Thomas Sandmann

Configuration page of Redmine.

How to install redmine on RHEL 8 / CentOS 8 Linux

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Redmine is a popular open source project management web application. It supports mayor databases like MySQL and PostgreSQL as backend, and you can also change the frontend to Apache from the WEBrick (recommended for production use) webserver shipped with the installation. In this article we will install the latest Redmine on RHEL 8 / CentOS 8, using PostgreSQL as backend, but we will leave the default WEBrick as frontend, which will serve our tests perfectly.

Do not expect this process to be an easy one, nor error-free. Even following these steps to the letter, some errors will surely happen, the setup seem to handle sudo steps somewhat inconsistently – but the solutions are also included which will guide trough these errors.

In this tutorial you will learn:

  • How to install required operating system packages
  • How to setup the database
  • How to install the Redmine application
  • How to start and login to the application

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Allowing access from a certain network segment to sshd.

How to install and setup an example service with xinetd on RHEL 8 / CentOS 8 Linux

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Xinetd, or the Extended Internet Services Daemon, is a so-called super-server. You can configure it to listen in the place of many services, and start the service that should handle an incoming request only when there it actually arrives to the system – thus saving resources. While this may not seem to be a big deal on a system where traffic is relatively permanent, this service in the front of another approach does have some neat advantages, like logging or access control.

In this article we will install xinetd on a RHEL 8 / CentOS 8, and we’ll put the sshd daemon under it’s care. After verifying the setup, we’ll tweak the configuration a bit to see the access control in action.

In this tutorial you will learn:

  • How to install xinetd
  • How to setup sshd on RHEL 8 / CentOS 8 as an xinetd service
  • How to allow access only from a specific network to the sshd service from xinetd
  • How to audit traffic from xinetd log entries

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Checking a website's SSL certificate with openssl.

How to install ssl on RHEL 8 / CentOS 8

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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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Examples page served by Apache Tomcat

How to install apache tomcat on Linux RHEL 8 / CentOS 8

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In this tutorial we will learn how to install Apache Tomcat 8 application container to RHEL 8 / CentOS 8. We will be using the zip package available to download from the Apache Tomcat website. As this package will not handle setting up the environment, we will create it from the command line.

In this tutorial you will learn:

  • How to install Apache Tomcat from zip file
  • How to create the environment for the Tomcat server from command line
  • How to add basic service file to systemd
  • How to enable autostart, start and stop the Tomcat server
  • How to verify Tomcat is reachable

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VNC connection to RHEL8 with Remmina.

How to install vnc server on RHEL 8 / CentOS 8

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Remote connection to computers is as old as computer networks. Accessing the graphical interface (GUI) is a convenient way of working on a remote desktop. We can leave our graphical programs running and working, and we don’t need to keep the session open – we simply reconnect when we feel to do so.

VNC server is well-known graphical session server enabling remote connections that we can run with a non-privileged user. This way many users can access their own desktop on the same machine remotely, and will not block each other (apart from maybe using up the resources of the remove machine).

In this tutorial you will learn:

  • How to install required packages.
  • How to setup and start the VNC server on RHEL 8.
  • How to connect to a graphical session remotely.
  • How to run graphical programs in the xterm session.

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Status output of rsyslog service with systemctl.

How to install syslog on RHEL 8 / CentOS 8

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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.

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Reading local mail delivered by Postfix.

How to install postfix mail server on RHEL 8 / CentOS 8

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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.

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