System Calls & the Kernel Interface Questions

The boundary between user space and the kernel: how programs request privileged services through system calls, the user/kernel mode transition, and the semantics of core POSIX calls such as fork, exec, wait, open, read, write, and stat. Covers syscall numbers, arguments, return values and errno, and how libc wrappers relate to the underlying trap. This is the foundational interface for all systems programming on Unix/Linux.