Linux tutorials, system administration, web hosting, programming

Make bootable flash drives with Rufus 4.3

botond published 2023. 12. 04., h - 22:18 time
Rufus is a very popular free and open source portable application for Windows operating systems that can be used to easily create bootable USB flash drives. Thanks to its active development, new editions are released regularly, which contain many new features. In this tutorial, we will try Rufus version 4.3 and use it to create a Debian 12 installation flash drive.

How to fix "554 5.7.1 Service unavailable; Client host blocked using zen.spamhaus.org; Error: open resolver;" from our server delivery of bounced letters with an error message?

botond published Jan. 2023, 03, 22:11 p.m. time
When conducting electronic correspondence, mail servers strive to filter out unsolicited mail (spam) as efficiently as possible. From time to time it happens that these spam filtering services get blocked by letters that do not contain anything that would justify this. Therefore, it may happen with us that we cannot send an email to a recipient, or that we cannot receive mail from others on our own server. In this description, we will investigate one of the more common server-side "554 5.7.1 Service unavailable; Client host blocked using zen.spamhaus.org; Error: open resolver;" type error.

Postfix

botond published Jan. 2023, 03, 22:05 p.m. time
Postfix is ​​an extremely popular free and open source MTA (Mail Transfer Agent) software developed by Wietse Venema in 1997 and first released in December 1998. Postfix aims to provide a secure and reliable mail service that is resistant to Internet attacks and spam. To this end, Postfix has a number of security features, such as traffic restriction, server and client authentication, virus and spam filtering, and content filtering.

FTP (File Transfer Protocol)

botond published 2023. 03. 20., h - 10:10 time
File Transfer Protocol (FTP) is a standard network protocol on TCP/IP networks used to transfer computer files between a client and a server. The FTP protocol was originally developed for file sharing on the Internet and plays a very important role in data transfer services to this day.

Midnight Commander (mc)

botond published 2023. 03. 20., h - 07:35 time
Midnight Commander (MC) is a text-mode file management program that is extremely popular on Linux and other Unix-like operating systems. The development of the program was started by Miguel de Icaza in 1994, and many versions have been released since then. MC allows users to easily navigate the file system and perform various operations such as copying, deleting, moving files, etc.

How to defend against attacks resulting in large volumes of 404 or other 4xx HTTP error codes with Fail2Ban

botond published 2023/03/14, k - 00:38 time
Our websites are constantly under attack from the outside world. The vast majority of these are done by robots, which try to discover the weak points of the websites running on the server. Some of the robots with this purpose try to do this by making various seemingly random HTTP requests to our websites, most of which are directed to non-existent URL addresses. As a result, our server responds with a 404 HTTP response code. In this description, we will look at how to ban the large number of attempts resulting in 404 and other 4xx HTTP response codes using Fail2Ban.

CIDR (Classless Inter-Domain Routing)

botond published 2023/03/14, k - 00:28 time
CIDR (Classless Inter-Domain Routing) is a network protocol that enables more efficient use of the network addressing system on the Internet and other networks. CIDR was created to overcome the limitations of the traditional classful addressing system.

HTTP/2 (protocol)

botond published 2023/03/14, k - 00:11 time
HTTP/2 (HyperText Transfer Protocol / 2) is a protocol that is an improved version of the HTTP/1.1 protocol, released by the HTTP Working Group in 2015. HTTP/2 is supported by most modern browsers and allows web pages to load faster than previous versions.

How to fix "dovecot: master: Error: socket() failed: Address family not supported by protocol" errors

botond published 2023/02/25, Sat - 08:03 time
After updating ISPConfig, not all services restarted. In this case, the Dovecot POP3/IMAP mail server and even Postfix threw warnings. Although we fixed these errors earlier, our settings were overwritten again during the ISPConfig update. In this troubleshooter, on the one hand, we fix "Address family not supported by protocol" type errors that cause the service to be inoperable, and we also make their permanent settings so that they remain even after further ISPConfig updates.