MySQL can sometimes create big problems on a server when you have users abusing it.
This article will teach you how to correctly identify the queries that are creating a problem for your server.

MySQL can log those queries that are taking longer then X seconds but this future is not turned on by default.
Here’s how you turn it on:
Login to your server as root
Open my.cnf with your favorite editor. Example:
vim /etc/my.cnf

Into the [mysqld] section add the fallowing lines
log-slow-queries = /var/log/mysql-slow.log
long_query_time = 3

This is just an example. You can use any file name that you want and you can modify the long_query_time to any value. In this example I will be logging to /var/log/mysql-slow.log any queries that are taking longer then 3 seconds.

Go ahead and save the configuration.
For vim: CTRL+X and YES

Now we have to actually create the log file.
touch /var/log/mysql-slow.log

Now we are changing the owner of the file so that mysql and actually write to it.
chown mysql.root /var/log/mysql-slow.log

Now we restart mysql
service mysql restart

It should restart successfully. If it doesn’t check that you didn’t brake my.cnf by examining the error file in your data directory.

Wait a few minutes and then examine the slow queries log
A few examples on how to do it:

cat /var/log/mysql-slow.log
tail /var/log/mysql-slow.log
tail -50 /var/log/mysql-slow.log

After you have identified the offending query go ahead and optimize or remove it.
Again test the results by looking at your server load and the mysql slow queries log.

After you fixed all the problems go ahead and comment the slow queries logging as it will slow your server a bit if you leave it on. my.cnf should now look similar to this:

#log-slow-queries = /var/log/mysql-slow.log
#long_query_time = 3

And don’t forget to restart MySQL after this.

service mysql restart

Hope this helps !

Install MySQL Performance Tuning Primer Script

Tuning the performance of MySQL can be a really hard job to do.
There are many things to consider and no two servers are identical so there is no universal solution.
Tuning Primer is a script that will help you tune your mysql installation by providing very healthy recommendations based on past mysql records.
For the script to be efficient you must run the mysql server for at least 48 hours.
Installation is extremely simple:

Download the script
wget http://day32.com/MySQL/tuning-primer.sh

Change the permissions for the file
chmod 755 tuning-primer.sh

Run it
./tuning-primer.sh

Apply the sugesttions

Enjoy!

The fix is really simple, chkconfig wants to see 2 lines in your apachectrl that tell it what it is and what to do with it. At that point, chkconfig will recognize the service as your script name. So here it is:

1. Add the following lines to the top of the apachectrl script that you’ll find in the apache2/bin directory of your install.#!/bin/sh
   #
   # chkconfig: 35 85 15
   # description: Apache is a World Wide Web server.
   #
   # Licensed to the Apache Software Foundation (ASF) under one or more

   The first line:
   # chkconfig: 35 85 15
   The 35 tells chkconfig you want the service running at run level 3 and run level 5.
   The 85 is the start priority.
   The 15 is the stop priority.

   The second line:
   # description: Apache is a World Wide Web server.
   This is merely a description of the service.
   *note* Both lines start with a comment “#” (pound sign).

2. Once your lines are in place you can move or link your apachectrl to /etc/init.d/httpd
3. Once the script is in /etc/init.d/ you can run the following command to make it all go:
   chkconfig httpd on(this is of course assuming that you named the script in /etc/init.d/ “httpd”, if you named the script “chuck” then you’ll run: chkconfig chuck on, I think you get the point).

That is all.

Basically, I wanted sendmail to take all inbound email and immediately relay it to another host. In my situation it makes sense because my servers have no direct access to the outside world (security thing). But in reality with the complexities involved in sending email these days, why bother setting up every host or every NAT to be capable of dependably delivering email.

So the solution is, setup one host that you know is a good mail host, and one host that you can monitor for throughput, then point all your other hosts at it for delivery. Piece of cake right? Odd that it took me 30 minutes and then a final trip to the sendmail documentation to find it.

In the end we’re talking about 1 line in your sendmail.mc (I’ve consistently found that most of life’s problems can be solved with 5 to 50 characters in the right text file).

At any rate, the directive you are looking for is:

define(`SMART_HOST', `smart.host.com')dnl

Just replace “smart.host.com” with the smtp server you intend to use as the relay.

For those of you who don’t use the sendmail.mc, you need to modify the DS variable in your sendmail.cf (but really, find something better to do with your time than edit that file).

For all you sendmail.mc users, once that line is in place, run a “make” in your /etc/mail directory and then restart sendmail.

Actually, I was using this mess of a line to test:

touch /tmp/mail.txt; /etc/init.d/sendmail restart ; mail -s "Test2" me@myemail.com < /tmp/mail.txt ; tail -f /var/log/maillog

You’ll come up in a tail of maillog and you should watch for the relay host accepting your message. If it doesn’t get delivered, it’s time to look at the relay server.

That is all, have fun!

First:

Take the YouTube URL as an argument

$url = $argv[1];

Next:

Use a little shell magic to grab the video arguments for later use:

$vid_args = `lynx -source "$url" | grep video_id | grep fullscreen | awk -F'video_id=' '{print $2}' | awk -F'&title'

Next:

use basically the same command to grab the title of the video:

$title = 'lynx -source "$url" | grep video_id | grep fullscreen | awk -F'video_id=' '{print $2}' | awk -F'&title=' '{print $2}' ';

Then:

Do a little formatting of the title to make it useable:

$title = preg_replace("| |", "_", $title);
$title = trim($title);
$title = preg_replace("/^[^a-z0-9]?(.*?)[^a-z0-9]?$/i", "$1", $title);
$title = preg_replace("|'|", "", $title);
$title = preg_replace("|\)|", "", $title);
$title = preg_replace("|\(|", "", $title);
$title = preg_replace("|\/|", "_", $title);

Then:

Grab the flv with the video arguments you captured from the line above:

'wget -O /tmp/$title.flv "http://www.youtube.com/get_video?video_id=$vid_args"';

Next:

Use ffmpeg to break it down to mp3 format:

'ffmpeg -i /tmp/$title.flv -ar 44100 -ab 160k -ac 2 /tmp/$title.mp3';

Finally:

Dump the flv and enjoy:

'rm -f /tmp/$title.flv';

These files are of course only for educational purposes when you are finished so make sure you delete them

Download The Whole Script

Chroot Jail

It’s quite nice.

Basically, you just pull that script down and get it on your machine. Then you feed it a username and let it go to work.

When it’s done, you’ll have a new user who is isolated to /home/jail. Their home dir will be in /home/jail/home and they can shell in and do whatever.