On many UNIX systems (tested on Debian GNU/Linux), SUID is disabled for scripts and works only for binaries. If you need to setuid, you must use a wrapper binary that runs setuid() php script. Here's an example:
$ nano suexec.cpp
#include <stdlib>
using namespace std;
int main()
{
system("php /home/php/php_user.php");
return 0;
}
$ g++ -o suexec suexec.cpp
$ sudo chown root:root suexec
$ sudo chmod 4755 root
Then we create short PHP script to set process uid (you should already know how to do this). Don't even try to experiment with auto_prepend_file in php.ini, it doesn't work as expected.
