a Unix? and Is Mac OS X, UNIX? for related discussions.
â Gilles
Apr 25 '11 at 20:34
@fred-bear Many people argue that the POSIX standard is nowadays guided by the Linux kernel development community, which (if true) IMHO is not a good thing...
â sakisk
Apr 26 '11 at 14:05
1
@faif I've never heard this and find it unlikely, can you post a reference?
â penguin359
Apr 28 '11 at 4:06
2
@Gilles The Open Group, owner of the UNIX® trademark is also in charge of the UNIX® certification and specification which they call Single UNIX Specification or SUS. POSIX is developed by the IEEE who are not in charge of UNIX®. Since 2001, they have been developed largely in sync, but it technically SUS which is now at version 4 that defined UNIX®.
â penguin359
Apr 28 '11 at 4:11
 |Â
show 1 more comment
up vote
14
down vote
POSIX is a subset of UNIX which is intended to cover various Unix-like environments for other operating systems; this originally included environments such as Eunice for VMS, Windows NT's POSIX personality, and Apollo Domain/OS. You can think of it as a standard portability API for the subset of operating system services whose behavior is in common between Unix and non-Unix. See http://standards.ieee.org/develop/wg/POSIX.html for more information.
I've read more about it now, and it certainly seems that Uinx was the chicken and POSIX was the egg.. but I do wonder if UNIX still rules the roost.. ie..Does POSIX have a life of its own now, and UNIX must comply to POSIX? ... btw. it seems the name POSIX was coinded by Richard Stallman ....
â Peter.O
Apr 25 '11 at 19:11
@fred.bear: Short answer: UNIX (the trade mark) must conform to POSIX; Unix (the product) was the main basis for POSIX; unices (the family of OSes) mostly conform but have more in common. See Is Linux a Unix? and Is Mac OS X, UNIX? for related discussions.
â Gilles
Apr 25 '11 at 20:34
@fred-bear Many people argue that the POSIX standard is nowadays guided by the Linux kernel development community, which (if true) IMHO is not a good thing...
â sakisk
Apr 26 '11 at 14:05
1
@faif I've never heard this and find it unlikely, can you post a reference?
â penguin359
Apr 28 '11 at 4:06
2
@Gilles The Open Group, owner of the UNIX® trademark is also in charge of the UNIX® certification and specification which they call Single UNIX Specification or SUS. POSIX is developed by the IEEE who are not in charge of UNIX®. Since 2001, they have been developed largely in sync, but it technically SUS which is now at version 4 that defined UNIX®.
â penguin359
Apr 28 '11 at 4:11
 |Â
show 1 more comment
up vote
14
down vote
up vote
14
down vote
POSIX is a subset of UNIX which is intended to cover various Unix-like environments for other operating systems; this originally included environments such as Eunice for VMS, Windows NT's POSIX personality, and Apollo Domain/OS. You can think of it as a standard portability API for the subset of operating system services whose behavior is in common between Unix and non-Unix. See http://standards.ieee.org/develop/wg/POSIX.html for more information.
POSIX is a subset of UNIX which is intended to cover various Unix-like environments for other operating systems; this originally included environments such as Eunice for VMS, Windows NT's POSIX personality, and Apollo Domain/OS. You can think of it as a standard portability API for the subset of operating system services whose behavior is in common between Unix and non-Unix. See http://standards.ieee.org/develop/wg/POSIX.html for more information.
answered Apr 25 '11 at 17:59
geekosaur
22k25853
22k25853
I've read more about it now, and it certainly seems that Uinx was the chicken and POSIX was the egg.. but I do wonder if UNIX still rules the roost.. ie..Does POSIX have a life of its own now, and UNIX must comply to POSIX? ... btw. it seems the name POSIX was coinded by Richard Stallman ....
â Peter.O
Apr 25 '11 at 19:11
@fred.bear: Short answer: UNIX (the trade mark) must conform to POSIX; Unix (the product) was the main basis for POSIX; unices (the family of OSes) mostly conform but have more in common. See Is Linux a Unix? and Is Mac OS X, UNIX? for related discussions.
â Gilles
Apr 25 '11 at 20:34
@fred-bear Many people argue that the POSIX standard is nowadays guided by the Linux kernel development community, which (if true) IMHO is not a good thing...
â sakisk
Apr 26 '11 at 14:05
1
@faif I've never heard this and find it unlikely, can you post a reference?
â penguin359
Apr 28 '11 at 4:06
2
@Gilles The Open Group, owner of the UNIX® trademark is also in charge of the UNIX® certification and specification which they call Single UNIX Specification or SUS. POSIX is developed by the IEEE who are not in charge of UNIX®. Since 2001, they have been developed largely in sync, but it technically SUS which is now at version 4 that defined UNIX®.
