197 lines
9.5 KiB
Plaintext
197 lines
9.5 KiB
Plaintext
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SERIAL CONSOLE USAGE NOTES
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Written by
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Bill Paul <wpaul@ctr.columbia.edu>
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Revised for 3.0-CURRENT by
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Kazutaka Yokota <yokota@zodiac.mech.utsunomiya-u.ac.jp>
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The FreeBSD boot block can now be used to boot FreeBSD on a system with
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only a dumb terminal on a serial port as a console. This feature
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is provided for the benefit of people who wish to install FreeBSD on
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dedicated file/compute/terminal server machines that have no keyboard
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(or monitor) attached, just as is possible with Sun workstations and
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servers. People who don't need this extra functionality shouldn't notice
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the changes at all (unless I've screwed something up horribly).
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To boot FreeBSD in serial console mode, you must do the following:
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- UNPLUG YOUR KEYBOARD. Most PC systems probe for the keyboard during the
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Power-On Self-Test (POST) and will generate an error if the keyboard
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isn't detected. Some BIOSes may be set to ignore this error. Many other
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machines will pause the boot process and wait for you to reattach the
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keyboard and press a key before proceeding any further. Consult the manual
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of your motherboard to see how it responds to the error and how to
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set the BIOS to ignore the error. If your computer complains about
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the lack of a keyboard but boots anyway, then you don't have to do
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anything special. (One machine with a PHOENIX BIOS that I have here
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merely says 'Keyboard failed' then continues to boot normally.) If your
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machine complains loudly about the lack of a keyboard and won't continue
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to boot until you plug it back in, you'll have to go into your CMOS
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configuration menu and change the 'Keyboard' setting to 'Not installed'
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in order to bypass the keyboard probe.
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NOTE #1:
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Setting the keyboard to 'Not installed' in the CMOS configuration
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does *NOT* mean that you won't be able to use your keyboard. All this
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does is tell the BIOS not to probe for a keyboard at power-on so that
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it won't bitch and moan if the keyboard isn't plugged in. You can leave the
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keyboard plugged in even with this flag set to 'Not installed' and the
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keyboard will still work. I repeat: changing the CMOS 'keyboard' setting
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to 'Not installed' only disables the BIOS's keyboard probe; it does
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*NOT* actually disable the keyboard.
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NOTE #2:
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If your system has a PS/2 mouse, chances are very good that you will
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need to unplug your mouse as well as your keyboard. This is because
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PS/2 mice share some hardware with the keyboard, and leaving the mouse
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plugged in can fool the keyboard probe into thinking the keyboard is
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still there. I have access to a Gateway 2000 Pentium 90Mhz system with
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an AMI BIOS that behaves this way. In general this is not a problem
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since the mouse isn't much good without the keyboard anyway.
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- PLUG A DUMB TERMINAL INTO COM1. If you don't have a dumb terminal, you
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can use an old PC/XT with a modem program, or the serial port on
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another UNIX box. If you don't have a COM1, get one. At this time,
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there is no way to select a port other than COM1 for the boot blocks
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without recompiling the boot blocks. If you're already using COM1 for
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another device, you'll have to temporarily remove that device and
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install a new boot block and kernel once you get FreeBSD up and running.
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(It is assumed that COM1 will be available on a file/compute/terminal
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server anyway; if you really need COM1 for something else (and you can't
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switch that something else to COM2), then you probably shouldn't even
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be bothering with all this in the first place.)
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NOTE #1:
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The serial port settings are hardcoded to 9600 baud, 8 bits, no parity,
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1 stop bit, by default. If you wish to change the speed, you need to
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recompile at least the boot blocks. Add the following line to
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/etc/make.conf and compile new boot blocks:
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BOOT_COMCONSOLE_SPEED=115200
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If the serial console is configured in some other way than by booting with
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-h, or if the serial console used by the kernel is different from the one
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used by the boot blocks, then you must also add the following option to the
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kernel configuration file and compile a new kernel:
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options CONSPEED=115200
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NOTE #2:
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In addition to a serial cable, you will need a null modem adapter
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in order to connect the terminal to the PC's serial port. If you don't
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have one, go to Radio Shack and buy one: they're cheap.
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NOTE #3:
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If you wish to drop into the kernel debugger from the serial console
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(useful for remote diagnostics, but also dangerous if you generate a
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spurious BREAK on the serial port!) then you should compile your kernel
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with the following options:
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options BREAK_TO_DEBUGGER
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options DDB
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- MAKE SURE THE CONFIGURATION FILE OF YOUR KERNEL HAS APPROPRIATE FLAGS
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SET FOR COM1.
