System Administration Guide: Devices and File Systems

Additional Virtual File Systems

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

Virtual File System 



CTFS (the contract file system) is the interface for creating, controlling, and observing contracts. A contract enhances the relationship between a process and the system resources it depends on by providing richer error reporting and (optionally) a means of delaying the removal of a resource.

The service management facility (SMF) uses process contracts (a type of contract) to track the processes which compose a service, so that a failure in a part of a multi-process service can be identified as a failure of that service. 

FIFOFS (first-in first-out) 

Named pipe files that give processes common access to data

FDFS (file descriptors) 

Provides explicit names for opening files by 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


The OBJFS (object) file system describes the state of all modules currently loaded by the kernel. This file system is used by debuggers to access information about kernel symbols without having to access the kernel directly.


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

SPECFS (special) 

Provides access to character special devices and block devices


Used by the kernel for swapping