SSH or Secure Shell is a cryptographic network protocol for operating network services securely over an unsecured network. Typical applications include remote command-line, login, and remote command execution, but any network service can be secured with SSH.

SSH was designed as a replacement for Telnet and for unsecured remote shell protocols such as the Berkeley rsh and the related rlogin and rexec protocols. Those protocols send information, notably passwords, in plaintext, rendering them susceptible to interception and disclosure using packet analysis. The encryption used by SSH is intended to provide confidentiality and integrity of data over an unsecured network, such as the Internet.

There are many ways to make a server running SSH more secure. Here are some examples: Disable root logins, use private key authentications (rather than ssh passwords), enable two-factor authentication, change the port used by SSH, don’t listen on every interface, limit users’ SSH access, and make sure the operating system is kept up-to-date.

There are more steps you can take to harden the server. This article recommends open source software that employ different techniques to make it harder for a server running SSH to be compromised.

We list our recommendations below captured in a legendary LinuxLinks-style ratings chart. All of the software featured here is published under an open source license.

This article has been updated to reflect the changes outlined in our recent announcement.

Explore our comprehensive directory of recommended free and open source software. Our carefully curated collection spans every major software category.

This directory is part of our ongoing series of informative articles for Linux enthusiasts. It features hundreds of detailed reviews, along with open source alternatives to proprietary solutions from major corporations such as Google, Microsoft, Apple, Adobe, IBM, Cisco, Oracle, and Autodesk.

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