Today's software has a very complex structure with multiple components, making it difficult to identify the cause of a fault. The process of identifying the cause of a fault may include referring to the logs from the system if they exist. But large and complex systems may generate a huge amount of logs, making the task of finding the important log messages to be a tedious task. In the case of systems that require continuous operation, the cause of faults must be identified quickly in an efficient manner. In this paper, we propose a method that identifies the log messages that are key for finding faults in server-side applications that has a tiered structure, such as LAMP (Linux, Apache, MySQL, PHP), and outputs logs (including traces during operation). The key part of our proposed approach is the application of Spectrum-Based Fault Localization (SBFL) to log files.