Linux Network Administrator Guide, Second Edition

G

This is the System V Release 4 version of the g protocol. It is also understood by some other versions of UUCP.

a

This protocol is similiar to ZMODEM. It requires an 8-bit connection, but quotes certain control characters like XON and XOFF.

Tuning the Transmission Protocol

All protocols allow for some variation in packet sizes, timeouts, etc. Usually, the defaults work well under standard circumstances, but may not be optimal for your situation. The g protocol, for instance, uses window sizes from 1 to 7, and packet sizes in powers of 2 ranging from 64 through 4096. If your telephone line is usually so noisy that it drops more than 5 percent of all packets, you should probably lower the packet size and shrink the window. On the other hand, on very good telephone lines the protocol overhead of sending acknowledgments for every 128 bytes may prove wasteful, so you might increase the packet size to 512 or even 1,024. Most binaries included in Linux distributions default to a window size of 7 and 128-byte packets.

Taylor UUCP lets you tune parameters with the protocol-parameter command in the sys file. For instance, to set the g protocol's packet size to 512 when talking to pablo, you have to add:

system pablo
…
protocol-parameter g packet-size 512

The tunable parameters and their names vary from protocol to protocol. For a complete list of them, refer to the documentation enclosed in the Taylor UUCP source.

Selecting Specific Protocols

Not every implementation of uucico speaks and understands each protocol, so during the initial handshake phase, both processes have to agree on a common one. The master uucico offers the slave a list of supported protocols by sending P protlist, from which the slave may pick one.

Based on the type of port used (modem, TCP, or direct), uucico will compose a default list of protocols. For modem and direct connections, this list usually comprises i, a, g, G, and j. For TCP connections, the list is t, e, i, a, g, G, j, and f. You can override this default list with the protocols command, which may be specified in a system entry as well as a port entry. For instance, you might edit the port file entry for your modem port like this:

port serial1
…
protocols igG

This will require any incoming or outgoing connection through this port to use i, g, or G. If the remote system does not support any of these, the conversation will fail.

Troubleshooting

This section describes what may go wrong with your UUCP connection and makes location suggestions to fix the error. Although these problems are encountered on a regular basis, there is much more that can go wrong than what we have listed.

If you have a problem, enable debugging with -xall, and take a look at the output in Debug in the spool directory. The file should help you to quickly recognize the problem. It is often helpful to turn on the modem's speaker when it doesn't connect. With Hayes-compatible modems, you can turn on the speaker by adding ATL1M1 OK to the modem chat in the dial file.

The first check should always be whether all file permissions are set correctly. uucico should be setuid uucp, and all files in /usr/lib/uucp, /var/spool/uucp, and /var/spool/uucppublic should be owned by uucp. There are also some hidden files in the spool directory which must be owned by uucp as well.[104]

When you're sure you have the permissions of all files set correctly, and you're still experiencing problems, you can then begin to take error messages more literally. We'll now look at some of the more common errors and problems.

uucico Keeps Saying 'Wrong Time to Call'

This probably means that in the system entry in sys, you didn't specify a time command that details when the remote system may be called, or you gave one that actually forbids calling at the current time. If no call schedule is given, uucico assumes the system can never be called.

uucico Complains That the Site Is Already Locked

This means that uucico detects a lock file for the remote system in /var/spool/uucp. The lock file may be from an earlier call to the system that crashed or was killed. Another possible explanation is that there's another uucico process sitting around that is trying to dial the remote system and has gotten stuck in a chat script, or stalled for some other reason.

To correct this error, kill all uucico processes open for the site with a hangup signal, and remove all lock files that they have left lying around.

You Can Connect to the Remote Site, but the Chat Script Fails

Look at the text you receive from the remote site. If it's garbled, you might have a speed-related problem. Otherwise, confirm that it really agrees with what your chat script expects. Remember, the chat script starts with an expect string. If you receive the login prompt and send your name, but never get the password prompt, insert some delays before sending it, or even in between the letters. You might be too fast for your modem.