julz · November 20, 2015 12:39 · Nov 20, 2015
diff --git a/main.go b/main.go
@@ -0,0 +1,57 @@
+package main
+
+import (
+	"fmt"
+	"os"
+	"os/exec"
+	"syscall"
+)
+
+func main() {
+	switch os.Args[1] {
+	case "run":
+		parent()
+	case "child":
+		child()
+	default:
+		panic("wat should I do")
+	}
+}
+
+func parent() {
+	cmd := exec.Command("/proc/self/exe", append([]string{"child"}, os.Args[2:]...)...)
+	cmd.SysProcAttr = &syscall.SysProcAttr{
+		Cloneflags: syscall.CLONE_NEWUTS | syscall.CLONE_NEWPID | syscall.CLONE_NEWNS,
+	}
+	cmd.Stdin = os.Stdin
+	cmd.Stdout = os.Stdout
+	cmd.Stderr = os.Stderr
+
+	if err := cmd.Run(); err != nil {
+		fmt.Println("ERROR", err)
+		os.Exit(1)
+	}
+}
+
+func child() {
+	must(syscall.Mount("rootfs", "rootfs", "", syscall.MS_BIND, ""))
+	must(os.MkdirAll("rootfs/oldrootfs", 0700))
+	must(syscall.PivotRoot("rootfs", "rootfs/oldrootfs"))
+	must(os.Chdir("/"))
+
+	cmd := exec.Command(os.Args[2], os.Args[3:]...)
+	cmd.Stdin = os.Stdin
+	cmd.Stdout = os.Stdout
+	cmd.Stderr = os.Stderr
+
+	if err := cmd.Run(); err != nil {
+		fmt.Println("ERROR", err)
+		os.Exit(1)
+	}
+}
+
+func must(err error) {
+	if err != nil {
+		panic(err)
+	}
+}