SCO Unix Serial Communications and UUCP

This article is from a FAQ concerning SCO operating systems. While some of the information may be applicable to any OS, or any Unix or Linux OS, it may be specific to SCO Xenix, Open Desktop or Openserver.

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I increased my SCO Unix UUCP window size and UUCP broke!

If your modem, or the modem on a remote site, has small data buffers, a large window size may cause the modem's buffers to overrun. If the site that broke polls your system, you may wish to create a separate copy of uucico with a smaller window size, and specify it as the login shell in /etc/passwd. If you are the polling site, you may have to restore your original uucico. Alternatively, you could try a window size of 4, then 5, then 6, then 7, and see at what point UUCP stops working. You will then know the maximum window size you can use. You may also wish to ask the sysadmin at the remote site if there is anything they can do, such as forcing flow control to be used on their modem, that may remedy the problem. You may, however, have no choice but to return to using a window size of 3. If you have a Telebit modem, see the notes below relating to Telebit modems.

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