This config will describe a procedure on how to persistently load kernel modules during a boot time on CentOS or Redhat Linux system. In the below commands will use nf_conntrack_pptp as a sample module. Replace the name of this module with a module name you wish to load.

First, create a script within /etc/sysconfig/modules/ directory with a file extension modules. Where the name of the script can be any name of your choice. In our case the script will be called nf_conntrack_pptp.modules. Enter a following code into your new nf_conntrack_pptp.modules script while replacing the name of the module with the one you wish to load:
#!/bin/sh
exec /sbin/modprobe nf_conntrack_pptp  >/dev/null 2>&1

Every time you update your CentOS Linux and the update includes a new kernel image update the system will not remove your old kernel but it will cumulatively add new kernel to the top of your Linux kernel installed list. Normally, this does not present any issue to your running system and you are not required to take any action to remove any old and unused kernel images.

The reason why you may wish to remove/uninstall unused kernel images is that you need to reduce disk usage space of your system, especially if your /boot mount point is mounted separately and has a limited disk space
$ df -h /boot/
Filesystem      Size  Used Avail Use% Mounted on
/dev/sda1       331M  198M  112M  64% /boot

The following linux commands will help you to install Amazon s3cmd Command Line S3 tool on CentOS Linux.
First, enable EPEL repository:
# wget http://dl.fedoraproject.org/pub/epel/7/x86_64/e/epel-release-7-5.noarch.rpm
# rpm -Uvh epel-release*.rpm

debootstrap is Debian GNU/Linux bootstrapper which allows you to install Debian base systems such as Debian or Ubuntu into a directory of your currently running system. This config is a getting started guide on how to debbootstrap on CentOS/RHEL. The debootstrap package is not available in a standard CentOS repository. To make it available we first need to enable EPEL repository. Download EPEL repository package:
# wget http://dl.fedoraproject.org/pub/epel/7/x86_64/e/epel-release-7-5.noarch.rpm
and install it using RPM command:
# rpm -Uvh epel-release-7-5.noarch.rpm
The EPEL repository should now be enabled. To confirm run:
# yum repolist | grep epel                                                                                  
 * epel: epel.mirror.digitalpacific.com.au

In order to disable YUM package repository on CentOS we first need to get a unique repository ID using the following yum command:
# yum repolist
Loaded plugins: fastestmirror, langpacks
Loading mirror speeds from cached hostfile
 * base: mirror.optus.net
 * epel: epel.mirror.digitalpacific.com.au
 * extras: mirror.ventraip.net.au
 * updates: mirror.optus.net
repo id              repo name                                            status
base/7/x86_64        CentOS-7 - Base                                      8,652
epel/x86_64          Extra Packages for Enterprise Linux 7 - x86_64       8,935
extras/7/x86_64      CentOS-7 - Extras                                      285
google-chrome        google-chrome                                            3
isv_ownCloud_desktop The ownCloud Desktop Client (CentOS_7)                  63
updates/7/x86_64     CentOS-7 - Updates                                   1,726
virtualbox/7/x86_64  Oracle Linux / RHEL / CentOS-7 / x86_64 - VirtualBox    13

To install Google Chrome Internet browser on your CentOS 7 Linux box first download the actual Chrome 64 bit .rpm (For Fedora/openSUSE) ) package from Google's website https://www.google.com/chrome/#eula. Locate your downloaded .rpm and use yum command to install it allong with all other prirequsites:
# yum localinstall google-chrome-stable_current_x86_64.rpm 
Loaded plugins: fastestmirror, langpacks
Examining google-chrome-stable_current_x86_64.rpm: google-chrome-stable-44.0.2403.155-1.x86_64
Marking google-chrome-stable_current_x86_64.rpm to be installed
Resolving Dependencies
--> Running transaction check
---> Package google-chrome-stable.x86_64 0:44.0.2403.155-1 will be installed
--> Processing Dependency: lsb >= 4.0 for package: google-chrome-stable-44.0.2403.155-1.x86_64
...
Complete!

