2002 08 08

                    LINUX NEWS
            August 8, 2002 -- Issue #93


1) Sean’s Notes

2) Linux News

Security Bug in Popular Library
Codeweavers Releases 1.2
Linux Scores Big
MySQL Certification Announced

3) Linux Resources

Using RAID
How many System Administrators are Enough?
Traffic Monitoring With MRTG
Using apt-get
OpenSSH Vulnerability

4) App o’ the Week

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1) Sean's Notes

Last week I started to look at the /etc/inittab file, which
led into a description of the SysV startup scripts:


Basically, each service that wants to be started or stopped
this way has a script in /etc/rc.d/init.d.  It is called
with either the "start" or "stop" argument, depending on if
it is to be started or stopped respectively.  Entering
runlevel N, /etc/rc.d/rcN.d is checked.  All the files
starting with K are run with the stop argument, then all the
files starting with S are run with the start argument.  Each
of these files is in fact a symlink back to the init.d

Through the magic of inittab, this can happen.  Recall that
each line in the file looks like this:


Where the id is just a unique ID, the runlevel says when
the action is valid, the action says what is to be done,
and the command specifies how it is to be done.  We saw that...

l3:3:wait:/etc/rc.d/rc 3

...will take care of setting things in motion to get
ourselves into runlevel 3.

"wait" means that the command is to be executed when the
system enters the given runlevel, and that init is to wait
for it's termination.

There is another, equally handy, action that does something
similar.  It's called "respawn".  The command is run, and
upon termination, it is re-run.

"Listen on the first virtual terminal, and give the user a
login session.  When they finish, do it again."

This translates to:

1:2345:respawn:/sbin/mingetty tty1

mingetty is what we call a "getty"; it sits on a device
(virtual terminal, serial port, modem) and provides a tty
(a terminal).  When you're logging in to your console,
you're talking to a getty.

We can also use this technique in runlevel 5 to give a
graphical X login:

x:5:respawn:/etc/X11/prefdm -nodaemon

That line fires up your preferred display manager (xdm, kdm,
gdm), which gives you the cute graphical username and password
dialogue.  It hands off control to GNOME or whatever you're
using once you log in.  When you log out, it it exits. init,
noticing that it's gone, restarts it.  Pretty handy, eh?

Some of the other events that init can handle are the
starting of the system through the "sysinit" action:


This part of the bootup takes care of mounting the
filesystems, swapfiles, and other housekeeping before you
enter your default runlevel.  Read through it some time,
it'll give you some insight into how your computer goes from
being just a running kernel, to a multiuser system.

init also handles power problems.  If you've got a UPS or
other hardware that can provide advance warning of a power
outage, init can shut down your system cleanly:

pf::powerfail:/sbin/shutdown -f -h +2 "Power Failure; System Shutting Down"

or, if power is restored, stop the shutdown:

pr:12345:powerokwait:/sbin/shutdown -c "Power Restored; Shutdown Cancelled"

There are a few other actions I didn't cover, but you can
read about them in the inittab(5) man page.

/etc/inittab is a pretty simple file, but it controls the
actions of init.  Almost everything in your system passes
through init in some way or another, which means that inittab
is a pretty critical file in the grand scheme of things.
>From inittab, all the bootup and runlevel scripts are run.
If you want to learn how your system operates, inittab is a
great place to start.

Long live the Penguin,


2) Linux News

Security Bug in Popular Library
Thanks to the lovely and talented Cherina for pointing me
toward this article. Seems there is a bug in parts of the
Sun RPC code that other OSes, including Linux and Solaris,
use for the Kerberos authentication mechanism. This bug
could lead to a compromise of the Key Distribution Centre,
which is not a happy thing.


Codeweavers Releases 1.2
Codeweavers is a commercial company that is pouring work
into the WINE project, which will let Windows binaries run
on Linux. 1.2 promises both Quicken and Visio support, along
with some support for QuickBooks! I'll see what I can do about
getting a demo and letting you know first-hand how it works.

http://www.codeweavers.com/about/press_releases/?id 020807

Linux Scores Big
Here is a small success story about a company that was
providing systems to the companies that lost their servers
on September 11th. Seems the Windows box couldn't keep up
to the load, so they tried a Linux box and were impressed.


MySQL Certification Announced
MySQL, that SQL database we all love, has come out with a
certification program. If you dig around, you can sign up to
be a beta tester. A big rip if you ask me, it's $100 as
opposed to the $150 they plan to charge, and you have to
answer three times as many questions. Still, it's good to
see that some of the tools out there are looking at getting
people qualified.


3) Linux Resources

Using RAID

RAID, the "Redundant Array of Independent Disks", adds fault
tolerance to a system by spreading data over multiple drives.
This article goes over the different types of RAID, how to
implement it in software, and most importantly, how to
maintain and recover from a failure.


How many System Administrators are Enough?
This paper explains some factors to consider when determining
how many admins are needed to maintain a site. Not
surprisingly, things like automation play a vital role in
this calculation. Accordingly, shell scripting and
perl/python programming are valuable skills when determining
your worth to an organization.


Traffic Monitoring With MRTG
I picked this up from another one of Cramsession's
newsletters, and had to pass it along. MRTG is a set of
utilities that let you graph data obtained from SNMP (such
as routers). It's very easy to set up, if you have this
set of instructions...

(requires TechRepublic login)


Using apt-get
Whenever people talk about Debian, they seem to always talk
about the associated package manager. Here's an article
describing the basic usage of apt-get, along with some basic
troubleshooting commands.


OpenSSH Vulnerability
If you've built OpenSSH from source since the end of July
(versions 3.2.2p1, 3.4p1 and 3.4), you'll want to update
your systems. Somehow, a trojan got inserted into the
distribution tarballs.


4) App o' the Week
If you're into Voice Over IP, the Open H.323 project will
make you happy. Here is the latest release of the Open
Gatekeeper, which will let you get your video through that
pesky NAT firewall, among many other things.


(C) 2002 BrainBuzz.com, Inc. All Rights Reserved.

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