2 SERIAL CONSOLE USAGE NOTES
4 Bill Paul <wpaul@ctr.columbia.edu>
5 Revised for 3.0-CURRENT by
6 Kazutaka Yokota <yokota@zodiac.mech.utsunomiya-u.ac.jp>
8 The FreeBSD boot block can now be used to boot FreeBSD on a system with
9 only a dumb terminal on a serial port as a console. This feature
10 is provided for the benefit of people who wish to install FreeBSD on
11 dedicated file/compute/terminal server machines that have no keyboard
12 (or monitor) attached, just as is possible with Sun workstations and
13 servers. People who don't need this extra functionality shouldn't notice
14 the changes at all (unless I've screwed something up horribly).
16 To boot FreeBSD in serial console mode, you must do the following:
18 - UNPLUG YOUR KEYBOARD. Most PC systems probe for the keyboard during the
19 Power-On Self-Test (POST) and will generate an error if the keyboard
20 isn't detected. Some BIOSes may be set to ignore this error. Many other
21 machines will pause the boot process and wait for you to reattach the
22 keyboard and press a key before proceeding any further. Consult the manual
23 of your motherboard to see how it responds to the error and how to
24 set the BIOS to ignore the error. If your computer complains about
25 the lack of a keyboard but boots anyway, then you don't have to do
26 anything special. (One machine with a PHOENIX BIOS that I have here
27 merely says 'Keyboard failed' then continues to boot normally.) If your
28 machine complains loudly about the lack of a keyboard and won't continue
29 to boot until you plug it back in, you'll have to go into your CMOS
30 configuration menu and change the 'Keyboard' setting to 'Not installed'
31 in order to bypass the keyboard probe.
34 Setting the keyboard to 'Not installed' in the CMOS configuration
35 does *NOT* mean that you won't be able to use your keyboard. All this
36 does is tell the BIOS not to probe for a keyboard at power-on so that
37 it won't bitch and moan if the keyboard isn't plugged in. You can leave the
38 keyboard plugged in even with this flag set to 'Not installed' and the
39 keyboard will still work. I repeat: changing the CMOS 'keyboard' setting
40 to 'Not installed' only disables the BIOS's keyboard probe; it does
41 *NOT* actually disable the keyboard.
44 If your system has a PS/2 mouse, chances are very good that you will
45 need to unplug your mouse as well as your keyboard. This is because
46 PS/2 mice share some hardware with the keyboard, and leaving the mouse
47 plugged in can fool the keyboard probe into thinking the keyboard is
48 still there. I have access to a Gateway 2000 Pentium 90Mhz system with
49 an AMI BIOS that behaves this way. In general this is not a problem
50 since the mouse isn't much good without the keyboard anyway.
52 - PLUG A DUMB TERMINAL INTO COM1. If you don't have a dumb terminal, you
53 can use an old PC/XT with a modem program, or the serial port on
54 another UNIX box. If you don't have a COM1, get one. At this time,
55 there is no way to select a port other than COM1 for the boot blocks
56 without recompiling the boot blocks. If you're already using COM1 for
57 another device, you'll have to temporarily remove that device and
58 install a new boot block and kernel once you get FreeBSD up and running.
59 (It is assumed that COM1 will be available on a file/compute/terminal
60 server anyway; if you really need COM1 for something else (and you can't
61 switch that something else to COM2), then you probably shouldn't even
62 be bothering with all this in the first place.)
65 The serial port settings are hardcoded to 9600 baud, 8 bits, no parity,
66 1 stop bit, by default. If you wish to change the speed, you need to
67 recompile at least the boot blocks. Add the following line to
68 /etc/make.conf and compile new boot blocks:
70 BOOT_COMCONSOLE_SPEED=115200
72 If the serial console is configured in some other way than by booting with
73 -h, or if the serial console used by the kernel is different from the one
74 used by the boot blocks, then you must also add the following option to the
75 kernel configuration file and compile a new kernel:
77 options CONSPEED=115200
80 In addition to a serial cable, you will need a null modem adapter
81 in order to connect the terminal to the PC's serial port. If you don't
82 have one, go to Radio Shack and buy one: they're cheap.
85 If you wish to drop into the kernel debugger from the serial console
86 (useful for remote diagnostics, but also dangerous if you generate a
87 spurious BREAK on the serial port!) then you should compile your kernel
88 with the following options:
90 options BREAK_TO_DEBUGGER
94 - MAKE SURE THE CONFIGURATION FILE OF YOUR KERNEL HAS APPROPRIATE FLAGS
98 0x10 enable console support for this unit. The other console flags
99 are ignored unless this is set. Currently, at most one unit can
100 have console support; the first one (in config file order) with
101 this flag set is preferred. This option alone will not make
102 the serial port the console. Set the following flag or use the -h
103 option described below, together with this flag.
