diff --git a/common/tool_cmd.py b/common/tool_cmd.py
index 9bfe41bed9872f8d189850517185bd027495b4d1..38d951ac1a5da5fb6aecf7f97f1ec5870d43ca42 100644
--- a/common/tool_cmd.py
+++ b/common/tool_cmd.py
@@ -3,8 +3,6 @@
 # cython:language_level=3
 
 import argparse
-import datetime
-import sys
 import platform
 
 from common.command import Command
@@ -18,7 +16,7 @@ class ToolCmd:
 
     # start add for perf/offcpu command line parser check
     def __check_perf_cmdline(self, args):
-        error_msg = []
+        error_msg = ""
         if args.perf_enable_type:
             if not args.perf_pid:
                 error_msg = "need to specify --pid option"
@@ -30,7 +28,7 @@ class ToolCmd:
         return error_msg
 
     def __check_offcpu_cmdline(self, args):
-        error_msg = []
+        error_msg = ""
         if args.offcpu:
             if not args.offcpu_pid:
                 error_msg = "need to specify --offcpu_pid option"