Install and integrate DKIM with OpenDKIM and Postfix on a CentOS 6


Before going any further, make sure you’re in a screen session and your system is fully up-to-date by running:

## screen -U -S opendkim-screen
## yum update


OpenDKIM is available in the EPEL repository, so we need to enable it on the system before we can install OpenDKIM

## wget -P /tmp
## rpm -Uvh /tmp/epel-release-6-8.noarch.rpm
## rm -f /tmp/epel-release-6-8.noarch.rpm


Install the package using yum:

## yum install opendkim


Next thing to do is to configure OpenDKIM. Its main configuration file is located in /etc/opendkim.conf, so before making any changes create a backup and add/edit the following: Continue reading “Install and integrate DKIM with OpenDKIM and Postfix on a CentOS 6” »


Nginx Reverse Proxying Multiple Domains Using map Module

map_hash_bucket_size 128;
map $http_host $backend_servers {
    default               ;         
proxy_set_header X-Real-IP $remote_addr;
proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
proxy_set_header Host $http_host;
server {
    location / {
        proxy_pass  http://$backend_servers

Install PHP 7.3, 7.2, 7.1 on CentOS/RHEL 6.10

Configure Yum Repository

First of all, you need to enable Remi and EPEL yum repositories on your system. Use the following command to install EPEL repository on your CentOS and Red Hat 7/6 systems

Use this command to install epel-release yum repository

yum install epel-release

and now execute one of the following commands as per your operating system version to install Remi repository.

rpm -Uvh

Install PHP 7 on CentOS 6

Your system is prepared for the PHP installation from yum repositories. Use one of the following commands to install PHP 7.3 or PHP 7.2 or PHP 7.1 on your system based on your requirements.

## Install PHP 7.3 
yum --enablerepo=remi-php73 install php
## Install PHP 7.2 
yum --enablerepo=remi-php72 install php
## Install PHP 7.1 
yum --enablerepo=remi-php71 install php

I have installed the latest version PHP 7.3 on my system. Now running the following command to check current active PHP version on my system. Continue reading “Install PHP 7.3, 7.2, 7.1 on CentOS/RHEL 6.10” »


Apache Virtual Hosts on CentOS

Step One— Create a New Directory

The first step in creating a virtual host is to a create a directory where we will keep the new website’s information.

This location will be your Document Root in the Apache virtual configuration file later on. By adding a -p to the line of code, the command automatically generates all the parents for the new directory.

sudo mkdir -p /var/www/

You will need to designate an actual DNS approved domain, or an IP address, to test that a virtual host is working. In this tutorial we will use as a placeholder for a correct domain name.

However, should you want to use an unapproved domain name to test the process you will find information on how to make it work on your local computer in Step Six.

Step Two—Grant Permissions

We need to grant ownership of the directory to the user, instead of just keeping it on the root system.

sudo chown -R apache:apache /var/www/

Additionally, it is important to make sure that everyone will be able to read our new files.

sudo chmod 755 /var/www

Now you are all done with permissions. Continue reading “Apache Virtual Hosts on CentOS” »


Find Out NFS Clients Connected To My NFS Server

You can use the following commands. SSH or login into your nfs server and type the following command:

netstat -an | grep nfs.server.ip:port

If your nfs server IP address and port is 2049, enter:

netstat -an | grep

Sample outputs:


Where, – NFS serer IP address
2049 – NFS server port and – NFS clients IP address Continue reading “Find Out NFS Clients Connected To My NFS Server” »


How to Change Hostname on Ubuntu 18.04

Display the Current Hostname

To view the current hostname, enter the following command:


As you can see in the image above, the current hostname is set to ubuntu1804.localdomain.

Change the Hostname

The following steps outline how to change the hostname in Ubuntu 18.04.

1. Change the hostname using hostnamectl

In Ubuntu 18.04 we can change the system hostname and related settings using the command hostnamectl.

For example, to change the system static hostname to linuxize, you would use the following command: Continue reading “How to Change Hostname on Ubuntu 18.04” »


Split large file and combine file in Linux

$ du -h Linux\ Security.mp4

Sample output:

1.1G Linux Security.mp4

As you see, the video file size is 1.1 GiB, which is very large to upload to my google drive. Even though, Google Drive lets users upload files up to 5TB in size, it is really time consuming process. With my low speed Internet connection, I presume it would take more than 30 minutes to upload. I don’t want to wait that much longer. So, what I am going to do is split this file into multiple smaller size files, for example 100 MB each, to make upload process faster.

Now, let us split the above file into multiple smaller files, say for example 100MB each. To do so, run:

$ split -b 100M Linux\ Security.mp4 ls.

Continue reading “Split large file and combine file in Linux” »


Install Netdata on CentOS 6

Installing Netdata

[root@linuxhelp Desktop]# yum install zlib-devel libuuid-devel libmnl-devel gcc make git autoconf autogen automake pkgconfig -y
Loaded plugins: fastestmirror, refresh-packagekit, security
Setting up Install Process
Determining fastest mirrors
perl-Error.noarch 1:0.17015-4.el6 perl-Git.noarch 0:1.7.1-9.el6_9 
ppl.x86_64 0:0.10.2-11.el6


It doesn’t end with that, you should also install additional packages. Run the following command for the same purpose. Continue reading “Install Netdata on CentOS 6” »