/share/doc/psd/05.sysman/2.0.t
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- .\" @(#)2.0.t 8.1 (Berkeley) 6/8/93
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- .ds ss 1
- .sh "System facilities
- This section discusses the system facilities that
- are not considered part of the kernel.
- .PP
- The system abstractions described are:
- .IP "Directory contexts
- .br
- A directory context is a position in the UNIX file system name
- space. Operations on files and other named objects in a file system are
- always specified relative to such a context.
- .IP "Files
- .br
- Files are used to store uninterpreted sequence of bytes on which
- random access \fIreads\fP and \fIwrites\fP may occur.
- Pages from files may also be mapped into process address space.\(dg
- A directory may be read as a file.
- .FS
- \(dg Support for mapping files is not included in the 4.3 release.
- .FE
- .IP "Communications domains
- .br
- A communications domain represents
- an interprocess communications environment, such as the communications
- facilities of the UNIX system,
- communications in the INTERNET, or the resource sharing protocols
- and access rights of a resource sharing system on a local network.
- .IP "Sockets
- .br
- A socket is an endpoint of communication and the focal
- point for IPC in a communications domain. Sockets may be created in pairs,
- or given names and used to rendezvous with other sockets
- in a communications domain, accepting connections from these
- sockets or exchanging messages with them. These operations model
- a labeled or unlabeled communications graph, and can be used in a
- wide variety of communications domains. Sockets can have different
- \fItypes\fP\| to provide different semantics of communication,
- increasing the flexibility of the model.
- .IP "Terminals and other devices
- .br
- Devices include
- terminals, providing input editing and interrupt generation
- and output flow control and editing, magnetic tapes,
- disks and other peripherals. They often support the generic
- \fIread\fP and \fIwrite\fP operations as well as a number of \fIioctl\fP\|s.
- .IP "Processes
- .br
- Process descriptors provide facilities for control and debugging of
- other processes.
- .ds ss 2