TITLE: Adding extra stuff to inittab
LFS VERSION: 3.0-rc1
AUTHOR: Laurence Withers <lwithers@lwithers.demon.co.uk>
SYNOPSIS:
Adding extra things to inittab gives you options such as more
consoles (if 6 isn't enough!), log files on a virtual terminal, and
programs such as `top'.
HINT:
0. Contents
-----------
1. Introduction
2. Adding extra consoles
3. Log files on a virtual terminal
4. Top on a virtual terminal
5. Caveats
Appendix A. Format of /etc/inittab explained
1. Introduction
---------------
By editing /etc/inittab, you can achieve all sorts of nifty and
useful things. This file is the configuration of `init', the utility
which controls booting, shutting down, etc.; look at the LFS book for
some details, and also examine the /etc/inittab file given.
In this hint, I will show you how to add extra consoles (if, like
me, you appreciate having 10 or so consoles available), how to have a
virtual terminal display a log file, and how to run `top' (or any other
utility you like) on a virtual terminal.
Note that the virtual terminals used in this hint, /dev/tty1 to
/dev/tty12, correspond to the screens you get when you press Alt+F1 to
Alt+F12. If a VT is unused, then it won't pop up when you press its key;
it will only appear once some data has been sent to it.
2. Adding extra consoles
------------------------
With the /etc/inittab that ships with LFS, you get six consoles (on
VTs 1 through 6). First, decide which VTs you want to have terminals on.
Then, add the following line to /etc/inittab for each console that you
want:
XXX:2345:respawn:/sbin/agetty ttyXXX 9600
(replace XXX with the number of the VT, 7-12).
If, like me, you don't want other people to see what was on the
screen after you finished with your console, you can use some trickery
to clear the screen after you logout. Firstly, create a script:
# cat >/sbin/agetty-init.sh <<EOF
>#!/bin/sh
># /sbin/agetty-init.sh
># For clearing the screen after you have finished with a console.
>
>/sbin/agetty tty$1 9600
>clear >/dev/tty$1
>
>EOF
# chmod +x /sbin/agetty-init.sh
Then, in /etc/inittab, change the console lines. These are in the
same format as above. The stock LFS file will contain entries starting
1:, 2:, 3:, 4:, 5: and 6: (not l1: et al.; these are something else).
Find each such line and delete it. Now add the following line once for
each console you want:
cXXX:2345:respawn:/sbin/agetty-init.sh XXX
(replace XXX with the number of the VT you want, 1 through 12).
Remember that agetty will print the contents of /etc/issue to the
screen before its login prompt; you can use this to customise the
appearance of your login screens. Also, you can put any additional
actions into `agetty-init.sh' (before or after agetty is called); these
allow you to customise your system even more.
3. Log files on a virtual terminal
----------------------------------
If you want a VT to display the contents of a log file, you can use
a simple entry in /etc/inittab. Add a line like the following:
log:2345:respawn:/usr/bin/tail -f --retry /var/log/sys.log >/dev/ttyXXX
Replace the initial `log:' with any 4-character name you like; as
long as each identifier is unique, there is no problem. For instance,
you could use `9x3d:', if it meant something to you. Replace the final
filename with the name of the log file you want to examine. Finally,
replace XXX with the number of the VT you want to output to.
4. Top on a virtual terminal
----------------------------
`top' is a great program to have running on a spare VT! It lets you
see which processes are running, what your CPU is up to, how much memory
is in use, and so on. To get it running on a spare VT, use the following
line in /etc/inittab:
top:2345:respawn:/usr/bin/top d 1 s S c >/dev/ttyXXX </dev/ttyXXX
Replace XXX with the number of the VT you want to use. Also note the
parameters we pass to top: `d 1' sets the delay between updates to 1s
(change this if you want), `s' runs top in secure mode (see the man page
for details; basically, this stops any old user from killing processes),
and `S c' are aesthetic options. See `man top' for more info.
You can use this sort of line to add any program you like on a VT.
Note that you need to redirect both output and input for an interactive
program like top to work.
5. Caveats
----------
If you are trying anything ambitious, please read the information
in Appendix A, below. This explains the format of /etc/inittab, so you
are less likely to make a mistake which needs rectifying. Also, before
you start messing with /etc/inittab, you should probably have some
backup way of booting into your system (for instance, I use an old SuSE
6.3 bootable CDROM).
Although nothing can really go disastrously wrong with this sort of
setup, sometimes your VTs can get scrambled by programs such as X and
any sort of graphical login manager. I don't know when this happens, or
how to avoid or rectify it, but it hasn't caused me any problems. Note
that I don't use a graphical login, however.
Jurgen Nagel has reported that his extra consoles don't work
correctly. He has fixed this by adding an initialisation field to the
agetty call:
c2:2345:respawn:/sbin/agetty -I [H[J tty2 9600
The initialisation is <escape>[H<escape>[J and this fixes his
problem. I can't reproduce this on any of my systems but if you get this
problem, just add the -I parameter to the agetty call. Thanks Jurgen!
Appendix A. Format of /etc/inittab explained
--------------------------------------------
For the version of init used in LFS, the /etc/inittab file has the
following format:
identifier:runlevels:actiontype:command
`identifier' is a unique identifier, from 1 to 4 characters. Make sure
you don't use duplicate identifiers in your file. The identifier has no
bearing on how init works; the names don't have to mean anything.
`runlevels' is a list of the runlevels in which this line should be
activated. Read `man init' for more detail about runlevels.
`actiontype' is one of the following:
respawn run the command every time it finishes
wait run the command when entering the runlevel, and wait
for it to finish before moving on
once run the command once when entering the runlevel
boot executed only during system bootup (ignores
runlevels)
bootwait as above, only wait for finish
off ignore this entry
initdefault this actually specifies which runlevel is considered
the default on the system (usually 3)
sysinit executed during bootup, before boot/bootwait
ctrlaltdel what to do when the user hits ctrl+alt+del
There are some more actions, but these are more advanced. Details
are available (see `man inittab' and possibly `man init').
`command' is the commandline to run. Note that the PATH environment
variable isn't set: you need to specify the whole path to any executable
files.