LINUX NEWS
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November 21, 2002 - Issue #108TABLE OF CONTENTS
1) Sean’s Notes
2) Linux News
Codeweavers Releases Crossover 1.3.1
Evolution 1.2
Mathematica Supports Itanium
SCO Linux 4.0 Announced3) Linux Resources
An Interview With The Knoppix Creator
The Peon's Guide To Secure System Development
Clustering 101
Shell Internal Variables
Name-Based Hosting With Apache4) App o’ the Week
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1) Sean’s Notes
Windows folks don’t seem to think much of them, but serial ports and Unix go hand in hand like Windows and a blue screen. Many of the things you see in Unix are based off the ancient concept of the user logging in through a dumb terminal. (If the phrase “dumb terminal” is new to you, I’m not cursing a terminal, I’m referring to a device that doesn’t have any “smarts” and speaks serially.)
Everyone who logs into a Unix system interactively is assigned a TTY, which handles their input and output to the rest of the system. The older folks in the crowd might recognize this as an acronym for “Teletype”, and they’d be right. It came right from the original style of logging in through a terminal/teletype to your mainframe. These days, we’re a bit more enlightened, and can telnet/ssh to our servers. Regardless, we’re still assigned a tty. It’s been modernized a bit, the 2.4 kernels implement a virtual file system called “devpts” just for creating these TTYs on the fly. I digress, though.
Like everything else in Unix, a serial port is represented as a file. /dev/ttyS0 is the first serial port, /dev/ttyS1 is the second, and so forth (there’s that tty again). COM1: and COM2: might be the more familiar names to you. Just remember than in Unix, like the C language it’s built with, we normally start counting at zero (the reasons for this are the subject of another article, or, preferably, to be discussed over a pint or six of ale).
ls -l /dev/ttyS0
crw——- 1 uucp uucp 4, 64 May 20 2002 /dev/ttyS0
We see that the first serial port is a character device (that’s the leading ‘c’). Character devices operate on one character at a time, as opposed to block devices like disk drives, which deal in–guess what?–blocks of data. Available serial ports are often owned by the UUCP user for tradition’s sake. (And some of the utilities that communicate over a serial port set their ID and group to that of UUCP, expecting these permissions).
On the x86 platform, at least, serial ports need an IRQ and an ioport to operate. “setserial” is a program that you can use to set this up.
setserial /dev/ttyS0
/dev/ttyS0, UART: 16550A, Port: 0x03f8, IRQ: 4
As I’d expect, my first serial port (COM1: if you will) is at ioport 0x3f8 and IRQ4. If, for some reason, you wanted to change this, you could:
setserial /dev/ttyS0 irq 5
will change to IRQ5. The man page for setserial has a list of all the options that can be poked and peeked. Tread lightly! Several times you’ll come across warnings that improper use of setserial can lock up your system.
Attributes associated with the port itself can be changed with the “stty” command. The baud rate, flow control, echoing, etc. Unless you’re dumping raw data to the serial port (and there are valid reasons for doing that), most programs will provide a clean interface to adjust those for you.
As a network guy, I often find myself connecting out my serial port to devices such as switches and routers. Instead of fussing with Hyperterm, I just run:
cu -l /dev/ttyS0
and “poof”, a console prompt. Truth be told, I’m pretty lazy, so I ran…
ln -s /dev/ttyS0 /dev/rack
…on my workstation at home, so that when I want to connect to my routers, I use “/dev/rack” instead of having to crawl under my desk and remember what serial port I used. A similar method is recommended for modems and such.
“cu” is part of the UUCP utilities (Unix-to-Unix Copy Protocol. Boy am I feeling old, now). It is very bare bones, as there are no menus. As an idea of how friendly it is, the command to exit is:
~.
Yep. A squiggle and a period. Minicom is much more friendly, so we’ll use that instead.
First, as root, run:
minicom -s
You probably want to go to “Serial port setup” to set up your ports and speeds, and then “Save setup as dfl” (meaning default). Then, you can enter minicom at any time by typing “minicom”.
Minicom is very easy to navigate; all commands start with control A (^A). ^A followed by Z (^A Z) brings up help. ^A Q exits. If you are connected to a modem, you can dial out from here. If you’re attached to a network device, you should be able to see a command prompt.
