Linux tutorials, system administration, web hosting, programming

UNC (Universal Naming Convention)

botond published 2022/11/01, k - 21:14 time
The Universal Naming Convention (UNC) is a naming standard for identifying servers, printers, and other network resources that originated in the Unix community.

Basic port scanning - Or how to check the security of our Linux server against unauthorized intruders

botond published 2022/10/23, v - 09:30 time
When checking ports from the outside, we perform a port scan on the computer to be checked to find out which ports are open, which services monitor these ports, etc. Port scanning is usually performed by system administrators to check the security of the server, but unfortunately, it is also often used by malicious attackers to map the weak points of the selected target computer. On this page, we review the basic use of the nmap command.

How can we check the used and free TCP/UDP ports of our Debian or Ubuntu Linux operating system?

botond published 2022/10/23, v - 08:20 time
Several services can run on a Linux operating system, especially on a more complex web server installation. These services communicate through different TCP (Transmission Control Protocol) or UDP (User Datagram Protocol) ports on the network interface. A listening port is a network port on which an application or process listens and acts as a communication endpoint. Checking ports is an important task from several points of view. On the one hand, for the sake of security, we must monitor the open ports and the communication on them, and on the other hand, we can also reduce the number of error possibilities that result from several similar services using the same port.

How can we change the default tcp port 22 of our SSH server on our Debian or Ubuntu Linux server for better security?

botond published 2022/10/23, v - 08:10 time
There are several ways to manage web servers and other servers remotely, of which SSH is the most common command line solution. The SSH protocol communicates over an encrypted channel between the server and the client. Like all similar communications, SSH transmits data through a specific port, which by default is the well-known tcp port 22. Since the function of this port is known to many people, it exposes the servers to regular attacks. This is usually avoided - or at least to reduce the number of attempts - by switching this well-known port to another, unknown port number, which can only be detected externally by port scanning, which is a more time-consuming task.
In this write-up, we will look at how to change SSH's well-known TCP port 22 to a unique port number to minimize the number of attack attempts via SSH.

How to fix "AH00124: Request exceeded the limit of 10 internal redirects due to probable configuration error." types of Apache errors?

botond published March 2022, 09, Thu - 22:16 time
.htaccess files are very useful accessories for the Apache web server, with the effective use of which we can solve many problems. However, in the case of a more complex server configuration, we need to pay attention to several things, otherwise we can easily generate Apache errors.
In this troubleshooter, we deal with redirects, where in certain situations we can end up in an endless redirect cycle, which eventually results in "AH00124: Request exceeded the limit of 10 internal redirects due to probable configuration error." leads to content errors.

Debian 11 (Bullseye) LAMP server v1.0 installation

botond published 2022/09/06, k - 17:12 time
With the help of LAMP systems, we can run dynamic websites on our server or even on our home computer. In this description, we will create a LAMP server on the Debian 11 (Bullseye) operating system, on which the following components will be installed: Apache 2.4.54, MariaDB 10.5.15, PHP 7.4 and phpMyAdmin 5.0.4, UFW firewall.

How can we manually unmask services that are masked (service is masked) that we cannot unmask with the unmask option of the systemctl command?

botond published 2022/08/16, k - 05:50 time
Linux services are programs running in the background, which do not have a separate user interface, but respond to the requests of other programs through some communication mechanism (mostly on the network). Services in modern Linux systems are managed by systemd, and they can be started, stopped, masked, unlocked, etc. using the systemctl command. There are cases when the systemctl command cannot unmask, in which case a manual solution must be applied.

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.