Linux tutorials, system administration, web hosting, programming

Installing, configuring and using a UFW firewall on Debian / Ubuntu systems

botond published 2022. 06. 27., h - 12:54 time
UCW (Uncomplicated Firewall) is an easy-to-use netfilter firewall management program. It uses a command line interface that consists of a few simple commands and uses iptables for configuration, so it is the frontend of iptables. In this description we will look at the installation and basic use and configuration of the UFW firewall, the steps of which I will perform on a minimal Debian 11 server.

UFW (Uncomplicated Firewall)

botond published 2022/06/26, v - 15:52 time
Uncomplicated Firewall (UFW) is one such frontend of iptables and is particularly suitable for server-based firewalls. Ufw provides a framework for managing netfilter, as well as a command-line interface for managing a firewall that uses few and simple commands. Ufw is designed to provide an easy-to-use interface for those unfamiliar with firewall concepts, while simplifying complex iptables commands to help administrators who know what they are doing. UFW is also an upstream software package for other distributions and graphical frontends.

How to handle "WARNING: POSSIBLE DNS SPOOFING DETECTED!" and "REMOTE HOST IDENTIFICATION HAS CHANGED!" error at ssh login time?

botond published March 2022, 06, Thu - 16:17 time
When you use ssh access, your computer (client) retrieves the server's ECDSA (Elliptic Curve Digital Signature Algorithm) fingerprint each time it connects, which it stores in the list of known servers during the first connection (by default in the ~ / .ssh / known_hosts file). From now on, for future ssh connections, our machine will recognize the ECDSA fingerprint of the remote machine, verifying that we are connecting to the exact same machine later. If the newly retrieved fingerprint does not match the previously stored version during a subsequent connection, ssh throws the following error: "WARNING: POSSIBLE DNS SPOOFING DETECTED!" and "WARNING: REMOTE HOST IDENTIFICATION HAS CHANGED!". These error messages alert you to the possibility that you may be a victim of DNS spoofing, or that the server's ECDSA fingerprint, that is, the public key of the SSH server, has changed.

How to protect our server from attacks on our databases with "Access denied for user root@ip address (using password: YES / NO)" using Fail2Ban

botond published 2022/06/05, v - 01:45 time
When we run websites, our server and the websites and services that run on it are often vulnerable to external attacks, and our MySQL / MariaDB database server is no exception. If the Fail2Ban protection software is also available on your server, this short description will show you how to make your server more secure against attacks on your "Access denied for user root @ ip address (using password: YES / NO)" database server.

Repositories

botond published 2022/05/29, v - 11:05 time
In all Linux distributions, programs that can be installed on the system are distributed as software packages. Software packages are typically a set of data packaged in a file that contains the software itself, as well as a number of additional information (metadata) about the software, such as package descriptions, installation scripts, dependency data, and so on. Linux distributions maintain their own repositories, into which software packages can only be accessed after strict checks. Packages consist of a package database containing package information and an organized structure of downloadable binary package files.

How do we show or hide the GRUB boot menu at boot time in Ubuntu operating systems?

botond published 2022. 05. 23., h - 13:05 time
GRUB is a boot program that starts the selected operating system when you start your computer. For Ubuntu Linux systems, the GRUB menu will only appear by default if you have more than one operating system installed on your computer, giving the user the option to select the system they want to boot. However, sometimes you may need to display the GRUB menu for an instance of Ubuntu. In this short description, we'll look at how to bring up the GRUB menu for a single Ubuntu system.

Ubuntu 22.04 LTS (Jammy Jellyfish) UEFI Mode Installation

botond published 2022/05/21, Sat - 10:35 time
Ubuntu 22.04 LTS (Jammy Jellyfish) was officially released on April 2022, 21, and will receive software support through LTS (Long Term Support) for another 5 years, meaning we won’t have to worry about updates coming until April 2027. The operating system includes the GNOME 42.0 desktop environment. In this description, it is installed on a 64-bit machine running UEFI, where a hard disk with a GPT partitioning scheme is used for this purpose.

How to install Guest additions on Debian 11 (Bullseye) running in VirtualBox

botond published March 2022, 04, Thu - 21:17 time
If you are running operating systems in VirtualBox, it is a good idea to install Guest Additions on the guest system, which will provide a greater degree of compatibility with the virtual hardware so that the guest system can make better use of the available hardware resources. In this description, we will install the Guest Additions package on a system with a Debian 6.1 (Bullseye) KDE desktop environment running in VirtualBox 11.