In this chapter, we will learn some advanced and essential concepts related to the system, such as logging, controlling system services, firewalls, and Security Enhanced Linux (SELinux). Logging plays a key role in debugging and troubleshooting system applications. A solid understanding of logging will make your daily operations easier to handle and will also give you a deep insight into the application's functioning.

In this final chapter, we will learn the different logging mechanisms available in CentOS 7, such as journald and rsyslog. By now, you have seen how to install, update, and remove applications. Now, we will see how to control these applications and system services using the systemd and systemctl utilities. Finally, we will understand the basic usage of firewalld and SELinux to secure running services and harden the security of the system.

We will cover the following:

• Understanding system logging
• Working with rsyslogd and journald
• Understanding control of systems and services
• Working with systemd and systemctl
• Understanding SELinux concepts
• Working with SELinux
• Understanding firewall concepts in CentOS 7
• Working with firewalld