This thesis presents the design and implementation of XML_based Linux File System Runner (XML_LFS), a file system simulator that integrates the representation ability of Extensible Markup Language (XML) with the beauty of Linux file system architecture. XML_LFS uses a layered approach to design a generic file system runner from scratch utilizing Java programming language and JDOM. The hierarchical directory structure of the file system is kept in an XML file for easy manipulation as well as on disk for crash recovery. UNIX-like file systems such as the Second Extended File System (Ext2), a native mini file system (mini3fs) and Linux kernel codes for file system operations are explored for the real implementation work.;Traditional file system consists of a hierarchical tree, composed of directories and files. Each directory can contain both files and subdirectories. This is an equivalent concept to "semi-structured" elements in XML. Embedding an XML log file layer into the Linux file system architecture can speed up the directory look up by combining the power of XML and XQuery as well as eliminating the limitations of the existing fixed-attribute file system model by treating files as elements to a customizable XML document. Thus, the whole development environment is more useful for future file system research. The future of XML file system is discussed in detail. Complete system architecture and functionalities are built and the process is described in the thesis. Initial Bonnie-like and Andrew-like benchmarks of the prototype implementation show that XML_LFS achieves the expected performance results.