If you SSH into a machine to work, tmux is an essential tool you can use. tmux allows you to create long-lasting sessions, which outlive a single SSH connection.
If you're in a tmux session, you can detach from it by pressing Ctrl + b followed by d. You will be sent back in your shell with the following message:
[detached (from session 0)]
The session will be alive until your machine is powered off. To list tmux sessions, execute the following:
$ tmux list-sessions0: 2 windows (created Sat Aug 18 19:17:59 2018) [80x23]
As you can see, we currently have one session available. Let's open the session, or—in tmux terms—attach to it:
$ tmux attach -t 0
Running tmux without any arguments always creates a new session.