Just as we can log into a router over a serial connection, we can log into a Unix box this way. It’s wonderful, because you don’t need to have a monitor or keyboard attached, you just plug in your laptop (or better yet, you use some sort of serial concentrator). A discussion of that will have to wait a bit, because I’ve yet to dig up my dumb terminal from the garage!
Even though they’re old technology, serial ports play a useful role in Unix. Not only is the concept of a user’s session being tied to what used to be a serial device central to Unix, but it’s also a simple and reliable technology that can solve a variety of problems.
Long live the Penguin,
Sean mailto:swalberg@cramsession.com
2) Linux News
Codeweavers Releases Crossover 1.3.1
Crossover is a product that helps you to run Windows binaries under Linux. I’ve been using 1.2 for a little while now, and believe me, it’s a great product. This latest release fixes up a whack of bugs.
http://codeweavers.com/about/press_releases/?id 021104
Evolution 1.2
Evolution has fast become my favourite email program. The latest version has some great new features, not to mention some features that we’ve been waiting for (such as playing a sound when email arrives).
http://www.ximian.com/about_us/press_center/press_releases/index.ht ml?pr=evolution1_2
Mathematica Supports Itanium
Mathematica is a rich and complex mathematical toolkit, used heavily by engineers and scientists. They’ve supported Linux for a while, but this native port to the Itanium platform ensures that Mathematica benefits from both Linux, and the chip’s expanded capabilities.
http://www.wolfram.com/news/itanium.html
SCO Linux 4.0 Announced
The SCO group announced the release of United Linux based “SCO Linux 4.0”. Correct me if I’m wrong, but it’s the first release from the United Linux cabal. Best of luck, folks.
http://www.linuxandmain.com/modules.php?name=News&file=article&sid( 7
3) Linux Resources
An Interview With The Knoppix Creator
“Knoppix” is a Linux distribution that runs completely off a CD, X-Windows and all! It’s started to get some fame because of its excellent hardware detection routines, making it the perfect tool to demonstrate Linux without needing to wipe the machine’s hard drive. Here’s an interview with the creator, with some links to documentation and the downloads.
http://www.distrowatch.com/interview-knoppix.php
The Peon’s Guide To Secure System Development
I don’t know whether to be ashamed or hopeful after reading this article. It’s all about how to think securely when building systems, holding back no punches when blaming the current cadre of programmers and admins for all the security bugs. Once you get past the venom, it’s a great article.
http://m.bacarella.com/papers/secsoft/html/
Clustering 101
This is a free (registration required, though) tutorial from IBM about clustering. It’s got basic information on clustering to help you get started. Unsurprisingly, lots of information on what IBM hardware fits the bill, too!
http://www-1.ibm.com/servers/esdd/tutorials/clustering.html?open&t= gr,lnxw06=clust101
Shell Internal Variables
Print this out and keep it next to you: it’s all the bash shell variables, even examples as to their use. The next time you’re trying to remember what variable sets the prompt ($PS1), the PID of the last job run ($!), or even the commonly set variables, it’s in here.
http://www.digitaltoad.net/docs/guide/advshell/internalvariables.ht ml
Name-Based Hosting With Apache
Name-based hosting lets you stack multiple virtual hosts on top of one IP address. It can be tricky to set up; this document gives you the skinny on this handy feature.
http://www.linuxorbit.com/modules.php?op=modload&name=Sections&file
4) App o’ the Week
Keeping your systems up-to-date is essential. Most vendors offer an FTP server or service from where you can get updates. Scripts, such as AutoUpdate can help out here if you have multiple systems.
“AutoUpdate is a Perl script which performs a task similar to RedHat’s up2date or autorpm. It can be used to automatically download and upgrade rpms from different (s)ftp or http(s) sites. Moreover, it can also be used to keep a server with a customized (RedHat) distribution plus all clients up to date. I have tried to write it in such a way that it is not RedHat specific and hence it should work with any other rpm-based distribution as well.”
http://www.mat.univie.ac.at/~gerald/ftp/autoupdate/index.html
(C) 2002 BrainBuzz.com, Inc. All Rights Reserved.
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