Serial CommunicationsSynopsisserial communications&unix; has always had support for serial communications. In fact,
the very first &unix; machines relied on serial lines for user input
and output. Things have changed a lot from the days when the average
terminal consisted of a 10-character-per-second serial
printer and a keyboard. This chapter will cover some of the ways in
which FreeBSD uses serial communications.After reading this chapter, you will know:How to connect terminals to your FreeBSD
system.How to use a modem to dial out to remote
hosts.How to allow remote users to login to your
system with a modem.How to boot your system from a serial console.Before reading this chapter, you should:Know how to configure and install a new kernel ().Understand &unix; permissions and processes ().Have access to the technical manual for the serial hardware
(modem or multi-port card) that you would like to use with
FreeBSD.IntroductionAs of &os; 8.0, device nodes for serial ports have been
renamed from
/dev/cuadN to
/dev/cuauN and
from
/dev/ttydN to
/dev/ttyuN.
&os; 7.X users will have to adapt the following
documentation according to these changes.Terminologybits-per-secondbpsBits per Second — the rate at which data is
transmittedDTEDTEData Terminal Equipment — for example, your
computerDCEDCEData Communications Equipment — your modemRS-232RS-232C cablesEIA standard for hardware serial communicationsWhen talking about communications data rates, this section
does not use the term baud. Baud refers to the
number of electrical state transitions that may be made in a
period of time, while bps (bits per second) is
the correct term to use (at least it does not
seem to bother the curmudgeons quite as much).Cables and PortsTo connect a modem or terminal to your FreeBSD system, you
will need a serial port on your computer and the proper cable to
connect to your serial device. If you are already familiar with your
hardware and the cable it requires, you can safely skip this
section.CablesThere are several different kinds of serial cables. The
two most common types for our purposes are null-modem cables
and standard (straight) RS-232 cables. The
documentation for your hardware should describe the type of cable
required.Null-modem Cablesnull-modem cableA null-modem cable passes some signals, such as
Signal Ground, straight through, but switches other
signals. For example, the Transmitted Data pin on
one end goes to the Received Data pin on the other
end.You can also construct your own null-modem cable for use with
terminals (e.g., for quality purposes). This table shows the
RS-232C signals
and the pin numbers on a DB-25 connector. Note that the standard
also calls for a straight-through pin 1 to pin 1
Protective Ground line, but it is often
omitted. Some terminals work OK using only pins 2, 3 and 7,
while others require different configurations than the examples
shown below.
When one pin at one end connects to a pair of pins
at the other end, it is usually implemented with one short
wire between the pair of pins in their connector and a
long wire to the other single pin.The above designs seems to be the most popular. In another
variation (explained in the book RS-232 Made
Easy) SG connects to SG, TD connects to RD, RTS and
CTS connect to DCD, DTR connects to DSR, and vice-versa.Standard RS-232C CablesRS-232C cablesA standard serial cable passes all of the RS-232C signals
straight through. That is, the Transmitted Data
pin on one end of the cable goes to the
Transmitted Data pin on the other end. This is
the type of cable to use to connect a modem to your FreeBSD
system, and is also appropriate for some terminals.PortsSerial ports are the devices through which data is transferred
between the FreeBSD host computer and the terminal. This section
describes the kinds of ports that exist and how they are addressed
in FreeBSD.Kinds of PortsSeveral kinds of serial ports exist. Before you purchase or
construct a cable, you need to make sure it will fit the ports on
your terminal and on the FreeBSD system.Most terminals will have DB-25 ports. Personal computers,
including PCs running FreeBSD, will have DB-25 or DB-9 ports. If
you have a multiport serial card for your PC, you may have RJ-12 or
RJ-45 ports.See the documentation that accompanied the hardware for
specifications on the kind of port in use. A visual inspection of
the port often works too.Port NamesIn FreeBSD, you access each serial port through an entry in
the /dev directory. There are two different
kinds of entries:Call-in ports are named
/dev/ttyuN
where N is the port number,
starting from zero. Generally, you use the call-in port for
terminals. Call-in ports require that the serial line assert
the data carrier detect (DCD) signal to work correctly.Call-out ports are named
/dev/cuauN.
You usually do not use the call-out port for terminals, just
for modems. You may use the call-out port if the serial cable
or the terminal does not support the carrier detect
signal.If you have connected a terminal to the first serial port
(COM1 in &ms-dos;), then you will
use /dev/ttyu0 to refer to the terminal. If
the terminal is on the second serial port (also known as
COM2), use
/dev/ttyu1, and so forth.Kernel ConfigurationFreeBSD supports four serial ports by default. In the
&ms-dos; world, these are known as
COM1,
COM2,
COM3, and
COM4. FreeBSD currently supports
dumb multiport serial interface cards, such as
the BocaBoard 1008 and 2016, as well as more
intelligent multi-port cards such as those made by Digiboard
and Stallion Technologies. However, the default kernel only looks
for the standard COM ports.To see if your kernel recognizes any of your serial ports, watch
for messages while the kernel is booting, or use the
/sbin/dmesg command to replay the kernel's boot
messages. In particular, look for messages that start with the
characters sio.To view just the messages that have the word
sio, use the command:&prompt.root; /sbin/dmesg | grep 'sio'For example, on a system with four serial ports, these are the
serial-port specific kernel boot messages:sio0 at 0x3f8-0x3ff irq 4 on isa
sio0: type 16550A
sio1 at 0x2f8-0x2ff irq 3 on isa
sio1: type 16550A
sio2 at 0x3e8-0x3ef irq 5 on isa
sio2: type 16550A
sio3 at 0x2e8-0x2ef irq 9 on isa
sio3: type 16550AIf your kernel does not recognize all of your serial
ports, you will probably need to configure your kernel
in the /boot/device.hints file. You can
also comment-out or completely remove lines for devices you do not
have.Please refer to the &man.sio.4; manual page for
more information on serial ports and multiport boards configuration.
