Background: Logging is an important part of modern software projects; logs are used in several tasks such as debugging and testing. Due to the complex nature of logging, it remains a difficult task with several pitfalls that could have serious consequences. Several other domains of software engineering have mitigated such threats by identifying the early signs of more serious issues, i.e., "smells". However, this concept is not yet properly defined for logging. Objective: The goal of this study is to create a taxonomy of log smells that can help developers write better logging code. To further help the developers and to identify issues that need more attention from the research community, we also map the identified smells to existing tools addressing them. Methods: We identified logging issues and tools by conducting a survey of the scientific literature. After extracting relevant data from 45 articles, we used them to define logging issues using open coding technique and classified the defined issues using card sorting. We classify the tools based on their reported output. Results: The paper presents a taxonomy of ten log smells, describing several facets for each of them. We also review existing tools addressing some of these facets, highlighting the lack of tools addressing some log smells and identifying future research opportunities to close this gap.

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