diff --git a/cmd/ctr/delete.go b/cmd/ctr/delete.go
index 4a31d57cb..f555d9681 100644
--- a/cmd/ctr/delete.go
+++ b/cmd/ctr/delete.go
@@ -19,7 +19,7 @@ var deleteCommand = cli.Command{
 		}
 		id := context.Args().First()
 		if id == "" {
-			return errors.New(" id must be provided")
+			return errors.New("container id must be provided")
 		}
 		_, err = containers.Delete(gocontext.Background(), &execution.DeleteRequest{
 			ID: id,
diff --git a/cmd/ctr/exec.go b/cmd/ctr/exec.go
index e2cd1e506..67f440e55 100644
--- a/cmd/ctr/exec.go
+++ b/cmd/ctr/exec.go
@@ -7,6 +7,7 @@ import (
 	"github.com/Sirupsen/logrus"
 	"github.com/containerd/containerd/api/services/execution"
 	"github.com/crosbymichael/console"
+	"github.com/pkg/errors"
 	"github.com/urfave/cli"
 )
 
@@ -32,6 +33,9 @@ var execCommand = cli.Command{
 			id  = context.String("id")
 			ctx = gocontext.Background()
 		)
+		if id == "" {
+			return errors.New("container id must be provided")
+		}
 
 		containers, err := getExecutionService(context)
 		if err != nil {
diff --git a/cmd/ctr/kill.go b/cmd/ctr/kill.go
index a6d72811c..f5deb607e 100644
--- a/cmd/ctr/kill.go
+++ b/cmd/ctr/kill.go
@@ -10,7 +10,7 @@ import (
 
 var killCommand = cli.Command{
 	Name:  "kill",
-	Usage: "signal a container",
+	Usage: "signal a container (default: SIGTERM)",
 	Flags: []cli.Flag{
 		cli.StringFlag{
 			Name:  "id",