Laptop Lid Closure Settings on Linux

# Don't go to sleep if lid closed and monitor connected:
sed --in-place .backup 's/#HandleLidSwitchDocked=ignore/HandleLidSwitchDocked=ignore/' /etc/systemd/logind.conf

$ /etc/systemd/logind.conf
HandleLidSwitch=suspend                # suspend when on battery
HandleLidSwitchExternalPower=ignore    # inhibit suspend when on AC 
HandleLidSwitchDocked=ignore           # inhibit suspend when on external monitor

$ reboot
# ↓ or ↑
$ sudo systemctl restart systemd-logind  # will kill current X/Wayland session