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Showing posts from September, 2014

How a mail server works

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I had originally written this tutorial for xmodulo.com Email service is one of the most often used services globally. Today almost everyone has at least one email account. Although clicking on the email send button and delivery of an email message appear seamless, a lot of events take place behind the scenes to make sure that the email reaches its final destination. The functionality of a mail server can be divided broadly into two processes: sending and receiving emails. The following two protocols oversee these processes. Sending email: Simple Mail Transfer Protocol (SMTP)Receiving email: Post Office Protocol (POP) / Internet Message Access Protocol (IMAP) Terminology The following terminology is important in understanding the operation of a mail server. Mail User Agent (MUA): The MUA is a component which interacts with end users directly. Examples of MUA are Thunderbird, MS Outlook, Zimbra Desktop. Web mail interfaces like Gmail and Yahoo! are also MUA.Mail Transfer Agent (MTA): The…

How to configure SNMPv3 in Ubuntu, CentOS and Cisco

I had originally written this tutorial for xmodulo.com Simple Network Management Protocol (SNMP) is a widely used protocol for gathering information about what is going on within a device. For example, CPU and RAM usage, load on a server, traffic status in a network interface, and many other interesting properties of a device can be queried using SNMP. Currently, three versions of SNMP are available: v1, v2c and v3. SNMP v1 and v2c can be easily configured, which has been discussed in a previous article. SNMPv3 adds some additional features, including authentication and encryption schemes (e.g., MD5, SHA, AES and DES). This makes SNMPv3 more secure and advisable while you run SNMP queries over the Internet. SNMPv3 configuration is a bit different compared to SNMP v1 or v2c. The following sections explain in detail how the configuration is done. Configure SNMPv3 on Ubuntu or Debian The net-snmp-config tool is used for configuration. The following example creates a read-only SNMPv3 use…

How to monitor common services with Nagios

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I had originally written this tutorial for xmodulo.com. Nagios comes with a wide range of built-in scripts for monitoring services. This tutorial will cover the process of using some of these scripts for checking common services, such as MySQL, Apache web server, DNS, etc. To keep the article focused on service monitoring, we will not be configuring hostgroups or templates, as they have been covered in a previous tutorial. Nonetheless, they can be tuned to match the requirements. Running Nagios Check in CLI It is generally recommended to run the Nagios service check scripts in CLI before adding them to Nagios. This will give an idea on whether the execution will be successful and what the output of the script will look like. All of the scripts are located at /etc/nagios-plugins/config/ with the executable files stored at/usr/lib/nagios/plugins/ Here is how it is done. root@nagios:~# cd /etc/nagios-plugins/config/ The provided scripts contain help on the syntax. The example contains p…

How to configure Nagios for audio alerts and mobile notifications

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I had originally written this tutorial for xmodulo.com In a Network Operation Centre (NOC) environment, setting up alerts is extremely important. As one of the most popular NOC monitoring systems, Nagios features powerful alerting services. Alerts generated by Nagios can be sent out in various means, so that they can be acted upon immediately. Email notification is the most commonly used option. This tutorial presents two other ways to send out Nagios alerts: (1) audio alerts via web browser, and (2) audio/vibration alerts via an Android app. Nagios Checker - A Firefox Add-on A small Mozilla Firefox add-on named Nagios Checker written by Petr ┼áimek can be used to gather information from Nagios, and generate audio alarms whenever a problem is detected. It is very easy to set up. Requirements Nagios Checker will gather information from a Nagios server every minute.Nagios Checker will generate audio alarms only when there is a change in network
health, i.e., alarms will not be produced for…