diff --git a/common/common_darwin.go b/common/common_darwin.go
index 6cdefb4..4d41382 100644
--- a/common/common_darwin.go
+++ b/common/common_darwin.go
@@ -74,7 +74,7 @@ func CallLsof(invoke Invoker, pid int32, args ...string) ([]string, error) {
 	}
 	out, err := invoke.Command(lsof, cmd...)
 	if err != nil {
-		// if not pid found, lsof returnes code 1
+		// if no pid found, lsof returnes code 1
 		if err.Error() == "exit status 1" && len(out) == 0 {
 			return []string{}, nil
 		}
diff --git a/net/net_darwin.go b/net/net_darwin.go
index bcf2915..b9275e8 100644
--- a/net/net_darwin.go
+++ b/net/net_darwin.go
@@ -109,7 +109,7 @@ func NetConnectionsPid(kind string, pid int32) ([]NetConnectionStat, error) {
 	case "all":
 		fallthrough
 	case "inet":
-		args = append(args, "tcp")
+		args = append(args, "tcp", "-i", "udp")
 	case "inet4":
 		args = append(args, "4")
 	case "inet6":
diff --git a/net/net_freebsd.go b/net/net_freebsd.go
index 7cc93a5..54dc1b5 100644
--- a/net/net_freebsd.go
+++ b/net/net_freebsd.go
@@ -82,8 +82,57 @@ func NetIOCounters(pernic bool) ([]NetIOCountersStat, error) {
 	return ret, nil
 }
 
-func NetConnections(kind string) ([]NetConnectionStat, error) {
+// Return a list of network connections opened by a process.
+func NetConnectionsPid(kind string, pid int32) ([]NetConnectionStat, error) {
 	var ret []NetConnectionStat
 
-	return ret, common.NotImplementedError
+	args := []string{"-i"}
+	switch strings.ToLower(kind) {
+	default:
+		fallthrough
+	case "":
+		fallthrough
+	case "all":
+		fallthrough
+	case "inet":
+		args = append(args, "tcp", "-i", "udp")
+	case "inet4":
+		args = append(args, "4")
+	case "inet6":
+		args = append(args, "6")
+	case "tcp":
+		args = append(args, "tcp")
+	case "tcp4":
+		args = append(args, "4tcp")
+	case "tcp6":
+		args = append(args, "6tcp")
+	case "udp":
+		args = append(args, "udp")
+	case "udp4":
+		args = append(args, "6udp")
+	case "udp6":
+		args = append(args, "6udp")
+	case "unix":
+		return ret, common.NotImplementedError
+	}
+
+	// we can not use -F filter to get all of required information at once.
+	r, err := common.CallLsof(invoke, pid, args...)
+	if err != nil {
+		return nil, err
+	}
+	for _, rr := range r {
+		if strings.HasPrefix(rr, "COMMAND") {
+			continue
+		}
+		n, err := parseNetLine(rr)
+		if err != nil {
+			// fmt.Println(err) // TODO: should debug print?
+			continue
+		}
+
+		ret = append(ret, n)
+	}
+
+	return ret, nil
 }
diff --git a/net/net_linux.go b/net/net_linux.go
index 6e54244..7c1d015 100644
--- a/net/net_linux.go
+++ b/net/net_linux.go
@@ -108,7 +108,7 @@ func NetConnectionsPid(kind string, pid int32) ([]NetConnectionStat, error) {
 	case "all":
 		fallthrough
 	case "inet":
-		args = append(args, "tcp")
+		args = append(args, "tcp", "-i", "udp")
 	case "inet4":
 		args = append(args, "4")
 	case "inet6":