System Administration Guide, Volume 1

Types of File Systems

The Solaris operating environment supports three types of file systems:

To identify the type for a particular file system, see "Determining a File System's Type".

Disk-Based File Systems

Disk-based file systems are stored on physical media such as hard disks, CD-ROMs, and diskettes. Disk-based file systems can be written in different formats. The available formats are:

Disk-Based File System  

Format Description 


UNIX file system (based on the BSD Fast File system that was provided in the 4.3 Tahoe release). UFS is the default disk-based file system for the Solaris operating environment.

Before you can create a UFS file system on a disk, the disk must be formatted and divided into slices. See Chapter 28, Disk Management (Overview) for complete information on formatting disks and dividing disks into slices.


High Sierra, Rock Ridge, and ISO 9660 file system. High Sierra is the first CD-ROM file system; ISO 9660 is the official standard version of the High Sierra File System. The HSFS file system is used on CD-ROMs, and is a read-only file system. Solaris HSFS supports Rock Ridge extensions to ISO 9660, which, when present on a CD-ROM, provide all UFS file system features and file types except for writability and hard links.


PC file system, which allows read/write access to data and programs on DOS-formatted disks written for DOS-based personal computers.


The UDF file system, the industry-standard format for storing information on the optical media technology called DVD (Digital Versatile Disc or Digital Video Disc).  

Each type of disk-based file system is customarily associated with a particular media device:

These associations are not, however, restrictive. For example, CD-ROMs and diskettes can have UFS file systems created on them.

Network-Based File Systems

Network-based file systems can be accessed over the network. Typically, network-based file systems reside on one system, typically a server, and are accessed by other systems across the network. NFSTM is the only available network-based or distributed computing file system.

With NFS, you can administer distributed resources (files or directories) by exporting them from a server and mounting them on individual clients. See "The NFS Environment" for more information.

Virtual File Systems

Virtual file systems are memory-based file systems that provide access to special kernel information and facilities. Most virtual file systems do not use file system disk space. However, the Cache File System (CacheFS) uses a file system on the disk to contain the cache, and some virtual file systems, such as the Temporary File System (TMPFS), use the swap space on a disk.

The Cache File System

The Cache File System (CacheFSTM) can be used to improve performance of remote file systems or slow devices such as CD-ROM drives. When a file system is cached, the data read from the remote file system or CD-ROM is stored in a cache on the local system. See Chapter 37, The Cache File System (Tasks) for detailed information on setting up and administering CacheFS File Systems.

The Temporary File System

The Temporary File System (TMPFS) uses local memory for file system reads and writes, which is typically much faster than a UFS file system. Using TMPFS can improve system performance by saving the cost of reading and writing temporary files to a local disk or across the network. For example, temporary files are created when you compile a program, and the operating system generates a lot of disk or network activity while manipulating these files. Using TMPFS to hold these temporary files can significantly speed up their creation, manipulation, and deletion.

Files in TMPFS file systems are not permanent. They are deleted when the file system is unmounted and when the system is shut down or rebooted.

TMPFS is the default file system type for the /tmp directory in the Solaris operating environment. You can copy or move files into or out of the /tmp directory, just as you would in a UFS file system.

The TMPFS file system uses swap space as a temporary backing store. If a system with a TMPFS file system does not have adequate swap space, two problems can occur:

See Chapter 35, Creating File Systems (Tasks) for information about creating TMPFS file systems. See Chapter 38, Configuring Additional Swap Space (Tasks) for information about increasing swap space.

The Loopback File System

The Loopback File System (LOFS) lets you create a new virtual file system, so you can access files by using an alternative path name. For example, you can create a loopback mount of root (/) on /tmp/newroot, which will make the entire file system hierarchy look like it is duplicated under /tmp/newroot, including any file systems mounted from NFS servers. All files will be accessible either with a path name starting from root (/), or with a path name starting from /tmp/newroot.

See Chapter 35, Creating File Systems (Tasks) for information on how to create LOFS file systems.

The Process File System

The Process File System (PROCFS) resides in memory. It contains a list of active processes, by process number, in the /proc directory. Information in the /proc directory is used by commands like ps. Debuggers and other development tools can also access the address space of the processes by using file system calls.

Caution - Caution -

Do not delete the files in the /proc directory. Deleting processes from the /proc directory will not kill them. Remember, /proc files do not use disk space, so there is little reason to delete files from this directory.

The /proc directory does not require system administration.

Additional Virtual File Systems

These additional types of virtual file systems are listed for your information. They do not require administration.

Virtual File System 


FIFOFS (first-in first-out) 

Named pipe files that give processes common access to data

FDFS (file descriptors) 

Provides explicit names for opening files using file descriptors


Used mostly by STREAMS for dynamic mounts of file descriptors on top of files

SPECFS (special) 

Provides access to character special and block devices


File system used by the kernel for swapping