0.8 The Go labs: the OS from inside a program

The commands in this guide show the operating system from the outside: ps, strace, free, docker stats. Part 20 shows it from the inside, with Go programs that make the kernel's behaviour visible: how many OS threads a goroutine really costs, what happens when a container's memory limit meets Go's garbage collector, why PID 1 must reap zombies, how to write a file that survives a power cut, and a working container runtime in about 150 lines.

Every lab was run on Linux (in Docker on an Apple-silicon Mac) while writing this guide, and the outputs shown are real. Most labs are Linux-only (//go:build linux). On a Mac, cross-compile and run them in a container:

mkdir -p ~/oslabs && cd ~/oslabs && go mod init oslabs
mkdir threads    # save the lab as threads/main.go
CGO_ENABLED=0 GOOS=linux GOARCH=arm64 go build -o bin/threads ./threads   # GOARCH=amd64 on Intel
docker run --rm -v "$PWD/bin":/b debian:bookworm /b/threads