diff --git a/integration/execin_test.go b/integration/execin_test.go
new file mode 100644
index 00000000..cf8f548e
--- /dev/null
+++ b/integration/execin_test.go
@@ -0,0 +1,83 @@
+package integration
+
+import (
+	"os"
+	"os/exec"
+	"strings"
+	"sync"
+	"testing"
+
+	"github.com/docker/libcontainer"
+	"github.com/docker/libcontainer/namespaces"
+)
+
+func TestExecIn(t *testing.T) {
+	if testing.Short() {
+		return
+	}
+
+	rootfs, err := newRootFs()
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer remove(rootfs)
+
+	config := newTemplateConfig(rootfs)
+	if err := writeConfig(config); err != nil {
+		t.Fatalf("failed to write config %s", err)
+	}
+
+	// start the container
+	containerErr := make(chan error, 1)
+	containerCmd := &exec.Cmd{}
+	var statePath string
+	createCmd := func(container *libcontainer.Config, console, dataPath, init string,
+		pipe *os.File, args []string) *exec.Cmd {
+		containerCmd = namespaces.DefaultCreateCommand(container, console, dataPath, init, pipe, args)
+		statePath = dataPath
+		return containerCmd
+	}
+	var containerStart sync.WaitGroup
+	containerStart.Add(1)
+	go func() {
+		buffers := newStdBuffers()
+		_, err := namespaces.Exec(config,
+			buffers.Stdin, buffers.Stdout, buffers.Stderr,
+			"", config.RootFs, []string{"sleep", "10"},
+			createCmd, containerStart.Done)
+		containerErr <- err
+	}()
+	containerStart.Wait()
+
+	defer func() {
+		// kill the container
+		if containerCmd.Process != nil {
+			containerCmd.Process.Kill()
+		}
+		if err := <-containerErr; err != nil {
+			t.Fatal(err)
+		}
+	}()
+
+	// start the exec process
+	state, err := libcontainer.GetState(statePath)
+	if err != nil {
+		t.Fatalf("failed to get state %s", err)
+	}
+	buffers := newStdBuffers()
+	execErr := make(chan error, 1)
+	go func() {
+		_, err := namespaces.ExecIn(config, state, []string{"ps"},
+			os.Args[0], "exec", buffers.Stdin, buffers.Stdout, buffers.Stderr,
+			"", nil)
+		execErr <- err
+	}()
+	if err := <-execErr; err != nil {
+		t.Fatalf("exec finished with error %s", err)
+	}
+
+	out := buffers.Stdout.String()
+	if !strings.Contains(out, "sleep 10") || !strings.Contains(out, "ps") {
+		t.Fatalf("unexpected running process, output %q", out)
+	}
+}
diff --git a/integration/init_test.go b/integration/init_test.go
index 9954c0f8..3106a5fb 100644
--- a/integration/init_test.go
+++ b/integration/init_test.go
@@ -1,33 +1,76 @@
 package integration
 
 import (
+	"encoding/json"
 	"log"
 	"os"
 	"runtime"
 
+	"github.com/docker/libcontainer"
 	"github.com/docker/libcontainer/namespaces"
+	_ "github.com/docker/libcontainer/namespaces/nsenter"
 )
 
 // init runs the libcontainer initialization code because of the busybox style needs
 // to work around the go runtime and the issues with forking
 func init() {
-	if len(os.Args) < 2 || os.Args[1] != "init" {
+	if len(os.Args) < 2 {
 		return
 	}
-	runtime.LockOSThread()
+	// handle init
+	if len(os.Args) >= 2 && os.Args[1] == "init" {
+		runtime.LockOSThread()
 
-	container, err := loadConfig()
-	if err != nil {
-		log.Fatal(err)
+		container, err := loadConfig()
+		if err != nil {
+			log.Fatal(err)
+		}
+
+		rootfs, err := os.Getwd()
+		if err != nil {
+			log.Fatal(err)
+		}
+
+		if err := namespaces.Init(container, rootfs, "", os.NewFile(3, "pipe"), os.Args[3:]); err != nil {
+			log.Fatalf("unable to initialize for container: %s", err)
+		}
+		os.Exit(1)
 	}
 
-	rootfs, err := os.Getwd()
-	if err != nil {
-		log.Fatal(err)
-	}
+	// handle execin
+	if len(os.Args) >= 2 && os.Args[0] == "nsenter-exec" {
+		runtime.LockOSThread()
 
-	if err := namespaces.Init(container, rootfs, "", os.NewFile(3, "pipe"), os.Args[3:]); err != nil {
-		log.Fatalf("unable to initialize for container: %s", err)
+		// User args are passed after '--' in the command line.
+		userArgs := findUserArgs()
+
+		config, err := loadConfigFromFd()
+		if err != nil {
+			log.Fatalf("docker-exec: unable to receive config from sync pipe: %s", err)
+		}
+
+		if err := namespaces.FinalizeSetns(config, userArgs); err != nil {
+			log.Fatalf("docker-exec: failed to exec: %s", err)
+		}
+		os.Exit(1)
 	}
-	os.Exit(1)
+}
+
+func findUserArgs() []string {
+	for i, a := range os.Args {
+		if a == "--" {
+			return os.Args[i+1:]
+		}
+	}
+	return []string{}
+}
+
+// loadConfigFromFd loads a container's config from the sync pipe that is provided by
+// fd 3 when running a process
+func loadConfigFromFd() (*libcontainer.Config, error) {
+	var config *libcontainer.Config
+	if err := json.NewDecoder(os.NewFile(3, "child")).Decode(&config); err != nil {
+		return nil, err
+	}
+	return config, nil
 }