See
Text-Terminal-HOWTO for a more detailed (but still
incomplete) discussion of terminals. The instructions in this
section will work for connecting terminals, as well as other
computers to the serial port on your Linux box.
Make sure you have the right kind of cable. A null modem cable bought at a computer store may do it, but it probably will not work for hardware flow control. But it must be a null modem cable! Many computer stores advertise this kind of cable as a serial printer cable. Make sure you are using your serial port, the male DB25 or the DB9, and not your parallel port (female DB25 or centronics).
For a DB25 connector, you need a minimum of:
PC male DB25 Terminal DB25
TxD Transmit Data 2 --> 3 RxD Receive Data
RxD Receive Data 3 <-- 2 TxD Transmit Data
SG Signal Ground 7 --- 7 SG Signal Ground
This null modem cable works OK between two computers that use RTS/CTS hardware handshaking signals, but many terminals use DTR handshaking which can't be set in linux with "stty". A workaround is to stty crtscts and connect terminal pin 20 (DTR) with the PC pin 5 (CTS).
PC male DB25 Terminal DB25
TxD Transmit Data 2 --> 3 RxD Receive Data
RxD Receive Data 3 <-- 2 TxD Transmit Data
RTS Request To Send 4 --> 5 CTS Clear To Send
CTS Clear To Send 5 <-- 4 RTS Request To Send
DSR Data Set Ready 6
|
DCD Carrier Detect 8 <-- 20 DTR Data Terminal Ready
SG Signal Ground 7 --- 7 SG Signal Ground
6 DSR Data Set Ready
|
DTR Data Terminal Ready 20 --> 8 DCD Carrier Detect
If you have a DB9 connector on your serial port, try the following:
PC DB9 Terminal DB25
RxD Receive Data 2 <-- 2 TxD Transmit Data
TxD Transmit Data 3 --> 3 RxD Receive Data
SG Signal Ground 5 --- 7 SG Signal Ground
Alternatively, a full DB9-DB25 null modem cable (Not likely to work with terminal hardware handshaking; see above):
PC DB9 Terminal DB25
RxD Receive Data 2 <-- 2 TxD Transmit Data
TxD Transmit Data 3 --> 3 RxD Receive Data
6 DSR Data Set Ready
|
DTR Data Terminal Ready 4 --> 8 DCD Carrier Detect
GND Signal Ground 5 --- 7 GND Signal Ground
DCD Carrier Detect 1
|
DSR Data Set Ready 6 <-- 20 DTR Data Terminal Ready
RTS Request To Send 7 --> 5 CTS Clear To Send
CTS Clear To Send 8 <-- 4 RTS Request To Send
(RI Ring Indicator 9 not needed)
(Yes, the pins 2 and 3 really do have the opposite meanings in
DB9 connectors than in DB25 connectors!)
If you are not using a full null modem cable, you might have to do the following trick: on your computer side of the connector, connect RTS and CTS together, and also connect DSR, DCD and DTR together. This way, when the computer wants a certain handshaking signal, it will get it (from itself).
Now that you have the right kind of cable?, connect your terminal to your computer. If you can, tell the terminal to ignore modem control signals. Try using 9600 bps, 8 data bits, 1 stop bit, no parity bits for the terminal's setup (or enable parity if you want to be more sophisticated).
getty (part of getty_ps)
Consult your getty manual for other getty programs such as agetty.
Add entries for getty to use for your terminal in
/etc/gettydefs if there they aren't already there:
# 38400 bps Dumb Terminal entry
DT38400# B38400 CS8 CLOCAL # B38400 SANE -ISTRIP CLOCAL #@S @L login: #DT38400
# 19200 bps Dumb Terminal entry
DT19200# B19200 CS8 CLOCAL # B19200 SANE -ISTRIP CLOCAL #@S @L login: #DT19200
# 9600 bps Dumb Terminal entry
DT9600# B9600 CS8 CLOCAL # B9600 SANE -ISTRIP CLOCAL #@S @L login: #DT9600
If you want, you can make getty print interesting things in the
login banner. In my examples, I have the system name and the serial
line printed. You can add other things:
@B The current (evaluated at the time the @B is seen) bps rate.
@D The current date, in MM/DD/YY.
@L The serial line to which getty is attached.
@S The system name.
@T The current time, in HH:MM:SS (24-hour).
@U The number of currently signed-on users. This is a
count of the number of entries in the /etc/utmp file
that have a non-null ut_name field.
@V The value of VERSION, as given in the defaults file.
To display a single '@' character, use either '\@' or '@@'.
When you are done editing /etc/gettydefs, you can verify that
the syntax is correct by doing:
linux# getty -c /etc/gettydefs
Make sure there is no getty or uugetty config file for the
serial port that your terminal is attached to
(/etc/default/{uu}getty.ttySN or
/etc/conf.{uu}getty.ttySN), as this will probably
interfere with running getty on a terminal. Remove the file if
it exits.
Edit your /etc/inittab file to run getty on the serial
port (substituting in the correct information for your environment -
port, speed, and default terminal type):
S1:456:respawn:/sbin/getty ttyS1 DT9600 vt100
init:
linux# init q
At this point, you should see a login prompt on your terminal. You may have to hit return to get the terminal's attention.
Many people set up other PCs as terminals connected to Linux
boxes. For example, old 8088 or 80286 PCs are perfect for this purpose.
All you need is a DOS boot disk containing a version of DOS suitable
for your terminal-PC, and a communications program for your
terminal-PC to run. kermit works very well for this purpose.
You can find pre-compiled versions of kermit for every
OS in existence at
http://www.columbia.edu/kermit/.
Other popular DOS comm programs such as telix and procomm
will work equally well. Be sure to input correct serial port
information into your terminal-PC's communications setup.