diff --git a/README.md b/README.md
index 071f55541..ceb33b170 100644
--- a/README.md
+++ b/README.md
@@ -307,5 +307,4 @@ See `circle.yml` and `_ci/build-and-push-release-asset.sh` for details.
 * Add a `show-lock` command.
 * Add a command to automatically set up best-practices remote state storage in a versioned, encrypted, S3 bucket.
 * Add a command to list the different versions of state available in a versioned S3 bucket and to diff any two state
-  files.
-* Use IAM username instead of the local OS username in lock metadata.
\ No newline at end of file
+  files.
\ No newline at end of file
diff --git a/cli/cli_app.go b/cli/cli_app.go
index 4df9d4578..0fe0dfed3 100644
--- a/cli/cli_app.go
+++ b/cli/cli_app.go
@@ -70,6 +70,12 @@ func runApp(cliContext *cli.Context) error {
 		return err
 	}
 
+	// If someone calls us with no args at all, show the help text and exit
+	if !cliContext.Args().Present() {
+		cli.ShowAppHelp(cliContext)
+		return nil
+	}
+
 	if err := downloadModules(cliContext); err != nil {
 		return err
 	}
diff --git a/dynamodb/dynamo_lock.go b/dynamodb/dynamo_lock.go
index c6f1fe161..4fc4bd21d 100644
--- a/dynamodb/dynamo_lock.go
+++ b/dynamodb/dynamo_lock.go
@@ -7,6 +7,7 @@ import (
 	"github.com/aws/aws-sdk-go/service/dynamodb"
 	"github.com/gruntwork-io/terragrunt/util"
 	"github.com/gruntwork-io/terragrunt/errors"
+	"github.com/aws/aws-sdk-go/aws"
 )
 
 // A lock that uses AWS's DynamoDB to acquire and release locks
@@ -82,6 +83,16 @@ func (dynamoLock DynamoDbLock) String() string {
 
 // Create an authenticated client for DynamoDB
 func createDynamoDbClient(awsRegion string) (*dynamodb.DynamoDB, error) {
+	config, err := createAwsConfig(awsRegion)
+	if err != nil {
+		return nil, err
+	}
+
+	return dynamodb.New(session.New(), config), nil
+}
+
+// Returns an AWS config object for the given region, ensuring that the config has credentials
+func createAwsConfig(awsRegion string) (*aws.Config, error) {
 	config := defaults.Get().Config.WithRegion(awsRegion)
 
 	_, err := config.Credentials.Get()
@@ -89,7 +100,7 @@ func createDynamoDbClient(awsRegion string) (*dynamodb.DynamoDB, error) {
 		return nil, errors.WithStackTraceAndPrefix(err, "Error finding AWS credentials (did you set the AWS_ACCESS_KEY_ID and AWS_SECRET_ACCESS_KEY environment variables?)")
 	}
 
-	return dynamodb.New(session.New(), config), nil
+	return config, nil
 }
 
 var StateFileIdMissing = fmt.Errorf("The dynamodb.stateFileId field cannot be empty")
diff --git a/dynamodb/dynamo_lock_item.go b/dynamodb/dynamo_lock_item.go
index 326e1baca..5485715bb 100644
--- a/dynamodb/dynamo_lock_item.go
+++ b/dynamodb/dynamo_lock_item.go
@@ -8,6 +8,8 @@ import (
 	"github.com/aws/aws-sdk-go/aws"
 	"fmt"
 	"github.com/gruntwork-io/terragrunt/errors"
+	"github.com/aws/aws-sdk-go/service/iam"
+	"github.com/aws/aws-sdk-go/aws/session"
 )
 
 // Create a DynamoDB key for the given item id
@@ -87,8 +89,13 @@ func getAttribute(item map[string]*dynamodb.AttributeValue, attribute string) (s
 
