Systems Cheatsheet
A quick-reference guide for systems and networking.
Networking Layers
OSI vs TCP/IP, encapsulation, and an interactive zoom that unwraps a single HTTPS request from bits on the wire down to the HTTP payload.
TCP Handshake
The three-way handshake that establishes a reliable byte stream — segments, flags, state transitions, and teardown.
TLS Handshake
Authentication, key exchange, and cipher negotiation — TLS 1.3 flow, certificate verification, and 0-RTT resumption.
Linux Binary Execution
From ./prog to main() — execve, ELF layout, ld.so, the startup path, and exec-time security.
Linux Signals
How an async notification becomes a handler call — generation, pending sets, kernel-exit dispatch, sigaction flags, and async-signal safety.
Linux System Calls
From libc wrapper to SYSCALL to kernel dispatch — the x86-64 ABI, MSR setup, do_syscall_64, the vDSO fast path, and return-path work.
Linux Process States
What R, S, D, Z actually mean — the task_struct state model, why D counts toward load average, zombies, and how to inspect via /proc.