Now that we are familiar with fundamental concepts related to filesystem implementations, we will explore filesystem services supported by Linux systems. The kernel's filesystem branch has implementations of numerous filesystem services, which support diverse file types. Based on the type of files they manage, the kernel's filesystems can be broadly categorized into:
- Storage filesystems
- Special filesystems
- Distributed filesystems or network filesystems
We shall discuss special filesystems in a later section of this chapter.
- Storage filesystems: Kernel supports various persistent storage filesystems, which can be broadly categorized into various groups based on the type of storage device they are designed to manage.
- Disk filesystems: This category includes various standard storage disk filesystems supported by the kernel, which includes the Linux native ext family of disk filesystems, such as Ext2, Ext3, Ext4, ReiserFS, and Btrfs; Unix variants such as the sysv filesystem, UFS, and MINIX filesystem; Microsoft filesystems such as MS-DOS, VFAT, and NTFS; other proprietary filesystems such as IBM's OS/2 (HPFS), Qnx based filesystems such as qnx4 and qnx6, Apple's Macintosh HFS and HFS2, Amiga's Fast Filesystem (AFFS), and Acorn Disk Filing System (ADFS); and journaling filesystems like IBM's JFS and SGI's XFS.
- Removable media filesystems: This category includes filesystems designed for CD, DVD, and other movable storage media devices, such as the ISO9660 CD-ROM filesystem and Universal Disk Format (UDF) DVD filesystem, and squashfs used in live CD images for Linux distributions.
- Semiconductor storage filesystems: This category includes filesystems designed and implemented for raw flash and other semiconductor storage devices that require support of wear-leveling and erase operations. The current set of filesystems supported include UBIFS, JFFS2, CRAMFS, and so on.
We shall discuss in brief a few native disk filesystems in the kernel, which are used across various distributions of Linux as default.