Secure Shell SSH

Connect as <user> to remote <host> on specified <port> If you do not specify a username it uses your current username

ssh -p <port> <user>@<host>

SSH Config

Location of SSH settings and host configuration

~/.ssh

If the SSH directory does not exist create it at ~/.ssh

mkdir ~/.ssh
chmod 700 ~/.ssh

If an SSH config file doesn't exist create it at ~/.ssh/config

cd ~/.ssh
touch config
chmod 600 config

Add details for a host entry

Host <nickname>
  HostName <server>
  User <username>
  Port <port>

Use SSH configuration

ssh <nickname>

Add SSH key passphrase to MacOS Keychain

ssh-add -K ~/.ssh/<key-file>

If config file cannot be edited using sudo check the file is not locked in macOS Finder

Check the file for the macOS user immutable flag uchg (which disallows editing even by the file owner)

ls -lO ~/.ssh/config

To remove the uchg (user immutable) flag and allow the file to be sudo edited by the owner

chflags nouchg ~/.ssh/config

Connect to remote machine using SSH public / private key instead of username and password.

On the remote machine, if there is no existing ~/.ssh directory or ~/.ssh/authorized_keys file, create one:

mkdir ~/.ssh && cd ~/.ssh
nano authorized_keys

Then past your public key into the file and save.

If an authorized_keys file exists, append your key to that file on a new line.