This config describes an installation of NVIDIA GeFNVIDIA GeForce Driver on CentOS 7 Linux 64-bit.

Prerequisites

First update your system. We do not wand to build NVidia modules on based on outdated Linux kernel. Do a full updated and reboot your system:
# yum update
# reboot

The Vagrant installation on CentOS Linux is a fairly simple few commands process. First, we need to download a official RPM from http://www.vagrantup.com/downloads.html. Open up your terminal and use wget command to download latest Vagrant RPM package eg:
$ wget -q https://dl.bintray.com/mitchellh/vagrant/vagrant_1.7.4_x86_64.rpm

The easiest way to swap between keymaps and thus temporarily set keys to different language by use of loadkeys command. If the loadkeys command is unavailable install kbd package:
# yum install kbd
As for an example the following linux command will temporarily change system's keymap to Slovak:
# loadkeys sk
Loading /lib/kbd/keymaps/xkb/sk.map.gz
To list all available keymaps on your CentOS system run:
# localectl list-keymaps

At the moment Skype.com does not provide and installation package for CentOS Linux. The closest package we can use to install Skype communicator on CentOS is is based on Fedora Linux. Navigate to http://www.skype.com/en/download-skype/skype-for-linux/ and download a Fedora i386 skype package. At the time of writing the package version is skype-4.3.0.37-fedora.i586.rpm. Once downloaded run the below yum command as a privileged user to install Skype on your CentOS linux system:
# yum localinstall skype-4.3.0.37-fedora.i586.rpm

The python version 3 is not available from CentOS 7 repositories. The following config will show you how to compile and install Python version 3 from source on CentOS 7 Linux. Let's start by installation of some required tools which you will need for this tutorial.
# yum install yum-utils make wget
Next, we will install all python build prerequisites to meet all compilation requirements:
# yum-builddep python

In order to install VirtualBox virtualization software on CentOS Linux first install prerequisites:
yum install kernel-devel gcc
Next, download relevant RPM package to your CentOS version from https://www.virtualbox.org/wiki/Linux_Downloads.

Once downloaded, navigate to directory where you have downloaded the VirtualBox RPM and execute check its signature eg.:
# rpm --import https://www.virtualbox.org/download/oracle_vbox.asc
# rpm --checksig VirtualBox-5.0-5.0.0_101573_el7-1.x86_64.rpm
If signature match use below command to install VirtualBox package while replacing package version number with the one you have downloaded previously:
yum localinstall VirtualBox-5.0-5.0.0_101573_el7-1.x86_64.rpm

The default installation of CentOS Linux 7 does not come with installation of adobe flash player for Firefox web browser and thus must be installed separately. To begin flash player installation first we need to include Adobe's repository. This can be achieved by the following linux command:
# yum -y install http://linuxdownload.adobe.com/linux/x86_64/adobe-release-x86_64-1.0-1.noarch.rpm
Confirm that Adobe repository has been included:
# yum repolist | grep -i adobe
adobe-linux-x86_64      Adobe Systems Incorporated                            2
At this stage we are ready to install adobe flash player using yum command:
# yum install flash-plugin

This article will describe a way on how to change/set a primary display on CentOS/RHEL 7 with dual monitors and GNOME. The easiest and perhaps recommended way is to use GUI and navigate to Applications->System Tools->Settings->Displays.
show current primary display redhat/centos

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The current primary screen is highlighted by a black top bar. To change you primary display simply drag-n-drop the black top bar from one screen to another:
change primary display redhat/centos
. Another alternative is to you command line tool xrandr. First get all your connected screens:
$ xrandr | grep -w connected
DVI-D-1 connected 1680x1050+0+0 (normal left inverted right x axis y axis) 474mm x 296mm
HDMI-1 connected primary 1920x1080+1680+0 (normal left inverted right x axis y axis) 598mm x 336mm

If you currently do not hold a Red Hat Subscription and yet you need to enable EPEL ( Extra Packages for Enterprise Linux ) repository on your RHEL 7 Linux you need to download and install following file directly from Fedora project:
epel-release-7-5.noarch.rpm

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