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Relevant `flags' are:
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0x10 enable console support for this unit. The other console flags
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are ignored unless this is set. Currently, at most one unit can
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have console support; the first one (in config file order) with
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this flag set is preferred. This option alone will not make
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the serial port the console. Set the following flag or use the -h
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option described below, together with this flag.
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0x20 force this unit to be the console (unless there is another
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higher priority console). This replaces the COMCONSOLE option.
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Example:
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device sio0 at isa? port "IO_COM1" tty flags 0x10 irq 4
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If the flags were not set, you need to run UserConfig (on a different
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console) or recompile the kernel.
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- CREATE THE FILE "boot.config" IN THE ROOT DIRECTORY of the `a' partition
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on the boot drive. Put the kernel name and options in one line. The
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kernel name is optional. Options are subset of those described in boot(8):
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-h toggle internal and serial consoles. You can use this to switch
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console devices. For instance, if you boot from the VGA console,
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you can use -h to force the kernel to use the serial port as its
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console device. Alternatively, if you boot from the serial port,
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you can use the -h to force the kernel to use the VGA display
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as the console instead. (Can you say 'toggle' boys and girls?
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I knew you could. :)
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-D toggle single and dual console configurations. In the single
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configuration the console will be either the VGA display (internal
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console) or the serial port, depending on the state of the -h option
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above. In the dual console configuration, both the VGA display
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and the serial port will become the console at the same time,
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regardless of the state of the -h option.
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However, the dual console configuration takes effect only during
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the boot prompt. Once the kernel is loaded, the console specified
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by the -h option becomes the only console.
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-P probe the keyboard. If no keyboard is found, the -D and -h options
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are automatically set.
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Use either the -P option to select the console automatically, or the -h
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option to force the serial console.
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- BOOT THE MACHINE. You'll see a prompt appear on the terminal that looks
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something like this:
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No keyboard found
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>> FreeBSD BOOT @ 0x10000: 640/7168 k of memory, serial console
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Boot default: 0:wd(0,a)kernel
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boot:
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This is identical to the prompt that normally appears on the VGA console,
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except for the 'No keyboard found' message that indicates a keyboard
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couldn't be detected, if the -P option is in `boot.config'.
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From here you can boot the system (or let it autoboot by itself) just
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like you can from the VGA console and the kernel will automatically
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use COM1 as the console device. This is done by passing a special flag
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to the kernel in the 'boothowto' word. (The curious can refer to
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<sys/reboot.h> and the sio driver sources for details.)
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CAVEATS:
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- The idea here is to allow people to set up dedicated servers that require
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no graphics hardware or attached keyboards. Unfortunately, while (most?)
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every system will let you boot without a keyboard, there are quite a few
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that will not let you boot without a graphics adapter. Machines with
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AMI BIOSes can be configured to boot with no graphics adapter installed
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simply by changing the 'graphics adapter' setting in the CMOS configuration
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to 'Not installed.' However, many machines do not support this option
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and will refuse to boot if you have no display hardware in the system. With
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these machines, you'll have to leave some kind of graphics card plugged in,
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(even if it's just a junky mono board) although you won't have to attach
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a monitor into it. You might also try installing an AMI BIOS. :)
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- Using a port other than COM1 as the console requires some recompiling.
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Again, it's usually assumed that COM1 will be available for use as a
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console device on a dedicated file/compute/terminal server, so hopefully
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you'll never need to do this. But if you feel you must change the console
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to a different port, here's how:
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o Get the kernel source package.
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o Edit /etc/make.conf and set BOOT_COMCONSOLE_PORT to the
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address of the port you want to use (0x3F8, 0x2F8, 0x3E8 or
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0x2E8). Only COM1 through COM4 can be used; multiport serial
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cards will not work. No interrupt setting is needed.
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o Create a custom kernel configuration file and add appropriate
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`flags' for the serial port you want to use. For example, if you
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want to make COM2 the console:
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device sio1 at isa? port "IO_COM2" tty flags 0x10 irq 3
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The console flags for the other serial ports should not be set.
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o Recompile both the boot blocks and the kernel.
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o Install the boot blocks with the disklabel command and boot
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from the new kernel.
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$Id: README.serial,v 1.9 1997/06/16 06:32:51 charnier Exp $
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