There are three system configuration files in the /etc
directory that you'll probably need to edit to allow dialup access to
your FreeBSD system. The first, /etc/gettytab, contains
configuration information for the /usr/libexec/getty daemon.
Second, /etc/ttys holds information that tells
/sbin/init what tty devices should have getty
processes running on them. Lastly, you can place port initialization
commands in the /etc/rc.serial script if you have FreeBSD
1.1.5.1 or higher; otherwise, you can initialize ports in the
/etc/rc.local script.
There are two schools of thought regarding dialup modems on UNIX. One group likes to configure their modems and system so that no matter at what speed a remote user dials in, the local computer-to-modem RS-232 interface runs at a locked speed. The benefit of this configuration is that the remote user always sees a system login prompt immediately. The downside is that the system doesn't know what a user's true data rate is, so full-screen programs like Emacs won't adjust their screen-painting methods to make their response better for slower connections.
The other school configures their modems' RS-232 interface to vary its
speed based on the remote user's connection speed. For example,
V.32bis (14.4 Kbps) connections to the modem might make the modem run
its RS-232 interface at 19.2 Kbps, while 2400 bps connections make the
modem's RS-232 interface run at 2400 bps. Because getty doesn't
understand any particular modem's connection speed reporting,
getty gives a login: message at an initial speed and watches
the characters that come back in response. If the user sees junk,
it's assumed that they know they should press the
<Enter> key until they see a recognizable prompt. If
the data rates don't match, getty sees anything the user types as
``junk'', tries going to the next speed and gives the login:
prompt again. This procedure can continue ad nauseum, but normally
only takes a keystroke or two before the user sees a good prompt.
Obviously, this login sequence doesn't look as clean as the former
``locked-speed'' method, but a user on a low-speed connection should
receive better interactive response from full-screen programs.
The author will try to give balanced configuration information, but is biased towards having the modem's data rate follow the connection rate.
/etc/gettytab is a termcap(5)-style file of
configuration information for getty(8). Please see the
gettytab(4) manual page for complete information on the format of
the file and the list of capabilities.
If you are locking your modem's data communications rate at a
particular speed, you probably won't need to make any changes to
/etc/gettytab.
You'll need to setup an entry in /etc/gettytab to give
getty information about the speeds you wish to use for your
modem. If you have a 2400 bps modem, you can probably use the
existing D2400 entry. This entry already exists in the FreeBSD
1.1.5.1 gettytab file, so you don't need to add it unless it is
missing under your version of FreeBSD:
#
# Fast dialup terminals, 2400/1200/300 rotary (can start either way)
#
D2400|d2400|Fast-Dial-2400:\
:nx=D1200:tc=2400-baud:
3|D1200|Fast-Dial-1200:\
:nx=D300:tc=1200-baud:
5|D300|Fast-Dial-300:\
:nx=D2400:tc=300-baud:
If you have a higher speed modem, you'll probably need to add an entry
in /etc/gettytab; here's an entry you could use for a 14.4
Kbps modem with a top interface speed of 19.2 Kpbs:
#
# Additions for a V.32bis Modem
#
um|V300|High Speed Modem at 300,8-bit:\
:nx=V19200:tc=std.300:
un|V1200|High Speed Modem at 1200,8-bit:\
:nx=V300:tc=std.1200:
uo|V2400|High Speed Modem at 2400,8-bit:\
:nx=V1200:tc=std.2400:
up|V9600|High Speed Modem at 9600,8-bit:\
:nx=V2400:tc=std.9600:
uq|V19200|High Speed Modem at 19200,8-bit:\
:nx=V9600:tc=std.19200:
On FreeBSD 1.1.5 and later, this will result in 8-bit, no parity
connections. Under FreeBSD 1.1, add :np: parameters to the
std.xxx entries at the top of the file for 8 bits, no
parity; otherwise, the default is 7 bits, even parity.
The example above starts the communications rate at 19.2 Kbps (for a
V.32bis connection), then cycles through 9600 bps (for V.32), 2400
bps, 1200 bps, 300 bps, and back to 19.2 Kbps. Communcations rate
cycling is implemented with the nx= (next table) capability.
Each of the lines uses a tc= (table continuation) entry to
pick up the rest of the ``standard'' settings for a particular data
rate.
