diff --git a/agent/agent.go b/agent/agent.go
index 417a951..67a02ac 100644
--- a/agent/agent.go
+++ b/agent/agent.go
@@ -139,9 +139,13 @@ func listen(key string) {
 			}
 			if !verify(keyBuf, key) {
 				fmt.Fprintf(os.Stderr, "gops: access denied. client: %s\n", fd.RemoteAddr())
+				fd.Write([]byte{0}) // login failed
 				fd.Write([]byte("access denied. Please set right GOPS_KEY\n"))
 				fd.Close()
 				continue
+
+			} else {
+				fd.Write([]byte{1}) // login success
 			}
 		}
 
diff --git a/cmd.go b/cmd.go
index 52b8ff0..a6819a6 100644
--- a/cmd.go
+++ b/cmd.go
@@ -209,10 +209,17 @@ func cmdLazy(addr net.TCPAddr, c byte, params ...byte) (io.Reader, error) {
 	key := os.Getenv("GOPS_KEY")
 	if key != "" {
 		keyBuf := make([]byte, 64)
+		restBuf := make([]byte, 1)
 		copy(keyBuf, []byte(key))
 		if _, err := conn.Write(keyBuf); err != nil {
 			return nil, err
 		}
+		if _, err := conn.Read(restBuf); err != nil {
+			return nil, err
+		}
+		if restBuf[0] == 0 { // login failed.
+			return conn, nil
+		}
 	}
 
 	buf := []byte{c}
diff --git a/gops b/gops
new file mode 100755
index 0000000..0d8d5b9
Binary files /dev/null and b/gops differ