that old GNU/Linux argument

Les Mikesell lesmikesell at
Fri Jul 25 13:35:45 UTC 2008

Alexandre Oliva wrote:

>> Recall, the name of this line that joins the kernel (Linux) and
>> application space (think HelloWorld, X-windows and more) is the "question
>> I am asking".  Of interest the "omissions" in the list of system calls 
>> commonly show up as hardware specific ioctl() side doors.
>> Perhaps the answer is as simple as "glibc".  I suspect that Posix is
>> slightly more apropos.
> The interface is mostly Posix, although there are GNU extensions to
> it.

I've forgotten the timing, but I don't think Posix had a full/useful 
spec until well after Linux.  AT&T's SVID spec (published for sysvr4 
around 1989) would have been about right.  Posix wasn't very complete 
until 1995 or so.

> The implementation of the interface (with or without extensions)
> is provided by GNU libc.  GNU libc borrows little more than system
> call numbers from Linux header files.  At times, even the headers with
> this information had to be maintained separately from Linux, because
> Linux developers didn't want these headers to be ever included by
> userland.
> That's why I say Linux offers only an ABI to userland; there's no
> actual API to use from userland.  Whatever APIs there are, they're
> provided by GNU libc.

Doesn't that make glibc an extension of Linux instead of the other way 
around?  Will that same version run anywhere else?

   Les Mikesell
     lesmikesell at

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