If you have a 28.8 Kbps modem and/or you want to take advantage of
compression on a 14.4 Kbps modem, you need to use a higher
communications rate than 19.2 Kbps. Here's an example of a
gettytab entry starting a 57.6 Kpbs:
#
# Additions for a V.32bis or V.34 Modem
# Starting at 57.6 Kpbs
#
vm|VH300|Very High Speed Modem at 300,8-bit:\
:nx=VH57600:tc=std.300:
vn|VH1200|Very High Speed Modem at 1200,8-bit:\
:nx=VH300:tc=std.1200:
vo|VH2400|Very High Speed Modem at 2400,8-bit:\
:nx=VH1200:tc=std.2400:
vp|VH9600|Very High Speed Modem at 9600,8-bit:\
:nx=VH2400:tc=std.9600:
vq|VH57600|Very High Speed Modem at 57600,8-bit:\
:nx=VH9600:tc=std.57600:
If you have a slow CPU or a heavily loaded system and you don't have 16550A-based serial ports, you may receive sio ``silo'' errors at 57.6 Kbps.
/etc/ttys is the list of ttys for init to monitor.
/etc/ttys also provides security information to login
(user root may only login on ttys marked secure). See the
manual page for ttys(5) for more information.
You'll need to either modify existing lines in /etc/ttys or
add new lines to make init run getty processes automatically
on your new dialup ports. The general format of the line will be the
same, whether you are using a locked-speed or matching-speed
configuration:
ttyd0 "/usr/libexec/getty xxx" dialup on
The first item in the above line is the device special file for this
entry - ttyd0 means /dev/ttyd0 is the file that this
getty will be watching. The second item, "/usr/libexec/getty
xxx" (xxx will be replaced by the initial gettytab
capability) is the process init will run on the device. The
third item, dialup, is the default terminal type. The fourth
parameter, on, indicates to init that the line is
operational. There can be a fifth parameter, secure, but it
should only be used for terminals which are physically secure (such as
the system console).
The default terminal type (dialup in the example above) may
depend on local preferences. dialup is the traditional default
terminal type on dialup lines so that users may customize their login
scripts to notice when the terminal is dialup and automatically
adjust their terminal type. However, the author finds it easier at
his site to specify vt102 as the default terminal type, since the
users just use VT102 emulation on their remote systems.
After you have made changes to /etc/ttys, you may send the
init process a HUP signal to re-read the file. You can use
the command
kill -1 1
to send the signal. If this is your first time setting up the system,
though, you may want to wait until your modem(s) are properly
configured and connected before signalling init.
For a locked-speed configuration, your ttys entry needs to
have a fixed-speed entry provided to getty. For a modem whose
port speed is locked at 19.2 Kbps, the ttys entry might look like
this:
ttyd0 "/usr/libexec/getty std.19200" dialup on
If your modem is locked at a different data rate, substitute the
appropriate name for the std.speed entry for
std.19200 from /etc/gettytab for your modem's data rate.
In a matching-speed configuration, your ttys entry needs to
reference the appropriate beginning ``auto-baud'' (sic) entry in
/etc/gettytab. For example, if you added the above suggested
entry for a matching-speed modem that starts at 19.2 Kbps (the
gettytab entry containing the V19200 starting point), your
ttys entry might look like this:
ttyd0 "/usr/libexec/getty V19200" dialup on
High-speed modems, like V.32, V.32bis, and V.34 modems, need to use
hardware (RTS/CTS) flow control. You can add stty
commands to /etc/rc.serial on FreeBSD 1.1.5.1 and up, or
/etc/rc.local on FreeBSD 1.1, to set the hardware flow
control flag in the FreeBSD kernel for the modem ports.
For example, on a sample FreeBSD 1.1.5.1 system,
/etc/rc.serial reads:
#!/bin/sh
#
# Serial port initial configuration
stty -f /dev/ttyid1 crtscts
stty -f /dev/cuai01 crtscts
which sets the termios flag crtscts on serial port #1's
(COM2:) dialin and dialout initialization devices.
On an old FreeBSD 1.1 system, these entries were added to
/etc/rc.local to set the crtscts flag on the devices:
# Set serial ports to use RTS/CTS flow control
stty -f /dev/ttyd0 crtscts
stty -f /dev/ttyd1 crtscts
stty -f /dev/ttyd2 crtscts
stty -f /dev/ttyd3 crtscts
Since there isn't an initialization device special file on FreeBSD 1.1, one has to just set the flags on the sole device special file and hope the flags aren't cleared by a miscreant.