From 2851e188e1d471388cb2ef2120b94fc4698dbccf Mon Sep 17 00:00:00 2001
From: Mitchell Hashimoto <mitchell.hashimoto@gmail.com>
Date: Sat, 9 Nov 2013 17:27:30 -0800
Subject: [PATCH] builder/docker: show stderr if docker fails to run

---
 builder/docker/driver_docker.go | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/builder/docker/driver_docker.go b/builder/docker/driver_docker.go
index 15029d202..932d46101 100644
--- a/builder/docker/driver_docker.go
+++ b/builder/docker/driver_docker.go
@@ -67,6 +67,11 @@ func (d *DockerDriver) StartContainer(config *ContainerConfig) (string, error) {
 
 	log.Println("Waiting for container to finish starting")
 	if err := cmd.Wait(); err != nil {
+		if _, ok := err.(*exec.ExitError); ok {
+			err = fmt.Errorf("Docker exited with a non-zero exit status.\nStderr: %s",
+				stderr.String())
+		}
+
 		return "", err
 	}