Security of storage and archival systems has become a basic necessity in recent years. Due to the increased vulnerability of the existing systems and the need to comply with government regulations, different methods have been explored to attain a secure storage system. One of the primary problems to ensuring the integrity of storage systems is to make sure a file cannot be changed without proper authorization. Immutable storage is storage whose content cannot be changed once it has been written. For example, it is apparent that critical system files and other important documents should never be changed and thus stored as immutable. In multimedia systems, immutability provides proper archival of indices as well as content. In this paper we present a survey of existing techniques for immutability in file systems.