SSH

Generate

ssh-keygen -a 100 -t ed25519

ssh-keygen -a 100 -t rsa -b 4096

Permissions

chmod 700 ~/.ssh
chmod 600 ~/.ssh/*
chmod 644 -f ~/.ssh/*.pub ~/.ssh/authorized_keys ~/.ssh/known_hosts* ~/.ssh/config

SSH Banner

Before Login

Giving a warning BEFORE a user attempts to login to a server that they may not own can be a simple yet effective deterrent from basic mischief.

ALERT! You are entering into a secured area! Your IP, Login Time, Username have been noted and has been sent to the server administrator! This service is restricted to authorized users only.

In order to create a banner like this create a file /etc/issue.net. This file can actually be placed anywhere secure and point to it in sshd config.

chown root:root /etc/issue.net
chmod 644 /etc/issue.net

Inside your /etc/ssh/sshd_config file, find the "Banner" line, uncomment it and point to you issue.net file.

sudo systemctl restart ssh

After Login

To give a custom message after a user has logged into a server create or edit the /etc/motd file. You can create elaborate login messages with a directory /etc/update-motd.d and pass files that are parsed in lexical order.

10-login-header
30-login-sysinfo
35-tips