Be careful if you are using a configuration
file that was previously used for a different version of
FreeBSD because the device flags and the syntax have changed between
versions.port IO_COM1 is a substitution for
port 0x3f8, IO_COM2 is
0x2f8, IO_COM3 is
0x3e8, and IO_COM4 is
0x2e8, which are fairly common port addresses for
their respective serial ports; interrupts 4, 3, 5, and 9 are fairly
common interrupt request lines. Also note that regular serial ports
cannot share interrupts on ISA-bus PCs
(multiport boards have on-board electronics that allow all the
16550A's on the board to share one or two interrupt request
lines).Device Special FilesMost devices in the kernel are accessed through device
special files, which are located in the
/dev directory. The sio
devices are accessed through the
/dev/ttyuN (dial-in)
and /dev/cuauN
(call-out) devices. FreeBSD also provides initialization devices
(/dev/ttyuN.init and
/dev/cuauN.init)
and
locking devices
(/dev/ttyuN.lock and
/dev/cuauN.lock).
The
initialization devices are used to initialize communications port
parameters each time a port is opened, such as
crtscts for modems which use
RTS/CTS signaling for flow control. The locking
devices are used to lock flags on ports to prevent users or programs
changing certain parameters; see the manual pages &man.termios.4;,
&man.sio.4;, and &man.stty.1; for
information on the terminal settings, locking and initializing
devices, and setting terminal options, respectively.Serial Port ConfigurationttyucuauThe ttyuN (or
cuauN) device is the
regular device you will want to open for your applications. When a
process opens the device, it will have a default set of terminal I/O
settings. You can see these settings with the command&prompt.root; stty -a -f /dev/ttyu1When you change the settings to this device, the settings are in
effect until the device is closed. When it is reopened, it goes back to
the default set. To make changes to the default set, you can open and
adjust the settings of the initial state device. For
example, to turn on mode, 8 bit communication,
and flow control by default for
ttyu5, type:&prompt.root; stty -f /dev/ttyu5.init clocal cs8 ixon ixoffrc filesrc.serialSystem-wide initialization of the serial devices is
controlled in /etc/rc.d/serial. This file
affects the default settings of serial devices.To prevent certain settings from being changed by an
application, make adjustments to the lock state
device. For example, to lock the speed of
ttyu5 to 57600 bps, type:&prompt.root; stty -f /dev/ttyu5.lock 57600Now, an application that opens
ttyu5 and tries to change the speed of
the port will be stuck with 57600 bps.Naturally, you should make the initial state and lock state devices
writable only by the root account.SeanKellyContributed by TerminalsAs of &os; 8.0, device nodes for serial ports have been
renamed from
/dev/cuadN to
/dev/cuauN and
from
/dev/ttydN to
/dev/ttyuN.
&os; 7.X users will have to adapt the following
documentation according to these changes.terminalsTerminals provide a convenient and low-cost way to access
your FreeBSD system when you are not at the computer's console or on
a connected network. This section describes how to use terminals with
FreeBSD.Uses and Types of TerminalsThe original &unix; systems did not have consoles. Instead, people
logged in and ran programs through terminals that were connected to
the computer's serial ports. It is quite similar to using a modem and
terminal software to dial into a remote system to do text-only
work.Today's PCs have consoles capable of high quality graphics, but
the ability to establish a login session on a serial port still exists
in nearly every &unix; style operating system today; FreeBSD is no
exception. By using a terminal attached to an unused serial port, you
can log in and run any text program that you would normally run on the
console or in an xterm window in the X Window
System.For the business user, you can attach many terminals to a FreeBSD
system and place them on your employees' desktops. For a home user, a
spare computer such as an older IBM PC or a &macintosh; can be a
terminal wired into a more powerful computer running FreeBSD. You can
turn what might otherwise be a single-user computer into a powerful
multiple user system.For FreeBSD, there are three kinds of terminals:Dumb terminalsPCs acting as terminalsX terminalsThe remaining subsections describe each kind.Dumb TerminalsDumb terminals are specialized pieces of hardware that let you
connect to computers over serial lines. They are called
dumb because they have only enough computational power
to display, send, and receive text. You cannot run any programs on
them. It is the computer to which you connect them that has all the
power to run text editors, compilers, email, games, and so
forth.There are hundreds of kinds of dumb terminals made by many
manufacturers, including Digital Equipment Corporation's VT-100 and
Wyse's WY-75. Just about any kind will work with FreeBSD. Some
high-end terminals can even display graphics, but only certain
software packages can take advantage of these advanced
features.Dumb terminals are popular in work environments where workers do
not need access to graphical applications such as those provided by
the X Window System.PCs Acting as TerminalsIf a dumb terminal has just
enough ability to display, send, and receive text, then certainly
any spare personal computer can be a dumb terminal. All you need is
the proper cable and some terminal emulation
software to run on the computer.Such a configuration is popular in homes. For example, if your
spouse is busy working on your FreeBSD system's console, you can do
some text-only work at the same time from a less powerful personal
computer hooked up as a terminal to the FreeBSD system.There are at least two utilities in the base-system of
&os; that can be used to work through a serial connection:
&man.cu.1; and &man.tip.1;.To connect from a client system that runs &os; to the
serial connection of another system, you can use:&prompt.root; cu -l serial-port-deviceWhere serial-port-device is the name of a
special device file denoting a serial port of your system.
These device files are called
/dev/cuauN.The N-part of a device name is the serial
port number.Note that device numbers in &os; start from zero and not
one (like they do, for instance in &ms-dos;-derived systems).
This means that what &ms-dos;-based systems call
COM1 is usually
/dev/cuau0 in &os;.Some people prefer to use other programs, available
through the Ports Collection. The Ports include quite a few
utilities which can work in ways similar to &man.cu.1; and
&man.tip.1;,
i.e., comms/minicom.X TerminalsX terminals are the most sophisticated kind of terminal
available. Instead of connecting to a serial port, they usually
connect to a network like Ethernet. Instead of being relegated to
text-only applications, they can display any X application.We introduce X terminals just for the sake of completeness.
However, this chapter does not cover setup,
configuration, or use of X terminals.ConfigurationThis section describes what you need to configure on your FreeBSD
system to enable a login session on a terminal. It assumes you have
already configured your kernel to support the serial port to which the
terminal is connected—and that you have connected it.Recall from that the
init process is responsible for all process
control and initialization at system startup. One of the
tasks performed by init is to read the
/etc/ttys file and start a
getty process on the available terminals.
