Cramsession Linux Newsletter

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Aug 8 2002

                    LINUX NEWS
            http://www.Cramsession.com
            August 8, 2002 -- Issue #93

TABLE OF CONTENTS

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:

http://newsletters.cramsession.com/Newsletters/NewsletterArchive/Li nuxNews/august-1-2002linux.txt

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 directory.

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

id:runlevel:action:command

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:

si::sysinit:/etc/rc.d/rc.sysinit

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,

Sean mailto:swalberg@cramsession.com

2) Linux News

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.

http://www.eweek.com/article2/0,3959,439927,00.asp

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.

http://newsforge.com/newsforge/02/08/06/1432203.shtml?tid=3

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.

http://www.mysql.com/training/certification.html

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.

http://www.linuxplanet.com/linuxplanet/tutorials/4349/2/

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.

http://www.verber.com/mark/sysadm/how-many-admins.html

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)

http://www.techrepublic.com/article.jhtml?id=r00220020802noo01.htm& src=search

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.

http://www.linuxnewbie.org/nhf/Distribution_Specific/Debian_GNULinu x/Debian__Using_Apt.html

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.

http://www.openssh.org/txt/trojan.adv

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.

http://www.gnugk.org/

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

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