Running Linux, 5th Edition - Matthias Kalle Dalheimer [183]
The main difference between the Second Extended filesystem on the one hand and the Reiser and the Third Extended filesystem on the other hand is that the latter two are journaled. Journaling is an advanced technique that keeps track of the changes made to a filesystem, making it much easier (and faster!) to restore a corrupted filesystem (e.g., after a system crash or a power failure). Another journaled filesystem is IBM's Journaling File System, JFS.
You will rarely need the ROM filesystem , which is very small, does not support write operations, and is meant to be used in ramdisks at system configuration, startup time, or even in EPROMS. Also in this group is the Cram filesystem, which is used for ROMs as well and compresses its contents. This is primarily meant for embedded devices, where space is at a premium.
The UMSDOS filesystem is used to install Linux under a private directory of an existing MS-DOS partition. This is a good way for new users to try out Linux without repartitioning, at the expense of poorer performance. The DOS-FAT filesystem, on the other hand, is used to access MS-DOS files directly. Files on partitions created with Windows 95 or 98 can be accessed via the VFAT filesystem, whereas the NTFS filesystem lets you access Windows NT filesystems . The HPFS filesystem is used to access the OS/2 filesystem.
/proc is a virtual filesystem; that is, no actual disk space is associated with it. See "The /proc Filesystem," later in this chapter.[*]
The ISO9660 filesystem (previously known as the High Sierra Filesystem and abbreviated hsfs on other Unix systems) is used by most CD-ROMs. Like MS-DOS, this filesystem type restricts filename length and stores only limited information about each file. However, most CD-ROMs provide the Rock Ridge Extensions to ISO 9660, which allow the kernel filesystem driver to assign long filenames, ownerships, and permissions to each file. The net result is that accessing an ISO 9660 CD-ROM under MS-DOS gives you 8.3-format filenames, but under Linux gives you the "true," complete filenames.
In addition, Linux now supports the Microsoft Joliet extensions to ISO 9660, which can handle long filenames made up of Unicode characters. This is not widely used now but may become valuable in the future because Unicode has been accepted internationally as the standard for encoding characters of scripts worldwide.
Linux also supports UDF, a filesystem that is meant for use with CD-RWs and DVDs.
Next, we have many filesystem types for other platforms. Linux supports the formats that are popular on those platforms in order to allow dual-booting and other interoperation. The systems in question include UFS, EFS, BFS, XFS, System V, and BeOS. If you have filesystems created in one of these formats under a foreign operating system, you'll be able to access the files from Linux.
Finally, there is a slew of filesystems for accessing data on partitions; these are created by operating systems other than the DOS and Unix families. Those filesystems support the Acorn Disk Filing System (ADFS), the Amiga OS filesystems (no floppy disk support except on Amigas), the Apple Mac HFS, and the QNX4 filesystem. Most of the specialized filesystems are useful only on certain hardware architectures; for instance, you won't have hard disks formatted with the Amiga FFS filesystem in an Intel machine. If you need one of those drivers, please read the information that comes with them; some are only in an experimental state.
Besides these filesystems that are used to access local hard disks, there are also network filesystems for accessing remote resources. We talk about those to some extent later.
Finally, there are specialty filesystems , such as those that store the data in RAM instead of on the hard disk (and consequentially are much faster, but also lose all their data when the computer is powered off), and those that provide access to kernel objects and kernel data.
Mounting Filesystems
In order to access any filesystem under Linux, you must mount