LINUX NEWS
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Thursday, February 22, 2001TABLE OF CONTENTS
1) Sean’s Notes
2) Linux News
Planning GNOME 2.0
Linux and POS systems
Bastille Linux Update
Real World Linux Security Book Review3) Linux Resources
Tired of FSCKing?
GNOME 1.4 Beta 1 Released
Fun With Netfilter
Linuxsecurity.com on Netfilter
KDE 2.1 Released4) App o’ the week
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1) Sean’s Notes
The way that Linux knows what processes to start up, and the order in which it does this, tends to be a source of confusion for many. This week, I hope that I’ll be able to clarify this for you.
The first thing to do is to define a runlevel. UNIX uses runlevels as a way to keep track of what state the system is in. There are 7 default runlevels, numbered 0-6. Each one is associated with a particular state. 0 and 6 are halt and reboot respectively. So, another way of saying “reboot that machine” is to say “switch to runlevel 6!”. Runlevel 1 is called “single user mode”. In this state we’re either bringing up the system or are in maintenance mode. No users can log in remotely, and there is limited functionality. The idea is to get the system at a state where it is stable so file system checks and others can be run.
Runlevels 2 and 4 aren’t really used anymore, which leaves us with 3 and 5. 3 is called “multiuser”. If anyone remembers the way Slackware used to boot up, it would say “going multiuser…” at which point it would switch into RL3. This is the normal operation for a server, as all the normal services are running. 5 is the same as 3, except that you add your X window system. Most of us will be in runlevel 5.
Another thing to note is that to get to runlevel 5, you don’t have to hit 0-4. You can jump between them all you want. To actually change runlevels, use
/sbin/init newrunlevel
That’s all well and good, but how does one define what services are started in what run level? Glad you asked. The answer is in the SysV init system. Take a peek in /etc/rc.d:
[sean ~]$ ls /etc/rc.d init.d rc rc.sysinit rc1.d rc3.d rc5.d rc.local rc0.d rc2.d rc4.d rc6.d
The important ones to note are init.d, and the rc?.d directories. First take a peek in init.d. You’ll see a bunch of files, one for each service, in that directory. Each one is responsible for starting and stopping a service. If you have a file called httpd, which starts and stops the web server, you can run
httpd start # start the web server httpd stop # stop the web server httpd status # is the web server running?
The next piece in the puzzle is the rc?.d directories. You probably guessed it, but the number has something to do with the runlevel. Looking in the directory, you’ll see that the files are links to the respective file in ../init.d, and that the names are funny. S80sendmail? What’s that mean? A good question!
Upon entering runlevel N, the system does the following:
-
Iterate through all the files in /etc/rc.d/rcN.d that start with K, processing them in order of the number, ie. K10abc before K20def. For each file, run it with the “stop” parameter
-
Do the same thing for all the “S” files, but with the “start” parameter
So, if you want a service to start in runlevel 3, say, between cron (40) and inetd (50), give it a start priority of 45. (Note that the priorities aren’t necessarily essential, but it allows you to ensure that networking is up before you start your web server and the like). You’ll also want to make sure that all the other runlevels have a corresponding Kill script, since it’s entirely possible that you switched from a runlevel where it was running into one where it shouldn’t.
Managing those symlinks is a big task. Fear not, Red Hat- based distributions include “chkconfig” to help manage, and Debian-based ones use “update-rc.d” (thanks to faithful reader and Debian aficionado Guitarlynn for finding that one!) Alas, the use of those commands will have to wait for another newsletter, but the man pages are pretty good!
Don’t forget about the Linux Newsletter board, where you can talk to myself and other subscribers:
http://boards.brainbuzz.com/boards/vbt.asp?b2
Long Live the Penguin.
Sean swalberg@brainbuzz.com
2) Linux News
Planning GNOME 2.0
Miguel de Icaza, guru of all GNOME, shares his vision of what’s going in to GNOME 2.0, and even closer, 1.4. There are lots of things in there, like GNOME-VFS (a shared filesystem), and better interoperability between applications.
http://primates.ximian.com/~miguel/gnome-2.0/
Linux and POS Systems
“Red Hat and Wincor Nixdorf to Deliver a Linux and JavaPOS Solution Platform for Retail POS Systems”. Linux is easily deployable, and runs on a variety of different hardware, making it an ideal candidate to run a Point of Sale (POS) system. Home Depot uses it, so have a look!
http://www.redhat.com/about/presscenter/2001/press_wincor.html
Bastille Linux Update
Bastille Linux is a set of scripts that really harden a Linux box. They’ve gone through some rapid development lately after some cash infusion, so now is a good time to look at this. It’s great for people just getting started in Linux, because all the options are well explained.
http://bastille-linux.sourceforge.net/
Real World Linux Security Book Review
If you’re looking to start taking security into your own hands, this cookbook style manual is a good one. Real World Linux Security walks you through the ways to lock down Linux, to monitor for weaknesses, and how to minimize the damage if you do get broken.
http://itresources.brainbuzz.com/tutorials/tutorial.asp?t=S1TU1171
3) Linux Resources
Tired of FSCKing?
Journalling file systems allow quick recovery after an unclean shutdown. Did you know that they can also make your file system faster and make more efficient use of space? This article investigates some of the various journalling file systems out there, with an eye on how they improve performance.
http://freshmeat.net/articles/view/212/
GNOME 1.4 Beta 1 Released
With features like a newer panel, better help, better applications, and the usual bug fixes (and fresh bugs, of course), a Beta of GNOME has been released. I wonder if this has anything to do with the upcoming KDE 2.1 release?
http://slashdot.org/articles/01/02/18/1343236.shtml
Fun With Netfilter
This tuneup article from Linux.com takes you through some basic and advanced iptables commands. iptables has some really fancy modules, so you can trigger a rule based on traffic volumes and the like.
http://linux.com/tuneup/database.phtml/Networking/2192.html
Linuxsecurity.com on Netfilter
Linuxsecurity.com is a pretty good place to pick up tips and tricks about securing your Linux system. Dave Wreski, security guru and all around nice guy, has put together an informative article on what netfilter is all about.
http://www.linuxsecurity.com/feature_stories/kernel-netfilter.html
KDE 2.1 Released
According to the KDE home page, 2.1 was supposed to be released by the time you get this. At any rate, 2.1beta was released a couple of weeks ago in anticipation of the 2.1 release. KDE is a great WM that doesn’t seem to have received the breaks that GNOME has.
http://www.kde.org
4) App o’ the week
Need a system to run your helpdesk, track trouble tickets, or software issues? Look no further than Request Tracker! Featuring powerful tracking, multiple users and queues, and a great web interface, this software is sure to help you out.
http://www.fsck.com/projects/rt/
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