Encrypt a File on Linux Using OpenSSL

December 30th, 2013

LockIt is possible to encrypt a file for secure transmission or backup using a strong cryptographic algorithm on Linux. We do that using OpenSSL:
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Preventing Multiple Instances of a Script From Running Using flock

August 26th, 2013

Linux command line programSometimes you want to limit a script to just one instance. Say the script accesses a resource that you don’t want to be shared. So how do you prevent multiple instances of a single script from running?
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Finding Number of Unique IP Addresses Involved in an Attack

August 8th, 2013

Linux command line programWeb servers sometimes get lots of requests from bots looking to exploit security holes. For example previously I have written about brute force WordPress login attempts. Attacks like these can involve thousands of IP addresses and how you block the attack depends on how many unique IPs are involved and the frequency with which they are used. Here’s how you can find out.
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Upgrading from Debian Squeeze to Debian Wheezy

May 14th, 2013

Debian LogoThe latest Debian stable version named Wheezy was recently released. It is possible to upgrade from Squeeze to Wheezy without reinstalling the operating system from scratch. Let’s look at how that can be done.

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Localhost as remote host in Apache log file

May 14th, 2013

ApacheI recently noticed something weird in my Apache access log files. There were entries like this:

abdussamad.com:80 localhost - - [09/May/2013:14:26:47 +0500] "POST /wp-login.php HTTP/1.0" 200 3784 "abdussamad.com/wp-login.php" "Mozilla/5.0 (Windows NT 6.1; rv:19.0) Gecko/20100101 Firefox/19.0"

Now the second column above is supposed to contain the remote host that made this request i.e. the user’s computer. But here it is shown as localhost. One possibility is that the requests originated on my server but I ruled that out. So how is this possible?

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