Add first draft

.gitignore

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+container-root
+.idea

README.md

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+# containers-from-scratch
+
+This repository contains my re-implementation of 
+[Containers From Scratch • Liz Rice • GOTO 2018](https://www.youtube.com/watch?v=8fi7uSYlOdc).
+
+## Setup
+
+One time setup:
+
+```shell
+docker run --rm -it ubuntu bash
+
+# Copy contents of the container:
+docker cp 9405abfa4a78:/ container-root
+```
+
+Then, just run the Go program as *root*:
+
+```shell
+sudo go run main.go run bash
+```

go.mod

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+module containers-from-scratch
+
+go 1.21.5

main.go

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+package main
+
+import (
+	"fmt"
+	"os"
+	"os/exec"
+	"strconv"
+	"syscall"
+	"time"
+)
+
+// docker 		run <container-name>	<command> <args>
+// go main.go	run						<command> <args>
+
+func main() {
+	if len(os.Args) < 3 {
+		panic("found too few arguments for the program.")
+	}
+	switch os.Args[1] {
+	case "run":
+		executeRun()
+	case "child":
+		executeChild()
+	default:
+		panic(fmt.Sprintf("found an unsupported command: %s", os.Args[0]))
+	}
+}
+
+func executeRun() {
+	fmt.Printf("starting: 'run' in PID: %d\n", os.Getpid())
+
+	cmd := exec.Command("/proc/self/exe", append([]string{"child"}, os.Args[2:]...)...)
+	cmd.Stdin = os.Stdin
+	cmd.Stdout = os.Stdout
+	cmd.Stderr = os.Stderr
+
+	cmd.SysProcAttr = &syscall.SysProcAttr{
+		Cloneflags:   syscall.CLONE_NEWUTS | syscall.CLONE_NEWPID | syscall.CLONE_NEWNS,
+		Unshareflags: syscall.CLONE_NEWNS,
+	}
+
+	must(cmd.Run())
+}
+
+func executeChild() {
+	fmt.Printf("starting: %s in PID: %d\n", os.Args[2], os.Getpid())
+
+	setupCgroup()
+
+	syscall.Sethostname([]byte("container"))
+	syscall.Chroot("./container-root")
+	os.Chdir("/")
+
+	syscall.Mount("proc", "proc", "proc", 0, "")
+	defer syscall.Unmount("/proc", 0)
+
+	cmd := exec.Command(os.Args[2])
+	cmd.Stdin = os.Stdin
+	cmd.Stdout = os.Stdout
+	cmd.Stderr = os.Stderr
+
+	must(cmd.Run())
+}
+
+func setupCgroup() {
+	cgroupDir := fmt.Sprintf("/sys/fs/cgroup/pids/%d", time.Now().Unix())
+	must(os.Mkdir(cgroupDir, 0755))
+
+	os.WriteFile(fmt.Sprintf("%s/pids.max", cgroupDir), []byte("20"), 0644)
+	os.WriteFile(fmt.Sprintf("%s/notify_on_release", cgroupDir), []byte("1"), 0644)
+	os.WriteFile(fmt.Sprintf("%s/cgroup.procs", cgroupDir), []byte(strconv.Itoa(os.Getpid())), 0644)
+}
+
+func must(err error) {
+	if err != nil {
+		panic(err)
+	}
+}