Override hostname for container

Adds the ability to override the container's hostname.  Also, uses
the first twelve characters of the container ID as the default hostname
if none is provided.

Signed-off-by: baude <bbaude@redhat.com>

Closes: #248
Approved by: baude

libpod/container_api.go

@@ -90,6 +90,18 @@ func (c *Container) Init() (err error) {
 		return errors.Wrapf(err, "unable to copy /etc/hosts to container space")
 	}
 
+	if c.Spec().Hostname == "" {
+		id := c.ID()
+		if len(c.ID()) > 11 {
+			id = c.ID()[:12]
+		}
+		c.config.Spec.Hostname = id
+	}
+	runDirHostname, err := c.generateEtcHostname(c.config.Spec.Hostname)
+	if err != nil {
+		return errors.Wrapf(err, "unable to generate hostname file for container")
+	}
+
 	// Save OCI spec to disk
 	g := generate.NewFromSpec(c.config.Spec)
 	// If network namespace was requested, add it now
@@ -122,6 +134,14 @@ func (c *Container) Init() (err error) {
 		Options:     []string{"rw", "bind"},
 	}
 	g.AddMount(hostsMnt)
+	// Bind hostname
+	hostnameMnt := spec.Mount{
+		Type:        "bind",
+		Source:      runDirHostname,
+		Destination: "/etc/hostname",
+		Options:     []string{"rw", "bind"},
+	}
+	g.AddMount(hostnameMnt)
 
 	if c.config.User != "" {
 		if !c.state.Mounted {

libpod/container_internal.go

@@ -508,3 +508,8 @@ func (c *Container) generateHosts() (string, error) {
 	}
 	return c.WriteStringToRundir("hosts", hosts)
 }
+
+// generateEtcHostname creates a containers /etc/hostname
+func (c *Container) generateEtcHostname(hostname string) (string, error) {
+	return c.WriteStringToRundir("hostname", hostname)
+}