Beeping LILO (Was: Re: Booting Linux)

["T. V. Raman" <raman@adobe.com>]

Sometimes I get the feeling that people on this list are not taking time to
absorb the answers people have already given.

The "making lilo beep" thread is a case in point.

I'm reposting an excellent message on this topic (not posted by me originally
--credits go to original author) that in my opinion should have been the end
of story on this issue.

From: doyons@JSP.UMontreal.CA (Stephane Doyon)
To: Chris Foote <cabot@ee.mcgill.ca>, blinux-list@goldfish.cube.net
Subject: Re: Booting Linux
Date: Thu, 25 Jul 1996 23:05:07 -0400

Some hints about booting Linux and reading boot messages

- Finding out when the LILO boot prompt is on: It is easy to just hold down
the left shift key when the computer boots, but the only way to make sure
you have reached the "boot" prompt is to listen to the HD and wait. Well
here are two tricks.

One of the things LILO can do, is print a customized message before giving
the prompt (that is the "boot" prompt, not the "LILO" prompt). Just put a
line in your lilo.conf that looks like:
message = /boot/message
and put your customized message in /boot/message. The interesting thing is
that if that file contains an ASCII 7 character (control-G), you will here a
short beep when the message is actually printed by LILO. So when you hear
that beep, you know you can release the shift key and type in your command
line.

Another thing LILO can do, is print all its stuff to a com port, so you can
read it on an attached serial terminal. Just put a line in your lilo.config
like
serial = 1,9600n8

- Reading kernel boot-time messages:

On a running system, pretty much every thing is in the log in
/var/adm/something... But for a buggy system, or for installing a new
system, that's another story. Two things you can do.

First, you can, as someone suggested, redirect the console to a serial port,
and read all messages on an attached serial terminal. I have done it in the
past (a long time ago though). Here's how to do it, if I remember correctly.
On your Linux partition or on your root disk, do:
cd /dev
rm console
mknod console c 4 64 # 4,64 are the major and minor for ttyS0
#alternatively: mknod console c 4 65 # for ttyS1.

I haven't done that in quite a while, so I might be forgetting something, or
getting something wrong. I don't remember if it will come at you at 9600 or
38400... Perhaps someone would care to try it out...

Only problem is, of course, now you might not have any screen output anymore
(I don't think I ever had a sighted person tell me what happens), so it
might be hard to put it back. Before you try this, make sure you can login
safely either from a network or from the other com port.

To put back the console device, just
cd /dev
rm console
ls -l tty0 # it's the same as console, so you can find the numbers there
           # if you forget
mknod console c 4 0
chmod 622 console

It's useful when you really have to find out what it says on the screen. Of
course you have to be able to get to /dev and have rm and mknod and ls and
such working. But it can be useful when you prepare a root disk to install a
new machine.

FInally, I'd like to point out that any access program that works by
grabbing the screen contents from the console driver (interfacing through
the /dev/vcs* devices) can potentially allow you to read all messages
printed to the screen since boot, even the initial BIOS print out!

BRLTTY uses this scheme, so I know it can be done because I have done it
several times. BRLTTY runs in user space, so I have to wait for it to be
started (from my rc.S). But once it's there, I can use the scrollback
feature of the console driver, which is available if you have extra RAM on
your video card (like any SVGA card). Just press shift+pgup and shift+pgdn
to skim through the buffer. Unless the buffer has overflowed from all boot
messages (which has never been the case for me) you can scroll back up even
before the console driver starts. You'll see the LILO prompt and above it
the BIOS initial print out.

Hope any of this helps

-- 

Stephane Doyon
  Bacc. specialise en informatique                    doyons@IRO.umontreal.ca
  Universite de Montreal                              doyons@JSP.umontreal.ca

       A quote from StarTrek:

Virtue is a relative term.
    -- Spock, "Friday's Child," stardate 3499.1.


-- 
Best Regards,
--raman

      Adobe Systems                 Tel: 1 (415) 962 3945   (B-1 115)
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Disclaimer: The opinions expressed are my own and in no way should be taken
            as representative of my employer, Adobe Systems Inc.
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