[techtalk] X win

[Samantha Jo Moore]

Hi all,
 
> Hi, Jack,
> 
> Reboot, and type in "linux 3" at the LILO prompt.  That will boot to the
> command line.
> 
> To make the change permanent, you need to edit your /etc/inittab file and
> change your run level at boot from 5 (GUI) to 3 (command line).
> 
> That's all it takes  :)

This seems like a good opportunity to talk about run levels.  This is another
topic that Windows admins have to experience with because that OS doesn't
incorporate that concept.

Run levels:

A run level is simply a state that the OS run in.  There are at least 6
run levels that a Linux (or any unix) kernel runs in.  The difference in
these run levels is simply the set of daemons or programs that get executed
at boot time and pretty much nothing else.  The list of these daemons or
programs can be customized by the sysadmin at any time by modifying some
config files which vary from distro to distro.  To cause the kernel to 
switch to a different run level you use the "init" command followed by the
desired run level number (i.e. init 3).  Of course, you must be logged in
as root to perform this operations since changing run levels is a privileged
operation.

A summary of what each run level means or is supposed to accomplish follows:

init 0:
	Causes the system to shut down.  This is equivalent to typing
	"shutdown -h now".

init 1:
	Causes the kernel to go into single user mode, and the single user is
	"root".  This run level is usually used to system maintenance operations.
	None of the networking or additional services are active at this time.

init 2:
	Is traditionally used to put the kernel in multi user mode.  This allows
	other users to log in from hardwired terminals.  No networking services
	are available in this run level.

init 3:
	Is traditionally a state where full networking is enabled.  It's kinda 
	like run level 2 with network	services.

init 4:
	When X was developed this run level was designated as the "GUI mode for
	the system console" run level.

init 5:
	User defined.

init 6:
	Reboot.  This run level is equivalent to typing "shutdown -r now".

The run levels are controlled by the /etc/inittab file.  However, in distros
like Red Hat this mechanism has been used to ease and optimize the management
of processes by simply running a script that in turn runs additional scripts
to fire up or shut down processes assigned to run at each level.  The scripts
used to do this can be found in /etc/rc.d/init.d and /etc/rc.d/rc?.d.  For 
more information on the init states (or run levels) consult the man pages for
init (man init).

Samantha Jo Moore
CTO - The Tahoe Group, Inc.
http://www.thetahoegroup.com
sjmoore at thetahoegroup.com

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