diff --git a/backend/src/engine.cpp b/backend/src/engine.cpp
index cf4a5da..f5ada9c 100644
--- a/backend/src/engine.cpp
+++ b/backend/src/engine.cpp
@@ -115,8 +115,10 @@ std::vector<std::string> BookStoreEngineClass::ExecuteSu(
   std::string user_id, password;
   if (!CommandSuLexer(cmd, user_id, password))
     return std::vector<std::string>({"Invalid"});
+  // debugPrint("su", user_id, " ", password);
   if (login_stack.size() > 0 &&
       user_data_base.GetPrevilege(login_stack.top().first) == 7) {
+    // debugPrint("has root previlege");
     if (user_data_base.GetPrevilege(user_id) == -1)
       return std::vector<std::string>({"Invalid"});
     login_stack.push(std::make_pair(user_id, ""));
diff --git a/backend/src/lexer.cpp b/backend/src/lexer.cpp
index a73d2d2..cab8ca1 100644
--- a/backend/src/lexer.cpp
+++ b/backend/src/lexer.cpp
@@ -18,7 +18,7 @@
 bool CommandSuLexer(const std::string &command, std::string &user_id,
                     std::string &password) {
   static std::basic_regex main_pattern(
-      R"(^ *su +(?:[0-9a-zA-Z_]{1,30}) +(?:[0-9a-zA-Z_]{1,30})? *$)",
+      R"(^ *su +(?:[0-9a-zA-Z_]{1,30})(?: +[0-9a-zA-Z_]{1,30})? *$)",
       std::regex_constants::optimize);
   if (std::regex_match(command, main_pattern)) {
     std::stringstream ss(command);