OpenSSH
OpenSSH is a SSH client and server.
OpenSSH is widely deployed on Linux and BSD operating systems, with Windows systems preferring access by RDP.
The service is sshd(8) and the utility is ssh(1).
Installation
Most Linux and BSD distributions will include it by default. Otherwise, it should be available through an openssl package.
Furthermore, many Linux distributions have sshd(8) running by default.
For systemd(1)-capable systems, start and enable sshd.service.
For OpenRC-based systems, start and add the sshd service.
For BSDs, start the sshd service. To have it automatically start on boot, try editing /etc/rc.conf like:
sshd_enable="YES"
Configuration
Require Authentication by Key
To require that all client logins use keys, use:
PubkeyAuthentication yes AuthorizedKeysFile .ssh/authorized_keys PasswordAuthentication no
To make an exception for a user, add at the bottom of the file:
Match User git PasswordAuthentication yes Match all
To make an exception for the local network, add (also at the bottom of the file):
Match Address 192.168.*.* PasswordAuthentication yes Match all
Login Messages
Usually any messages printed on login are actually handled by PAM. This can be tricky to configure, so instead disable the default login messages and configure the shell profile to print the desired messages.
To disable all PAM login messages for a user, try:
touch ~/.hushlogin
Note that default PAM configurations print /etc/motd and the output of /usr/bin/lastlog --user USERNAME on login.
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Usage
The primary use of ssh(1) is to access a remote host:
ssh [email protected]
See here for details on creating and using SSH tunnels.