ssh (SSH client) is a program for logging into a remote machine and for executing commands on a remote machine.
sshd (OpenSSH Daemon) is the daemon program for ssh.
ssh protocol is intended to provide secure encrypted communications between two untrusted hosts over an insecure network. X11 connections, arbitrary TCP ports and UNIX-domain sockets can also be forwarded over the secure channel.
Install sshd (remote machine)
FROM REMOTE MACHINE
sudo apt-get update && sudo apt-get install -y openssh-server
Ensure ssh is enabled and active
systemctl is-enabled ssh && systemctl is-active ssh
If it not the case then you should run
sudo systemctl enabled ssh sudo systemctl start ssh
You can also want to see status
systemctl status ssh
If you have a personal firewall on this machine, you need to allow to use port 22
sudo ufw allow 22/tcp
More informations about firewall configuration (external link)
You can do a quick test to see if you can join sshd at least from remote machine.
ssh <REMOTE_MACHINE_IP> # from remote machine
If it ask for a password, just cancel (CTRL+c) - everything is okay. Otherwise check previous steps.
Connect through ssh to remote machine (from local machine)
FROM LOCAL MACHINE
First connection test
ssh <REMOTE_MACHINE_IP> # from local machine
If it ask for a password, just cancel (CTRL+c) - everything is okay. Otherwise check previous steps and your network.
Setup ssh accounts (required for each account)
ssh simple manual
See ssh for dummies.