Книга: Linux Network Administrator Guide, Second Edition

Identifying Available Devices Through the port File

Identifying Available Devices Through the port File

The port file tells uucico about the available ports. These are usually modem ports, but other types, such as direct serial lines and TCP sockets, are supported as well.

Like the sys file, port consists of separate entries starting with the keyword port followed by the port name. This name may be used in the sys file's port statement. The name need not be unique; if there are several ports with the same name, uucico will try each in turn until it finds one that is not currently being used.

The port command should be followed immediately by the type statement, which indicates what type of port is described. Valid types are modem, direct for direct connections, and tcp for TCP sockets. If the port command is missing, the port type defaults to modem.

In this section, we cover only modem ports; TCP ports and direct lines are discussed in a later section.

For modem and direct ports, you have to specify the device for calling out using the device directive. Usually, this is the name of a device special file in the /dev directory, like /dev/ttyS1.

In the case of a modem device, the port entry also determines what type of modem is connected to the port. Different types of modems have to be configured differently. Even modems that claim to be Hayes-compatible aren't always really compatible with one another. Therefore, you have to tell uucico how to initialize the modem and make it dial the desired number. Taylor UUCP keeps the descriptions of all dialers in a file named dial. To use any of these, you have to specify the dialer's name using the dialer command.

Sometimes, you will want to use a modem in different ways, depending on which system you call. For instance, some older modems don't understand when a high-speed modem attempts to connect at 56 kbps; they simply drop the line instead of negotiating a connect at 9,600 bps, for instance. When you know site drop uses such a dumb modem, you have to set up your modem differently when calling them. For this, you need an additional port entry in the port file that specifies a different dialer. Now you can give the new port a different name, such as serial1-slow, and use the port directive in the drop system entry in sys.

A better to distinguish the ports is by the speeds they support. For instance, the two port entries for the above situation may look like this:

# NakWell modem; connect at high speed
port            serial1         # port name
type            modem           # modem port
device          /dev/ttyS1      # this is COM2
speed           115200          # supported speed
dialer          nakwell         # normal dialer
# NakWell modem; connect at low speed
port            serial1         # port name
type            modem           # modem port
device          /dev/ttyS1      # this is COM2
speed           9600            # supported speed
dialer          nakwell-slow    # don't attempt fast connect

The system entry for site drop would now give serial1 as the port name, but request to use it at only 9,600 bps. uucico then automatically uses the second port entry. All remaining sites that have a speed of 115,200 bps in the system entry will be called using the first port entry. By default, the first entry with a matching speed will be used.

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