Running linux with a Serial console


OK. So you're building a server, and you disapprove of GUIs. Or you're
using up all your PCI/ISA slots with networks cards for a router and
you don't have an AGP slot. Or you "want to".

Note: My serial console is set to 9600bps [the highest speed that's
available everywhere]. No parity, and 8 data bits. It's plugged into ttyS0
[com1]. Feel free to modify your stuff suitably, but I don't recommend
"just using 115200" for everything, as it can cause random and unexpected
breakage.


There're three main things about getting linux to run with a serial
console instead of a "normal" display:

1) Booting
2) Getting linux to spam important messages to the right place
3) Getting a console up on the terminal so you can actually do_stuff

All of which are actually pretty easy. First, you need to get LILO doing
prompt-type stuff. To the global section of lilo.conf, add the following:

serial = 0,9600n8

The "0," refers to ttyS0. The others are obvious, and if they're not,
read your terminal's documentation.

LILO is actually exceedingly cool. In this particular case, it is still
also showing the menu on the main screen - so if you have a head as well
as the terminal, the server will quite happily let you boot using either
[note that a properly set up lilo will probably boot with no interaction,
anyways]


As an aside, here, I set lilo up so that it'll automatically boot to
your default kernel, but if you want to give it parameters, you need
a password; just add the following two lines to /etc/lilo.conf, in the
global section [or individual images, if you really feel the urge. I've
not yet discovered a use for that]:

restricted
password = a-password

Remember, kids, to remove read permission to that file for anyone
except root.


Next, you need to get the kernel to spout important information to the
right place. Notably, all of the boot messages, but also some other
important things; if there's a panic, it needs to write the info to
the right place [that's a bit of an extreme example, but there are
others.]

To the global lilo.conf section, add the following:"
append = "console=ttyS0,9600n8"

If you're already appending something, remmeber that these options are
whitespace-separated, so, on my machine [with a CD burner], the option
looks like:
append = "hdg=ide-scsi console=ttyS0,9600n8"

Finally, you actually need a console to be spawned in the relevant
place. In inittab, add the following:
s1:12345:respawn:/sbin/agetty -L ttyS0 9600 vt100

You may well find something akin to that already existing, but commented
out. So be it.

Now, at this point, all is well if you have an 80-column terminal. What
about people who only have 40-column screens? Notably, palm
pilot users making use of something like PhaethonH's vt100 client
[http://icculus.org/~phaethon/palmos/vt100/]?

The two terms you're looking for are
stty cols 40
and
export COLUMNS=40
[for good measure, thanks Phaethon (=]

Gary (-;

PS. If you're using grub to bootload, that's your choice. Apparently
it does all this stuff. I imagine it does, as it's a lot like every
other travesty the FSF put out - completely out of sync with the unix
"one tool for each job", the appear to have taken on the "one tool for
every job" thing. I don't know how to use it.