LINUX NEWS
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Thursday, June 21, 2001
Read By Over 6,000 Linux Enthusiasts Weekly!TABLE OF CONTENTS
1) Sean’s Notes
2) Linux News
Red Hat in the Black
GCC 3.0 Released
Linux Firewalls
Linux Comparison...Or is it?3) Linux Resources
Diary of a Linux Newbie
Setting up PostgreSQL
Linux Newbie Administrator's Guide
System Maintenance Can be Fun
GIMP-PERL Debugging4) App o’ the week
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1) Sean’s Notes
One of the directories you’ll find on your Linux box is known as /dev. In it are a bunch of strange filenames, lots of numbers and the like. If you do an ls -l on one of them, you’ll notice they look different than normal files:
$ ls -l /etc/passwd /dev/hda1 brw-rw—- 1 root disk 3, 1 Mar 23 22:37 /dev/hda1 -rw-r–r– 1 root root 976 May 29 21:56 /etc/passwd
The first thing you’ll notice is the first character of the line. passwd has a ‘-‘, meaning a normal file (you might also be familiar with ‘d’ for Directory), while hda1 has a ‘b’. The ‘b’ means “block device”, which is part of something central to Unix:
Everything is a file. (well, almost everything)
hda1 happens to be the first partition of the first IDE hard drive. Yea, that’s a file. If you have the rights, you can cat it, vi it, or send it to your speaker. It’s just a file. But it’s got that ‘b’. Unix knows that /dev/hda1 is your hard drive because of the “3,1” in the fifth column. Those numbers make up the major and minor device numbers respectively. Numbers are reserved within the kernel, so when the kernel is doing an operation on a file marked as a block device with id 3,1, it knows where to look.
A block device is one that reads and writes in blocks, usually disk drives, RAM disks, and the like. On a similar vein are character devices, which read and write a character at a time, like your keyboard, memory, or serial devices. Surprisingly enough, they have a ‘c’ in the beginning.
Like other files, devices have an owner and a group, timestamps, and a name. (That’s a Good Thing – you don’t want anyone to be able to read and write directly to a hard drive!) You create devices with the “mknod” command (but the kernel has to understand the numbers you assign), and delete them with the “rm” command (but deleting the file doesn’t destroy the device, just your link to it).
Some of the more popular devices are IDE drives: hdXN, where X is a letter and N is either nothing (meaning the disk itself), or a non-zero, positive integer (meaning the Nth partition). SCSI drives look the same, except instead of hd you have sd. Serial ports are ttySN, so COM1 is ttyS0, COM2 is ttyS1, etc.
One common device is /dev/null, otherwise known as the bit bucket. Anything sent there is lost, so if you mv a file there, say goodbye. This is a great place to redirect output that you don’t care about, especially in crontabs or scripts:
myprog > /dev/null # output suppressed
/dev/zero will spit out 0’s until the cows come home, /dev/urandom will do the same thing with pseudo-random numbers, and /dev/random does much the same thing except that it’ll pause every so often to collect entropy from the computer.
Some devices (things) that aren’t devices (files) are your network cards (eth0), though PPP devices (ppp0) have a corresponding file (/dev/ppp). This is nothing to worry about, as there are ways to do it if you want to be able to read and write packets to your NIC by a file.
By habit, device files live in /dev (because it would suck if you accidentally cleaned up your hard drive and lost it in the process). So, tread carefully in /dev!
Long Live the Penguin,
Sean mailto:swalberg@brainbuzz.com
Visit the Linux News Board at http://boards.brainbuzz.com/boards/vbt.asp?b2
2) Linux News
Red Hat in the Black
Even with IT budgets shrinking, Red Hat managed to post a profit for the first quarter, a sign that Open Source software is great value. This press release lists some big customers that even surprised me, someone who likes to follow what this company is up to.
http://www.redhat.com/about/presscenter/2001/press_Q12002.html
GCC 3.0 Released
Formerly the GNU C Compiler, now the GNU Compiler Collection, this ubiquitous piece of software has reached a milestone, Version 3.0. Look forward to better optimization and more targets, not to mention a slew of fixes and features.
http://gcc.gnu.org/gcc-3.0/gcc-3.0.html
Linux Firewalls
I found this book to be a solid text on using ipchains in many different firewalling situations. If you thought that firewalling meant setting up masquerading and walking away, you are in for a surprise!
http://itresources.brainbuzz.com/tutorials/tutorial.asp?t=S1TU1328
Linux Comparison… Or is it?
I initially thought that this was another benchmark showing Linux on top, but after a while it turned into a prime example of how benchmarks can be skewed. The test in question is a UNIX application that was ported to Windows, so WIN32 performance suffers off the hop. Add to it some bad assumptions, and you can make the data look almost any way you want. Validity of the data aside, there is some good info on how sockets work, not to mention a couple of nuggets about tuning.
http://www.sysadminmag.com/articles/2001/0107/0107a/0107a.htm
3) Linux Resources
Diary of a Linux Newbie
In ten installments, this fellow chronicles his trek from a Linux newbie to… er… non newbie, I guess. It is pretty interesting reading, even for folk that have been down this path.
http://www.linuxdot.org/diary/
Setting up PostgreSQL
PostgreSQL is one of the more popular Open Sourced SQL engines out there. Compared to the ever famous MySQL, it offers transactions, sub-selects, and a whole whack more stuff. However, it’s not quite as friendly as it’s lean and mean cousin, which is why this article will come in handy.
http://phpbuilder.com/columns/kevin20010314.php3
Linux Newbie Administrator’s Guide
This guide is designed to help you out after you’ve installed your system. Everything from X, to devices, to networking seems to be covered here, so you’ll want to bookmark this one!
http://sunsite.dk/linux-newbie/
System Maintenance Can be Fun
Are your users sucking up CPU and memory? Blast ‘em with the BFG! Oh yea, I forgot to mention, I’m talking about a version of Doom where processes are represented by monsters, and you can kill them (or just knock down their priority) with various weaponry. Who said UNIX isn’t user friendly?
http://www.cs.unm.edu/~dlchao/flake/doom/
GIMP-PERL Debugging
If you’ve used the GIMP, an awesome graphics editor, you’ll know that there are a lot of plugins available. If you’ve ever wanted to try your hand at writing one, perhaps to automate a task you regularly perform, you’ll need a way to debug as you go. This tutorial covers the making of a simple script, and the way to debug it.
http://www.gimp.org/~sjburges/perl_debug/intro.html
4) App o’ the week
For those of us who can’t live without our Palm Pilots, this is a pretty handy app to have around. Abacus is a spreadsheet for the pilot that…here’s the Linux connection…syncs up with Linux. The format you’ll see is Lotus 1-2-3, which should be readable by StarOffice and Gnumeric, so you can work on those numbers wherever you go!
http://www.pmdc.pt/abacus/
(C) 2001 BrainBuzz.com. All Rights Reserved.
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