docs: Add more information about the tool and some instructions

README.md

@@ -2,4 +2,19 @@
 
 > docker but simpler
 
-Usage: `miniroot -root "/opt/something" -workdir "/usr/src/app" -init "/usr/loacal/bin/npm start"`
+In contrast to Docker, miniroot **does not**:
+- have a concept of images and layers
+- isolate networks
+- handle volumes or bind mounts
+- have a central daemon
+
+It's just a simple tool that utilises namespaces to run applications in a semi-isolated environment.
+
+### Usage
+
+- get rootfs (you can use `docker export container_name > export.tar` for that)
+- extract it somewhere
+- run miniroot; example:
+```
+miniroot -root "/opt/something" -workdir "/usr/src/app" -init "/usr/local/bin/npm start"
+```

main.go

@@ -5,6 +5,7 @@ import (
 	"fmt"
 	"os"
 	"os/exec"
+	"os/signal"
 	"strings"
 	"syscall"
 )
@@ -12,6 +13,7 @@ import (
 var rootPath = flag.String("root", "", "path to root directory")
 var initCmd = flag.String("init", "/sbin/init", "init command")
 var workdir = flag.String("workdir", "/", "work directory")
+var pidns = flag.Bool("pidns", false, "create pid namespace")
 
 func main() {
 	flag.Parse()
@@ -26,7 +28,7 @@ func main() {
 	cmd.Dir = *workdir
 	cmd.SysProcAttr = &syscall.SysProcAttr{
 		Chroot:       *rootPath,
-		Cloneflags:   syscall.CLONE_NEWUSER|syscall.CLONE_NEWPID,
+		Cloneflags:   syscall.CLONE_NEWUSER,
 		UidMappings: []syscall.SysProcIDMap{
 			{ContainerID: 0, HostID: os.Getuid(), Size: 1},
 		},
@@ -34,6 +36,9 @@ func main() {
 			{ContainerID: 0, HostID: os.Getgid(), Size: 1},
 		},
 	}
+	if *pidns {
+		cmd.SysProcAttr.Cloneflags |= syscall.CLONE_NEWPID
+	}
 	cmd.Stdin = os.Stdin
 	cmd.Stdout = os.Stdout
 	cmd.Stderr = os.Stderr
@@ -42,6 +47,15 @@ func main() {
 		fmt.Printf("failed to start: %s\n", err)
 	}
 
+	sigs := make(chan os.Signal, 1)
+	go func() {
+		for {
+			_ = <-sigs
+			cmd.Process.Signal(syscall.SIGTERM)
+		}
+	}()
+	signal.Notify(sigs, syscall.SIGINT, syscall.SIGTERM)
+
 	err = cmd.Wait()
 	if err != nil {
 		fmt.Printf("process exited with error: %s\n", err)