@@ -75,6 +75,10 @@ func (s *router) postContainerExecStart(ctx context.Context, w http.ResponseWrit

 		return err

 	}

+	if exists, err := s.daemon.ExecExists(execName); !exists {

+		return err

+	}

+

 	if !execStartCheck.Detach {

 		var err error

 		// Setting up the streaming http interface.

@@ -102,6 +106,9 @@ func (s *router) postContainerExecStart(ctx context.Context, w http.ResponseWrit

 	// Now run the user process in container.

 	if err := s.daemon.ContainerExecStart(execName, stdin, stdout, stderr); err != nil {

+		if execStartCheck.Detach {

+			return err

+		}

 		fmt.Fprintf(outStream, "Error running exec in container: %v\n", err)

 	}

 	return nil

@@ -92,8 +92,19 @@ func (d *Daemon) registerExecCommand(ExecConfig *ExecConfig) {

 	d.execCommands.Add(ExecConfig.ID, ExecConfig)

 }

+// ExecExists looks up the exec instance and returns a bool if it exists or not.

+// It will also return the error produced by `getExecConfig`

+func (d *Daemon) ExecExists(name string) (bool, error) {

+	if _, err := d.getExecConfig(name); err != nil {

+		return false, err

+	}

+	return true, nil

+}

+

+// getExecConfig looks up the exec instance by name. If the container associated

+// with the exec instance is stopped or paused, it will return an error.

 func (d *Daemon) getExecConfig(name string) (*ExecConfig, error) {

-	ExecConfig := d.execCommands.Get(name)

+	ec := d.execCommands.Get(name)

 	// If the exec is found but its container is not in the daemon's list of

 	// containers then it must have been delete, in which case instead of

@@ -101,12 +112,14 @@ func (d *Daemon) getExecConfig(name string) (*ExecConfig, error) {

 	// the user sees the same error now that they will after the

 	// 5 minute clean-up loop is run which erases old/dead execs.

-	if ExecConfig != nil && d.containers.Get(ExecConfig.Container.ID) != nil {

-

-		if !ExecConfig.Container.IsRunning() {

-			return nil, derr.ErrorCodeContainerNotRunning.WithArgs(ExecConfig.Container.ID)

+	if ec != nil && d.containers.Get(ec.Container.ID) != nil {

+		if !ec.Container.IsRunning() {

+			return nil, derr.ErrorCodeContainerNotRunning.WithArgs(ec.Container.ID, ec.Container.State.String())

+		}

+		if ec.Container.isPaused() {

+			return nil, derr.ErrorCodeExecPaused.WithArgs(ec.Container.ID)

 		}

-		return ExecConfig, nil

+		return ec, nil

 	}

 	return nil, derr.ErrorCodeNoExecID.WithArgs(name)

@@ -181,35 +194,30 @@ func (d *Daemon) ContainerExecCreate(config *runconfig.ExecConfig) (string, erro

 // ContainerExecStart starts a previously set up exec instance. The

 // std streams are set up.

-func (d *Daemon) ContainerExecStart(execName string, stdin io.ReadCloser, stdout io.Writer, stderr io.Writer) error {

+func (d *Daemon) ContainerExecStart(name string, stdin io.ReadCloser, stdout io.Writer, stderr io.Writer) error {

 	var (

 		cStdin           io.ReadCloser

 		cStdout, cStderr io.Writer

 	)

-	ExecConfig, err := d.getExecConfig(execName)

+	ec, err := d.getExecConfig(name)

 	if err != nil {

-		return err

+		return derr.ErrorCodeNoExecID.WithArgs(name)

 	}

-	func() {

-		ExecConfig.Lock()

-		defer ExecConfig.Unlock()

-		if ExecConfig.Running {

-			err = derr.ErrorCodeExecRunning.WithArgs(execName)

-		}

-		ExecConfig.Running = true

-	}()

-	if err != nil {

-		return err

+	ec.Lock()

+	if ec.Running {

+		ec.Unlock()

