Category: Linux

Link: List of Free And Open Source Monitoring System

The Linux monitoring systems are often used to follow system resources, such as CPU load, the amount of free RAM, network traffic statics or memory consumption. Which are ones from the most important tasks for every administrators. Furthermore, those tools notify the network administrator (via email, SMS or other alarms) when something interrupts or goes down which makes their life easier.

From those monitoring tools we will list the 7 most important in this article which will be described and identified by giving their features and mentioning their current version.

Full article here:
List of Free And Open Source Monitoring System (Unixmen)

Link: An Introduction To Access Control Lists (ACL)

Access Control List (ACL) provides an additional, more flexible permission mechanism for file systems. ACLs allow you to provide different levels of access to files and folders for different users. It is designed to assist with UNIX file permissions. ACL allows you to give permissions for any user or group to any disc resource.

Full article here:
An Introduction To Access Control Lists (ACL) (Unixmen)

Link: Cron Jobs for Beginners

Cron Jobs are used for scheduling tasks to run on the server. They’re most commonly used for automating system maintenance or administration. However, they are also relevant to web application development. There are many situations when a web application may need certain tasks to run periodically. Today we are going to explore the fundamentals of Cron Jobs.

Full article here:
Cron Jobs for Beginners (Project: Fenix)

How to set up an alternate SIP port (other than 5060) using Webmin

One problem that some VoIP users are experiencing these days is that they have trouble connecting to their home Asterisk, FreeSWITCH, YATE, or other software PBX server, but only when using certain ISP’s.  One suspicion is that certain ISP’s that offer their own VoIP or traditional landline service attempt to mess with packets using the common SIP port 5060, hoping customers will think that VoIP is unreliable and will subscribe to the company’s overpriced offering instead (see this thread at BroadbandReports.com).

There are various ways to enable an alternate SIP port on the server (in addition to the usual port 5060) but if you are using Webmin to manage your firewall, here’s an easy way, in just three steps:

Step 1:

If you use Webmin to manage your firewall, then you already know how to get to the Linux Firewall page.  So go there and select the Network Address Translation (nat) table in the dropdown at the top of the page.  Then when the page changes, click the topmost Add Rule button (in the Packets before routing (PREROUTING) section):

SIP Port Forwarding 1

Step 2:

Now you should see this page. The items you need to change are indicated by the red ovals.  The Destination TCP or UDP port is set to 7654 in this example, but don’t use that.  Pick your own unique port; just make sure that it’s not used by anything else on the server already.  And yes, you really do put the alternate SIP port you want to use in the Destination setting; it may not make intuitive sense but that’s just how it is.  Avoid using ports in the range 10000 through 20000 because those are used for RTP traffic, and avoid ports below 1024 because those are protected ports that are reserved by the system.  There are also other ports you should avoid (those used by other software on your system) but if you don’t know how to find ports in use on your system, a bit of time with a search engine will lead you to several pages that show you how to detect already active ports.  It can vary a bit depending on your operating system, and it’s beyond the scope of this article.

SIP traffic is UDP only, not TCP (there may be rare exceptions but most software PBX’s use UDP by default).  If by some very odd chance you are using TCP for SIP traffic (why?!?) then you will need to specify that under the Network Protocol item.  Also, note that the incoming interface is set to eth0 in this example – Webmin will usually show the correct one by default, but you want to select the interface used by incoming SIP traffic if you happen to have more than one.  Don’t forget to click Save when you’re finished.

SIP Port Forwarding 2

Step 3:

After you have saved the page you should be back at the page you came from, and it should now show your new forwarding rule.  If it does, just click Apply Configuration at the bottom of the page to make it active:

SIP Port Forwarding 3One other thing you might need to to is add a rule on the main Linux Firewall page allowing incoming traffic on your selected alternate port, if you have a restrictive firewall that blocks most traffic by default.  Try it first without doing that, but if your clients can’t connect on the alternate port, just be aware that you may need to do that before they will be able to connect.  For more security, you can enable access to your SIP ports only from specific IP addresses, if your remote clients are at fixed IP addresses.

Now you should be able to change the port number on your SIP endpoints from the default 5060 to your alternate port.  Of course I can’t guarantee it will always work, but if you try it and suddenly find that your SIP connections become far more reliable, you might want to leave a comment, and mention the ISP that you suspect might be messing with SIP traffic.

By the way, if you are NOT using Webmin to manage your firewall, and have iptables installed, then all you should need to do is enter these two lines from a command prompt (replace 7654 with your chosen alternate port).  But I strongly caution you NOT to do this if you are using Webmin to manage your firewall:

iptables -t nat -A PREROUTING -i eth0 -p udp --dport 7654 -j REDIRECT --to-ports 5060
/etc/init.d/iptables save

Link: Linux Basics: How To Check The State Of A Network Interface Card

Normally, we can easily check the state of a network interface card like whether the cable plugged in to the slot or the network card is up or down in Graphical mode. What if you have only command line mode? Ofcourse, you can turn around the system and check for the cable is properly plugged in, or you can do the same easily from your Terminal. Here is how to do that. This method is almost same for Debian and RPM based systems.

Full article here:
Linux Basics: How To Check The State Of A Network Interface Card (Unixmen)

Link: 4 Useful Cron Alternatives For Linux

For those who are familiar with the Unix system, you will also be familiar with the cron application that allows you to schedule and automate tasks to run on their own. We even have tutorials that show you how to get started with cron and crontabs. However, cron is not perfect, as it requires your system to be running 24 hours a day. If you have a habit of turning off your computer at night, and a cron job is scheduled in the sleeping hours, the task won’t be executed. Luckily, there are several cron alternatives that can do a better job than cron. Let’s check them out.

Full article here:
4 Useful Cron Alternatives For Linux (Make Tech Easier)

Link: How To Install Openfire On CentOS 7

Openfire is a real time collaboration (RTC) server licensed under the Open Source Apache License. It is also known as Jabber. It uses the only widely adopted open protocol for instant messaging, XMPP. The full name of XMPP is Extensible Messaging and Presence Protocol. It is a real-time communication protocol (which includes chat) based on XML. Installation and the management of Openfire is pretty simple.

It should be noted that with Openfire, no chat is possible yet. A client is needed: Openfire cannot be used alone, just like web servers need a browser.

In this tutorial we will see, how to install Openfire in a clean minimal installation of CentOS 7.

Full article here:
How To Install Openfire On CentOS 7 (Unixmen)

Link: Easily Update Your Raspbian SD Cards for the Pi 2 with These Commands

The Raspberry Pi 2 is a serious upgrade over older versions, and that means you’ll need to update a lot of your software to use it. You could make a whole new SD card, but if you have old projects that you don’t want to lose, The Pi Hut shows off the upgrade process in Raspbian.

Full article here:
Easily Update Your Raspbian SD Cards for the Pi 2 with These Commands (Lifehacker)