The getty process is responsible for
reading a login name and starting the login
program.Thus, to configure terminals for your FreeBSD system the
following steps should be taken as root:Add a line to /etc/ttys for the entry in
the /dev directory for the serial port if it
is not already there.Specify that /usr/libexec/getty be run on
the port, and specify the appropriate
getty type from the
/etc/gettytab file.Specify the default terminal type.Set the port to on.Specify whether the port should be
secure.Force init to reread the
/etc/ttys file.As an optional step, you may wish to create a custom
getty type for use in step 2 by making an
entry in /etc/gettytab. This chapter does
not explain how to do so; you are encouraged to see the
&man.gettytab.5; and the &man.getty.8; manual pages for more
information.Adding an Entry to /etc/ttysThe /etc/ttys file lists all of the ports
on your FreeBSD system where you want to allow logins. For example,
the first virtual console ttyv0 has an entry
in this file. You can log in on the console using this entry. This
file also contains entries for the other virtual consoles, serial
ports, and pseudo-ttys. For a hardwired terminal, just list the
serial port's /dev entry without the
/dev part (for example,
/dev/ttyv0 would be listed as
ttyv0).A default FreeBSD install includes an
/etc/ttys file with support for the first
four serial ports: ttyu0 through
ttyu3. If you are attaching a terminal
to one of those ports, you do not need to add another entry.Adding Terminal Entries to
/etc/ttysSuppose we would like to connect two terminals to the
system: a Wyse-50 and an old 286 IBM PC running
Procomm terminal software
emulating a VT-100 terminal. We connect the Wyse to the
second serial port and the 286 to the sixth serial port (a
port on a multiport serial card). The corresponding
entries in the /etc/ttys file would
look like this:ttyu1 "/usr/libexec/getty std.38400" wy50 on insecure
ttyu5 "/usr/libexec/getty std.19200" vt100 on insecure
The first field normally specifies the name of
the terminal special file as it is found in
/dev.The second field is the command to execute for
this line, which is usually &man.getty.8;.
getty initializes and opens the
line, sets the speed, prompts for a user name and then
executes the &man.login.1; program.The getty program accepts one
(optional) parameter on its command line, the
getty type. A
getty type configures
characteristics on the terminal line, like bps rate
and parity. The getty program reads
these characteristics from the file
/etc/gettytab.The file /etc/gettytab
contains lots of entries for terminal lines both old
and new. In almost all cases, the entries that start
with the text std will work for
hardwired terminals. These entries ignore parity.
There is a std entry for each bps
rate from 110 to 115200. Of course, you can add your
own entries to this file. The &man.gettytab.5; manual
page provides more information.When setting the getty
type in the /etc/ttys file, make
sure that the communications settings on the terminal
match.For our example, the Wyse-50 uses no parity and
connects at 38400 bps. The 286 PC uses no parity
and connects at 19200 bps.The third field is the type of terminal usually
connected to that tty line. For dial-up ports,
unknown or
dialup is typically used in this
field since users may dial up with practically any
type of terminal or software. For hardwired
terminals, the terminal type does not change, so you
can put a real terminal type from the &man.termcap.5;
database file in this field.For our example, the Wyse-50 uses the real
terminal type while the 286 PC running
Procomm will be set to
emulate at VT-100. The fourth field specifies if the port should be
enabled. Putting on here will have
the init process start the program
in the second field, getty. If you
put off in this field, there will
be no getty, and hence no logins on
the port.The final field is used to specify whether the
port is secure. Marking a port as secure means that
you trust it enough to allow the
root account (or any account with
a user ID of 0) to login from that port. Insecure
ports do not allow root logins.
On an insecure port, users must login from
unprivileged accounts and then use &man.su.1; or a
similar mechanism to gain superuser privileges.It is highly recommended that you use
insecure
even for terminals that are behind locked doors. It
is quite easy to login and use su
if you need superuser privileges.Force init to Reread
/etc/ttysAfter making the necessary changes to the
/etc/ttys file you should send a SIGHUP
(hangup) signal to the init process to
force it to re-read its configuration file. For example:&prompt.root; kill -HUP 1init is always the first process run
on a system, therefore it will always have PID 1.If everything is set up correctly, all cables are in
place, and the terminals are powered up, then a
getty process should be running on each
terminal and you should see login prompts on your terminals
at this point.Troubleshooting Your ConnectionEven with the most meticulous attention to detail, something could
still go wrong while setting up a terminal. Here is a list of
symptoms and some suggested fixes.No Login Prompt AppearsMake sure the terminal is plugged in and powered up. If it
is a personal computer acting as a terminal, make sure it is
running terminal emulation software on the correct serial
port.Make sure the cable is connected firmly to both the terminal
and the FreeBSD computer. Make sure it is the right kind of
cable.Make sure the terminal and FreeBSD agree on the bps rate and
parity settings. If you have a video display terminal, make
sure the contrast and brightness controls are turned up. If it
is a printing terminal, make sure paper and ink are in good
supply.Make sure that a getty process is running
and serving the terminal. For example, to get a list of
running getty processes with
ps, type:&prompt.root; ps -axww|grep gettyYou should see an entry for the terminal. For
example, the following display shows that a
getty is running on the second serial
port ttyu1 and is using the
std.38400 entry in
/etc/gettytab:22189 d1 Is+ 0:00.03 /usr/libexec/getty std.38400 ttyu1If no getty process is running, make sure
you have enabled the port in /etc/ttys.
Also remember to run kill -HUP 1
after modifying the ttys file.If the getty process is running
but the terminal still does not display a login prompt,
or if it displays a prompt but will not allow you to
type, your terminal or cable may not support hardware
handshaking. Try changing the entry in
/etc/ttys from
std.38400 to
3wire.38400 (remember to run
kill -HUP 1 after modifying
/etc/ttys). The
3wire entry is similar to
std, but ignores hardware
handshaking. You may need to reduce the baud rate or
enable software flow control when using
3wire to prevent buffer
overflows.If Garbage Appears Instead of a Login PromptMake sure the terminal and FreeBSD agree on the bps rate and
parity settings. Check the getty processes
to make sure the
correct getty type is in use. If
not, edit /etc/ttys and run kill
-HUP 1.Characters Appear Doubled; the Password Appears When
TypedSwitch the terminal (or the terminal emulation software)
from half duplex or local echo to
full duplex.GuyHelmerContributed by SeanKellyAdditions by Dial-in ServiceAs of &os; 8.0, device nodes for serial ports have been
renamed from
/dev/cuadN to
/dev/cuauN and
from
/dev/ttydN to
/dev/ttyuN.
