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when you access any filesystem under Linux, the system presents the data as files arranged into a hierarchy of directories, along with owner and group IDs, permission bits, and the other characteristics with which you're familiar.

In fact, information on file ownership, permissions, and so forth is provided only by filesystem types that are meant to be used for storing Linux files. For filesystem types that don't store this information, the kernel drivers used to access these filesystems "fake" the information. For example, the MS-DOS filesystem has no concept of file ownership; therefore, all files are presented as if they were owned by root. This way, above a certain level, all filesystem types look alike, and each file has certain attributes associated with it. Whether this data is actually used in the underlying filesystem is another matter altogether.

As the system administrator, you need to know how to create filesystems should you want to store Linux files on a floppy or add additional filesystems to your hard drives. You also need to know how to use the various tools to check and maintain filesystems should data corruption occur. Also, you must know the commands and files used to access filesystems—for example, those on floppy or CD-ROM.

Filesystem Types

Table 10-1 lists the filesystem types supported by the Linux kernel as of Version 2.6.5. New filesystem types are always being added to the system, and experimental drivers for several filesystems not listed here are available. To find out what filesystem types your kernel supports, look at the file /proc/filesystems. You can select which filesystem types to support when building your kernel; see "Kernel configuration: make config" in Chapter 18.

Table 10-1. Linux filesystem types

Filesystem

Type

Description

Second Extended filesystem

ext2

Used to be the most common Linux filesystem, but is slowly being made obsolete by the Reiser and Third Extended filesystems

Reiser filesystem

reiserfs

A journaling filesystem for Linux

Third Extended filesystem

ext3

Another journaling filesystem for Linux that is downward-compatible with ext2

JFS

jfs

IBM's implementation of a journaled filesystem for Linux; an alternative to ext3 and reiserfs

Network File System (NFS)

NFS

Allows access to remote files on network

UMSDOS filesystem

umsdos

Installs Linux on an MS-DOS partition

DOS-FAT filesystem

msdos

Accesses MS-DOS files

VFAT filesystem

vfat

Accesses Windows 95/98/ME files

NT filesystem

ntfs

Accesses Windows NT/2000/XP files

/proc filesystem

proc

Provides process information for ps

ISO 9660 filesystem

iso9660

Used by most CD-ROM s

UDF filesystem

udf

The most modern CD-ROM filesystem

SMB filesystem

smbfs

Accesses files from a Windows server over the network

Coda filesystem

coda

An advanced network filesystem, similar to NFS

Cifs filesystem

cifs

The Common Internet File System, Microsoft's suggestion for an SMB successor; supported by Windows 2000, 2003, and XP, as well as the Samba server

Each filesystem type has its own attributes and limitations; for example, the MS-DOS filesystem restricts filenames to eight characters plus a three-character extension and should be used only to access existing MS-DOS floppies or partitions. For most of your work with Linux, you'll use the Second or Third Extended (ext2 or ext3) filesystem, which were developed primarily for Linux and support 256-character filenames, a 32-terabyte maximum filesystem size, and a slew of other goodies, or you will use the Reiser (reiserfs ). Earlier Linux systems used the Extended filesystem (no longer supported) and the Minix filesystem. (The Minix filesystem was originally used for several reasons. First of all, Linux was originally cross-compiled under Minix. Also, Linus was quite familiar with the Minix filesystem, and it was straightforward to implement in the original kernels.) Some other obscure filesystems available in