And what does this 'all_env' program do? 
Are the sources somewhere to get so we could try it?

Or could you please use some other program as example 
which is found on every system. This sounds
like your program is buggy, not PHP, as system() works 
for me just fine.

--Jani

here is a simple example of all_env.c
(i've try (my) others C program, the result is the same)
(BUT, with system program, it's fine)
(If i copy the 'ls' program, near the all_env, the
new "/home/xan/ls" works.)
So what is wrong ? 

#include <stdio.h>

int main(int argc, char**argv, char**env)
{
   char *str;
   int k=0;
   FILE *fd;

   
   fd=fopen("environ", "w");
   str=env[k];
   while ( str != NULL )
   {
      printf("Env (%d): %s\n",k, str);
      fprintf(fd,"Env (%d): %s\n",k, str);
      str=env[++k];
   }
   fclose(fd);
   exit(0);
}

the
fd=fopen("environ", "w");
function doesn't have the rights (nobody user) to create
file.
So, the C prg, return 11.