Re: runlevels/boot stuff
To quote "M.B.Midden" <dunki@dds.nl>,
# Im looking for some info about runlevels. Is there a howto for it?
What is
# the best runlevel for a server en when should u switch ( how can you
switch)
# ( i tried man runlevel ofcourse ) etc
I'm sort of bored, so here's a little tutorial ;)
Each runlevel has an associated directory in /etc .
/etc/rc0.d/* : Used to halt the system.
/etc/rc1.d/* : Used to put the system into single-user mode(after
another runlevel has already been reached). Similar to "Safe Mode" from
MS Windows.
/etc/rc2.d/* : Regular multi-user runlevel.
/etc/rc3.d/* : Regular multi-user runlevel.
/etc/rc4.d/* : Regular multi-user runlevel.
/etc/rc5.d/* : Regular multi-user runlevel.
/etc/rc6.d/* : Used to reboot the system.
/etc/rcS.d/* : General not used manually, it's used to put the system
into single-user mode right after the kernel has been started. Usually
entered by typing "linux single" at the LILO prompt.
Runlevels 0, 1, 6, and S generally arn't modified by the user, which
leaves runleves 2, 3, 4, and 5.
Within all of these directories are a number of symbolic links to
scripts within /etc/init.d . When the symbolic link's name start with
"S", that means the appropriate script is executed with the argument
"start". So, for instance, if there is a symbolink link
/etc/rc2.d/S20gpm -> /etc/init.d/gpm , then '/etc/init.d/gpm start' is
run.
You'll notice there's a number between the "S" and the script name.
That's the priority by which the script is run. The scripts are executed
serially, lower numbers starting first.
When a symbolic link's name starts with "K", the appropriate script is
run with the "stop" argument. The same rules about priorities are used.
When you enter a runlevel, all the scripts are called. Runlevel 6, for
instance, calls(at the very end) /etc/init.d/reboot, so the computer
reboots. When you type 'reboot' at the command line, you're basically
entering runlevel 6. By default, your Debian system enters runlevel 2 on
boot. Also by default on your Debian system, runlevels 2, 3, 4, and 5
are exactly the same. There's no difference between them until you make
them different.
Now, to answer your question :) By default, the user-defined runlevels
are all the same, so there's no "best server runlevel". However, you can
manually change the symbolic links(either using strict 'ln' and 'rm'
commands, or(prefferably) using 'update-rc.d'), so that runlevel 3, for
instance, starts all your regular Internet/Intranet services(apache,
inetd, pop3d, and friends), and you can make runlevel 2 start your
regular desktop(no apache, no identd, nothing you don't use) with X and
your font servers and everything else you regularily use.
Okay, I've wasted enough of your time ;)
For some good, in-depth(but still understandable) information, check out
the man pages for 'init' and 'update-rc.d'. You can also read the man
page for /bin/init's configuration file, 'inittab', but I find t
somewhat more difficult to understand. Oh, and if you do decide to
change which services go into which runlevels, always use 'update-rc.d'.
:)
Dave
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