Terminals, Modems, Ports, and Services
Terminals and modems provide both local and remote access to system and network
resources. Setting up terminals and modem access is an important responsibility of a
system administrator. This section explains some of the concepts behind modem and terminal
management in the Solaris Operating System.
Your system's bitmapped graphics display is not the same as an alphanumeric terminal.
An alphanumeric terminal connects to a serial port and displays only text. You
don't have to perform any special steps to administer the graphics display.
Modems can be set up in three basic configurations:
A modem connected to your home computer might be set up to provide
dial-out service. With dial-out service, you can access other computers from your own
home. However, nobody outside can gain access to your machine.
Dial-in service is just the opposite. Dial-in service allows people to access a
system from remote sites. However, it does not permit calls to the outside
Bidirectional access, as the name implies, provides both dial-in and dial-out capabilities.
A port is a channel through which a device communicates with the operating
system. From a hardware perspective, a port is a “receptacle” into which a
terminal or modem cable might be physically connected.
However, a port is not strictly a physical receptacle, but an entity with
hardware (pins and connectors) and software (a device driver) components. A single physical
receptacle often provides multiple ports, allowing connection of two or more devices.
Common types of ports include serial, parallel, small computer systems interface (SCSI), and
A serial port, using a standard communications protocol, transmits a byte of information bit-by-bit over
a single line.
Devices that have been designed according to RS-232-C or RS-423 standards, this include
most modems, alphanumeric terminals, plotters, and some printers. These devices can be connected
interchangeably, using standard cables, into serial ports of computers that have been
When many serial port devices must be connected to a single computer, you
might need to add an adapter board to the system. The adapter board,
with its driver software, provides additional serial ports for connecting more devices than
could otherwise be accommodated.
Modems and terminals gain access to computing resources by using serial port software.
Serial port software must be set up to provide a particular “service” for
the device attached to the port. For example, you can set up
a serial port to provide bidirectional service for a modem.
The main mechanism for gaining access to a service is through a port monitor.
A port monitor is a program that continuously monitors for requests to log
in or access printers or files.
When a port monitor detects a request, it sets whatever parameters are required
to establish communication between the operating system and the device requesting service. Then,
the port monitor transfers control to other processes that provide the services needed.
The following table describes the two types of port monitors included in the
Solaris Operating System.
Table 1-1 Port Monitor Types
Controls access to network services, such as handling
remote print requests prior to the Solaris 2.6 release. The default Solaris Operating
System no longer uses this port monitor type.
Provides access to the login
services needed by modems and alphanumeric terminals. The Serial Ports tool automatically sets
up a ttymon port monitor to process login requests from these devices.
You might be familiar with an older port monitor called getty. The new ttymon
port monitor is more powerful. A single ttymon port monitor can replace
multiple occurrences of getty. Otherwise, these two programs serve the same function. For
more information, see the getty(1M) man page.