SSH

Enable service to run at boot: systemctl enable sshd.service

Start the SSH service: systemctl start sshd.service

Offending ECDSA key in /home/someuser/.ssh/known_hosts:4
Remove with:
ssh-keygen -f "/home/someuser/.ssh/known_hosts" -R "theservername.com"

Copy SSH public key to remote computer: ssh-copy-id -i ~/.ssh/id_rsa.pub user@hostname

SSH: Broadcast message: The system will suspend now! client_loop: send disconnect: Broken pipe

You can display the current sleep/suspend settings with a command like this one:

sudo -u gdm dbus-run-session gsettings list-recursively org.gnome.settings-daemon.plugins.power | grep sleep

The problem of getting kicked out of the remote computer when the computer goes into hybernate mode was solved with the following:
systemctl mask sleep.target suspend.target hibernate.target hybrid-sleep.target
Source: