Linux / Unix logtop: Realtime Log Line Rate Analyser

How can I analyze line rate taking log file as input on a Linux system? How do I find the IP flooding my Apache/Nginx/Lighttpd web-server on a Debian or Ubuntu Linux?

Tutorial details
Difficulty	Easy (rss)
Root privileges	Yes
Requirements	None
Estimated completion time	N/A

You need to use a tool called logtop. It is a system administrator tool to analyze line rate taking log file as input. It reads on stdin and print a constantly updated result displaying, in columns in the following format:

Line number, count, frequency, and the actual line

How do install logtop on a Debian or Ubuntu based system?

Simply type the following apt-get command:
$ sudo apt-get install logtop
Sample outputs:

Reading package lists... Done
Building dependency tree
Reading state information... Done
The following NEW packages will be installed:
  logtop
0 upgraded, 1 newly installed, 0 to remove and 3 not upgraded.
Need to get 15.7 kB of archives.
After this operation, 81.9 kB of additional disk space will be used.
Get:1 http://mirrors.service.networklayer.com/ubuntu/ precise/universe logtop amd64 0.3-1 [15.7 kB]
Fetched 15.7 kB in 0s (0 B/s)
Selecting previously unselected package logtop.
(Reading database ... 114954 files and directories currently installed.)
Unpacking logtop (from .../logtop_0.3-1_amd64.deb) ...
Processing triggers for man-db ...
Setting up logtop (0.3-1) ...

Syntax

The syntax is as follows:

 
logtop [OPTIONS] [FILE]
command | logtop
command1 | filter | logtop
command1 | filter | logtop [options] [file]
 

Examples

Here are some common examples of logtop.

Show the IP address flooding your LAMP server

Type the following command:

 
tail -f www.cyberciti.biz_access.log | cut -d' ' -f1 | logtop
 

Sample outputs:

Fig.01: logtop command in action

See squid cache HIT and MISS log

 
tail -f cache.log | grep -o "HIT\|MISS" | logtop
 

To see realtime hit / miss ratio on some caching software log file, enter:
tail -f access.log | cut -d' ' -f1 | logtop -s 20000
The -s option set logtop to work with the maximum of K lines instead of 10000.