Serverless computing, as an emerging cloud com- puting paradigm, has been adopted to develop a wide range of software applications because of its simplicity of infrastructure management. Unfortunately, its characteristics also introduce new types of faults (e.g., faults due to insufficient computing resource allocation) and challenges to serverless computing-based applications (abbreviated as serverless applications). While prior studies have highlighted that serverless developers encounter various challenges, no attempts have been made to understand the faults in serverless applications. These faults may cause catastrophic consequences such as application crash, thereby hindering the further spread of serverless computing. We aim in this paper to understand the symptoms, root causes, and fix patterns of faults in serverless applications. To this end, we conduct an empirical study investigating developers’ issues on GitHub and posts on Stack Overflow (SO). We first identify 546 real-world serverless-related faults from GitHub and SO. Then, we manually analyze and construct taxonomies of the symptoms, root causes, and fix patterns for these faults, respectively. Our study leads to the first taxonomy for symptoms of serverless- related faults, covering 5 categories and 21 subcategories. The findings of our study inform that the Permission Denied error is the most common type (10.81%) of faults. Besides, the Incorrect Code Logic is the main cause (17.95%) behind the faults. Furthermore, we summarize 15 fix patterns that can resolve 73.63% of faults in this study. Based on the results, we provide actionable implications which can potentially facilitate research and assist developers in improving the development of serverless applications. Finally, we implement a knowledge-based Q&A tool named SAFHELPER to help developers in understanding and fixing faults