all: support older version of Openwrt

cmd/ctrld/service.go

@@ -13,7 +13,8 @@ import (
 
 func newService(s service.Service) service.Service {
 	// TODO: unify for other SysV system.
-	if router.IsGLiNet() {
+	switch {
+	case router.IsGLiNet(), router.IsOldOpenwrt():
 		return &sysV{s}
 	}
 	return s

internal/router/openwrt.go

@@ -23,6 +23,16 @@ func IsGLiNet() bool {
 	return bytes.Contains(buf, []byte(" (glinet"))
 }
 
+// IsOldOpenwrt reports whether the router is an "old" version of Openwrt,
+// aka versions which don't have "service" command.
+func IsOldOpenwrt() bool {
+	if Name() != OpenWrt {
+		return false
+	}
+	cmd, _ := exec.LookPath("service")
+	return cmd == ""
+}
+
 func setupOpenWrt() error {
 	// Delete dnsmasq port if set.
 	if _, err := uci("delete", "dhcp.@dnsmasq[0].port"); err != nil && !errors.Is(err, errUCIEntryNotFound) {