System Administration Guide: Basic Administration

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 CacheFS file system uses a file system on the disk to contain the cache. Also, some virtual file systems, such as the temporary file system (TMPFS), use the swap space on a disk.

The CacheFS File System

The CacheFSTM file system 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 that is read from the remote file system or CD-ROM is stored in a cache on the local system.

If you want to improve the performance and scalability of an NFS or CD-ROM file system, you should use the CacheFS file system. The CacheFS software is a general purpose caching mechanism for file systems that improves NFS server performance and scalability by reducing server and network load.

Designed as a layered file system, the CacheFS software provides the ability to cache one file system on another. In an NFS environment, CacheFS software increases the client per server ratio, reduces server and network loads, and improves performance for clients on slow links, such as Point-to-Point Protocol (PPP). You can also combine a CacheFS file system with the AutoFS service to help boost performance and scalability.

For detailed information about the CacheFS file system, see Chapter 41, Using The CacheFS File System (Tasks).

The Universal Disk Format (UDF) File System

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

The UDF file system is provided as dynamically loadable, 32–bit and 64–bit modules, with system administration utilities for creating, mounting, and checking the file system on both SPARC and x86 platforms. The Solaris UDF file system works with supported ATAPI and SCSI DVD drives, CD-ROM devices, and disk and diskette drives. In addition, the Solaris UDF file system is fully compliant with the UDF 1.50 specification.

The UDF file system provides the following features:

The following features are not included in the UDF file system:

The UDF file system requires the following:

The Solaris UDF file system implementation provides:

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 activity 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:

For information about creating TMPFS file systems, see Chapter 39, Creating File Systems (Tasks). For information about increasing swap space, see Chapter 42, Configuring Additional Swap Space (Tasks).

The Loopback File System

The loopback file system (LOFS) lets you create a new virtual file system so that 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 that starts from /tmp/newroot.

For information on how to create LOFS file systems, see Chapter 39, Creating File Systems (Tasks).

Process File System

The process file system (PROCFS) resides in memory and 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. The deletion of processes from the /proc directory does 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 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


Provides read-only access to the table of mounted file systems for the local system 


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

SPECFS (special) 

Provides access to character special devices and block devices


Used by the kernel for swapping