â penguin359
Apr 28 '11 at 4:11
 |Â
show 1 more comment
I've read more about it now, and it certainly seems that Uinx was the chicken and POSIX was the egg.. but I do wonder if UNIX still rules the roost.. ie..Does POSIX have a life of its own now, and UNIX must comply to POSIX? ... btw. it seems the name POSIX was coinded by Richard Stallman ....
â Peter.O
Apr 25 '11 at 19:11
@fred.bear: Short answer: UNIX (the trade mark) must conform to POSIX; Unix (the product) was the main basis for POSIX; unices (the family of OSes) mostly conform but have more in common. See Is Linux a Unix? and Is Mac OS X, UNIX? for related discussions.
â Gilles
Apr 25 '11 at 20:34
@fred-bear Many people argue that the POSIX standard is nowadays guided by the Linux kernel development community, which (if true) IMHO is not a good thing...
â sakisk
Apr 26 '11 at 14:05
1
@faif I've never heard this and find it unlikely, can you post a reference?
â penguin359
Apr 28 '11 at 4:06
2
@Gilles The Open Group, owner of the UNIX® trademark is also in charge of the UNIX® certification and specification which they call Single UNIX Specification or SUS. POSIX is developed by the IEEE who are not in charge of UNIX®. Since 2001, they have been developed largely in sync, but it technically SUS which is now at version 4 that defined UNIX®.
â penguin359
Apr 28 '11 at 4:11
I've read more about it now, and it certainly seems that Uinx was the chicken and POSIX was the egg.. but I do wonder if UNIX still rules the roost.. ie..Does POSIX have a life of its own now, and UNIX must comply to POSIX? ... btw. it seems the name POSIX was coinded by Richard Stallman ....
â Peter.O
Apr 25 '11 at 19:11
I've read more about it now, and it certainly seems that Uinx was the chicken and POSIX was the egg.. but I do wonder if UNIX still rules the roost.. ie..Does POSIX have a life of its own now, and UNIX must comply to POSIX? ... btw. it seems the name POSIX was coinded by Richard Stallman ....
â Peter.O
Apr 25 '11 at 19:11
@fred.bear: Short answer: UNIX (the trade mark) must conform to POSIX; Unix (the product) was the main basis for POSIX; unices (the family of OSes) mostly conform but have more in common. See Is Linux a Unix? and Is Mac OS X, UNIX? for related discussions.
â Gilles
Apr 25 '11 at 20:34
@fred.bear: Short answer: UNIX (the trade mark) must conform to POSIX; Unix (the product) was the main basis for POSIX; unices (the family of OSes) mostly conform but have more in common. See Is Linux a Unix? and Is Mac OS X, UNIX? for related discussions.
â Gilles
Apr 25 '11 at 20:34
@fred-bear Many people argue that the POSIX standard is nowadays guided by the Linux kernel development community, which (if true) IMHO is not a good thing...
â sakisk
Apr 26 '11 at 14:05
@fred-bear Many people argue that the POSIX standard is nowadays guided by the Linux kernel development community, which (if true) IMHO is not a good thing...
â sakisk
Apr 26 '11 at 14:05
1
1
@faif I've never heard this and find it unlikely, can you post a reference?
â penguin359
Apr 28 '11 at 4:06
@faif I've never heard this and find it unlikely, can you post a reference?
â penguin359
Apr 28 '11 at 4:06
2
2
@Gilles The Open Group, owner of the UNIX® trademark is also in charge of the UNIX® certification and specification which they call Single UNIX Specification or SUS. POSIX is developed by the IEEE who are not in charge of UNIX®. Since 2001, they have been developed largely in sync, but it technically SUS which is now at version 4 that defined UNIX®.
â penguin359
Apr 28 '11 at 4:11
@Gilles The Open Group, owner of the UNIX® trademark is also in charge of the UNIX® certification and specification which they call Single UNIX Specification or SUS. POSIX is developed by the IEEE who are not in charge of UNIX®. Since 2001, they have been developed largely in sync, but it technically SUS which is now at version 4 that defined UNIX®.
â penguin359
Apr 28 '11 at 4:11
 |Â
show 1 more comment
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2
SUS is the official definition of UNIX since The Open Group, not the IEEE, owns the UNIX trademark. Se my answer below.
â penguin359
Apr 25 '11 at 21:32
unix.stackexchange.com/tags/posix/info
â Premraj
May 27 '15 at 4:22
stackoverflow.com/questions/1780599/â¦
â Ciro Santilli æ°çÂÂæ¹é ä¸Âå¿ å ÂÃ¥ÂÂäºÂ件 æ³Âè½®åÂÂ
Aug 7 '15 at 22:19