&os; 7.X users will have to adapt the following
documentation according to these changes.dial-in serviceConfiguring your FreeBSD system for dial-in service is very
similar to connecting terminals except that you are dealing with
modems instead of terminals.External Versus Internal ModemsExternal modems seem to be more convenient for dial-up, because
external modems often can be semi-permanently configured via
parameters stored in non-volatile RAM and they usually provide
lighted indicators that display the state of important RS-232
signals. Blinking lights impress visitors, but lights are also very
useful to see whether a modem is operating properly.Internal modems usually lack non-volatile RAM, so their
configuration may be limited only to setting DIP switches. If your
internal modem has any signal indicator lights, it is probably
difficult to view the lights when the system's cover is in
place.Modems and CablesmodemIf you are using an external modem, then you will of
course need the proper cable. A standard RS-232C serial
cable should suffice as long as all of the normal signals
are wired:
Signal NamesAcronymsNamesRDReceived DataTDTransmitted DataDTRData Terminal ReadyDSRData Set ReadyDCDData Carrier Detect (RS-232's Received Line
Signal Detector)SGSignal GroundRTSRequest to SendCTSClear to Send
FreeBSD needs the RTS and
CTS signals for flow control at speeds above
2400 bps, the CD signal to detect when a
call has been answered or the line has been hung up, and the
DTR signal to reset the modem after a session is
complete. Some cables are wired without all of the needed signals,
so if you have problems, such as a login session not going away when
the line hangs up, you may have a problem with your cable.Like other &unix; like operating systems, FreeBSD uses the
hardware signals to find out when a call has been answered
or a line has been hung up and to hangup and reset the modem
after a call. FreeBSD avoids sending commands to the modem
or watching for status reports from the modem. If you are
familiar with connecting modems to PC-based bulletin board
systems, this may seem awkward.Serial Interface ConsiderationsFreeBSD supports NS8250-, NS16450-, NS16550-, and NS16550A-based
EIA RS-232C (CCITT V.24) communications interfaces. The 8250 and
16450 devices have single-character buffers. The 16550 device
provides a 16-character buffer, which allows for better system
performance. (Bugs in plain 16550's prevent the use of the
16-character buffer, so use 16550A's if possible). Because
single-character-buffer devices require more work by the operating
system than the 16-character-buffer devices, 16550A-based serial
interface cards are much preferred. If the system has many active
serial ports or will have a heavy load, 16550A-based cards are
better for low-error-rate communications.Quick OverviewgettyAs with terminals, init spawns a
getty process for each configured serial
port for dial-in connections. For example, if a modem is
attached to /dev/ttyu0, the command
ps ax might show this: 4850 ?? I 0:00.09 /usr/libexec/getty V19200 ttyu0When a user dials the modem's line and the modems connect, the
CD (Carrier Detect) line is reported by the modem.
The kernel
notices that carrier has been detected and completes
getty's open of the port. getty
sends a login: prompt at the specified initial line
speed. getty watches to see if legitimate
characters are received, and, in a typical configuration, if it finds
junk (probably due to the modem's connection speed being different
than getty's speed), getty tries
adjusting the line speeds until it receives reasonable
characters./usr/bin/loginAfter the user enters his/her login name,
getty executes
/usr/bin/login, which completes the login
by asking for the user's password and then starting the user's
shell.Configuration FilesThere are three system configuration files in the
/etc directory that you will probably need to
edit to allow dial-up 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.d/serial script.There are two schools of thought regarding dial-up modems on
&unix;. One group likes to configure their modems and systems 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 does not
know what a user's true data rate is, so full-screen programs like
Emacs will not 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 does not 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 is
assumed that they know they should press the
Enter key until they see a recognizable
prompt. If the data rates do not 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 nauseam, but normally only takes a keystroke
or two before the user sees a good prompt. Obviously, this login
sequence does not 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.This section will try to give balanced configuration information,
but is biased towards having the modem's data rate follow the
connection rate./etc/gettytab/etc/gettytab/etc/gettytab is a &man.termcap.5;-style
file of configuration information for &man.getty.8;. Please see the
&man.gettytab.5; manual page for complete information on the
format of the file and the list of capabilities.Locked-speed ConfigIf you are locking your modem's data communications rate at a
particular speed, you probably will not need to make any changes
to /etc/gettytab.Matching-speed ConfigYou will need to set up 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.#
# 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 will probably need to
add an entry in /etc/gettytab; here is an
entry you could use for a 14.4 Kbps modem with a top interface
speed of 19.2 Kbps:#
# 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:This will result in 8-bit, no parity connections.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. Communications 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 is an
example of a gettytab entry starting a
57.6 Kbps:#
# Additions for a V.32bis or V.34 Modem
# Starting at 57.6 Kbps
#
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 do
not have 16550A-based serial ports, you may receive
siosilo errors at 57.6 Kbps./etc/ttys/etc/ttysConfiguration of the /etc/ttys file
was covered in .
Configuration for modems is similar but we must pass a
different argument to getty and specify a
different terminal type. The general format for both
locked-speed and matching-speed configurations is:ttyu0 "/usr/libexec/getty xxx" dialup onThe first item in the above line is the device special file for
this entry — ttyu0 means
/dev/ttyu0 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 dial-up 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
&prompt.root; kill -HUP 1
to send the signal. If this is your first time setting up the
system, you may want to wait until your modem(s) are properly
configured and connected before signaling init.