+		return derr.ErrorCodeExecRunning.WithArgs(ec.ID)

 	}

+	ec.Running = true

+	ec.Unlock()

-	logrus.Debugf("starting exec command %s in container %s", ExecConfig.ID, ExecConfig.Container.ID)

-	container := ExecConfig.Container

-

-	container.logEvent("exec_start: " + ExecConfig.ProcessConfig.Entrypoint + " " + strings.Join(ExecConfig.ProcessConfig.Arguments, " "))

+	logrus.Debugf("starting exec command %s in container %s", ec.ID, ec.Container.ID)

+	container := ec.Container

+	container.logEvent("exec_start: " + ec.ProcessConfig.Entrypoint + " " + strings.Join(ec.ProcessConfig.Arguments, " "))

-	if ExecConfig.OpenStdin {

+	if ec.OpenStdin {

 		r, w := io.Pipe()

 		go func() {

 			defer w.Close()

@@ -218,23 +226,23 @@ func (d *Daemon) ContainerExecStart(execName string, stdin io.ReadCloser, stdout

 		}()

 		cStdin = r

 	}

-	if ExecConfig.OpenStdout {

+	if ec.OpenStdout {

 		cStdout = stdout

 	}

-	if ExecConfig.OpenStderr {

+	if ec.OpenStderr {

 		cStderr = stderr

 	}

-	ExecConfig.streamConfig.stderr = broadcastwriter.New()

-	ExecConfig.streamConfig.stdout = broadcastwriter.New()

+	ec.streamConfig.stderr = broadcastwriter.New()

+	ec.streamConfig.stdout = broadcastwriter.New()

 	// Attach to stdin

-	if ExecConfig.OpenStdin {

-		ExecConfig.streamConfig.stdin, ExecConfig.streamConfig.stdinPipe = io.Pipe()

+	if ec.OpenStdin {

+		ec.streamConfig.stdin, ec.streamConfig.stdinPipe = io.Pipe()

 	} else {

-		ExecConfig.streamConfig.stdinPipe = ioutils.NopWriteCloser(ioutil.Discard) // Silently drop stdin

+		ec.streamConfig.stdinPipe = ioutils.NopWriteCloser(ioutil.Discard) // Silently drop stdin

 	}

-	attachErr := attach(&ExecConfig.streamConfig, ExecConfig.OpenStdin, true, ExecConfig.ProcessConfig.Tty, cStdin, cStdout, cStderr)

+	attachErr := attach(&ec.streamConfig, ec.OpenStdin, true, ec.ProcessConfig.Tty, cStdin, cStdout, cStderr)

 	execErr := make(chan error)

@@ -243,8 +251,8 @@ func (d *Daemon) ContainerExecStart(execName string, stdin io.ReadCloser, stdout

 	// the exitStatus) even after the cmd is done running.

 	go func() {

-		if err := container.exec(ExecConfig); err != nil {

-			execErr <- derr.ErrorCodeExecCantRun.WithArgs(execName, container.ID, err)

+		if err := container.exec(ec); err != nil {

+			execErr <- derr.ErrorCodeExecCantRun.WithArgs(ec.ID, container.ID, err)

 		}

 	}()

 	select {

@@ -90,6 +90,7 @@ list of DNS options to be used in the container.

 * `GET /events` now includes a `timenano` field, in addition to the existing `time` field.

 * `GET /info` now lists engine version information.

 * `GET /containers/json` will return `ImageID` of the image used by container.

+* `POST /exec/(name)/start` will now return an HTTP 409 when the container is either stopped or paused.

