Return process exit code for attach

Fixes #2240

commands.go

@@ -1578,6 +1578,15 @@ func (cli *DockerCli) CmdAttach(args ...string) error {
 	if err := cli.hijack("POST", "/containers/"+cmd.Arg(0)+"/attach?"+v.Encode(), container.Config.Tty, in, cli.out, cli.err, nil); err != nil {
 		return err
 	}
+
+	_, status, err := getExitCode(cli, cmd.Arg(0))
+	if err != nil {
+		return err
+	}
+	if status != 0 {
+		return &utils.StatusError{Status: status}
+	}
+
 	return nil
 }
 

docs/sources/commandline/cli.rst

@@ -66,7 +66,8 @@ To run the daemon with debug output, use ``docker -d -D``
 
 You can detach from the container again (and leave it running) with
 ``CTRL-c`` (for a quiet exit) or ``CTRL-\`` to get a stacktrace of
-the Docker client when it quits.
+the Docker client when it quits.  When you detach from the container's 
+process the exit code will be retuned to the client.
 
 To stop a container, use ``docker stop``