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Protect SSH Server from Brute Force Attack

7/30/2014

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Other than remote login, there's various useful things you can do with ssh, like running a remote command, multiplexing connections to save on server resource, setting up ssh aliases to save you some keystrokes, and so forth. 

Recently, when my partner logged on a recently created CentOS server hosted at Digital Ocean, he saw the following messages:
Last failed login: Tue Jul 29 16:27:31 EDT 2014 from stuff2share.net on ssh:notty 
There were 20 failed login attempts since the last successful login
Clearly that wasn't us trying to log in. Obviously, there was some malicious user(s) likely trying to enter our server with brute-force attacks. We were under a ssh brute force attack. Such malicious scan is not uncommon these days. It came just a couple days after our new server was up.

I learned a few good ways to prevent this:

  1. Change default SSH port, 
  2. Only use SSH keys (and disable password authentication), and
  3. Use fail2ban

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Facebook App Development - Before Quickstart

6/5/2014

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Picture
FB released Graph API 2.0 on 4/30/2014 at f8. FB has changed a lot over time and it's hard to keep up. New Facebook App developers may feel frustrating and confusing. If so, you're not along. To develop an app using FB API, before you read FB Developer Quickstart, ready this post first which is supposed to help you get prepared quickly with less confusion.


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Analyze Heap Dump with Eclipse Memory Analyzer

9/9/2013

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Ever suspect your Java app leaking memory but not sure which class it is potentially causing OOM? 

In this post, I recommend Eclipse Memory Analyzer (MAT) for developers to analyze heap dumps so you can chase down leak suspects. MAT is much easier to use and read than stand-along jhat unix command, and while monitor memory usage using VisualVM is helpful, MAT gives you specific hints about which classes may be the suspects.

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Monitor Java Application with VisualVM

9/7/2013

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It is not uncommon that you need to watch the runtime performance of a Java application on a server. In this post, I'll show you how to set up a target JVM so you can monitor its cpu, heap memory, threads usage from a specific JMX client - VisualVM. VisualVM is similar to JConsole, a JMX-compliant monitoring tool, but is more advanced. 


To use a JMX client, the setup you need to do first are:

  1. On the Target server where JVM runs, you need to enable JMX Agent for the JVM.
  2. On the local machine where you want to monitor your Java application from, you need a JMX client. For this post, I chose VisualVM.
  3. To prevent other JMX client from accessing your JMX Agent, you want to turn on authentication when your JMX client connects to your JMX Agent.

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in loving memory of my mother  and my 4th aunt
Photos used under Creative Commons from net_efekt, schani, visnup, Dan Zen, gadl, bobbigmac, Susana López-Urrutia, jwalsh, Philippe Put, michael pollak, oskay, Creative Tools, Violentz, Kyknoord, mobilyazilar