1. Create systemd User Service Unit
Create ~/.config/systemd/user/tmux.service with the following daemon specification:
[Unit]
Description=tmux background daemon
[Service]
Type=forking
ExecStart=/usr/bin/tmux new-session -s default -d
ExecStop=/usr/bin/tmux kill-server
Restart=on-failure
[Install]
WantedBy=default.target