@@ -13,6 +13,7 @@ import (

 	"os"

 	"path"

 	"path/filepath"

+	"regexp"

 	"runtime"

 	"strings"

 	"sync"

@@ -1332,6 +1333,18 @@ func (daemon *Daemon) verifyContainerSettings(hostConfig *containertypes.HostCon

 				return nil, err

 			}

 		}

+

+		// Validate if the given hostname is RFC 1123 (https://tools.ietf.org/html/rfc1123) compliant.

+		if len(config.Hostname) > 0 {

+			// RFC1123 specifies that 63 bytes is the maximium length

+			// Windows has the limitation of 63 bytes in length

+			// Linux hostname is limited to HOST_NAME_MAX=64, not not including the terminating null byte.

+			// We limit the length to 63 bytes here to match RFC1035 and RFC1123.

+			matched, _ := regexp.MatchString("^(([[:alnum:]]|[[:alnum:]][[:alnum:]\\-]*[[:alnum:]])\\.)*([[:alnum:]]|[[:alnum:]][[:alnum:]\\-]*[[:alnum:]])$", config.Hostname)

+			if len(config.Hostname) > 63 || !matched {

+				return nil, fmt.Errorf("invalid hostname format: %s", config.Hostname)

+			}

+		}

 	}

 	if hostConfig == nil {

@@ -4295,15 +4295,33 @@ func (s *DockerSuite) TestRunTooLongHostname(c *check.C) {

 	hostname1 := "this-is-a-way-too-long-hostname-but-it-should-give-a-nice-error.local"

 	out, _, err := dockerCmdWithError("run", "--hostname", hostname1, "busybox", "echo", "test")

 	c.Assert(err, checker.NotNil, check.Commentf("Expected docker run to fail!"))

-	c.Assert(out, checker.Contains, "invalid hostname format for --hostname:", check.Commentf("Expected to have 'invalid hostname format for --hostname:' in the output, get: %s!", out))

+	c.Assert(out, checker.Contains, "invalid hostname format:", check.Commentf("Expected to have 'invalid hostname format:' in the output, get: %s!", out))

-	// HOST_NAME_MAX=64 so 65 bytes will fail

-	hostname2 := "this-is-a-hostname-with-65-bytes-so-it-should-give-an-error.local"

-	out, _, err = dockerCmdWithError("run", "--hostname", hostname2, "busybox", "echo", "test")

-	c.Assert(err, checker.NotNil, check.Commentf("Expected docker run to fail!"))

-	c.Assert(out, checker.Contains, "invalid hostname format for --hostname:", check.Commentf("Expected to have 'invalid hostname format for --hostname:' in the output, get: %s!", out))

+	// Addtional test cases

+	validHostnames := map[string]string{

+		"hostname":    "hostname",

+		"host-name":   "host-name",

+		"hostname123": "hostname123",

+		"123hostname": "123hostname",

+		"hostname-of-63-bytes-long-should-be-valid-and-without-any-error": "hostname-of-63-bytes-long-should-be-valid-and-without-any-error",

+	}

+	for hostname := range validHostnames {

+		dockerCmd(c, "run", "--hostname", hostname, "busybox", "echo", "test")

+	}

-	// 64 bytes will be OK

-	hostname3 := "this-is-a-hostname-with-64-bytes-so-will-not-give-an-error.local"

-	dockerCmd(c, "run", "--hostname", hostname3, "busybox", "echo", "test")

+	invalidHostnames := map[string]string{

+		"^hostname": "invalid hostname format: ^hostname",

+		"hostname%": "invalid hostname format: hostname%",

+		"host&name": "invalid hostname format: host&name",

+		"-hostname": "invalid hostname format: -hostname",

+		"host_name": "invalid hostname format: host_name",

+		"hostname-of-64-bytes-long-should-be-invalid-and-be-with-an-error": "invalid hostname format: hostname-of-64-bytes-long-should-be-invalid-and-be-with-an-error",

+	}

+

+	for hostname, expectedError := range invalidHostnames {

+		out, _, err = dockerCmdWithError("run", "--hostname", hostname, "busybox", "echo", "test")

+		c.Assert(err, checker.NotNil, check.Commentf("Expected docker run to fail!"))

+		c.Assert(out, checker.Contains, expectedError, check.Commentf("Expected to have '%s' in the output, get: %s!", expectedError, out))

+

+	}

 }

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

 	"fmt"

 	"io/ioutil"

 	"path"

-	"regexp"

 	"strconv"

 	"strings"

@@ -260,15 +259,6 @@ func Parse(cmd *flag.FlagSet, args []string) (*container.Config, *container.Host

 	if *flEntrypoint != "" {

 		entrypoint = strslice.StrSlice{*flEntrypoint}

 	}

-	// Validate if the given hostname is RFC 1123 (https://tools.ietf.org/html/rfc1123) compliant.

-	hostname := *flHostname

-	if hostname != "" {

-		// Linux hostname is limited to HOST_NAME_MAX=64, not including the terminating null byte.

-		matched, _ := regexp.MatchString("^(([[:alnum:]]|[[:alnum:]][[:alnum:]\\-]*[[:alnum:]])\\.)*([[:alnum:]]|[[:alnum:]][[:alnum:]\\-]*[[:alnum:]])$", hostname)

-		if len(hostname) > 64 || !matched {

-			return nil, nil, nil, cmd, fmt.Errorf("invalid hostname format for --hostname: %s", hostname)

-		}

-	}

 	ports, portBindings, err := nat.ParsePortSpecs(flPublish.GetAll())

 	if err != nil {

@@ -390,15 +390,7 @@ func TestParseHostname(t *testing.T) {

 		"host-name":   "host-name",

 		"hostname123": "hostname123",

 		"123hostname": "123hostname",

-		"hostname-of-64-bytes-long-should-be-valid-and-without-any-errors": "hostname-of-64-bytes-long-should-be-valid-and-without-any-errors",

-	}

-	invalidHostnames := map[string]string{

-		"^hostname": "invalid hostname format for --hostname: ^hostname",

-		"hostname%": "invalid hostname format for --hostname: hostname%",

-		"host&name": "invalid hostname format for --hostname: host&name",

-		"-hostname": "invalid hostname format for --hostname: -hostname",

-		"host_name": "invalid hostname format for --hostname: host_name",

-		"hostname-of-65-bytes-long-should-be-invalid-and-be-given-an-error": "invalid hostname format for --hostname: hostname-of-65-bytes-long-should-be-invalid-and-be-given-an-error",

+		"hostname-of-63-bytes-long-should-be-valid-and-without-any-error": "hostname-of-63-bytes-long-should-be-valid-and-without-any-error",

 	}

 	hostnameWithDomain := "--hostname=hostname.domainname"

 	hostnameWithDomainTld := "--hostname=hostname.domainname.tld"

@@ -407,11 +399,6 @@ func TestParseHostname(t *testing.T) {

 			t.Fatalf("Expected the config to have 'hostname' as hostname, got '%v'", config.Hostname)

 		}

 	}

-	for hostname, expectedError := range invalidHostnames {

-		if _, _, err := parse(t, fmt.Sprintf("--hostname=%s", hostname)); err == nil || err.Error() != expectedError {

-			t.Fatalf("Expected error '%v' with '--hostname=%s', got '%s'", expectedError, hostname, err)

-		}

-	}

 	if config, _ := mustParse(t, hostnameWithDomain); config.Hostname != "hostname.domainname" && config.Domainname != "" {

 		t.Fatalf("Expected the config to have 'hostname' as hostname.domainname, got '%v'", config.Hostname)

 	}