Warsaw, 1998.07.07
This README shortly describes the features of "oinit" - a very simplistic
version of init(8) combined with a shell.
Features
--------
* oinit is able to run system in multi- and single-user modes,
* it can be started on system with DEVFS/SLICE (i.e. empty /dev),
* provides minimalistic user interface, called "shell()",
* it can run the system startup script (/etc/rc),
* it can be compiled with -DOINIT_RC to use its own startup script
(*very* primitive, but doesn't require any real shell to run it!),
* doesn't require the whole chain of init->getty->login->shell to be run,
* it is extremely small, and is ideally suited for situations when
there is little memory.
As an additional bonus you receive some obvious and some hidden bugs... :-))
This code is at most alpha quality yet.
How it works
------------
Unlike normal init(8), it forks itself on given number of vty's immediately
providing shell() interface. Currently it doesn't require (and is unable to
perform) any authentication, but this is easy to add if needed.
Standard version of FreeBSD kernel looks for /sbin/init first, and then
tries to execute it. If it fails, it tries to find:
/sbin/oinit
/sbin/init.bak
/stand/sysinstall
So it is easy to make use of it even on standard system - just put it in
/sbin/oinit and rename /sbin/init to something else, e.g. /sbin/init.bak.
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!!! WARNING !!! WARNING !!! WARNING !!! WARNING !!! WARNING !!! WARNING !!!
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Init (or oinit) plays crucial role in the system. If you plan to do any
changes to your system's init, make sure you have a boot floppy with working
version of statically compiled init(8) on it - you can very easily put your
system in unusable state when fiddling with it.
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Shell() interface
-----------------
It allows you to issue built-in and external commands. Built-in commands
are listed below. For each command there is short help available, with
example of usage.
cd change working directory
pwd print working directory
set set environment variable (no expansion)
unset unset environment variable
env print all environment variables
echo echo arguments on stdout
exit exit from shell (oinit will start a new one after some delay)
. source-in a file with commands
? help
Any other command is passed to execvp(3) as it is.
EXCEPTION: if you end the command line with a '&', the command is started
as daemon. This is NOT the same as in normal shell, where the '&' puts a
process in background. Here the newly started process is totally dissociated
from terminal.
Prompt tells you:
* your `pwd`
* your PID
* and that you are root ('#').
WARNING: this pseudo-shell doesn't do any expansion whatsoever.
To do list
----------
- oinit proper:
* fix signal handling and transitions,
* invent a one-file configuration database (combining as many files
from /etc as possible into one) able to properly handle inter-
dependencies in running various daemons,
* allow for interpreting of such database, and running various
programs ourselves (this would eventually allow to make /bin/sh
an option, not necessity),
* better hooks for incorporating other modules into oinit (see e.g.
the telnet() below),
* add optional authentication,
- shell():
* more built-ins: perhaps 'kill' and 'ps',
* variable expansion,
* globbing,
* conditionals,
* history? (it depends on how much memory it needs).
* programmatic hooks for easy customisation of user interface (like
hierarchy of commands and contexts),
* ...
- implement as a routine (like shell()) a small remote login daemon telnet(),
as a built-in module to oinit. It would implement the simplest options of
normal telnet, and would itself handle authentication, passing control to
shell() on success. The authentication routine would be the same as for
checking console access.
And allow me for a moment of day-dreaming: I'd like to rewrite oinit one day
to be a monolithic one-in-all application, non-forking but multithreaded... It
would contain all the modules, such as shell(), telnet(), ifconfig() etc...
started as threads, not separate processes.
Credits
-------
The overall framework was taken from FreeBSD /sbin/init.
Andrzej Bialecki
<abial@freebsd.org>
$FreeBSD$
5a86d4eafc