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Thursday, April 12, 2001TABLE OF CONTENTS
1) Sean’s Notes
2) Linux News
Slashdot Interviews Bob Young
Linux PDA
W32.Winux a Sign of Things to Come?
New Digital Internet/TV has "Linux inside"3) Linux Resources
Clean up /tmp the Safe Way
A First Look at Linux Clustering
GIMP PERL Scripting
Free Chapters on mod_perl
Linux for Windows Users4) App o’ the week
1) Sean’s Notes
The syslogd daemon is one of the more important programs that is installed on a Unix box. Its job, like the name implies, is to log all the system messages. Without the benefit of syslog, the administrator is blind to what is going on with the other daemons. It is somewhat like the NT Event Viewer, except that in traditional Unix fashion, is very configurable.
If you’re familiar with the NT Event Log, you’ll know that you get a lot of messages sent into one of three different logs (System, Security, and Application if memory serves). Syslog lets you specify virtually unlimited different logs, and gives you the power to choose what goes into them.
To do this we introduce two attributes of a log entry, namely the facility and the priority (or severity).
The facility of the message tells us what type of application the message came from. auth, authpriv, cron, daemon, kern, lpr, mail, news, syslog, user, uucp, ftp, and local0-local7 are the available ones. auth and authpriv are security-related messages, with authpriv being used for things that should be kept private. The other ones are self-explanatory, such as kern for kernel messages, ftp for ftp messages, etc. local0 through local7 allow systems not covered by the above to be handled. For example, Cisco devices default to local7.
The priority field lets you differentiate between debugging messages and very important ones. In terms of ascending severity, you’ve got debug, info, notice, warning, err, crit, alert, and emerg.
So, each message has both a facility and a priority. Sendmail may log notification of handling an email to mail.info, and errors such as insufficient disk space to mail.err.
With the classification system in mind, it is up to the administrator to decide what messages are important, and where they should be logged. Most distributions of Linux have a pretty sane way of doing it, which serves as a basis for further tweaking. This is all controlled in /etc/syslog.conf. Generally, one line per file is the safe way to do it (some versions of syslogd support some extended syntax, which you should stay away from for portability reasons). Each line starts off with a list of the facility/ priority combinations, and the name of a logfile. These are separated by tabs. (In practice, the Linux syslogd accepts spaces too, but the Solaris one is very picky about requiring tabs).
When you specify a priority, all higher priorities are implied by default. This means if you select mail.info, you’re going to get mail.info all the way up to mail.emerg, unless you explicitly say mail.=info. The values of * and none refer to everything and nothing respectively. So, if you wanted to log all the kernel messages to /var/log/kernel you would have:
kern.* /var/log/kernel
and if you wanted all the info messages except for mail in /var/log/info:
*.info;mail.none /var/log/info
Looking at the default syslog.conf is helpful. Here, the definition of the messages file, which is usually a good place to find general messages about anything:
*.info;mail.none;authpriv.none /var/log/messages
This grabs any messages with a priority of info or above, unless they are from the mail or authpriv facility. Later on you’ll see definitions for authpriv.* and mail.* to split those off unto themselves.
Anything that isn’t caught in the config file gets dropped. Any changes to the file require that you restart the syslogd daemon. Furthermore, syslogd will not create the logfile, you have to use the touch command to create it yourself.
You can test your rules with the “logger” command. This same command is also great for shell scripts to provide status via syslog.
logger -p kern.info “Hey!”
–will write “Hey!” to kern.info.
The syslog system is very powerful, and allows you to take control over what you log. Since the back end communication works on sockets and files, unprivileged processes can safely write private messages. The man pages for both syslog.conf, syslogd, and logger will show you the other options available, such as having all your machines log to one central machine for security and ease of administration.
Long live the Penguin,
Sean mailto:swalberg@brainbuzz.com
2) Linux News
Slashdot Interviews Bob Young
Bob Young, Chairman of Red Hat software, gave his answer to some questions posed by Slashdot readers. Among them are his take on Linux’s future, and some pretty harsh criticism about recent comments made by Open Source opponents.
http://slashdot.org/article.pl?sid=/04/11/1555216
Linux PDA
The Agenda VR3 is the first commercially released PDA that runs Linux. Brainbuzz user mokjason gives some thoughts, links, and the start of a discussion.
http://boards.brainbuzz.com/boards/vbm.asp?rpg=1&wpg=1&sb=0&m’5587
W32.Winux a Sign of Things to Come?
An announcement earlier in the month about a virus that is supposed to be able to infect both Windows and Linux computers came as quite a surprise to me. Though at the moment a low risk, this article asks the question, “What Next?”
http://www.networkweek.com/wire/story/TWB20010402S0004
New digital Internet/TV has “Linux inside”
Embedded Linux devices may soon be making their way into homes by way of televisions. This TV offers Internet functionality, not to mention some sophisticated systems on the regular TV programming. In a market where price is paramount, the maker was able to drop the per unit cost by using Free software.
http://www.zdnet.com/zdnn/stories/news/0,4586,2694183,00.html
3) Linux Resources
Clean up /tmp the Safe Way
Automatically getting rid of temporary files may seem like an easy task, but if done improperly can cause problems. Most often, you may be working on files that other people can control, which requires some care. This article goes through the simple cases, and then into some more secure and correct ways of dealing with /tmp.
http://www.linuxgazette.com/issue18/tmp.html
A First Look at Linux Clustering
Most people are familiar with the concept of a Beowulf cluster, which has been popularized lately by companies like Shell. Have you ever wondered about the details behind such a beast? Are there other ways to accomplish the same thing? This article tries to answer those questions, and the reader comments at the end round it out.
http://www.linux.com/newsitem.phtml
GIMP PERL Scripting
I’m a big fan of the GNU Image Manipulation Tool. The wide range of plugins available is astounding, plus it’s really easy to write your own. I’ve always wondered how to use the Gimp perl module so that I could control it from Perl (rather than learning Scheme). Alex Harford, an author and fellow Canadian, wrote an excellent tutorial on the Gimp perl module.
http://www.dowco.com/~alexh/perl.html
Free Chapters on mod_perl
mod_perl is an apache module that embeds a perl interpreter within the web server itself to enhance performance. This site has some sample chapters from the O’Reilly book on writing perl apache modules, covering topics such as the Apache::Registry module (to replace CGI), and writing authentication and authorization modules.
http://www.modperl.com/book/chapters/
Linux for Windows Users
For those not wanting an in-depth technical discussion of how to migrate, this article takes a high level view of the differences and similarities in the GUIs. There are lots of screen shots presented together that highlight that Linux can be just as easy to use as Windows.
http://mozillaquest.com/Linux4Windows/Linux4Windows01/Linux4Windows_01_01_Story-01.html
4) App o’ the week
The first time I tried this out, I was hooked. PHPNuke is a PHP web site system that allows you to update news articles easily, host forums, FAQs, and downloads. It is all done within a theme structure, so you can easily change the look and feel of your site without having to know much PHP. MandrakeSoft, the makers of the Mandrake Linux distribution hired the author of this on a full time basis, ensuring that PHPNuke will be around for the long haul.
http://www.phpnuke.org
(C) 2001 BrainBuzz.com. All Rights Reserved.
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