CentOS

We all make mistakes and this is especially true for novice Linux system administrators. Linux can have a steep learning curve and sooner or later there will be a point in your career where your CentOS installation does not start up due to a broad number of reasons, including hardware problems or human mistakes such as configuration errors. If this has happened to you then you can use the CentOS rescue mode in order to boot an otherwise unbootable system and try to undo your mistakes or find out the root of the problems.

This process will rightly explain you the way to enhance the minimal install along with additional tools. This will provide you with various administrative and developmental options that might stand extremely vital for your server to work in its lifetime. 

No doubt you will frequently use programs and tools that use the program less or less-like navigation to view and read file content or display output. At first, the control can seem a bit unintuitive. Here, in this process, we will show you the basics of how to navigate through a file using fewer controls.

To Start With: What Do You Need?

In order to implement this process, you will require a working installation of the CentOS 7 operating system with root privileges.

Here in this process, we will give you a very brief introduction to the text editor, Vim, which is used as the standard text editor everywhere. You can also use any other text editor you prefer, such as nano or emacs, instead.

To Start With: What Do You Need?

For implementing this process, you will require a working installation of the CentOS 7 operating system with root privileges.

The Process

We will start this process by installing the vim-enhanced package, as it contains a tutorial you can use to learn to work with Vim:

To Start With: What Do You Need?

The Nagios Remote Plugin Executor (NRPE) is a system daemon that uses a special client-server protocol and should be installed on all client hosts that you want to monitor via your Nagios server remotely. It allows the central Nagios server to trigger any Nagios checks on these client hosts securely and with low overhead. Here, we will show you how to set up and configure any CentOS 7 client to use NRPE; if you’ve got more than one computer in your network that you want to monitor, you need to apply this process for every instance.

In this process, we will learn how to install Nagios Core version 4, an open-source network monitoring system that checks whether hosts and services are working and notifies users when problems occur or services become unavailable. Nagios provides solutions to monitor your complete IT infrastructure and is designed with an architecture that is highly extendable and customizable and goes far beyond simple bash scripts to monitor your services. (Refer to the Monitoring important server infrastructure process.)

In this process, you will learn how to troubleshoot SELinux policies, which is most often needed when access to some SELinux objects has been denied and you need to find out the reasons for it. In this process, we will show you how to work with the sealert tool, which will create human-readable and understandable error messages to work with.

At the core of every SELinux system are the policies. These are the exact rules that define the access rights and relationships between all our objects. As we have learned earlier, all our system’s objects have labels, and one of them is a type identifier that can then be used to enforce rules laid down by policies. In every SELinux enabled the system, by default, all access to any object is prohibited unless a policy rule has been defined otherwise. Here, in this process, we will show you how we can query and customize SELinux policies.

As we have learned from the previous process, SELinux is all about labels and policies. In this process, we will show you how to work with these labels, also known as security contexts.