System Administration Guide: Network Services

Protocol Definitions in /etc/uucp/Devices File

You can define the protocol to use with each device in /etc/uucp/Devices. This specification is usually unnecessary because you can use the default or define the protocol with the particular system you are calling. Refer to UUCP /etc/uucp/Systems File for details. If you do specify the protocol, you must use the following form:

Type,Protocol [parameters]

For example, you can use TCP,te to specify the TCP/IP protocol.

The following table shows the available protocols for the Devices file.

Table 26–2 Protocols Used in /etc/uucp/Devices




This protocol is commonly used for transmissions over TCP/IP and other reliable connections. t assumes error-free transmissions.


This protocol is UUCP's native protocol. g is slow, reliable, and good for transmission over noisy telephone lines.


This protocol assumes transmission over error-free channels that are message oriented, as opposed to byte-stream oriented, such as TCP/IP.  


This protocol is used for transmission over X.25 connections. f relies on flow control of the data stream and is meant for working over links that can (almost) be guaranteed to be error free, specifically X.25/PAD links. A checksum is enacted over a whole file only. If a transport fails, the receiver can request retransmission or retransmissions.

Here is an example that shows a protocol designation for a device entry:

TCP,te - - Any TCP - 

This example indicates that, for device TCP, you should try to use the t protocol. If the other end of the transmission refuses, use the e protocol.

Neither e nor t is appropriate for use over modems. Even if the modem assures error-free transmission, data can still be dropped between the modem and the CPU.