All variants of UFS have the basic concepts that I just described, and it should be obvious that they are the same concepts that we saw for ExtX. The differences among the UFS-based variants are in how each of the data structures is organized and what additional features are included. There are fewer experimental features in UFS than in ExtX that affect the on-disk data.
The UFS1 file system is the default file system of Open BSD and Solaris. It used to be the default file system of FreeBSD and Net BSD until FreeBSD 5.0 and NetBSD 2.0 included UFS2. UFS2 adds support for larger files and disks and other advanced features. At the time of this writing, only FreeBSD and Net BSD support UFS2. Apple OS X and Linux also support UFS1, but it is not their default file system. Solaris also has a version of UFS to support large files and disks. Note that Sun has not published the data structures for its version of UFS, but tools developed using the essential data in the data structures published by FreeBSD work on a Solaris file system. The non-essential data may be different, though.
- Extended File System ext2, ext3, ReiserFS used in Linux
- Extended Acer Fast File system EAFS used in SCO UNIX
- Extent File System EFS, XFS used in Irix
- Fast File System FFS, UFS – Unix File System UFS/UFS2 used in BSD
- Journaling file system JFS used in Linux, AIX
- Unix File System UFS used in older BSD
- Veritas file system VFS used in HPUX, Solaris, Linux and AIX