I can't find 'fdinfo' in the /proc file system

I've read about the great uses of /proc/<pid>/fd and sp开发者_StackOverflowecifically fdinfo in this article. But I can't find it on my Linux system: Red Hat Enterprise Linux ES release 4, kernel 2.6.9.

Where can I find the missing fdinfo ?

The article clearly says, "All of these tricks should work on a recent Linux kernel, though some will fail on older systems like RHEL version 4." As you can see, fdinfo is not available on your system.

/proc/<pid>/fd is present in Linux since 2.6.22 kernel version. You may want to upgrade your kernel.