A firewall is a program that monitors and controls your system’s network interfaces’ incoming and outgoing network traffic and can restrict the transmission to only useful and non-harmful data into and out of a computer system or network. By default, CentOS is made available with an extremely powerful firewall, built right into the kernel, called netfilter.
In this process, we will learn how to implement additional security measures for protecting the SSH server with a package called fail2ban. This is a tool that serves to protect a variety of services including SSH, FTP, SMTP, Apache, and many more against unwanted visitors. It works by reading log files for patterns based on failed login attempts and deals with the offending IP addresses accordingly.
In this process, we will learn how to provide additional security measures in order to harden the secure shell environment. The Secure Shell (SSH) is the basic toolkit that provides remote access to your server. The actual distance to the remote machine is negligible, but the shell environment enables you to perform maintenance, upgrades, the installation of packages and file transfers; you can also facilitate whatever action you need to carry out as the administrator in a secure environment.
CentOS 7 uses the Logical Volume Manager (LVM) to organize the structure and available capacity of your partitions. It is a very dynamic and flexible system that can be extended or rearranged over time, and which is essential in today’s most demanding and ever-changing environments. At the moment, buzzwords such as big data or cloud computing can be heard everywhere. Since massive amounts of data get produced all the time, storage requirements and disk space have to grow at the same steady pace.
In this process, we will learn how to check the consistency and optionally repair CentOS 7 filesystems. Filesystem inconsistencies are rare events and filesystem checks normally are running automatically at boot time. But system administrators should also know how to run such tests manually if they believe there is a problem with the filesystem.
When administering a Linux multiuser system with many system users, it is wise to set some kind of restrictions or limits to the resources shared by the system. On a filesystem level, you can either restrict the available hard disk space or the total file number to a fixed size at a user, group, or directory level. The introduction of such rules can prevent people from “spamming” the system, filling up its free space, and generally, users will get more aware of the differentiation between important and unimportant data and will be more likely to keep their home directories tidy and clean.
In this process, you will be introduced to the standard CentOS filesystems XFS, Ext4, and Btrfs. Filesystems form one of the most fundamental parts of any operating system and nearly everything depends on them. Here, you will learn how to create different types of standard filesystems available in CentOS 7, and how to link them to your system so that we can access them afterward for reading and writing. These two techniques are called formatting and mounting filesystems; while you do not do this very often, it remains one of the most fundamental Linux system administrator tasks.
In this process, we will create a virtual block device that we will use to simulate real devices and partitions so that we can test-drive concepts and commands used in all later processes. Working with real disks and partitions often involves the risk of losing important data or even having to re-install your complete system. A virtual block device is ideal to learn the techniques and try things out before switching to “production mode”. Later, if you have gained enough experience and feel safe, you can easily replace it with “real” hardware devices, partitions, and logical volumes.
All software on a CentOS 7 system is distributed through RPM packages. Most of the time the YUM package manager is the first choice of any system administrator, performing software installation and maintenance, and is highly recommended whenever possible as it provides system integrity checks and has excellent package dependency resolution. In this process, we will show you an alternative way to manage your packages. We will be exploring the RPM package manager, which is a powerful tool used to build, install, query, verify, update, and erase individual RPM software packages.
If you maintain multiple CentOS servers in your local network and want to save Internet bandwidth or speed up the downloading of the same remote repository packages over and over again, or are within a very restrictive network environment where access to any remote CentOS repository is blocked for your clients, you might want to consider running your own YUM repository.
