Systems Programming

Above the machine but below the framework sits the operating system, and you reach it through syscalls. This branch is about that boundary: how a read() becomes a trap into the kernel, how processes are created with fork/exec, what a file descriptor really is, how mmap maps memory and files, and how signals interrupt your control flow. It's the POSIX layer — the contract between your program and the OS — and it sets up everything you'll build by hand in the OS project.

A syscall is the one place your user-space program is allowed to ask the kernel to do something it can't do itself. Almost all "talking to the system" reduces to that.

Planned notes

• The syscall: crossing the boundary into the kernel
• Processes: fork, exec, and wait
• File descriptors and low-level I/O (open/read/write)
• The process address space and mmap
• Memory-mapping files and anonymous mappings
• Signals and signal handling
• Pipes and inter-process communication
• Sockets: the networking syscalls (intro)
• Threads (pthreads) and the OS view of them
• The POSIX layer and what it standardizes
• errno and error-handling discipline
• macOS/BSD vs Linux syscall differences

Core sources

• Michael Kerrisk — The Linux Programming Interface (TLPI) — the syscall bible. man7.org/tlpi
• Stevens & Rago — Advanced Programming in the UNIX Environment (APUE) — the classic.
• man7.org — Kerrisk's man pages, the authoritative syscall/API reference. man7.org
• Note the macOS/BSD vs Linux differences throughout (different syscall numbers, some APIs absent).

Connects to: Pointers & Memory · Concurrency & Performance · OS from Scratch