LINUX NEWS
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September 19, 2002 - Issue #99TABLE OF CONTENTS
1) Sean’s Notes
2) Linux News
XFS Enters the Kernel
KDE and GNOME Brought Together in Null
Xandros Beta 3 Preview
Installing NVIDIA Drivers3) Linux Resources
Where The Jobs Are
More on Certifications
Intrusion Detection
Develop Rock Solid Code in PHP
Headline4) App o’ the week
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1) Sean’s Notes
UNIX has some really great inter process communication (IPC) features. Processes can share memory with each other, they can send data over sockets and pipes, they can synchronize with semaphores, and more. Most of this is done through system calls, but today I’ll show you a technique that lets you do it through the command line.
A “FIFO” is otherwise known as a named pipe. FIFO stands for “First In, First Out”. So, you throw two things into a FIFO, they’ll come out of it, in order. Think of it like a one lane tunnel… Cars go in, and they have to come out the other end in the same order. With a FIFO, we can have one process write, and the other process read. We’ll see that like everything else in Unix, a FIFO is just a file, so the reader and writers are none the wiser!
A simple example…
Open two terminal sessions.
In the first, run:
$ mkfifo output $ echo “hi” > output
The first line builds our FIFO:
$ ls -l output prw-rw-r– 1 sean sean 0 Sep 18 20:23 output
The ‘p’ as the first letter in the permissions tells us that this file is a pipe. The second line simply dumps the string “hi” to the output. Note how the command “blocks”, that is, it doesn’t return. That’s because the FIFO needs someone to read it.
In the other terminal window, see what’s in the FIFO:
$ cat output hi
You’ll also notice that the first window returns you to the shell prompt. Let’s try something a bit different, namely slowly feeding data to the FIFO without closing the file.
In your first terminal window, run:
$ perl -e ‘open A, “>output”; while (1) { print A date; sleep 1 }’
(this script opens the FIFO for writing, and continuously prints the date and time every second)
In your second window run,
$ cat output
You’ll see that data comes through the pipe, as expected. When you stop one end, the other stops. If you close the reader (terminal #2), the writer says “broken pipe”. Close the writer, and both exit gracefully. That’s because an end of file is transmitted in the second case, but, in the first case, there is just an abrupt closure.
What use is this portal we’ve created? The original use I learned thistechnique on was to compress the output of tcpdump on the fly:
mkfifo output
gzip -c < output > output.gz &
tcpdump -i eth0 -w output
Here, we create the FIFO in line one. The second line continually reads from the FIFO, and passes it through gzip (to compress), and redirects the output the output.gz as a compressed stream. The ampersand (&) tosses it in the background so that terminals aren’t chewed up with blocked processes. Finally, tcpdump is run, with the output to the FIFO. Presto, the output is compressed without needing any extra disk space.
Another use would be to have syslogd log to a FIFO, and then pass it through an existing script that looks for key words and flags alerts. For secure applications, a privileged program could write to the FIFO, and have a lower level, unprivileged, program read and process the output.
FIFOs are another powerful tool in the sysadmin’s arsenal. It’ll let you hook two programs together that might normally not speak, or to separate privilege levels. It also speaks volumes about the general design of the operating system – as the admin, you have absolute control over the flow and operation of your box. Try doing that with your mouse!!!
Long live the Penguin,
Sean swalberg@cramsession.com
2) Linux News
XFS Enters the Kernel
Kernel 2.5.36 marks the event where SGI’s XFS becomes part of the base Linux kernel. While there are other journaling file systems already there, this is one that’s got some heritage behind it, not to mention that it’s been designed with performance in mind.
http://lwn.net/Articles/9998/
KDE and GNOME Brought Together in Null
The next version of Red Hat, codenamed “Null”, ships with the GNOME and KDE desktops looking very similar. This has drawn the ire of people who worked hard to make these default desktops look better than the other. The manager of Red Hat’s desktop responds, putting any conspiracy theories to rest. I, for one, think this is a great idea.
http://people.redhat.com/otaylor/rh-desktop.html
Headline
“Sun Microsystems will give away its StarOffice software to ministries of education in Europe and Africa, the company is expected to announce Tuesday, in an effort to undermine rival Microsoft.”
http://zdnet.com.com/2100-1104-958165.html
Xandros Beta 3 Preview
Xandros is the company that picked up the Corel Linux distribution, and has apparently been pretty busy. Here’s a review of their upcoming product.
http://www.osnews.com/story.php?news_id62
3) Linux Resources
Installing NVIDIA Drivers
NVIDIA distributes binary drivers for their 3D cards, requiring both some kernel work and some digging in the X server configuration. This can be difficult if you’ve never done it before, but the following article can guide you.
http://linuxjunkies.com/modules.php?name=Sections&op=viewarticle&ar tid=1
Where The Jobs Are
Here’s an interesting look at where Linux related jobs are, what you need to snag them, and some other general tidbits. Although it misses the fact that many jobs aren’t advertised, on the whole it has some good advice.
http://www.linuxjournal.com/article.php?mode=nested&sidb71
More on Certifications
This article looks at the return on investment of various certifications, including Linux ones. I found it interesting that in the small solution provider realm, the RHCE is far behind in ROI, but is number one in terms of the employers’ willingness to pay for all the costs.
http://www.crn.com/sections/special/certification/certification.asp ?ArticleID6937
Intrusion Detection
Security geek RobnHood has put together a good introduction to intrusion detection, including a primer on getting Snort and ACID speaking together.
http://infocenter.cramsession.com/techlibrary/gethtml.asp?ID92
Develop Rock Solid Code in PHP
Here’s a link to the second part of a two part series in developing rock solid code using PHP. It has good advice on making things easier to configure, and general coding practices that will help you develop better (and more secure) code.
http://www-106.ibm.com/developerworks/web/library/wa-phprock2/?t=gr ,lnxw06=PHBvariables2
4) App o’ the week
Looking for a cool, automated, way to store FAQs on the web, and let people submit changes? FAQ-O-Matic is for you! It’s remarkably configurable, and easy to set up.
http://faqomatic.sourceforge.net/
(C) 2002 BrainBuzz.com, Inc. All Rights Reserved.
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