Locked-speed ConfigFor 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:ttyu0 "/usr/libexec/getty std.19200" dialup onIf your modem is locked at a different data rate,
substitute the appropriate value for
std.speed
instead of std.19200. Make sure that
you use a valid type listed in
/etc/gettytab.Matching-speed ConfigIn 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:ttyu0 "/usr/libexec/getty V19200" dialup on/etc/rc.d/serialrc filesrc.serialHigh-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.d/serial to set the hardware flow
control flag in the FreeBSD kernel for the modem
ports.For example to set the termios flag
crtscts on serial port #1's
(COM2) dial-in and dial-out initialization
devices, the following lines could be added to
/etc/rc.d/serial:# Serial port initial configuration
stty -f /dev/ttyu1.init crtscts
stty -f /dev/cuau1.init crtsctsModem SettingsIf you have a modem whose parameters may be permanently set in
non-volatile RAM, you will need to use a terminal program (such as
Telix under &ms-dos; or
tip under FreeBSD) to set the parameters. Connect
to the modem using the same communications speed as the initial speed
getty will use and configure the modem's
non-volatile RAM to match these requirements:CD asserted when connectedDTR asserted for operation; dropping DTR
hangs up line and resets modemCTS transmitted data flow controlDisable XON/XOFF flow controlRTS received data flow controlQuiet mode (no result codes)No command echoPlease read the documentation for your modem to find out what
commands and/or DIP switch settings you need to give it.For example, to set the above parameters on a &usrobotics;
&sportster; 14,400 external modem, one could give these commands to
the modem:ATZ
AT&C1&D2&H1&I0&R2&WYou might also want to take this opportunity to adjust other
settings in the modem, such as whether it will use V.42bis and/or MNP5
compression.The &usrobotics; &sportster; 14,400 external modem also has some
DIP switches that need to be set; for other modems, perhaps you can
use these settings as an example:Switch 1: UP — DTR NormalSwitch 2: N/A (Verbal Result Codes/Numeric Result
Codes)Switch 3: UP — Suppress Result CodesSwitch 4: DOWN — No echo, offline commandsSwitch 5: UP — Auto AnswerSwitch 6: UP — Carrier Detect NormalSwitch 7: UP — Load NVRAM DefaultsSwitch 8: N/A (Smart Mode/Dumb Mode)Result codes should be disabled/suppressed for dial-up modems to
avoid problems that can occur if getty mistakenly
gives a login: prompt to a modem that is in command
mode and the modem echoes the command or returns a result
code. This sequence can result in a extended, silly conversation
between getty and the modem.Locked-speed ConfigFor a locked-speed configuration, you will need to configure the
modem to maintain a constant modem-to-computer data rate independent
of the communications rate. On a &usrobotics; &sportster; 14,400
external modem, these commands will lock the modem-to-computer data
rate at the speed used to issue the commands:ATZ
AT&B1&WMatching-speed ConfigFor a variable-speed configuration, you will need to configure
your modem to adjust its serial port data rate to match the incoming
call rate. On a &usrobotics; &sportster; 14,400 external modem,
these commands will lock the modem's error-corrected data rate to the
speed used to issue the commands, but allow the serial port rate to
vary for non-error-corrected connections:ATZ
AT&B2&WChecking the Modem's ConfigurationMost high-speed modems provide commands to view the modem's
current operating parameters in a somewhat human-readable fashion.
On the &usrobotics; &sportster; 14,400 external modems, the command
ATI5 displays the settings that are stored in the
non-volatile RAM. To see the true operating parameters of the modem
(as influenced by the modem's DIP switch settings), use the commands
ATZ and then ATI4.If you have a different brand of modem, check your modem's
manual to see how to double-check your modem's configuration
parameters.TroubleshootingHere are a few steps you can follow to check out the dial-up modem
on your system.Checking Out the FreeBSD SystemHook up your modem to your FreeBSD system, boot the system, and,
if your modem has status indication lights, watch to see whether the
modem's DTR indicator lights when the
login: prompt appears on the system's console
— if it lights up, that should mean that FreeBSD has started a
getty process on the appropriate communications
port and is waiting for the modem to accept a call.If the DTR indicator does not light, login to
the FreeBSD system through the console and issue a ps
ax to see if FreeBSD is trying to run a
getty process on the correct port. You should see
lines like these among the processes displayed: 114 ?? I 0:00.10 /usr/libexec/getty V19200 ttyu0
115 ?? I 0:00.10 /usr/libexec/getty V19200 ttyu1If you see something different, like this: 114 d0 I 0:00.10 /usr/libexec/getty V19200 ttyu0and the modem has not accepted a call yet, this means that
getty has completed its open on the
communications port. This could indicate a problem with the cabling
or a mis-configured modem, because getty should
not be able to open the communications port until
CD (carrier detect) has been asserted by the
modem.If you do not see any getty processes waiting
to open the desired
ttyuN port,
double-check your entries in /etc/ttys to see
if there are any mistakes there. Also, check the log file
/var/log/messages to see if there are any log
messages from init or getty
regarding any problems. If there are any messages, triple-check the
configuration files /etc/ttys and
/etc/gettytab, as well as the appropriate
device special files /dev/ttyuN, for any
mistakes, missing entries, or missing device special files.Try Dialing InTry dialing into the system; be sure to use 8 bits, no parity,
and 1
stop bit on the remote system. If you do not get a prompt right
away, or get garbage, try pressing Enter
about once per second. If you still do not see a
login: prompt after a while, try sending a
BREAK. If you are using a high-speed modem to do
the dialing, try dialing again after locking the dialing modem's
interface speed (via AT&B1 on a &usrobotics;
&sportster; modem, for example).If you still cannot get a login: prompt, check
/etc/gettytab again and double-check
thatThe initial capability name specified in
/etc/ttys for the line matches a name of a
capability in /etc/gettytabEach nx= entry matches another
gettytab capability nameEach tc= entry matches another
gettytab capability nameIf you dial but the modem on the FreeBSD system will not answer,
make sure that the modem is configured to answer the phone when
DTR is asserted. If the modem seems to be
configured correctly, verify that the DTR line is
asserted by checking the modem's indicator lights (if it has
any).If you have gone over everything several times and it still does
not work, take a break and come back to it later. If it still does
not work, perhaps you can send an electronic mail message to the
&a.questions; describing your modem and your problem, and the good
folks on the list will try to help.Dial-out ServiceAs of &os; 8.0, device nodes for serial ports have been
renamed from
/dev/cuadN to
/dev/cuauN.
&os; 7.X users will have to adapt the following
documentation according to these changes.dial-out serviceThe following are tips for getting your host to be able to connect
over the modem to another computer. This is appropriate for
establishing a terminal session with a remote host.This is useful to log onto a BBS.This kind of connection can be extremely helpful to get a file on
the Internet if you have problems with PPP. If you need to FTP
something and PPP is broken, use the terminal session to FTP it. Then
use zmodem to transfer it to your machine.My Stock Hayes Modem Is Not Supported, What Can I Do?Actually, the manual page for tip is out of
date. There is a generic Hayes dialer already built in. Just use
at=hayes in your /etc/remote
file.The Hayes driver is not smart enough to recognize some of the
advanced features of newer modems—messages like
BUSY, NO DIALTONE, or
CONNECT 115200 will just confuse it. You should
turn those messages off when you use tip (using
ATX0&W).Also, the dial timeout for tip is 60 seconds.
