I am a noob in system programming, I am posting this while i m studying my OS course. I am working on Ubuntu 12.04 with linux v3.2.0-29-generic-pae and I m running ubuntu using Oracle VM Virtual box windows 7 hosted. Now I m in "Adding a System call to the Linux Kernel" concept. it is said that, list of pointers to system call handlers is typically stored in the file /usr/src/linux-2.x/arch/i386/kernel/entry.S. But I could n't find i386 folder in linux-header files and entry.S file. where do can I find this entry.S file. Could any one please help me...!!!