LINUX NEWS
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Thursday, December 7, 2000TABLE OF CONTENTS
1) Sean’s Notes
2) Linux News
Do Your Part
Strut Your Stuff
Creative, but...
Windows Whistler vs. Gnome 1.2, KDE 2.03) Linux Resources
Command Line Weenies
System Basics
Journaling Filesystems
Keep Tux Safe
Using Snort4) App o’ the week
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1) Sean’s Notes
It’s hard to believe this is already the sixth week of the Linux newsletter! Thanks to all of you who sent your feedback to me at mailto:swalberg@brainbuzz.com … Keep it coming!
I was talking with a friend the other day, and he was wondering how he could get some of the email sent to his personal account forwarded to his Blackberry wireless device. Not all of them, mind you, just from certain people or certain subjects. Plus, the message still has to end up in his regular mailbox. This, along with other mail filtering problems, is the realm of procmail. Want to put your mailing lists in their own folders? Procmail is the answer. Filter out spam? You guessed it…
Procmail is a utility that is fed “recipes” which dictate what it should do with messages. It tends to be called from your mail transfer agent, such as sendmail. Most distributions tend to have procmail available, but if you can’t get it from there, the links at the end of this article will lead you to the sources.
Before putting procmail to work, you’ve got to get your MTA set up first. Some distributions, such as RedHat, make procmail your default local delivery agent so this is done for you. Otherwise, you need to create a .forward file with the following contents:
“|IFS=’ ‘&&exec /usr/bin/procmail -f-||exit 75 #username”
(you’ll want to replace the “username” with your username. Don’t forget the double and single quotes too!)
Recipes go into the .procmailrc file in your home directory, and must only be writable by the owner. Before you can start writing the rules though, you’ll have to tell procmail about your system (within .procmailrc):
PATH=/bin:/usr/bin:/usr/bin MAILDIR=$HOME/mail #you’d better make sure it exists LOGFILE=$MAILDIR/from #recommended
- The rules themselves take the form of
-
0 [flags] <zero or more conditions (one per line)> <exactly one action line>
- If the condition starts with a *, it means that we’re
- passing along a regular expression, or a string to match
- within the header:
-
0 * ^Sender: Bugtraq List <BUGTRAQ@SECURITYFOCUS.COM> bugtraq
This rule looks for the Sender: field in the header and matches it up against the Bugtraq phrase (a popular security mailing list). If so, the action “bugraq” means to dump the message into the folder called “bugtraq”, which is located in the directory specified above in $MAILDIR. This is your basic “sort my email into folders” type of recipe.
One of my favorite rules, and one that illustrates nested rules, is to pretend that my account doesn’t exist (ie send a bounce message) when the sender is from a certain domain, ie spammer.com:
:0
\* ^From: .\*spammer.com
{
EXITCODE = 67
:0 h:
bounce.log
}
The first condition is to match the From: field with anything ending in spammer.com (.* means match anything). The action is then enclosed in a nesting brace, and consists of an action and another rule. EXITCODEg means return a bounce, and the next two lines mean to dump the headers of the message into the “bounce.log” folder. Slick, eh?
Now, to help out my friend:
:0 c
* ^Subject: important
! me@blackberry
You’ll notice the “c” flag, which means to generate a carbon copy. In this recipe, we generate this copy with the subject begins with “important”, and send it to me@blackberry (the ! means to send to an email address).
To run this recipe on multiple incoming email addresses, we’ll have to craft the regexp with caution:
:0 c
* ^From: (fred@somewhere.com|joe@elsewhere.com)
! me@blackberry
If we had put two conditions in one rule, they would be ANDed, ie
:0 c
* ^From: (fred@somewhere.com|joe@elsewhere.com)
* ^Subject: important
! me@blackberry
would only generate the page if fred or joe sent an email with the subject of “important”. So, without getting into a lot of complex stuff, we’ll stick with the two separate rules to handle everything.
Through the use of a program called “formail”, you can rewrite the email in transit, i.e. to change the subject. That’s outside the scope of this week’s article, but check out the man page for “procmailrc” on how to do this. You can also pass the message through another program, or delete it entirely (action=/dev/null). Procmail is fun!
