In this article i'll try to give you a simple summary about the common networking services used in Linux systems. The services mentioned in this article are by no mean necessary to know these are just the ones i got to know why studying Linux at the university and i wrote a small essay about them as a part of my grading report.

For many years, Unix-like operating systems have had the ability to be administered remotely via a network. In the early days, before the general adoption of the Internet, there were a couple of popular programs used to log in to remote hosts. These were the rlogin and telnet programs. These programs, however, suffer from the same fatal flaw that the ftp program does; they transmit all their communications (including login names and passwords) in cleartext. This makes them wholly inappropriate for use in the internet age. ssh To address this problem, a new protocol called SSH (Secure Shell) was developed. SSH solves the two basic problems of secure communication with a remote host. First, it authenticates that the remote host is who it says it is (thus preventing so-called “man in the middle” attacks), and second, it encrypts all of the communications between the local and remote hosts. SSH consists of two parts. An SSH server runs on the remote host, listening for incoming connections on port 22, while an SSH client is used on the local system to communicate with the remote server. Most Linux distributions ship an implementation of SSH called OpenSSH from the OpenBSD project. Some distributions include both the client and the server packages by default (for example, Red Hat), while others (such as Ubuntu) only supply the client. To enable a system to receive remote connections, it must have the OpenSSH-server package installed, configured and running, and (if the system is either running or is behind a firewall) it must allow incoming network connections on TCP port 22.