 // Create a DynamoDB item for the given item id. This item represents a lock and will include metadata about the
 // current user, who is trying to acquire the lock.
-func createItem(itemId string) (map[string]*dynamodb.AttributeValue, error) {
-	lockMetadata, err := locks.CreateLockMetadata(itemId)
+func createItemAttributes(itemId string, client *dynamodb.DynamoDB) (map[string]*dynamodb.AttributeValue, error) {
+	iamUsername, err := getIamUsername(client)
+	if err != nil {
+		return nil, err
+	}
+
+	lockMetadata, err := locks.CreateLockMetadata(itemId, iamUsername)
 	if err != nil {
 		return nil, err
 	}
@@ -101,6 +108,17 @@ func createItem(itemId string) (map[string]*dynamodb.AttributeValue, error) {
 	}, nil
 }
 
+// Return the IAM username of the currently logged in user
+func getIamUsername(client *dynamodb.DynamoDB) (string, error) {
+	iamClient := iam.New(session.New(), &client.Config)
+	output, err := iamClient.GetUser(&iam.GetUserInput{})
+	if err != nil {
+		return "", errors.WithStackTrace(err)
+	}
+
+	return *output.User.UserName, nil
+}
+
 type AttributeMissing struct {
 	AttributeName string
 }
diff --git a/dynamodb/dynamo_lock_table.go b/dynamodb/dynamo_lock_table.go
index 51d2b6ae0..80147c5e5 100644
--- a/dynamodb/dynamo_lock_table.go
+++ b/dynamodb/dynamo_lock_table.go
@@ -114,7 +114,7 @@ func removeItemFromLockTable(itemId string, tableName string, client *dynamodb.D
 
 // Write the given item to the DynamoDB lock table. If the given item already exists, return an error.
 func writeItemToLockTable(itemId string, tableName string, client *dynamodb.DynamoDB) error {
-	item, err := createItem(itemId)
+	item, err := createItemAttributes(itemId, client)
 	if err != nil {
 		return err
 	}
diff --git a/locks/lock_metadata.go b/locks/lock_metadata.go
index be11d7260..47b423e41 100644
--- a/locks/lock_metadata.go
+++ b/locks/lock_metadata.go
@@ -3,7 +3,6 @@ package locks
 import (
 	"time"
 	"net"
-	"os/user"
 	"github.com/gruntwork-io/terragrunt/errors"
 	"fmt"
 )
@@ -19,13 +18,8 @@ type LockMetadata struct {
 	DateCreated time.Time
 }
 
-// Create the LockMetadata for the current user
-func CreateLockMetadata(stateFileId string) (*LockMetadata, error) {
-	user, err := user.Current()
-	if err != nil {
-		return nil, errors.WithStackTrace(err)
-	}
-
+// Create the LockMetadata for the given state file and user
+func CreateLockMetadata(stateFileId string, username string) (*LockMetadata, error) {
 	ipAddress, err := getIpAddress()
 	if err != nil {
 		return nil, errors.WithStackTrace(err)
@@ -35,7 +29,7 @@ func CreateLockMetadata(stateFileId string) (*LockMetadata, error) {
 
 	return &LockMetadata{
 		StateFileId: stateFileId,
-		Username: user.Username,
+		Username: username,
 		IpAddress: ipAddress,
 		DateCreated: dateCreated,
 	}, nil
diff --git a/locks/lock_metdata_test.go b/locks/lock_metdata_test.go
index 8c2076c9d..f3170a1f4 100644
--- a/locks/lock_metdata_test.go
+++ b/locks/lock_metdata_test.go
@@ -18,13 +18,14 @@ func TestCreateLockMetadata(t *testing.T) {
 	t.Parallel()
 
 	expectedStateFileId := "expected-state-file-id"
-	lockMetadata, err := CreateLockMetadata(expectedStateFileId)
+	expectedUsername := "jim"
+	lockMetadata, err := CreateLockMetadata(expectedStateFileId, expectedUsername)
 
 	assert.Nil(t, err)
 	assert.Equal(t, expectedStateFileId, lockMetadata.StateFileId)
 	assert.False(t, lockMetadata.DateCreated.IsZero())
 	assertIsValidIp(t, lockMetadata.IpAddress)
-	assert.NotEmpty(t, lockMetadata.Username)
+	assert.Equal(t, expectedUsername, lockMetadata.Username)
 }
 
 func assertIsValidIp(t *testing.T, ip string) {