Your modem should use something less, or else tip will think there is
a communication problem. Try ATS7=45&W.How Am I Expected to Enter These AT Commands?/etc/remoteMake what is called a direct entry in your
/etc/remote file. For example, if your modem is
hooked up to the first serial port, /dev/cuau0,
then put in the following line:cuau0:dv=/dev/cuau0:br#19200:pa=noneUse the highest bps rate your modem supports in the br capability.
Then, type tip cuau0 and you will be connected to
your modem.Or use cu as root with the
following command:&prompt.root; cu -lline -sspeedline is the serial port
(e.g., /dev/cuau0) and
speed is the speed
(e.g., 57600). When you are done entering the AT
commands type ~. to exit.The @ Sign for the pn Capability Does Not
Work!The @ sign in the phone number capability tells
tip to look in /etc/phones for a phone number.
But the @ sign is also a special character in
capability files like /etc/remote. Escape it
with a backslash:pn=\@How Can I Dial a Phone Number on the Command Line?Put what is called a generic entry in your
/etc/remote file. For example:tip115200|Dial any phone number at 115200 bps:\
:dv=/dev/cuau0:br#115200:at=hayes:pa=none:du:
tip57600|Dial any phone number at 57600 bps:\
:dv=/dev/cuau0:br#57600:at=hayes:pa=none:du:Then you can do things like:&prompt.root; tip -115200 5551234If you prefer cu over tip,
use a generic cu entry:cu115200|Use cu to dial any number at 115200bps:\
:dv=/dev/cuau1:br#57600:at=hayes:pa=none:du:and type:&prompt.root; cu 5551234 -s 115200Do I Have to Type in the bps Rate Every Time I Do That?Put in an entry for tip1200 or
cu1200, but go ahead and use whatever bps rate is
appropriate with the br capability. tip thinks a
good default is 1200 bps which is why it looks for a
tip1200 entry. You do not have to use
1200 bps, though.I Access a Number of Hosts Through a Terminal ServerRather than waiting until you are connected and typing
CONNECT host each time,
use tip's cm capability. For example, these entries
in /etc/remote:pain|pain.deep13.com|Forrester's machine:\
:cm=CONNECT pain\n:tc=deep13:
muffin|muffin.deep13.com|Frank's machine:\
:cm=CONNECT muffin\n:tc=deep13:
deep13:Gizmonics Institute terminal server:\
:dv=/dev/cuau2:br#38400:at=hayes:du:pa=none:pn=5551234:will let you type tip pain or tip
muffin to connect to the hosts pain or
muffin, and tip deep13 to get to
the terminal server.Can Tip Try More Than One Line for Each Site?This is often a problem where a university has several modem lines
and several thousand students trying to use them.Make an entry for your university in
/etc/remote and use @ for the
pn capability:big-university:\
:pn=\@:tc=dialout
dialout:\
:dv=/dev/cuau3:br#9600:at=courier:du:pa=none:Then, list the phone numbers for the university in
/etc/phones:big-university 5551111
big-university 5551112
big-university 5551113
big-university 5551114tip will try each one in the listed order, then
give up. If you want to keep retrying, run tip in
a while loop.Why Do I Have to Hit
CtrlP
Twice to Send
CtrlP
Once?CtrlP
is the default force character, used to tell
tip that the next character is literal data. You
can set the force character to any other character with the
~s escape, which means set a
variable.Type
~sforce=single-char
followed by a newline. single-char is any
single character. If you leave out
single-char, then the force character is
the nul character, which you can get by typing
Ctrl2
or
CtrlSpace.
A pretty good value for single-char is
ShiftCtrl6, which is only used on some terminal
servers.You can have the force character be whatever you want by
specifying the following in your
$HOME/.tiprc file:force=single-charSuddenly Everything I Type Is in Upper Case??You must have pressed
CtrlA, tip's
raise character, specially designed for people with
broken caps-lock keys. Use ~s as above and set the
variable raisechar to something reasonable. In
fact, you can set it to the same as the force character, if you never
expect to use either of these features.Here is a sample .tiprc file perfect for
Emacs users who need to type
Ctrl2
and
CtrlA
a lot:force=^^
raisechar=^^The ^^ is
ShiftCtrl6.How Can I Do File Transfers with tip?If you are talking to another &unix; system, you can send and
receive files with ~p (put) and
~t (take). These commands run
cat and echo on the remote
system to accept and send files. The syntax is:~plocal-fileremote-file~tremote-filelocal-fileThere is no error checking, so you probably should use another
protocol, like zmodem.How Can I Run zmodem with tip?To receive files, start the sending program on the remote end.
Then, type ~C rz to begin receiving them
locally.To send files, start the receiving program on the remote end.
Then, type ~C sz files
to send them to the remote system.KazutakaYOKOTAContributed by BillPaulBased on a document by Setting Up the Serial ConsoleAs of &os; 8.0, device nodes for serial ports have been
renamed from
/dev/ttydN to
/dev/ttyuN.
