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 2.x environment.

Terminals

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Note - Your system's bit-mapped graphics display is not the same as an alphanumeric terminal, which connects to a serial port and displays only text. You don't have to perform any special steps to administer the graphics display.

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Modems

Modems can be set up in three basic configurations:

• Dial-out
• Dial-in
• Bidirectional

A modem connected to your home computer might be set up to provide dial-out service, meaning you can access other computers from your own home, but nobody outside can gain access to your machine.

Dial-in service is just the converse. It allows people to access a system from remote sites, but it does not permit calls to the outside world.

Bidirectional access, as the name implies, incorporates both dial-in and dial-out capabilities.

Ports

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 may be plugged.

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 Ethernet.

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 includes most modems, alphanumeric terminals, plotters, and some printers) can be plugged interchangeably (using standard cables) into serial ports of computers that have been similarly designed.

When many serial port devices must be connected to a single computer, it may be necessary 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.

Services

Modems and terminals gain access to computing resources via the serial port software. The 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.

Port Monitors

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.

Table 54-1 describes the two types of port monitors included in the Solaris 2.x environment.

Table 54-1

Port Monitor	Description
listen(1M)	Controls access to network services, handling remote print and file system requests. A common use of the listen port monitor is to listen for requests from the LP print service. For more information on the listen port monitor, see Chapter 56, "Setting Up Terminals and Modems With the Service Access Facility." The listen port monitor is not used when you set up modems and alphanumeric terminals.
ttymon(1M)	Provides access to the login services needed by modems and alphanumeric terminals. Solstice Serial Port Manager automatically sets up a ttymon port monitor to process login requests from these devices. Using Solstice Serial Port Manager to set up terminals and modems is described in Chapter 55, "Setting Up Terminals and Modems With Serial Port Manager."

You may be familiar with an older port monitor called getty(1M). The new ttymon is more powerful; a single ttymon can replace multiple occurrences of getty. Otherwise, these two programs serve the same function.

Tools for Managing Terminals and Modems

In previous Solaris releases, you may have used Administration Tool or Solaris commands to set up terminals and modems on a local system or remote systems. In the Solaris 2.5 release, there are three ways to manage terminals and modems:

• Admintool - A new tool to set up terminals and modems on a local system only.
• Solstice AdminSuite - Includes the tool, Serial Port Manager, to set up terminals and modems on local and remote systems.
• Service Access Facility (SAF) - A collection of background processes and administrative commands, pmadm and sacadm, used from the command line to set up port services and monitors.

Table 54-2 highlights some situations when you may choose to use one tool or the other.

Table 54-2

Procedure	Suggested Tool	Comment
Set up terminals and modems	Serial Port Manager	Solstice Serial Port Manager quickly sets up typical port services for terminals and modems. Solstice Serial Port Manager provides most of the functionality of the pmadm command.
Inform users that a port is disabled	Service Access Facility ttyadm -i	ttyadmin -i specifies the inactive (disabled) response message. The message is sent to a terminal or modem when a user attempts to log in when the port is disabled. This functionality is not provided when a port is disabled using Solstice Serial Port Manager.
Not hanging up a modem when a user logs off a host	Service Access Facility ttyadm -h	ttyadm -h specifies that the system will not hang up on a modem before setting or resetting to the default or specified value. If ttyadm -h is not used, when the user logs out of a host, the host will hang up the modem.
Require the user to type a character before the system displays a prompt	Service Access Facility ttyadm -r	ttyadm -r specifies that ttymon should require the user to type a character or press Return a specified number of times before the login prompt appears. When -r is not specified, pressing Return one or more times will print the prompt anyway. This option prevents a terminal server from issuing a welcome message that the Solaris host might misinterpret to be a user trying to log in. Without the -r option, the host and terminal server might begin looping and printing prompts to each other.

Serial Port Manager

The Serial Port Manager sets up the serial port software to work with terminals and modems by calling the pmadm command with the appropriate information. It also provides:

• Templates for common terminal and modem configurations
• Multiple port setup, modification, or deletion
• Quick visual status of each port

Service Access Facility

The SAF is the tool used for administering terminals, modems, and other network devices. In particular, SAF enables you to set up:

• ttymon and listen port monitors (using the sacadm command)
• ttymon port monitor services (using the pmadm and ttyadm commands)
• listen port monitor services (using the pmadm and nlsadmin commands)
• And troubleshoot TTY devices
• And troubleshoot incoming network requests for printing service
• And troubleshoot the Service Access Controller (using the sacadm command)

The SAF is an open-systems solution that controls access to system and network resources through TTY devices and local-area networks (LANs). SAF is not a program. It is a hierarchy of background processes and administrative commands.