@@ -1043,10 +1043,15 @@ func (container *Container) setupLinkedContainers() ([]string, error) {

 }

 func (container *Container) createDaemonEnvironment(linkedEnv []string) []string {

+	// if a domain name was specified, append it to the hostname (see #7851)

+	fullHostname := container.Config.Hostname

+	if container.Config.Domainname != "" {

+		fullHostname = fmt.Sprintf("%s.%s", fullHostname, container.Config.Domainname)

+	}

 	// Setup environment

 	env := []string{

 		"PATH=" + DefaultPathEnv,

-		"HOSTNAME=" + container.Config.Hostname,

+		"HOSTNAME=" + fullHostname,

 		// Note: we don't set HOME here because it'll get autoset intelligently

 		// based on the value of USER inside dockerinit, but only if it isn't

 		// set already (ie, that can be overridden by setting HOME via -e or ENV

@@ -821,6 +821,26 @@ func TestRunLoopbackOnlyExistsWhenNetworkingDisabled(t *testing.T) {

 	logDone("run - test loopback only exists when networking disabled")

 }

+// #7851 hostname outside container shows FQDN, inside only shortname

+// For testing purposes it is not required to set host's hostname directly

+// and use "--net=host" (as the original issue submitter did), as the same

+// codepath is executed with "docker run -h <hostname>".  Both were manually

+// tested, but this testcase takes the simpler path of using "run -h .."

+func TestRunFullHostnameSet(t *testing.T) {

+	cmd := exec.Command(dockerBinary, "run", "-h", "foo.bar.baz", "busybox", "hostname")

+	out, _, err := runCommandWithOutput(cmd)

+	if err != nil {

+		t.Fatal(err, out)

+	}

+

+	if actual := strings.Trim(out, "\r\n"); actual != "foo.bar.baz" {

+		t.Fatalf("expected hostname 'foo.bar.baz', received %s", actual)

+	}

+	deleteAllContainers()

+

+	logDone("run - test fully qualified hostname set with -h")

+}

+

 func TestRunPrivilegedCanMknod(t *testing.T) {

 	cmd := exec.Command(dockerBinary, "run", "--privileged", "busybox", "sh", "-c", "mknod /tmp/sda b 8 0 && echo ok")

 	out, _, err := runCommandWithOutput(cmd)