In today's world securing file data is very important. The proposed Secure File System (SFS), we have designed, provides file data security using cryptographic techniques in a transparent and convenient way. The proposed SFS pushes encryption services into the Linux kernel space, mounting it between the virtual file system layer and underlying file system. After SFS is integrated with the Linux operating system (OS), it enables OS to provide file data security as its inherent functionality. SFS requires that the user creates a directory and name it with the prefix dasiaecryptpsila to store the encrypted file data, such as ecryptdir. Any directory on the system with the prefix dasiaecryptpsila will basically tells the system that the newly created directory will contain encrypted data. All files destined to be saved on this directory will be transparently encrypted on the fly without any user intervention. SFS is fully compatible with all underlying storage file systems. This paper describes the design and implementation of SFS for Linux which extends the operating system to provide file data security as its inherent functionality. We have discussed the motivation for the work, the proposed SFS architecture and its implementation details in the subsequent sections.