&os; 7.X users will have to adapt the following
documentation according to these changes.serial consoleIntroductionFreeBSD has the ability to boot on a system with only
a dumb terminal on a serial port as a console. Such a configuration
should be useful for two classes of people: system administrators who
wish to install FreeBSD on machines that have no keyboard or monitor
attached, and developers who want to debug the kernel or device
drivers.As described in , FreeBSD employs a three
stage bootstrap. The first two stages are in the boot block code which
is stored at the beginning of the FreeBSD slice on the boot disk. The
boot block will then load and run the boot loader
(/boot/loader) as the third stage code.In order to set up the serial console you must configure the boot
block code, the boot loader code and the kernel.Serial Console Configuration, Terse VersionThis section assumes that you are using the default setup
and just want a fast overview of setting up the serial
console.Connect the serial cable to COM1 and
the controlling terminal.To see all boot messages on the serial console, issue
the following command while logged in as the superuser:&prompt.root; echo 'console="comconsole"' >> /boot/loader.confEdit /etc/ttys and change
off to on and
dialup to vt100 for the
ttyu0 entry. Otherwise a password will
not be required to connect via the serial console, resulting in a
potential security hole.Reboot the system to see if the changes took effect.If a different configuration is required, a more in depth
configuration explanation exists in
.Serial Console ConfigurationPrepare a serial cable.null-modem cableYou will need either a null-modem cable or a standard serial
cable and a null-modem adapter. See for
a discussion on serial cables.Unplug your keyboard.Most PC systems probe for the keyboard during the Power-On
Self-Test (POST) and will generate an error if the keyboard is not
detected. Some machines complain loudly about the lack of a
keyboard and will not continue to boot until it is plugged
in.If your computer complains about the error, but boots anyway,
then you do not have to do anything special. (Some machines with
Phoenix BIOS installed merely say Keyboard
failed and continue to boot normally.)If your computer refuses to boot without a keyboard attached
then you will have to configure the BIOS so that it ignores this
error (if it can). Consult your motherboard's manual for details
on how to do this.Set the keyboard to Not installed in the
BIOS setup. You will still
be able to use your keyboard. All this does is tell the BIOS
not to probe for a keyboard at power-on. Your BIOS should not
complain if the keyboard is absent. You can leave the
keyboard plugged in even with this flag set to Not
installed and the keyboard will still work. If the
above option is not present in the BIOS, look for an
Halt on Error option instead. Setting this to
All but Keyboard or even to
No Errors, will have the same effect.If your system has a &ps2; mouse, chances are very good that
you may have to unplug your mouse as well as your keyboard.
This is because &ps2; mice share some hardware with the keyboard
and leaving the mouse plugged in can fool the keyboard probe
into thinking the keyboard is still there. It is said that a
Gateway 2000 Pentium 90 MHz system with an AMI BIOS that
behaves this way. In general, this is not a problem since the
mouse is not much good without the keyboard anyway.Plug a dumb terminal into COM1
(sio0).If you do not have a dumb terminal, you can use an old PC/XT
with a modem program, or the serial port on another &unix; box. If
you do not have a COM1
(sio0), get one. At this time, there is
no way to select a port other than COM1
for the boot blocks without recompiling the boot blocks. If you
are already using COM1 for another
device, you will have to temporarily remove that device and
install a new boot block and kernel once you get FreeBSD up and
running. (It is assumed that COM1 will
be available on a file/compute/terminal server anyway; if you
really need COM1 for something else
(and you cannot switch that something else to
COM2 (sio1)),
then you probably should not even be bothering with all this in
the first place.)Make sure the configuration file of your kernel has
appropriate flags set for COM1
(sio0).Relevant flags are:0x10Enables console support for this unit. The other
console flags are ignored unless this is set. Currently, at
most one unit can have console support; the first one (in
config file order) with this flag set is preferred. This
option alone will not make the serial port the console. Set
the following flag or use the option
described below, together with this flag.0x20Forces this unit to be the console (unless there is
another higher priority console), regardless of the
option discussed below.
The flag 0x20 must be used
together with the flag.0x40Reserves this unit (in conjunction with
0x10) and makes the unit
unavailable for normal access. You should not set
this flag to the serial port unit which you want to
use as the serial console. The only use of this
flag is to designate the unit for kernel remote
debugging. See The
Developer's Handbook for more information on
remote debugging.Example:device sio0 flags 0x10See the &man.sio.4; manual page for more details.If the flags were not set, you need to run UserConfig (on a
different console) or recompile the kernel.Create boot.config in the root directory
of the a partition on the boot drive.This file will instruct the boot block code how you would like
to boot the system. In order to activate the serial console, you
need one or more of the following options—if you want
multiple options, include them all on the same line:Toggles internal and serial consoles. You can use this
to switch console devices. For instance, if you boot from
the internal (video) console, you can use
to direct the boot loader and the kernel
to use the serial port as its console device. Alternatively,
if you boot from the serial port, you can use the
to tell the boot loader and the kernel
to use the video display as the console instead.Toggles single and dual console configurations. In the
single configuration the console will be either the internal
console (video display) or the serial port, depending on the
state of the option above. In the dual
console configuration, both the video display and the
serial port will become the console at the same time,
regardless of the state of the option.
However, note that the dual console configuration takes
effect only during the boot block is running. Once the boot
loader gets control, the console specified by the
option becomes the only console.Makes the boot block probe the keyboard. If no keyboard
is found, the and
options are automatically set.Due to space constraints in the current version of the
boot blocks, the option is capable of
detecting extended keyboards only. Keyboards with less
than 101 keys (and without F11 and F12 keys) may not be
detected. Keyboards on some laptop computers may not be
properly found because of this limitation. If this is
the case with your system, you have to abandon using
the option. Unfortunately there is no
workaround for this problem.Use either the option to select the
console automatically, or the option to
activate the serial console.You may include other options described in &man.boot.8; as
well.The options, except for , will be passed to
the boot loader (/boot/loader). The boot
loader will determine which of the internal video or the serial
port should become the console by examining the state of the
option alone. This means that if you specify
the option but not the
option in /boot.config, you can use the
serial port as the console only during the boot block; the boot
loader will use the internal video display as the console.Boot the machine.When you start your FreeBSD box, the boot blocks will echo the
contents of /boot.config to the console. For
example:/boot.config: -P
Keyboard: noThe second line appears only if you put in
/boot.config and indicates presence/absence
of the keyboard. These messages go to either serial or internal
console, or both, depending on the option in
/boot.config.OptionsMessage goes tononeinternal consoleserial consoleserial and internal consolesserial and internal consoles, keyboard presentinternal console, keyboard absentserial consoleAfter the above messages, there will be a small pause before
the boot blocks continue loading the boot loader and before any
further messages printed to the console. Under normal
circumstances, you do not need to interrupt the boot blocks, but
you may want to do so in order to make sure things are set up
correctly.Hit any key, other than Enter, at the console
to interrupt the boot process. The boot blocks will then prompt
you for further action. You should now see something like:>> FreeBSD/i386 BOOT
Default: 0:ad(0,a)/boot/loader
boot:Verify the above message appears on either the serial or
internal console or both, according to the options you put in
/boot.config. If the message appears in the
correct console, hit Enter to continue the boot
process.If you want the serial console but you do not see the prompt
on the serial terminal, something is wrong with your settings. In
the meantime, you enter and hit
Enter or Return (if possible)
to tell the boot block (and then the boot loader and the kernel)
to choose the serial port for the console. Once the system is
up, go back and check what went wrong.After the boot loader is loaded and you are in the third stage of
the boot process you can still switch between the internal console and
the serial console by setting appropriate environment variables in the
boot loader. See .SummaryHere is the summary of various settings discussed in this section
and the console eventually selected.Case 1: You Set the Flags to 0x10 for
sio0device sio0 flags 0x10Options in /boot.configConsole during boot blocksConsole during boot loaderConsole in kernelnothinginternalinternalinternalserialserialserialserial and internalinternalinternalserial and internalserialserial, keyboard presentinternalinternalinternal, keyboard absentserial and internalserialserialCase 2: You Set the Flags to 0x30 for sio0device sio0 flags 0x30Options in /boot.configConsole during boot blocksConsole during boot loaderConsole in kernelnothinginternalinternalserialserialserialserialserial and internalinternalserialserial and internalserialserial, keyboard presentinternalinternalserial, keyboard absentserial and internalserialserialTips for the Serial ConsoleSetting a Faster Serial Port SpeedBy default, the serial port settings are: 9600 baud, 8
bits, no parity, and 1 stop bit. If you wish to change the default
console speed, you have the following options:Recompile the boot blocks
with BOOT_COMCONSOLE_SPEED set to the new
console speed. See for
detailed instructions about building and installing new boot
blocks.If the serial console is configured in some other way than
by booting with , or if the serial console
used by the kernel is different from the one used by the boot
blocks, then you must also add the following option to the
kernel configuration file and compile a new kernel:options CONSPEED=19200Use the boot option of the kernel.
