There might come a time when you want to know if you have already installed a certain package on your RHEL 8 / CentOS 8. An application to be manually installed might require certain dependencies to work so you'll have to check beforehand if these are satisfied. Or you might want to compile something and want to make sure you have all the right header libraries on your system.

In this tutorial you will learn:
  • How to use yum and dnf in RHEL 8 / CentOS 8 to list all packages
  • How to use the repoquery command to accomplish the same task
  • How to use the rpm command to list all packages installed on RHEL 8 / CentOS 8
  • How to filter the output of each command to seek certain packages
Use the repoquery command to list all available packages in RHEL 8 / CentOS 8
Use the repoquery command to list all available packages in RHEL 8 / CentOS 8

The objective of this guide is to install GCC the C compiler on RHEL 8 / CentOS 8 and perform compilation of a basic C "Hello World" program. The GCC compiler can be installed in RHEL 8 by simply using the dnf install command.

In this tutorial you will learn:
  • How to install GCC compiler on RHEL 8 / CentOS 8.
  • How to install Development Tools installation group.
  • How to write C program.
  • How to compile and execute C program.

The syslog functionality is one of the main tools for a sysadmin. While writing logfiles with events of interest is a common feature of any application, having a system-wide logging functionality means all logs can be handled as one on the system. But syslog does not stop there. With these tool, a sysadmin can centralize log processing in the datacenter by forwarding the incoming events from applications to central logservers, where they can be processed at a large scale.

Centralized logging is an overkill on a home system with a few computers, but already have it's benefits around a dozen machine. For example, a dozen desktops sending all their logfiles to a central logserver mean they don't need to store them on the long run, the logs will occupy disk space in the logserver. The admin can check for problems in only one place (possibly by means of automated reports), the logs can be preserved in a safe way by the means of backups, stored more effective by means of heavy compressing, and will not be lost on a client's failure or user error.

In this tutorial you will learn:
  • How to install rsyslog package on RHEL 8 / CentOS 8.
  • How to verify successful install.
  • How to start, stop and autostart rsyslog service.
  • How to test syslog functionality with logger.

Postfix is a common mail server, many large distributions are shipped with Postfix installed by default. The default configuration allows local mailing only, but that in itself is very useful on a machine used by many users, and even if there is no such traffic, many services dump their reports and messages into e-mails, which is delivered to the root user locally, so the sysadmin will be noticed on any events of interest when he/she logs in and switches to root user.

A simple example would be scheduled cron jobs: any output not redirected from the output of a script running from cron will be wrapped to an e-mail and will be delivered to root's mailbox, so the administrator does not even have to make any effort to have the reports of the nightly backup jobs at hand.

While this standalone mode is certainly a nice service as it is, postfix is a full-fledged mail server, capable of receiving, forwarding, relaying, filtering of e-mails, it basically have every feature we need for a mail server.

In this tutorial you will learn:
  • How to install postfix on RHEL 8 / CentOS 8
  • How to verify the working service with standalone functionality.

As interconnected computer networks enter more and more fields of everyday life, cybersecurity is getting louder and louder. We protect our websites, the traffic on our websites, the computers we initiate the traffic from, maybe (part of) the disks our operating system run from, our connection to work, the computers we attach to at work, and so on.

openssl is an essential tool on any recent GNU/Linux distribution if one have to work with various certificates.

In this tutorial we will install (and reinstall) the openssl package, and test it's functionality by checking a website's certificate chain with it's help.

In this tutorial you will learn:
  • How to install openssl
  • How to reinstall openssl
  • How to check a website's SSL certificate chain with openssl

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