You may find that you want to modify the prompt. This can help you create visibility for special features or just modify it to something more useful. You can view the default settings for the prompt by using this command:

echo $PS1

As stated above it will show user, hostname, location and definition whether it is a normal user or root.

Create a single character

PS1=”$ ”

The space behind the $ is enforced by placing the quotes so it does not run into your text. The $ is typically used to show that it is a normal user not the root user indicated by the “#”.

Change options for the prompt

\d : the date Weekday Month Date format

\h : the hostname up to the first ‘.’

\A : the current time in 24-hour HH:MM format

\u : the username of the current user

\w : the current working directory, with $HOME abbreviated with a tilde

\$ : if the effective UID is 0, a #, otherwise a $

Create a colored prompt

You may want to create a color prompt that you can use for visibility. In this example the hostname has been dropped to make a shorter prompt and the prompt is turned red but the commands that you enter will be black. The export command will change these features.

mike@ub:~$ export PS1=’\e[0;31m[\u:\w]\$ \e[m '

[mike:~]$

This will color the prompt but not any commands that you enter.

List of Color codes

Color Code

Black 0;30

Blue 0;34

Green 0;32

Cyan 0;36

Red 0;31

Purple 0;35

Brown 0;33

Blue 0;34

Green 0;32

Cyan 0;36

Red 0;31

Purple 0;35

Brown 0;33

Replace digit 0 with 1 for a lighter color.

Make Changes permanent

All of the changes you make will be lost when you close the terminal or log out. Here are directions to make them permanent.

Ubuntu

# uncomment for a colored prompt, if the terminal has the capability; turned

# off by default to not distract the user: the focus in a terminal window

# should be on the output of commands, not on the prompt

#force_colored_prompt=yes

The .bashrc file in each user’s home directory allows you to change the default for the prompt to a color prompt by uncommenting the line:

#force_colored_prompt=yes

Unfortunately a typo in the line must also be corrected so that it should read:

force_color_prompt=yes

Ubuntu or CentOS

Place your custom prompt in the user .bashrc file with this command:

export PS1=’\e[0;31m[\u:\w]\$ \e[m ‘

REFERENCES

http://beginlinux.wordpress.com/2008/09/12/modify-your-command-prompt/

Issue

Denial of service attacks are popular nowadays. The most dangerous are the so-called distributed denial of service attacks, when network activity aimed at shutting the service down, is launched from a vast number of different locations (IPs). To handle that, in most cases one should have an expensive type of network hardware and software; however, there may be simpler solutions. Atlas Tuesday offers an example in Fighting off a DDOS attack on an Apache web server.

The story goes, when it rains it pours! It’s hard enough to keep websites running without hackers trying to break in. An even worse situation is when hackers simply want you off-line. A few days ago I experienced just that… my first DDOS (distributed denial of service) attack against a high-profile website we host.

The attacker original exploited some legacy code to gain access to the web sites administration tool. After thwarting their attack, our web server immediately started to hit “max client connections”. Even after restarting Apache the max client connections were reached within seconds.

We quickly created bad routes for IP addresses associated with the hack attempts; however this did not resolve the problem. Below is the syntax we used to add bad routes.

Route add –host xxx.xxx.xxx.xxx reject

The Apache log files left no clues as to who was connecting so we had to look elsewhere. After some quick searching we found a terrific PHP script which shows which IP’s are connecting to your web server too much. The script was just want we needed. After about a ½ hour of blocking listed IP addresses the problem went away. In all we blocked a little over 100 IP addresses.

If you’re ever in a situation where Apache is clearly being flooded with connections. Run this script! It will save you a ton of time identifying the attacker(s).

<pre class="php" name="code">

– BEGIN SCRIPT –

<?php

## Functions ##

function getIP($line) {

ereg("[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}",$line,$regMatch);

$ip = $regMatch[0];

if($ip) return $ip; else return "false";

}

function processString($string, $size = 18) {

$string = "[ ".$string;

$length = strlen($string);

$toAdd = $size - $length;

for($x = 0; $x < $toAdd; $x++) {

$string = $string." ";

}

$string = $string."]";

return $string;

}

## Code ##

while (true) {

$cmd = "netstat -n | awk '{ print $5 }'";

exec($cmd, $netstatArray);

$ipArray = array();

foreach($netstatArray as $line) {

$ip = getIP($line);

if($ip != "false" && ip != "127.0.0.1") {

if(array_key_exists($ip, $ipArray))

{

$ipArray[$ip]+=1;

}

else // if not, count=1

{

$ipArray[$ip] = 1;

}

}

}

asort($ipArray);

system("clear");

foreach($ipArray as $ip => $count) {

if ($count < 15)

continue;

echo processString($ip);

echo "\t" .processString(gethostbyaddr($ip), 55);

echo "\tTimes Accessed: " .$count ."\n";

}

echo str_repeat("-", 50) ."\n";

exec("top -n 1", $top_str);

preg_match("#load average:(.+)#i", $top_str[0], $match);

echo "Load Average: " .$match[1] ."\n";

echo str_repeat("-", 50) ."\n";

echo 'Showing $count >= 15: (Escape with ctrl+c)' ."\n";

sleep(10);

}

?>

One should also add that even the basic software firewall products, such as free iptables, are capable of thwarting most kidns of simple DoS attempts, by banning addresses temporarily when the rate of connections becomes too high.

For example, this is how SMTP connections can be limited to 1 per second per IP (burstable 10):



iptables -A INPUT -p tcp --dport 25 --syn -m limit --limit 1/s \

--limit-burst 10 -j ACCEPT

iptables -A INPUT -p tcp --dport 25 --syn -j DROP



Protection against DDoS is a hard task, and in most cases it should be handled with proper tools.

chown apache:apache .htaccess

 
   Options +FollowSymLinks
   RewriteEngine On
   RewriteBase /
   RewriteCond %{REQUEST_FILENAME} !-f
   RewriteCond %{REQUEST_FILENAME} !-d
   RewriteRule . /index.php [L]