You can get the procmail code from:
http://www.procmail.org
Some great sites on writing recipes:
http://www.procmail.org/jari/pm-tips.html http://www.uwasa.fi/~ts/info/proctips.html “man procmailrc”
Let’s hear what you’ve got to say on the discussion boards.
RedHat Board: http://boards.brainbuzz.com:80/boards/vbt.asp?b4
Linux/Unix Mail: http://boards.brainbuzz.com/boards/vbt.asp?b6
Finally, feel free to email me with your thoughts and comments!
Long live the Penguin,
Sean swalberg@brainbuzz.com
2) Linux News
Do your part
Brainbuzz, your community site, needs your help in changing the future of Microsoft’s head… Or is it Microsoft’s head’s head? How about the head of Microsoft’s head? There we go! Get all your friends to sign too!
http://www.cramsession.brainbuzz.com/petition/
Strut your stuff
Skilldrill is a new section of the Brainbuzz.com web site. Take a test in various subjects, including RedHat, and see how you rank with all the other Brainbuzz members. Link your transcript with your online Resume from the jobs section, and show potential employers that you know your stuff. Bragging rights are on the line!
http://www.skilldrill.com
Creative, but…
It seems someone has written a trojan whose payload is Linux propaganda. If you see a message with “Check out this new flash movie that I downloaded just now … It’s Great. Bye”, don’t run the attachment! I know us Linux folk can be a bit… insistent… when it comes to promoting Linux, but causing damage to Windows boxes is taking it too far. If you feel the need to write a virus in order to promote Linux, I think we’d all prefer you to put your energy into an open source project instead. At the end of the day, you’ll do more good for Linux that way.
http://www.msnbc.com/news/496999.asp?cp1=1
Windows Whistler vs. Gnome 1.2, KDE 2.0
KDE vs GNOME comparisons are pretty common, but how do these user interfaces stack up to the Redmond empire’s next release? This article highlights the key similarities and differences.
http://www.newsforge.com/article.pl?sid /11/20/0317238
3) Linux Resources
Command Line Weenies
Everyone using Linux is going to come into contact with the shell at one point or another. Often, it’s the fastest way to get something done. Learning how to make effective use of the shell is difficult, but this article will walk you through some of the basics, like how to chain commands together.
http://itresources.brainbuzz.com/tutorials/tutorial.asp?t=S1TU545&t n=A+comma nd+line+weenie+%26+proud+of+it&pi=S1C21&pn=Linux%2FUnix+Articles
System Basics
Learning how the filesystem is laid out, and how to work with files is fundamental to working with Linux. It isn’t obvious how everything is supposed to work, so follow this article for a primer on file operations.
http://www.linuxworld.com.au/article.php3?tid=8&aidw
Journaling Filesystems
I’ve talked about journaling filesystems before – a filesystem that commits data to a log, much like a database, so that in the event of an unclean shutdown no data is lost. This article explains how the default filesystem, ext2fs, works, and how a journaling filesystem is different. It also shows how to install ReiserFS, one of the more stable JFSs out there.
http://www.linux-mag.com/2000-08/journaling_01.html
Keep Tux Safe
As changes are made to a running machine, the security of the box can be compromised. It’s up to the administrator to keep on top of security all the time. Here are a few things to keep in mind.
http://www.zdnet.com/sp/stories/column/0,4712,2658066,00.html
Using Snort
Snort is an open sourced Intrusion Detection System (IDS). It listens on your network for any traffic matching known attack signatures. Like many security tools, it’s pretty hard to use if you’re new to the IDS game. Linuxsecurity.com takes you through the steps to install, update, and test your Snort IDS solutions. Happy hunting!
http://www.linuxsecurity.com/using-snort.html
4) App o’ the week
If you’re using Linux as a mail server, or as an SMTP gateway, you may want to get it to perform some basic virus scanning. The Anomy Mailtool is a powerful PERL script that will enforce policies on incoming and outgoing mail, such as removing .VBS files from email, protecting the Exchange server from the MIME vulnerabilities, and forcing executable attachments to be renamed before being executed.
http://mailtools.anomy.net/
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