Technotes

File System Reserved Characters

Different operating system have support different characters. In general, the following characters should not be used for file or directory names;

Linux CLI: Get MySQL Process Information

Gathering information about what's happening with a service on any machine is the first step in diagnosis. If you're experiencing performance issues with your MySQL server, exploring the logs and current activity is a must. Here are a couple of tools to get started.

Linux: Determine File Mime Type And/or Character Set

Simple command to determine a file's mime type and character set;

Ubuntu 11.04 Natty Narwahl Upgrade

Ubuntu 11.04, Natty Narwahl, was released last month and it's time to upgrade computers to the new OS. As always I approach OS upgrades with a bit of intrepidation. While most go just fine, some of the computers I use have had fits going from release to release. Before I upgrade the computers I use at work, I'll usually do my personal machine at home then my wife's machine. Followed by my work laptop, then my workstation. Here's how things have progressed;

Ubuntu: Dell OpenManage Installation

Anyone looking to install Dell OpenManage on a server running Ubuntu should start with the instuctions located at:

What Is Load Average?

Have you ever used top or uptime from CLI? Both display Load Average in 1, 5, 15 minute intervals. But what does it mean? The best analogy I've come across describes this as traffic crossing a one-way bridge. Odd, I know but bear with me...

First, the Load Average is the average number of CPU requests processed and waiting for execution in the displayed time period (1, 5 or 15 minutes). That's a rather vague description for a newbie. So, let's make it understandable;

Ubuntu Server With Minimal Gnome Desktop

Installing Ubuntu server leaves us with a CLI (Command Line Interface) only. Now there's nothing wrong with that. But, Linux sports all these tools on the GUI side that makes traditional server administration easier and more pleasant. Not-to-mention it helps training newbies a bit easier too. Besides, it's nice to have access to the GUI tools from time to time.

Apache: Error(98)

I ran across a situation where Apache wouldn't start. It generated the following error;

Ubuntu Lucid Upgrade: Dell T3500 Disaster

My system at work had been acting funky for months. Every now and again, the monitor would go non-linear and I'd get no response from the mouse or keyboard. It would normally still be accessible remotely. So, I'd just reboot it that way and move on. I was pretty sure it was a memory or video card issue.  But, I read where Ubuntu had some problems with the NVidia cards. I figured I'd wait 'til Ubuntu released 10.04 and do a fresh install.

Linux CLI: Copy MySQL Database

There is no command in MySQL to copy a database. One method to copy a database is as follows;

PostgreSQL: Copy Database

It's not uncommon to run across a need to duplicate a database for testing purposes. PostgreSQL provides for the ability to duplicate the structure and data content with a single command;

WinXP: Reset Administrator's Password

Here is one method used to replace or reset the Administrator's password in Window's XP;

SSH: Stop Asking To Add New Hosts

An annoying little thing. When connecting via SSH to another machine for the first time SSH always prompts;

---
The authenticity of host 'xxx.xxx.xxx.xxx (xxx.xxx.xxx.xxx)' can't be established.
RSA key fingerprint is ..............
Are you sure you want to continue connecting (yes/no)?
---

PHP CLI: Rsync Script

Here's a handy script to run rsync from the command-line that prompts for source and destination paths;

Ubuntu: Change Hostname

I had to snag this one for posterity from http://www.ducea.com/2006/08/07/how-to-change-the-hostname-of-a-linux-system/

Linux: Copy Directory Structure Only

I ran across the need to copy a large directory structure to a remote machine this week. I just needed the directory structure, not the files. There is a way to do this locally using the cp command with the --parent switch, though I haven't tried it yet.

PHP CLI: Apache Log Rotation Script

Here's a little PHP command line script to do Apache Log Rotation on your web server. This script uses zip to compress the files and retains the logs for 10 days before deletion.

Linux: Get Information About Your Hard Drive

Linux has many tools that can mystify a new user. A whole new world of information and manipulation awaits you with hdparm.

Ubuntu Jaunty: Restore Firefox And/or Thunderbird From Backup

Last weekend I decided it was time for a fresh installation of Ubuntu Linux. Upgrading from version to version sometimes leaves your system a little "off". So, I generally do a fresh installation every second or third release just to keep things neat and to use new or upgraded features. Network Manager comes to mind, it was a little buggy after upgrading. And I had some really weird stuff happening when I'd modify a text document over the internet, like the entire content of the document would be appended to the file upon saving, every save. Rather than spend the time debugging, a new installation was the way to go.

DDoS Defences

Extracted from Experiences with DDOS mitigation - Part I

Defenses

1. Web server anti-ddos modules (protect only against TCP attacks)

mod_evasive, mod_limitipconn, etc, are only effective against a single or handful of attacking IPs. Their limitations derive from their attempt to respond in SOME way (an error response, rather than ignoring the IPs), and lack of information these modules have on the current activity of an IP or its past activity. If you are expecting these modules to provide attack insurance then re-evaluate because even a small botnet of say 100 machines can easily succeed. One particular form of attack: "open and hold", is particularly difficult to counter by program-based ddos prevention. Admins struggle to identify open and hold attackers (see topics like this) due to the limitation apache has in reporting the IP of a new and as yet uncompleted request.
In the last week another apache module has come to my attention: mod_qos. It appears to be much more ambitious. In particular I like that it tries to give priority to IP addresses it has already seen. (VIPs). Unfortunately mod_qos appears to be very "alpha" with almost nobody using it in production yet. If it is debugged it will be the best apache module to use.

Mitigate The Effects Of A DDoS Attack

There's a great variety of attacks and hacks that black hats can perpetrate on your network. Fortunately, you can prevent most of them using an assortment of security measures.

However, a distributed denial-of-service attack (DDoS) is an entirely different story. You can't thwart a DDoS attack -- they attack an IP address or service that's available to the Internet.

If you can't prevent such an attack, what can you do to protect your organisation? You need to better understand it by learning the three phases of a DDoS attack and learn how to quickly mitigate the attack's effects.

Ubuntu: Gnome Or KDE

Debate about whether Linux is "ready" for the desktop continues to rage. There is no doubt that for many geek-types including myself, Linux is ready for the desktop. In many respects Linux on the desktop is a necessity for some. If you spend time administering Linux servers, then it makes sense to use a Linux desktop to do so. The same seems to hold true to Mac OS X and Windows environments.

If you spend any time on a desktop machine, you'll want a GUI. They just make computer life more pleasant and in some respects easier. Eventually the question of which "GUI is better?" enters the equation. The GUI a person chooses is often a matter of personal preference. In the end, there seems to be 2 choices most Linux desktop users go to; Gnome or KDE. We seem to end-up here, at least in part, because most Linux Desktop distributions feature one or the other.

Ubuntu: SSH - Change Welcome Message

Have you ever tired of seeing the standard SSH welcome message (a.k.a. banner)? Does it provide too much information about the system creating a security concern? If your answer to either of these questions is "Yes", then read on.

Ubuntu 9.04: Enable NumLock In KDM

I've tried following instructions found on the 'net for turning on the NumLock key at startup in KDE. Only problem; I don't have the keyboard element installed for some reason. So I'm trying the KDM solution;

Ubuntu 9.04: Location Of User's Crontab File

The location of a user's crontab file, in Linux, varies from distribution to distribution. It can even vary in different releases of a distribution. In Ubuntu (and variants) for release 9.04 the location is;

/var/spool/cron/crontabs

The user's crontab will be titled by the user's name.