Certification Objective 4.03: Red Hat Filesystem Basics

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There are as many, if not more, filesystem types as there are operating systems. RHEL 3 can work with many of these formats.

At the heart of every RHEL 3 installation are the filesystems on which it relies. Linux supports a rich variety of filesystem types. For Linux, we can divide filesystems into two categories: 'standard' formatting and journaling. While this is an oversimplification, it suffices to describe the filesystems important to Linux. To me, a standard filesystem is an older Linux filesystem or more static systems.

On The Job 

There are a large number of filesystem types, well described in the Filesystems HOWTO at www.tldp.org. Strictly speaking, there is no 'standard' filesystem, and in this book, I include a 'balanced tree' filesystem (ReiserFS) as a journaling filesystem, just to be more consistent with the Red Hat outlines.

The filesystems I describe in this book are just a small list of those available for RHEL 3. If you have the kernel source RPMs loaded on your system, you can find a list of the filesystems supported by your kernel. Navigate to the /usr/src/linux-2.4 directory. Run the make menuconfig command and use your arrow keys to navigate to the filesystems section.

Standard Formatting Filesystems

Linux is a clone of Unix. The Linux filesystems were developed from the Unix filesystems available at the time. The first Linux operating systems used the Extended Filesystem (ext). Until the past couple of years, Red Hat Linux operating systems formatted their partitions by default to the Second Extended Filesystem (ext2).

I also include some other filesystems that you might see in RHEL 3. These 'standard' filesystems don't include journaling features. I illustrate a sample of these filesystem types in Table 4-6.

Table 4-6: Linux Standard Filesystem Type

Filesystem Type	Description
ext	The first Linux filesystem, used only on early versions of that operating system.
ext2 (Second Extended)	The foundation for ext3, the default RHEL 3 filesystem. The ext3 filesystem is essentially ext2 with journaling.
swap	The Linux swap filesystem is associated with dedicated swap partitions. You've probably created at least one swap partition when you installed RHEL 3.
MS-DOS and VFAT	These filesystems allow you to read MS-DOS-formatted filesystems. MS-DOS lets you read pre-Windows 95 partitions, or regular Windows partitions within the limits of short filenames. VFAT lets you read Windows 9x/NT/2000/XP/2003 partitions formatted to the FAT16 or FAT32 filesystems.
ISO 9660	The standard filesystem for CD-ROMs. It is also known as the High Sierra File System, or HSFS, on other Unix systems.
NTFS	NTFS is the Microsoft Windows NT/2000/XP/2003 filesystem designed for username/password security. Currently supported as a read-only system.
/proc	The /proc filesystem is a Linux virtual filesystem. Virtual means that it doesn't occupy real disk space. Instead, files are created as needed. /proc is used to provide information on kernel configuration and device status.
/dev/pts	The /dev/pts filesystem is the Linux implementation of the Open Group's Unix98 PTY support.
NFS	The Network File System. This is the system most commonly used to share files and printers between Linux and Unix computers.
SMB	Server Message Block (SMB) is based on Microsoft and IBM network protocols. Linux can use SMB to share files and printers with Microsoft Windows operating systems. Works with Microsoft's Common Internet File System (CIFS).

Journaling Filesystems

As hard disks and partitions grow in size, Linux users are moving toward filesystems with journaling features. Journaling filesystems have two main advantages. First, it's faster to check them during the boot process. Second, if there's a crash, a journaling filesystem has a log (also known as a journal) which can be used to restore the metadata for the files on the relevant partition.

The default RHEL 3 filesystem is the Third Extended Filesystem, also known as ext3. However, it isn't the only journaling filesystem option available. I list a few of the options available for RHEL 3 in Table 4-7.

Table 4-7: Journaling Filesystems

Filesystem Type	Description
ext3	The default filesystem for RHEL 3.
JFS	JFS is IBM's journaled filesystem. This is commonly used on IBM enterprise servers.
ReiserFS	The Reiser File System is resizable and supports fast journaling. It's more efficient when most of the files are very small and very large. It's based on the concept of 'balanced trees.' While supported by RHEL 3, it is not the default Red Hat filesystem and is explicitly cited only in the RHCT course (RH133) syllabus. For more information, see www.namesys.com.
xfs	Developed by Silicon Graphics as a journaling filesystem. Supports very large files; as of this writing, xfs files are limited to 9 x 1018 bytes. Do not confuse this filesystem with the X Font Server; both use the same acronym.

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