An operating system uses a file system to manage the files and directories on secondary storage. The file system determines the structure on how files and directories are stored and organized on each media storage volume. The file systems reviewed are FAT16, FAT32, NTFS, Unix, Linux, and Windows. File system utilities used in a Unix environment are explained on their purpose and when they should be used as well as file security.
UNIX System Utilities
Each operating system has utilities for managing its file systems. A system utility is a tool to perform a specific task within the file system. The UNIX operating system has many command-line tools for managing its file system. Before user can access a file system in UNIX, it must be mounted. UNIX can mount numerous file systems during the boot-up process or they can be mounted manually as needed. To mount a file system, the mount command is used. Once the file system is no longer needed it may be removed using the unmount command.
The user can perform a number of file and directory management tasks after a file system has been mounted. Having the knowledge on how to navigate through the directories and find files within the file system is important to understand. Navigation is performed by using the cd command moving from the current directory to another directory. The ls command will list all the files in the current directory. As in all file systems, users can create, move, copy, delete, and change the attributes of files and directories. To create or remove a directory, use the mkdir and the rmdir commands respectively. The mv command will move a file. To delete a file use the rm command. The copy command is cp to make a duplicate file. Navigation, file and directory manipulation are used frequently and on a daily basis as a user works within their environment.
Two tools that administrators use daily to monitor the file system and ensure it maintains enough disk space are df and du. The df command reports free disk space by printing a list of free blocks and inodes on all mounted file systems. The command is du that prints a list of disk space usage by by block size for each directory and subdirectory. Some Unix systems allow creating disk partitions using dxdiskconfig command and defrag using fsadm defrag command (HP, 2010). To check a file system use fsck. To create file backups use dd and tar commands and to compress a file use either compress or gzip. Depending on the size of the system, some of these commands may be used daily for an administrator to monitor the system and creating a system backup. Unix systems rarely need defragmented, therefore the defrag command does not need to be used very often.
System security begins with user accounts and passwords. Each user is assigned to a group or an access control lists (ACL). To access files and directories, users must have permissions set using the chmod, chown, chgrp commands. Administrators use lsacl to display an ACL and chacl to make changes. Administrators use each of these commands to add, delete, or modify users. For added security, files can be encrypted using crypt command. Encrypting should be used any time sensitive data requires additional protection.
FAT
FAT was the first file system created by Microsoft for MS-DOS in the early 1980s. A file allocation table maps disk clusters to the physical location of a file. The FAT contains the address of a file’s first cluster and uses a pointer to next succeeding cluster. FAT12 was the first version that supported an 8MB partition size. FAT16 originally used 2KB cluster size and a maximum volume size of 16. Today it supports 4GB volume and 64KB cluster. FAT16 has a limitation on the number of clusters on a partition, therefore, it takes more disk space of larger harddrives (PC Tech Guide, 2009). A benefit for using FAT16 is that it is compatible with many other operating systems. The performance of FAT16 is better on smaller drives due to seek time to open files. External drives, floppy disks, and CDs use the FAT16 format which makes them compatible for use with several other operating systems.
FAT32
FAT32, an extension of FAT16 was introduced with Windows 95. A benefit of FAT32 is that it allows a larger number of clusters per partition which improved disk usage over FAT16. Maximum volume size is 2TB for some operating systems and a maximum file size of 4GB. A file name can contain up to 255 characters in length. Many operating systems are not compatible with FAT32 and cannot read its partition. Compatible operating systems are Windows 98, ME, 2000, 2003 Server, XP, Vista, and Windows 7 (NTFS.com, 2010). FAT32 file system can be shared on a network for other file systems to access and read it.
NTFS
NTFS was introduced with Windows NT to address privacy and security concerns that lacked in all FAT file systems. The features of NTFS are recoverability, security, large disk and file sizes, multiple data streams, journaling, compression, and encryption. NTFS allows for a larger volume and smaller cluster sizes to reduce wasted disk space. Windows operating systems that use NTFS are are 2000, XP, Server 2003 and 2008, Vista, and Windows 7. NTFS is not compatible with other operating systems installed on the same computer. It is also not available when booting from CD or floppy disk. Both FAT16 and FAT32 can be converted to NTFS. However, once converted they cannot revert back to FAT without reformating the drive or partition. NTFS should be used in a network environment for security reasons. If older programs are used or the computer is a dual-boot, then one disk partition must be FAT. NTFS is recommended when system security, recoveryability, or encryption are desired.
Unix File System
The Unix file system is a hierarachical, tree-like structure with the top level directory beginning at root and denoted with a / (slash). The root directory contains several subdirectories for I/O devices and system and user files. Unix views all devices and directories as files and each one are referenced by a name. There are six file types associated to Unix (Stallings, 2009, p. 580-581). A regular file type is any type of text, application data, or shell script. Directory file is a type that contains a list of other files. Special file types are I/O devices which are mapped to a file name. Named pipes is an interprocessor communications mechanism. Links and symbolic links are used to link file names to other files. Access control in early versions used permission bits pointing every file and directory to give read, write, and execute permissions for user, group, and other. Access control lists extends the traditional access control for added flexability.
Linux File System
Linux is very similar to Unix file system using a hierarachical structure beginning with the root directory indicated by a / (slash). However, it is designed to support a variety of file systems using a virtual file system (VFS), in an object-oriented scheme. File systems supported by Linux are IBM JFS, DOS, NTFS, ext2, and ext3. Linux views all files and devices as objects and each is represented in one of four object types. The superblock type represents a mounted file system (Stallings, 2009, p. 589). An inode object represents a file. The Dentry is a directory and a file object is a file opened by a process. VFS is the core level for managing each mounted file system and provides the interface for mounting new file systems using system function calls (Stallings, 2009, p. 588).
Windows File System
Windows legancy file systems are FAT and FAT32 used in older DOS and Windows formats. The modern Windows file system is NTFS is now the most common used today. The Windows file system uses an object-oriented implementation for I/O devices using device drivers stacked in layers (Stallings, 2009, p. 592). NTFS is capable of handling client/server and network environments and provide recoverability, security, journeling, compression, and encryption. NTFS provides file system redundancy to recover from disk failures. System security is enhanced by setting permission attributes on file and directories to users and groups. File system logging called journaling, records all activity and changes made to files on each volume. NTFS maintains a master file table to store file and directory attribute information. Recovery is an important role of NTFS using its I/O manager, logging service, and cache and memory managers. The recovery procedure only restores file system metadata for a volume or the directory structure. However, it does not recover user data.
Conclusion
The file system is a service provide by the operating system to manage and maintain the organization of files and directories on a disk. An operating system must be compatible to access a particular file system or be able to translate the format into a useable resource. The structure must be organized in a fashion that is useful for the user to manage their files. Files systems must ensure disk space is manage efficiently to provide maximum use of each volume and partition. Each operating system provides utilities to assist the user in managing its file system. Understanding the various types of file systems and their structure will help determine which type is compatible to use for a given requirement.
