What is lsyncd?

Lsyncd combines the advantages of inotify with the functionality of Rsync. This means lsyncd holds a remote copy of a directory permanently to the state that corresponds to the local directory.

Technically lsyncd begins at the start with a full Rsync run, but sets simultaneously on all the monitored directories and subdirectories inotify watches. All changes to the data reports through Kernel to lsyncd. This collects these messages and then initiates at short intervals for the changed files and re-run Rsync.

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10 questions about RAID Technology

Storage solutions, professionals, etc… always heavily loaded with RAID configuration. But do you know this technology. I guess, yes. However, today I am going to ask some basic questions about RAID; below each question you will see 3 options + correct answer. At first glance it will looks quite boring or rather uninteresting but did you know this information before, ask yourself.

Question 1/10 – What do the initials RAID?

Redundant Array of Independent Disks Redundant Association of Inexpensive Disks Asynchronous Data record of Informatics

The correct answer is – 1) Redundant Array of Independent Disks

Question 2/10 – What architecture does one opposes regularly RAID?

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Hyper-V: Protection against malicious DHCP with DHCP Guard

enable_dhcp_guard

Note: this option is available on Windows Server 2012

The service DHCP is ever present in networks of companies to distribute a network configuration to clients’ computers and even servers. Generally, multiple servers are present in order to make sure the availability and stability of the service. These servers manage a lot of things along with synchronization and avoid duplication.

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How to setup a Reverse Proxy with Apache Mod_Proxy?

Today, we will see the implementation of Apache as a reverse proxy in the front-end of another apache server that will be its back-end. We will use this module Mod_Proxy and Mod_Proxy_HTTP. We will just try to redirect the flow arriving at a destination server of a domain name to a server located further upstream in the architecture. We will not discuss here the subjects of Load distribution or load balancing that can perform the role of reverse proxy. The system of reverse proxy may here be summarized as follows:

Therefore, there is a first server front-end that receives all requests and multiple web servers’ backend that each contains a different website (or even as part of a load balancing). So we will set up the reverse proxy server to redirect requests according to each URL and the requested content. This can be done by folder (for example, just redirect / image to a specific server) or a full URL, what we see here:

Architecture

To illustrate the implementation of our Apache reverse proxy, here we will follow the below schedule:

So we have a first server with the public IP 10.10.10.21 that will receive all requests from clients. It contains the www.firstdomain.com, then a second server which contains the website www.seconddomain.com.

So we will configure our first server Reverse Proxy so that it redirects requests www.seconddomain.com by second sever, fulfilling its role as reverse proxy. However, it will continue to respond to those requests for www.firstdomain.com, to illustrate this how a normal website using a reverse proxy:

We assumed here that the machines are in place at the OS level, network and have a functional Apache server with a website on each machine meets the good URL.

Installation and Configuration

We will initially activate proxy_http on the reverse proxy server. This is the module mod_proxy specific to the HTTP protocol that we work with here. For this, we entered the below command:

| a2enmod proxy_http

1) The module “proxy” should be activated at the same time:
2) We will then restart apache2 so that the modules are active:

| Service apache2 restart

We will now create two virtual hosts. One that will lead www.firstdomain.com requests to local content and another who has the role of the reverse proxy and direct the requests to the second server www.secondserver.com with a standard configuration.

| touch /etc/apache2/sites-available/firstdomain.com
| touch /etc/apache2/sites-available/seconddomain.com

We will not perform these configurations: here we willingly place only the information that needed to keep the bulk seen in:

Here is the configuration firstdomain.com

< VirtualHost *:80 >
	ServerName www.firstdomain.com
	DocumentRoot /var/www/firstdomain
< /VirtualHost > 

Here is the configuration of seconddomain.com which is the one that will be the reverse proxy:

< VirtualHost *:80 >
	ServerName www.seconddomain.com
	ProxyPreserveHost On
	ProxyRequests On
	ProxyPass / http://10.10.10.23/
	ProxyPassReverse / http://10.10.10.23
< /VirtualHost >

Then we can enable them:

| a2ensite firstdomain.com
| a2ensite seconddomain.com

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How to find world writable files in Linux?

Tux

In Linux, a file “world writable” is a file which everyone can write. These files can be used as sensitive by people who did not aim at the base to write data to the system or out of a given directory. The world writable files are more dangerous when they can run by anyone on the system, as they can then make a script. Today, we will see how easily we can locate these files on a Linux system through the command “Find” that is available on the most of Linux systems.

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