Open System Services Programmer's Guide

Figure 2 OSS Filenames and Disks
Open System Services manages the directory tree using filesets. A fileset is a directory tree that
can be mounted or unmounted. Most literature about UNIX refers to filesets as file systems. In the
OSS and Guardian environments, the term file system also refers to the software that manages the
file system.
OSS files and directories are designated by pathnames. A pathname is the string of characters
that uniquely identifies a file within its file system. A pathname can be either relative or absolute.
An absolute pathname starts with a slash (/) and begins at the root directory. A relative pathname
does not start with a slash and begins with the current working directory. The PATH_MAX symbolic
constant in the limits.h header file defines how long OSS pathnames can be.
A directory or fileset can occupy many disk volumes. Pathnames are logical names. They have no
relationship to disk volumes, as shown in Figure 2. A file cannot occupy more than one disk volume.
Refer to the pathname(5) reference page either online or in the Open System Services System Calls
Reference Manual.
File Types
Open System Services supports these file types:
• Regular files (disk files)
• Directories
• FIFOs/pipes
• Sockets
• Symbolic links
• Character special files (Only /dev/tty terminal character files and /dev/null)
Two File Systems 29