Re: [PATCH v5 2/4] man/man5/tunables.conf: Document system-wide tunables config

Alejandro Colomar <[email protected]> Fri, 7 Aug 2026 02:06:57 +0200

Newsgroups	org.kernel.vger.linux-man
Message-ID	<anUbLZzOLY2qM6iP@devuan>

Hi DJ,

> Date: 2026-08-06 18:15:15-0400
> From: DJ Delorie <[email protected]>
>
> Alejandro Colomar <[email protected]> writes:
> > You forgot to sign.
> 
> I will never remember that... :-P
> 
> >> +The resulting data is read when a new process is created by
> >> +.IR ld.so .
> >
> > Sorry for noticing this in v4; I forgot about it.  I see this unresolved
> > issue from earlier versions remains.
> 
> A program is a file on disk.  A process is a running memory image.

Yup.  fork(3) creates a process (produces a new PID).  execve(2)
replaces the image of the current process with a program read from disk
(or in short, executes a program in the current process).

> 
> Neither fork() nor exec() cause the tunables to be loaded, the process
> itself has to do that.  For dynamic ELF programs/processes built with
> glibc, ld.so does it before it passes control to the ELF image.  There
> are other types of programs/processes that do not use ld.so and thus do
> not read the tunables cache (which is called "ld.so.cache" for a reason ;-)

Hmmmmm, let's say you call execve(2) several times without any fork(2)s.
Assuming a that the program paths that you pass to execve(2) are all
dynamic ELF programs built with glibc, I guess for every time you call
execve(2), ld.so(8) will be run, and the tunables stored in ld.so.cache
will be used.  Is this correct?

	#include <unistd.h>
	int
	main(int, char *argv[])
	{
		sleep(1);
		execve("proc/self/exe", argv, NULL);
	}

Let's also say you fork(2) several times, without any execve(2) calls.
I suppose that won't trigger any of this, right?

	#include <unistd.h>
	int
	main(void)
	{
		for (int i = 0; i < 10; i++) {
			sleep(1);
			fork();
		}
	}

From my understanding, only the first program will trigger this more
than once, right?

If so, I'd use the same wording that execve(2) uses:

	execve() executes the program referred to by path.

That is, execve(2) executes programs, and ld.so.cache is read when
a program is executed (in the current process).

> 
> I don't know how to say this clearly with fewer words...
> 
> >> +The syntax allows lines to start with the keyword
> >> +.I include
> >
> > s/I/B/  (since it's a literal, not a variable)
> 
> Fixed.
> 

Cheers,
Alex

-- 
<https://www.alejandro-colomar.es>

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