Configure DomainKeys- DKIM (OpenDKIM) with Postfix on CentOS 7

OpenDKIM is method to digitally sign & verify emails on the mail servers using public & private keys. In other words opendkim implements the DKIM (DomainKeys Identified Mail) standard for signing and verifying email messages on a per-domain basis. DomainKeys are implemented to reduce the chances of outgoing mails to be marked as SPAM.

In this post we will demonstrate how to install & configure DomainKeys with postfix (MTA) on CentOS 7, i am assuming Postfix is already installed with following domain and hostname.

Hostname = mail5.freshdaymall.com
Domain = freshdaymall.com

Step:1 Set EPEL Repository using below rpm command

OpenDKIM package is not available in the default yum repositories but available in CentOS 7 EPEL repositories

[root@mail5 ~]# rpm -Uvh https://dl.fedoraproject.org/pub/epel/epel-release-latest-7.noarch.rpm

Step:2 Install OpenDKIM Package using yum

[root@mail5 ~]# yum install -y opendkim

Step:3 Run below Command to create keys

Execute the below command to create public & private keys under folder “/etc/opendkim/keys” Continue reading “Configure DomainKeys- DKIM (OpenDKIM) with Postfix on CentOS 7” »

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Ping behind proxy using httping

You can use utility httping for that. It sends a HEAD request (by default) to a web server and measures the time it took to get a response.

The utility is available through a number of repositories for different OS’es and Linux distros:

Ubuntu:

sudo apt install httping

Alpine:

sudo apk add httping

macOS with Homebrew:

brew install httping

How to use it:

httping -x 192.68.1.12:1080 -g http://google.com

Continue reading “Ping behind proxy using httping” »

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enable SNMP on Xen (XCP-NG) hypervisors

There are six steps to correctly configuring SNMP on your Citrix Xen hypervisor. These steps don’t require a system restart and are non-service affecting.

To start, we assume you’re running Xen v6.x or v7.x, and are logged into the Xen CLI as root.

1. Enable the SNMP daemon

Enable the snmpd daemon by typing-

chkconfig snmpd

2. Configure the SNMP service

Make a backup of the snmpd.conf file. The default snmpd.conf file contains a lot of useful documentation for more advanced implementations of SNMP.

# cp /etc/snmp/snmpd.conf /etc/snmp/snmpd.conf.backup

Continue reading “enable SNMP on Xen (XCP-NG) hypervisors” »

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How to find out the connected interface using linux command

Method 1

To find out the connected state of a network cable in Linux, just run:

$ cat /sys/class/net/enp5s0/carrier

Sample output:

1

If you got output as “1” (Number one), It means that the network cable is connected with the network card. Also, you can do this with the following command too:

$ cat /sys/class/net/enp5s0/operstate

Sample output: Continue reading “How to find out the connected interface using linux command” »

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Install LAMP on CentOS 7 with PHP 5.4/7.0/7.1/7.2/7.3/7.4

Preliminary Note

In this tutorial, I use the hostname server1.example.com with the IP p 192.168.0.100. These settings might differ for you, so you have to replace them where appropriate.

I will add the EPEL repo here to install latest phpMyAdmin as follows:

rpm --import /etc/pki/rpm-gpg/RPM-GPG-KEY*
yum -y install epel-release

To edit files on the shell, I’ll install the nano editor. If you prefer vi for file editing, then skip this step.

yum -y install nano

Installing MySQL / MariaDB

MariaDB is a MySQL fork of the original MySQL developer Monty Widenius. MariaDB is compatible with MySQL and I’ve chosen to use MariaDB here instead of MySQL. Run this command to install MariaDB with yum:

yum -y install mariadb-server mariadb

Then we create the system startup links for MySQL (so that MySQL starts automatically whenever the system boots) and start the MySQL server: Continue reading “Install LAMP on CentOS 7 with PHP 5.4/7.0/7.1/7.2/7.3/7.4” »

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Remove Node from Proxmox Cluster

Step 1 : Migrate all VMs to another active node

Migrate all VMs to another active node. You can use the live migration feature if you have a shared storage or offline migration if you only have local storage.

Step 2 : Display all active nodes

Display all active nodes in order identify the name of the node you want to remove Continue reading “Remove Node from Proxmox Cluster” »

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Add Geolocation to Graylog 2

The Graylog Map Widget is the plugin providing geolocation capabilities to Graylog. The plugin is compatible with Graylog 2.0.0 and higher, and it is installed by default, although some configuration is still required on your side. This section explains how to configure the plugin in detail.

In case you need to reinstall the plugin for some reason, you can find it inside the Graylog tarball in our downloads page. Follow the instructions in Installing and loading plugins to install it.

Configure the database

In first place, you need to download a geolocation database. We currently support MaxMind City databases in the MaxMind DB format, as the GeoIP2 City Database or GeoLite2 City Database that MaxMind provides.

The next step is to store the geolocation database in all servers running Graylog. As an example, if you were using the Graylog OVA, you could save the database in the /var/opt/graylog/data folder, along with other data used by Graylog. Make sure you grant the right permissions so the user running Graylog can read the file. Continue reading “Add Geolocation to Graylog 2” »

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Reclaim disk space from a sparse image file qcow2/ vmdk

Sparse disk image formats such as qcow2 only consume the physical disk space which they need. For example, if a guest is given a qcow2 image with a size of 100GB but has only written to 10GB then only 10GB of physical disk space will be used. There is some slight overhead associated, so the above example may not be strictly true, but you get the idea.

Sparse disk image files allow you to over allocate virtual disk space – this means that you could allocate 5 virtual machines 100GB of disk space, even if you only have 300GB of physical disk space. If all the guests need 100% of their 100GB disk space then you will have a problem. If you use over allocation of disk space you will need to monitor the physical disk usage very carefully.

There is another problem with sparse disk formats, they don’t automatically shrink. Let’s say you fill 100GB of a sparse disk (we know this will roughly consume 100GB of physical disk space) and then delete some files so that you are only using 50GB. The physical disk space used should be 50GB, right? Wrong. Because the disk image doesn’t shrink, it will always be 100GB on the file system even if the guest is now using less. The below steps will detail how to get round this issue. Continue reading “Reclaim disk space from a sparse image file qcow2/ vmdk” »

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Install Jitsi Meet and configure load balancing

Jitsi Meet is an open-source (Apache) WebRTC JavaScript application that uses Jitsi Videobridge to provide high quality, secure and scalable video conferences. It can be used as a replacement for proprietary services like Zoom, Whereby, Teams, Skype and many others.

Requirements

  • At least two Linux systems with Debian 10
  • DNS Record for your domain (in our case meet.example.com)

Prepare your system
First of all we prepare our system by updating all package lists and packages. To do so run the following commands.

apt update && apt upgrade -y

Basic Jitsi Meet installation
Next, please be sure that your FQDN is configured correct. Continue reading “Install Jitsi Meet and configure load balancing” »

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Enable authentication of Jitsi Meet

A basic installation of Jitsi Meet gets you up and running within shortest time, probably in less than 15 minutes. There are hardly any configuration changes necessary. Most important information is a fully qualified domain name (FQDN), and that’s it.

However such a default installation of Jitsi Meet is open. Meaning, that anyone knowing the URL of your server can create a new meeting room and start to have video conferences using your instance and probably causing additional cost. Continue reading “Enable authentication of Jitsi Meet” »

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