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do fit, and beeping in case of an overflow. . Drop a comment about the ``FORCE_COMCONSOLE'' option into README.serial. . Increase the name buffer for the root directory from 100 bytes to 8 KB; this is in no way ideal, but (IMHO) the best that can be done by now. People did encounter problems with their root dir name listing overflowing the allocated buffer space. Once we've got the three-stage boot, we should implement some basic malloc(). Swap space is already getting tight now, perhaps the swap should go into another 64 KB segment instead. . Make the keyboard probe less paranoid. It should not give up in case of a keyboard that's continuously demanding RESEND's. Even though the keyboard reset apparently has not been reported to be complete, it's at the very least proven that there IS something like a keyboard available. This solves problems with the ``Gateway-2000 AllKey programmable'' (sp?) keyboard, that experienced a total hang with the previous probe. Thanks goes to Scott Blachowicz <scott@statsci.com> for his extensive testing of my various interim (debugging) bootblocks to get this working.
156 lines
7.7 KiB
Plaintext
156 lines
7.7 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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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 (COM1) 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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Note that 'options COMCONSOLE' can still be used to force the kernel to
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boot in 'serial console' mode regardless of what boot options you use.
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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. Additionally, many machines will pause the boot process
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and wait for you to reattach the keyboard and press a key before
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proceeding any further. If your computer complains about the lack of a
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keyboard but boots anyway, then you don't have to do anything special.
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(One machine with a PHOENIX BIOS that I have here merely says 'Keyboard
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failed' then continues to boot normally.) If your machine complains
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loudly about the lack of a keyboard and won't continue to boot until you
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plug it back in, you'll have to go into your CMOS configuration menu and
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change the 'Keyboard' setting to 'Not installed' in order to bypass the
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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 without recompiling
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both the kernel and 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.
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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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- BOOT THE MACHINE. The boot block will probe for a keyboard on your
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system. If it fails to find one, you'll see a prompt appear on the
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terminal that looks something like this:
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No keyboard found.
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>> FreeBSD BOOT @ 0x10000: 640/7168 k of memory
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Use hd(1,a)/kernel to boot sd0 when wd0 is also installed.
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Usage: [[[fd(0,a)]/kernel][-s][-r][-a][-c][-d][-b][-v][-h]]
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Use ? for file list or simply press Return for defaults
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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 a keyboard is detected, the boot prompt will
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appear on the VGA display as usual.)
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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. No recompilation or 'options COMCONSOLE'
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is required. This is done by passing a special flag to the kernel in
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the 'boothowto' word. (The curious can refer to <sys/reboot.h> and the
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sio driver sources for details.)
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- You will notice that there's a new boot flag: -h. You can use this to
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force the kernel to switch console devices. For instance, if you boot
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from the VGA console, you can use -h to force the kernel to use the
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serial port as its console device. Alternatively, if you boot from
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the serial port, you can use the -h to force the kernel to use the VGA
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display as the console instead. (Can you say 'toggle' boys and girls?
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I knew you could. :)
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Should you wish to force booting off a serial console no matter if
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there's a keyboard connected or not, you can also uncomment the line
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with the ``FORCE_COMCONSOLE'' definition in the Makefile. Remake and
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reinstall your bootblocks, and finally relabel your disk (disklabel -B)
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to pick up those boot blocks.
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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 kerndist kernel source package.
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o Edit /sys/i386/boot/biosboot/Makefile and set COMCONSOLE 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 the following
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lines:
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options "CONADDR=0x3F8"
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options "CONUNIT=0"
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Set CONADDR to the same address that you selected for COMCONSOLE
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in the bootbios Makefile. Set CONUNIT to the unit number of the
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serial port that this address corresponds to (0 = sio0, 1 = sio1,
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etc). This implies that the serial port you want to use must be
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configured into the kernel in the normal way first. I'm not
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going to list all the possible combinations here; just use your
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head and you should be okay.
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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 1.2 1995/02/16 07:37:35 wpaul Exp $
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