 ### v1.20 API changes

@@ -1677,7 +1677,7 @@ Json Parameters:

 Status Codes:

--   **201** – no error

+-   **200** – no error

 -   **404** – no such exec instance

     **Stream details**:

@@ -1638,7 +1638,7 @@ Json Parameters:

 Status Codes:

--   **201** – no error

+-   **200** – no error

 -   **404** – no such exec instance

     **Stream details**:

@@ -1801,7 +1801,7 @@ Json Parameters:

 Status Codes:

--   **201** – no error

+-   **200** – no error

 -   **404** – no such exec instance

     **Stream details**:

@@ -1922,7 +1922,7 @@ Json Parameters:

 Status Codes:

--   **201** – no error

+-   **200** – no error

 -   **404** – no such exec instance

     **Stream details**:

@@ -1984,7 +1984,7 @@ Json Parameters:

 Status Codes:

--   **201** – no error

+-   **200** – no error

 -   **404** – no such exec instance

     **Stream details**:

@@ -2126,7 +2126,7 @@ Json Parameters:

 Status Codes:

--   **201** – no error

+-   **200** – no error

 -   **404** – no such exec instance

     **Stream details**:

@@ -2226,8 +2226,9 @@ Json Parameters:

 Status Codes:

--   **201** – no error

+-   **200** – no error

 -   **404** – no such exec instance

+-   **409** - container is stopped or paused

     **Stream details**:

     Similar to the stream behavior of `POST /container/(id)/attach` API

@@ -654,7 +654,7 @@ var (

 		Value:          "CONTAINERNOTRUNNING",

 		Message:        "Container %s is not running: %s",

 		Description:    "An attempt was made to retrieve the information about an 'exec' but the container is not running",

-		HTTPStatusCode: http.StatusInternalServerError,

+		HTTPStatusCode: http.StatusConflict,

 	})

 	// ErrorCodeNoExecID is generated when we try to get the info

@@ -672,7 +672,7 @@ var (

 		Value:          "EXECPAUSED",

 		Message:        "Container %s is paused, unpause the container before exec",

 		Description:    "An attempt to start an 'exec' was made, but the owning container is paused",

-		HTTPStatusCode: http.StatusInternalServerError,

+		HTTPStatusCode: http.StatusConflict,

 	})

 	// ErrorCodeExecRunning is generated when we try to start an exec

@@ -7,6 +7,7 @@ import (

 	"encoding/json"

 	"fmt"

 	"net/http"

+	"strings"

 	"github.com/go-check/check"

 )

@@ -47,3 +48,44 @@ func (s *DockerSuite) TestExecApiCreateNoValidContentType(c *check.C) {

 		c.Fatalf("Expected message when creating exec command with invalid Content-Type specified")

 	}

 }

+

+func (s *DockerSuite) TestExecAPIStart(c *check.C) {

+	dockerCmd(c, "run", "-d", "--name", "test", "busybox", "top")

+

+	createExec := func() string {

+		_, b, err := sockRequest("POST", fmt.Sprintf("/containers/%s/exec", "test"), map[string]interface{}{"Cmd": []string{"true"}})

+		c.Assert(err, check.IsNil, check.Commentf(string(b)))

+

+		createResp := struct {

+			ID string `json:"Id"`

+		}{}

+		c.Assert(json.Unmarshal(b, &createResp), check.IsNil, check.Commentf(string(b)))

+		return createResp.ID

+	}

+

+	startExec := func(id string, code int) {

+		resp, body, err := sockRequestRaw("POST", fmt.Sprintf("/exec/%s/start", id), strings.NewReader(`{"Detach": true}`), "application/json")

+		c.Assert(err, check.IsNil)

+

+		b, err := readBody(body)

+		c.Assert(err, check.IsNil, check.Commentf(string(b)))

+		c.Assert(resp.StatusCode, check.Equals, code, check.Commentf(string(b)))

+	}

+

+	startExec(createExec(), http.StatusOK)

+

+	id := createExec()

+	dockerCmd(c, "stop", "test")

+

+	startExec(id, http.StatusNotFound)

+

+	dockerCmd(c, "start", "test")

+	startExec(id, http.StatusNotFound)

+

+	// make sure exec is created before pausing

+	id = createExec()

+	dockerCmd(c, "pause", "test")

+	startExec(id, http.StatusConflict)

+	dockerCmd(c, "unpause", "test")

+	startExec(id, http.StatusOK)

+}