HP-UX System Administrator's Guide: Routine Management Tasks

on the screen. Garbage on the screen comes in two types: garbage intermixed with
valid data characters and complete garbage.
What to check for when garbage is mixed with valid data
The following is a list of possible reasons for garbage characters intermixed with your
valid data:
• Noise on the data line:
— RS-232 Cable too long (maximum recommended length is 50 feet)
— Data cable near electrically noisy equipment (motors, etc.)
— Partially shorted or broken wires within the cable
— Noisy connection (if using phone lines)
• Hardware problem with a modem, interface card, or the terminal itself
• The program performing I/O could be sending the garbage
• The Display Functns* feature of your terminal is enabled (which displays characters
that would not normally print)
What to check for when everything printed is garbage
One of the most common reasons for total garbage on the screen (and certainly the first
thing you should check) is a Baud-rate mismatch. If your terminal’s speed setting is
different than that of the line (as set with the stty command), you will get garbage
on your screen (if anything at all).
Here is a list of other possible reasons for total garbage on your screen.
If you have not yet logged in, try pressing the break key. This tells getty to try the
next entry in the /etc/gettydefs file. The gettydefs file can be set up so that, as
getty tries various entries, it will also be trying various speed settings (this is usually
how it’s set up). getty will then try various speeds (with each press of the break key).
When the correct speed is matched, you will get a login prompt that is readable.
• The shell environment variable called TERM isn’t set to a value appropriate to your
terminal. If you have an HP terminal, try setting the value of TERM to hp
(lowercase) using your shell’s set command.
• A running process is producing garbage output
• A miswired cable
• Excessive noise on the data line
• A hardware failure (bad interface card, modem, MUX, etc.)
162 Managing Systems