The command line option can be added
to /boot.config. See the &man.boot.8;
manual page for a description of how to add options
to /boot.config and a list of the supported
options.Enable the comconsole_speed
option in your /boot/loader.conf
file.This option depends on console,
boot_serial, and
boot_multicons being set in
/boot/loader.conf too. An example of using
comconsole_speed to change the serial console
speed is:boot_multicons="YES"
boot_serial="YES"
comconsole_speed="115200"
console="comconsole,vidconsole"Using Serial Port Other Than sio0 for
the ConsoleUsing a port other than sio0 as the
console requires some recompiling. If you want to use another
serial port for whatever reasons, recompile the boot blocks, the
boot loader and the kernel as follows.Get the kernel source. (See )Edit /etc/make.conf and set
BOOT_COMCONSOLE_PORT to the address of the
port you want to use (0x3F8, 0x2F8, 0x3E8 or 0x2E8). Only
sio0 through
sio3 (COM1
through COM4) can be used; multiport
serial cards will not work. No interrupt setting is
needed.Create a custom kernel configuration file and add
appropriate flags for the serial port you want to use. For
example, if you want to make sio1
(COM2) the console:device sio1 flags 0x10ordevice sio1 flags 0x30The console flags for the other serial ports should not be
set.Recompile and install the boot blocks and the boot
loader:&prompt.root; cd /sys/boot
&prompt.root; make clean
&prompt.root; make
&prompt.root; make installRebuild and install the kernel.Write the boot blocks to the boot disk with
&man.bsdlabel.8; and boot from the new kernel.Entering the DDB Debugger from the Serial LineIf you wish to drop into the kernel debugger from the serial
console (useful for remote diagnostics, but also dangerous if you
generate a spurious BREAK on the serial port!) then you should
compile your kernel with the following options:options BREAK_TO_DEBUGGER
options DDBGetting a Login Prompt on the Serial ConsoleWhile this is not required, you may wish to get a
login prompt over the serial line, now that you
can see boot messages and can enter the kernel debugging session
through the serial console. Here is how to do it.Open the file /etc/ttys with an editor
and locate the lines:ttyu0 "/usr/libexec/getty std.9600" unknown off secure
ttyu1 "/usr/libexec/getty std.9600" unknown off secure
ttyu2 "/usr/libexec/getty std.9600" unknown off secure
ttyu3 "/usr/libexec/getty std.9600" unknown off securettyu0 through
ttyu3 corresponds to
COM1 through COM4.
Change off to on for the
desired port. If you have changed the speed of the serial port,
you need to change std.9600 to match the current
setting, e.g., std.19200.You may also want to change the terminal type from
unknown to the actual type of your serial
terminal.After editing the file, you must kill -HUP 1
to make this change take effect.Changing Console from the Boot LoaderPrevious sections described how to set up the serial console by
tweaking the boot block. This section shows that you can specify the
console by entering some commands and environment variables in the
boot loader. As the boot loader is invoked at the third stage of the
boot process, after the boot block, the settings in the boot loader
will override the settings in the boot block.Setting Up the Serial ConsoleYou can easily specify the boot loader and the kernel to use the
serial console by writing just one line in
/boot/loader.conf:console="comconsole"This will take effect regardless of the settings in the boot
block discussed in the previous section.You had better put the above line as the first line of
/boot/loader.conf so as to see boot messages on
the serial console as early as possible.Likewise, you can specify the internal console as:console="vidconsole"If you do not set the boot loader environment variable
console, the boot loader, and subsequently the
kernel, will use whichever console indicated by the
option in the boot block.The console can be specified in
/boot/loader.conf.local or in
/boot/loader.conf.See &man.loader.conf.5; for more information.At the moment, the boot loader has no option equivalent to the
option in the boot block, and there is no
provision to automatically select the internal console and the
serial console based on the presence of the keyboard.Using a Serial Port Other Than sio0 for
the ConsoleYou need to recompile the boot loader to use a serial port other
than sio0 for the serial console. Follow the
procedure described in .CaveatsThe idea here is to allow people to set up dedicated servers that
require no graphics hardware or attached keyboards. Unfortunately,
while most systems will let you boot without a keyboard, there
are quite a few that will not let you boot without a graphics adapter.
Machines with AMI BIOSes can be configured to boot with no graphics
adapter installed by changing the
graphics adapter setting in the CMOS configuration to
Not installed.However, many machines do not support this option and will refuse
to boot if you have no display hardware in the system. With these
machines, you will have to leave some kind of graphics card plugged in,
(even if it is just a junky mono board) although you will not have to
attach a monitor. You might also try installing an AMI
BIOS.