104 0x20 force this unit to be the console (unless there is another
105 higher priority console). This replaces the COMCONSOLE option.
108 device sio0 at isa? port "IO_COM1" tty flags 0x10 irq 4
110 If the flags were not set, you need to run UserConfig (on a different
111 console) or recompile the kernel.
113 - CREATE THE FILE "boot.config" IN THE ROOT DIRECTORY of the `a' partition
114 on the boot drive. Put the kernel name and options in one line. The
115 kernel name is optional. Options are subset of those described in boot(8):
116 -h toggle internal and serial consoles. You can use this to switch
117 console devices. For instance, if you boot from the VGA console,
118 you can use -h to force the kernel to use the serial port as its
119 console device. Alternatively, if you boot from the serial port,
120 you can use the -h to force the kernel to use the VGA display
121 as the console instead. (Can you say 'toggle' boys and girls?
123 -D toggle single and dual console configurations. In the single
124 configuration the console will be either the VGA display (internal
125 console) or the serial port, depending on the state of the -h option
126 above. In the dual console configuration, both the VGA display
127 and the serial port will become the console at the same time,
128 regardless of the state of the -h option.
129 However, the dual console configuration takes effect only during
130 the boot prompt. Once the kernel is loaded, the console specified
131 by the -h option becomes the only console.
132 -P probe the keyboard. If no keyboard is found, the -D and -h options
133 are automatically set.
135 Use either the -P option to select the console automatically, or the -h
136 option to force the serial console.
138 - BOOT THE MACHINE. You'll see a prompt appear on the terminal that looks
143 >> FreeBSD BOOT @ 0x10000: 640/7168 k of memory, serial console
144 Boot default: 0:wd(0,a)kernel
148 This is identical to the prompt that normally appears on the VGA console,
149 except for the 'No keyboard found' message that indicates a keyboard
150 couldn't be detected, if the -P option is in `boot.config'.
152 From here you can boot the system (or let it autoboot by itself) just
153 like you can from the VGA console and the kernel will automatically
154 use COM1 as the console device. This is done by passing a special flag
155 to the kernel in the 'boothowto' word. (The curious can refer to
156 <sys/reboot.h> and the sio driver sources for details.)
161 - The idea here is to allow people to set up dedicated servers that require
162 no graphics hardware or attached keyboards. Unfortunately, while (most?)
163 every system will let you boot without a keyboard, there are quite a few
164 that will not let you boot without a graphics adapter. Machines with
165 AMI BIOSes can be configured to boot with no graphics adapter installed
166 simply by changing the 'graphics adapter' setting in the CMOS configuration
167 to 'Not installed.' However, many machines do not support this option
168 and will refuse to boot if you have no display hardware in the system. With
169 these machines, you'll have to leave some kind of graphics card plugged in,
170 (even if it's just a junky mono board) although you won't have to attach
171 a monitor into it. You might also try installing an AMI BIOS. :)
173 - Using a port other than COM1 as the console requires some recompiling.
174 Again, it's usually assumed that COM1 will be available for use as a
175 console device on a dedicated file/compute/terminal server, so hopefully
176 you'll never need to do this. But if you feel you must change the console
177 to a different port, here's how:
179 o Get the kernel source package.
180 o Edit /etc/make.conf and set BOOT_COMCONSOLE_PORT to the
181 address of the port you want to use (0x3F8, 0x2F8, 0x3E8 or
182 0x2E8). Only COM1 through COM4 can be used; multiport serial
183 cards will not work. No interrupt setting is needed.
184 o Create a custom kernel configuration file and add appropriate
185 `flags' for the serial port you want to use. For example, if you
186 want to make COM2 the console:
188 device sio1 at isa? port "IO_COM2" tty flags 0x10 irq 3
190 The console flags for the other serial ports should not be set.
191 o Recompile both the boot blocks and the kernel.
192 o Install the boot blocks with the disklabel command and boot
196 $FreeBSD: src/sys/i386/boot/biosboot/README.serial,v 1.11 1999/08/28 00:43:10 peter Exp $
197 $DragonFly: src/sys/i386/boot/biosboot/Attic/README.serial,v 1.2 2003/06/17 04:28:34 dillon Exp $