diff --git a/client.c b/client.c
index 89c2b44..0a93be0 100644
--- a/client.c
+++ b/client.c
@@ -376,9 +376,6 @@
 							cmd->opcode);
 
 		switch (cmd->opcode) {
-		case FIO_NET_CMD_ACK:
-			free(cmd);
-			break;
 		case FIO_NET_CMD_QUIT:
 			remove_client(client);
 			free(cmd);
diff --git a/server.c b/server.c
index 74f5e6a..938f58b 100644
--- a/server.c
+++ b/server.c
@@ -271,6 +271,19 @@
 	return ret;
 }
 
+static int handle_probe_cmd(struct fio_net_cmd *cmd)
+{
+	struct cmd_probe_pdu probe;
+
+	memset(&probe, 0, sizeof(probe));
+	gethostname((char *) probe.hostname, sizeof(probe.hostname));
+	probe.fio_major = 1;
+	probe.fio_minor = 58;
+	probe.fio_patch = 0;
+
+	return fio_net_send_cmd(server_fd, FIO_NET_CMD_PROBE, &probe, sizeof(probe));
+}
+
 static int handle_command(struct fio_net_cmd *cmd)
 {
 	int ret;
@@ -280,17 +293,16 @@
 	switch (cmd->opcode) {
 	case FIO_NET_CMD_QUIT:
 		fio_terminate_threads(TERMINATE_ALL);
-		return 1;
+		return -1;
 	case FIO_NET_CMD_EXIT:
 		exit_backend = 1;
-		return 1;
-	case FIO_NET_CMD_ACK:
-		return 0;
-	case FIO_NET_CMD_NAK:
-		return 1;
+		return -1;
 	case FIO_NET_CMD_JOB:
 		ret = handle_cur_job(cmd);
 		break;
+	case FIO_NET_CMD_PROBE:
+		ret = handle_probe_cmd(cmd);
+		break;
 	default:
 		log_err("fio: unknown opcode: %d\n", cmd->opcode);
 		ret = 1;
@@ -308,7 +320,7 @@
 	while (!exit_backend) {
 		cmd = fio_net_recv_cmd(sk);
 		if (!cmd) {
-			ret = 1;
+			ret = -1;
 			break;
 		}
 
@@ -407,7 +419,7 @@
 #ifdef SO_REUSEPORT
 	if (setsockopt(fd, SOL_SOCKET, SO_REUSEPORT, &opt, sizeof(opt)) < 0) {
 		log_err("fio: setsockopt: %s\n", strerror(errno));
-		return 1;
+		return -1;
 	}
 #endif
 
@@ -615,7 +627,7 @@
 	pid = fork();
 	if (pid < 0) {
 		syslog(LOG_ERR, "failed server fork");
-		return 1;
+		return -1;
 	} else if (pid)
 		exit(0);
 
diff --git a/server.h b/server.h
index 61b61f3..4783238 100644
--- a/server.h
+++ b/server.h
@@ -34,12 +34,11 @@
 	FIO_NET_CMD_QUIT	= 1,
 	FIO_NET_CMD_EXIT	= 2,
 	FIO_NET_CMD_JOB		= 3,
-	FIO_NET_CMD_ACK		= 4,
-	FIO_NET_CMD_NAK		= 5,
-	FIO_NET_CMD_TEXT	= 6,
-	FIO_NET_CMD_TS		= 7,
-	FIO_NET_CMD_GS		= 8,
-	FIO_NET_CMD_ETA		= 9,
+	FIO_NET_CMD_TEXT	= 4,
+	FIO_NET_CMD_TS		= 5,
+	FIO_NET_CMD_GS		= 6,
+	FIO_NET_CMD_ETA		= 7,
+	FIO_NET_CMD_PROBE	= 8,
 
 	FIO_NET_CMD_F_MORE	= 1UL << 0,
 
@@ -53,6 +52,13 @@
 	struct group_run_stats rs;
 };
 
+struct cmd_probe_pdu {
+	uint8_t hostname[64];
+	uint8_t fio_major;
+	uint8_t fio_minor;
+	uint8_t fio_patch;
+};
+
 extern int fio_start_server(int);
 extern int fio_server_text_output(const char *, unsigned int len);
 extern int fio_server_log(const char *format, ...);